User manual - Valco Instrument Instrument Company
Contents
1. CAPILLARY COLUMN CAPILLARY COLUMN VENT lt __ VENT DOPANT INLET COLUMN INLET COLUMN INLET Figure 1 Schematic of the D 2 detector in the PDECD mode left and the PDHID mode right Introduction 2 Helium Ionization PDHID The PDHID is essentially non destructive 0 01 0 1 ionization and highly sensitive The response to organic compounds is linear over five orders of magnitude with minimum detectable quantities MDQs in the low or sub picogram range The response to fixed gases is positive the standing current increases with MDQs in the low ppb range For trace analysis of fixed gases optimized for packed columns low ppb range we offer a modified version of the detector dedicated to the ionization mode Product Number D 2 1 The PDHID response is universal except for neon which has an ionization potential of 21 56 eV Since this potential is close to the energy of the He metastable 19 8 eV but greater than the photon energy from the He continuum neon exhibits a low ionization efficiency and low detector response NOTE Valco makes an enhanced mode detector for neon Consult the factory for information Photoionization PDPID Changing the discharge gas from pure helium to helium doped with argon krypton or xenon changes the discharge emission profile resulting in resonance atomic and diatomic emissions of the rare gas added Response is limited to sample compounds with ioni2. COLUMN INLET NUT hit COLUMN INLET MANIFOLD DISCHARGE GAS INLET PD D2 IS COLUMN INLET TUBE Installation 14 Horizontal Mounting Some older GCs have access to the column oven through the side of the GC This does not present a problem as far as operation of the PDD is concerned Drill a hole at the appropriate location orient the detector for convenient connection and mark the position of the mounting holes Drill the mounting holes and secure the detector to the side of the GC with four sheet metal screws not supplied Gas Connections Remember these three points discussed earlier 1 all surfaces that contact the gas stream must be glass or stainless steel 2 do not use copper tubing or brass fittings and 3 all tubes must be thoroughly cleaned and baked before use The installation instructions below assume that the detector discharge will be supplied from a nearby cylinder of helium of the proper purity If your installation is different you may need to modify the instructions appropriately A number of Valco fittings have been supplied in the fittings kit to handle different situations Figure 3 illustrates gas connections for a typical detector system using a PD D2 detector in the ECD mode For HID and PID modes disconnect the restrictor TGA R O4F30P cap the line and plug the dopant inlet Figure 4 illustrates gas connections for the PD D2 IS detector system
3. If the system does not hold pressure check all the fittings with an electronic helium leak detector DO NOT use leak detecting liquids Tighten fittings as required Further leak testing is described on page 21 in the section entitled Checking for Leaks in the Discharge Gas Plumbing Installation 18 Peak height nA Peak height nA 4 0 ECD Mode Detector temperature 50C 3 5 Working current 15 nA Sample 50 ppb freon 11 2 loop 3 0 N o N ro a oO 1 0 0 5 0 0 i 9 2 9 4 9 6 9 8 10 0 10 2 10 4 10 6 Length of column in detector cm 3 5 HID Mode Detector temperature 50 C 3 0 Sample 100 ppm n C5 2 Iloop 2 5 2 0 1 5 1 0 0 5 t 10 6 10 8 11 0 11 2 11 4 11 6 11 8 Length of column in detector cm Figure 5 Effect of column position on detector response in ECD and HID modes Installation 19 Electrical Connections CAUTION Do not use a wrench to tighten the SMC connectors on the bias and electrometer cables Connections should be finger tight only 1 Referring to Figure 6 as necessary connect the bias and electrometer cables as follows the BIAS B cable to the top electrode closest to the discharge electrodes the electrometer cable ELECT to the middle and the BIAS A cable to the bottom electrode This setup is the same for both detector models 2 Connect the high voltage cable from the detector to the pulse s
4. The detector heater will operate if connected and high voltage is present on the bias cables DISCHARGE switch and indicator Controls power to the pulse supply module When the switch is on and the module is connected high voltage is generated by the unit and is present at the detector electrodes The indicator will not light if the detector is in the standby mode or if the pulse supply is not connected to the controller The indicator flashes until the discharge has been established then glows steadily Introduction Description Quantity Product number Detector cell PDHID PDECD 1 PD D2 Pulse supply module 1 PD M2 Includes Cable controller to pulse supply 1 23477 Controller unit with power cord 1 PD C2 Includes Cable computer unattenuated output 1 1 23136 Cable recorder attenuated output 1 1 23483 Instruction manual 1 MAN PDD Fittings kit 1 PD KIT ECD Includes 1 32 polyimide ferrule 5 ZF 5V 1 16 gold plated ferrule 5 ZF1GP 0 25 0 44 mm polyimide column ferrule 5 FS 4 0 4 0 5 mm polyimide column ferrule 5 FS 5 1 16 union 2 ZU1 1 16 tee 1 Z7T1 1 8 external to 1 16 internal reducer 2 EZR21 1 8 to 1 16 reducing union 2 EZRU21 1 32 external nut 1 EN 5KN Vent tube 1 1 23212 Restrictor 4 cc min 30 psi He 1 TGA R 04F30P Restrictor 30 cc min 60 psi He 1 TGA R 30F60P Table 1 Components of
5. 13 5 eV range to the 11 8 9 8 eV range The argon emission consists of resonance radiation at 11 8 eV and 11 6 eV and the diatomic Ar emission in the range of 9 2 10 3 eV Except for fixed gases and a few organic compounds like CH IP 12 5 eV CH CN IP 12 2 eV and some fluro chloro hydrocarbons the majority of organic compounds have ionization potentials lower than 11 8 eV Thus the Ar PDPID is nearly universal like the flame ionization detector but without the risks associated with the presence of an open flame and hydrogen Kr PDPID The recommended proportion is 1 4 Kr in He as the discharge gas The krypton emission consists principally of resonance lines at 10 6 eV and 10 1 eV The Kr PDPID can detect compounds with IP lt 10 6 eV which includes unsaturated and cyclic hydrocarbons alcohols aldehydes organic acids esters etc Xe PDPID The recommended proportion is 0 8 Xe in He as the discharge gas The xenon emission consists principally of resonance lines at 9 6 eV and 8 4 eV and can detect compounds with IP lt 9 6 like aromatics ethers alcohols aldehydes etc In addition to the specific compounds named in the three paragraphs above certain important inorganic compounds like ammonia hydrogen peroxide arsenic trichloride hydrogen sulfide arsine phosphine nitric oxide carbon disulfide etc can be selectively detected using the appropriate photoionization mode Each dopant gas requires an additio
6. Kr in 99 999 He balance e Xe PDPID mode 0 8 0 2 Xe in 99 999 He balance For Model D 2 I i Detector Mode PDHID Ar PDPID Kr PDPID Xe PDPID Discharge gas 2 Ar in He 1 5 Kr in He 0 8 Xe in He 7 Any gas including He which has an ionization potential greater than 12 eV Any gas including He which has an ionization potential greater than 11 eV Purity Specifications e Helium discharge and carrier gas must have a minimum purity of 99 999 with lt 20 ppm Ne impurity For trace analysis of fixed gases we strongly recomment 99 9999 purity He with lt 0 5 ppm Ne e Ar PDPID mode 2 0 2 Ar in 99 999 He balance e Kr PDPID mode 1 5 0 1 Kr in 99 999 He balance e Xe PDPID mode 0 8 0 2 Xe in 99 999 He balance System Requirements 12 GC Column Selection To prevent detector contamination we strongly recom mend disconnecting the column from the detector dur ing column bakeout procedures PD D2 The PD D2 is optimized for packed columns with OD of 1 16 or less Some of the stationary phases may not be compatible due to higher column bleed manifesting in high detector background current If you must use a packed column or a metal or metal coated fused silica capillary column consult the factory for more information Best detector performance is obtained with bonded phase fused silica capillary columns with an ID between 0 25 0 82 mm Megabore columns can be used but the column flow
7. Since the distance from the helium supply to the GC varies from installation to installation we do not supply tubing to go from that point to the GC HELIUM DISCHARGE GAS PURIFIER INLET TGA R 30F60P RESTRICTOR 30 mL min minimum DOPANT VENT O G vent ie DISCHARGE GAS 99 999 He COLUMN INLET fcon H necro H GAS CHROMATOGRAPH DOPANT GAS 3 Xe in He TGA R 04F30P RESTRICTOR Figure 3 Gas connections for a PD D2 in the ECD mode Installation DISCHARGE GAS 15 HELIUM PURIFIER INLET TGA R 50F50P TEE RESTRICTOR 211 50 mL min minimum DISCHARGE GAS 99 999 He COLUMN INLET GAS CHROMATOGRAPH VENT Figure 4 Gas connections for a PD D2 IS system Installing and Purging the Gas Regulator 1 Make sure the on off valve on the helium cylinder is completely closed Screw the CGA fitting nut of the regulator into the helium cylinder Go beyond finger tight but do not tighten the nut all the way some leakage is required for the purging operation 2 Turn the output pressure regulating knob completely counterclockwise 3 Open the cylinder on off valve slightly and quickly close it again 4 Adjust the tightness of the regulator connecting nut to allow a pressure reduction of 690 kPa sec 100 psi sec With a new bottle the gauge should start out at about 14 MPa 2000 psi When the pressure drops int
8. applies only to systems with the PD D2 detector On the PD D2 IS detector the column is connected to the column inlet tube with a 1 16 union and does not extend into the detector 1 Make a mark on the column at the length indicated below for PDHID or PDECD operation as appropriate for your application If a ruler is not handy place the end of the column over the figure below to determine how far into the detector body the column must be inserted Optimum length of column insertion in PDECD mode 101 mm Optimum length of column insertion in PDHID mode 116 mm Remove the knurled nut and plug from the column inlet manifold at the bottom of the detector Slide the nut over the end of the column followed by the appropriate column ferrule FS 4 or FS 5 or ZF 5V for megabore Insert the column through the column inlet manifold at the bottom of the detector Slide it in until the mark is flush with the surface of the knurled nut and secure the column by tightening the knurled nut finger tight only Figure 5 on the next page shows how the column position affects detector performance Testing for Leaks It is critical for the system to be leak tight and an additional check at this point can save many headaches later on To test for leaks 1 On a PD D2 insure that the dopant inlet and vent outlet are plugged Cap the vent outlet tube on the PD D2 IS 2 Pressurize the entire system with helium to 138 kPa 20 psi
9. below see nitial Power Up page 20 the standing current should be observed and logged after any system change Log ging the standing current with and without the column on a regular basis is also an effective monitor of system integrity leaktightness and cleanliness To check sensitivity continuity we recommend tracking the internal standard quantity on column area count Additional log pages can be down loaded from the support manuals section of www vici com Detector Model D 2 1 D 2 Serial Number Date of purchase Date Operator Comments Column Detector Noise Sample Standing temp temp level current C C nA Initial power up IPU 100 IPU detector to analysis temp _ IPU column installed Ambient IPU column to analysis temp
10. component of a truly remarkable detector system Functionally this controller does everything that our previous version did but the new one does it with less power greater efficiency and fewer parts There are some minor changes to the rear panel connectors in this most recent version of the PDD controller Figures 9 and 10 The same signal outputs are provided but they are now all accessed through one output connector ATTENUATED OUTPUT The attenuated signal is normally connected to a strip chart recorder or similar recording device This output is designed for a 1mV full scale strip chart input There is also an internal signal reference at zero volts For best noise performance the shield earth and signal reference should not be connected together The signal from this output is scaled by the attenuation factor set on the front panel HEATER MAINS FUSE MAINS INPUT SWITCH VALCO INSTRUMENTS CO INC MODEL PD C2 MAINS INPUT 115 230V 175VA MAX 50 60 Hz PULSE SUPPLY T2 0A 250V WARNING FOR CONTINUED PROTECTION AGAINST FIRE HAZARD REPLACE FUSE WITH SAME TYPE AND RATING ATTENTION UTILISER UN FUSIBLE DE RECHANGE DE M ME TYPE SIG COM 1V SSSI ATTEN Figure 9 DI OD D D DETECTOR INPUT 15V MAX CAT II OUTPUT CONNECTOR Rear panel of the control module 29 Appendix 30 UNATTENUA
11. our electronics is a reflec tion of newer faster and better components we work very hard to ensure that the final product is completely backwards compatible We acheived this goal with the latest updates to the pulsed discharge controller it will work with any PDD in the field We plan to continue support for older models for a very long time 32 Warranty This Limited Warranty gives the Buyer specific legal rights and a Buyer may also have other rights that vary from state to state For a period of 365 calendar days from the date of shipment Valco Instruments Company Inc hereinafter Seller warrants the goods to be free from defect in material and workmanship to the original purchaser During the warranty period Seller agrees to repair or replace defective and or nonconforming goods or parts without charge for material or labor or at the Sellers option demand return of the goods and tender repayment of the price Buyers exclusive remedy is repair or replacement of defective and nonconforming goods or at Seller s option the repayment of the price Seller excludes and disclaims any liability for lost profits personal injury interruption of service or for consequential incidental or special damages arising out of resuiting from or relating in any manner to these goods This Limited Warranty does not cover defects damage or nonconformity resulting from abuse misuse neglect lack of reasonable care modification
12. scale 20 fA VHz referred to the input 0 1 10 Hz 5 fA VHz referred to the input 0 1 10 Hz 10 msec 10 90 lt 1 Q attenuated 1 KQ unattenuated 1 V 10 V Environmental ratings 10 C 50 C 10 95 relataive humidity Controller only PDHID mode 10 V unattenuated output 10 System Requirements Components Not Included with the Detector System e Helium 99 999 purity and other support gases e Ultra high purity grade gas pressure regulator with stainless steel diaphragm e Any special adapters required for connection to the gas regulator e Flow measuring device System Purity Discharge Carrier Gas Considerations The performance of the detector is adversely affected by the presence of any impurities in the gas streams carrier discharge or dopant We recommend that a quality grade of helium 5 0 99 999 pure or better be used at all times Major gas suppliers offer research grade helium 99 9999 pure which is particularly low in fixed gas impurities and should give good results in a clean system but even the highest quality carrier gas may contain some water vapor and fixed gas impurities hence a helium purifier is included as part of the detector system The discharge gas must always be run through the helium purifier Whenever a new batch of discharge gas is received we recommend performing a blank GC analysis of the gas in the PDHID mode to detect and identify the presence of any imp
13. the D 2 system Description Quantity Product number Detector cell PDHID 1 PD D2 IS Pulse supply module 1 PD M2 Includes Cable controller to pulse supply 1 23477 Controller unit with power cord 1 PD C2 Includes Cable computer unattenuated output 1 1 23136 Cable recorder attenuated output 1 1 23483 Instruction manual 1 MAN PDD Fittings kit 1 PD KIT HID Includes 1 16 gold plated ferrule 5 ZF1GP 1 16 union 2 ZU1 1 16 tee 1 Z7T1 1 8 external to 1 16 internal reducer 1 EZR21 1 8 to 1 16 reducing union 1 EZRU21 Restrictor 50 cc min 50 psi He 1 TGA R 50F50P Table 2 Components of the D 2 I system 5 Introduction 6 MODE RANGE CURRENT SWITCH SWITCH SWITCH 240 Vil Valco Instruments Co Inc 163264128 8 256 280 1X INCREASE TEMPERATURE CONTROL 320 ATTENUATION is CONTROL 80 360 PDHID 10X DECREASE 40 400 ATTENUATION DETEGT R TEMA MODE RANGE CURRENT TEMPERATURE INDICATOR DISCHARGE INDICATOR y V ECD DISCHARGE nA HID ZERO PUSH SWITCH BUTTON DISCHARGE PULSED DISCHARGE CONTROLLER DISPLAY If your controller rear panel does not look jane Bice MANS like this refer to the Appendix on page 29 INPUT SWITCH VALCO INSTRUMENTS CO INC HEATER MODEL PD C2 m 115 230V 175VA MAX MAINSINPUT HEATER ee 50 60 Hz OUTPUT vug T2 0A 250V OUTPUTS WARNING FOR CONTINUED PROTECTION AGAINST FIRE HAZARD REPLACE FUSE WITH SAME TYPE AND RATING ATTEN UNA
14. the gauge registers 345 KPA 50 psi Allow five minutes for equilibration then turn the regulating knob all the way counterclockwise Observe the needle of the output pressure gauge for 15 minutes There will be a slight initial drop but if it doesn t move after that consider that all the connections are tight If necessary use an electronic leak detector to locate any leaks Ifa leak detector is not available tighten all the fittings including the output pressure guage and repressurize the system for another test CAUTION Never use leak detecting fluids on any part of this system Upcap the outlet tube of the purifier and purge the system for 15 to 30 minutes at 60 80 mL min to eliminate air from the purifier getter material Connecting the Discharge Gas to the Detector ie If you are supplying the GC from the helium purifier use the Valco tee ZT1 Otherwise use one of the Valco 1 16 unions ZU1 to connect the outlet tube of the purifier to the inlet of the supplied discharge gas restrictor TGA R 30F60P or TGA R 50F50P Connect the outlet end of the restrictor to a flow measuring device and adjust the helium pressure to obtain a flow of 30 mL min for the PD D2 and 50 mL min for the PD D2 IS After setting the flow rate connect the outlet of the restrictor to the discharge gas inlet tube at the top of the detector Installation 17 Column Connection The following
15. 4 Turn on the MAINS switch located on the back of the controller 5 Set the detector temperature to 100 C with the TEMPERATURE control knob Allow time for the detector and helium purifier to reach temperature 6 Turn on the DISCHARGE switch located on the front of the controller The discharge should start within five minutes Once a system has been up and running the discharge will start within a few seconds In a clean system the discharge will have a peach pink color A purple discharge indicates impurities and or leaks in the discharge gas stream 7 Check the detector standing background current indicated in the LED DISPLAY on the controller and record it in the Detector Performance Log on the last page of this manual The optimum detector background current is 0 5 to 1 5 nA The initial value may be higher but as the detector bakes out at its operating temperature the background current should decrease to the optimum value 8 The recommended detector temperature is 20 C above the column temperature with a minimum of 100 C Set the detector to the operating temperature required for the intended analysis When the detector has reached the set temperature read and record the standing current 9 Install the column as described on page 17 leaving the oven at ambient temperature Start carrier flow then read and record the standing current The difference between this reading and the one previous is the ionization of t
16. A at 10X which does not normally need to be changed A higher set current results in a more sensitive detector but with a correspondingly reduced linear range Mode Selection and Setup 26 10 If the bias voltage is not 1 V or less with a set current of 10 nA the dopant flow rate may need to be adjusted The optimum flow rate is determined by varying the rate until the indicated bias voltage is minimized and then increasing the rate very slightly Figure 7 illustrates the effect on background bias voltage and detector sensitivity with varying dopant flow rates The detector temperature may also have a substantial effect on background bias voltage and sensitivity depending on the compound of interest These effects are illustrated in Figure 8 If the detector background bias voltage still does not reach optimum value try a 12 hour bakeout at 300 C If it still does not optimize there is either a leak in the system or the column effluent is not clean To see if the high background bias voltage is due to the column 1 Loosen the knurled nut and pull the column out 20 mm Secure the nut 2 Watch the detector standing background current indicated in the con troller DISPLAY If the current decreases dramatically then the column must be removed and baked out If the current remains high the system probably has a leak 3 Reinstall the column and repeat the leak test described on page 17 before proceeding Mode Selection an
17. Doped helium is used rather than other pure gases in order to retain the benefits of the helium namely its transparency for Ar Kr an Xe resonance radiation and its efficient cooling of the electrodes Any problems associ ated with the presence of a window between the photon source and the ionization chamber are eliminated In most applications involving current commercial PIDs analyte condensation and decomposition on the window attenuate the lamp energy necessitating frequent cleaning and recalibration Custom gas blends for the pulsed discharge detector are available from leading gas suppliers at special prices Alternatively they may be formu lated on the spot by using appropriate fixed restrictors to mix appropriate Mode Selection and Setup 24 amounts of pure helium and pure dopant through a tee Since all gas streams must pass through a Valco purifier the second option requires an additional purifier for each dopant This may still be more cost effective than requesting a custom blend of the more expensive Kr or Xe since the typical flow rate required for the pure dopant rare gas is about 0 3 1 mL min a small lecture bottle can last for a long time In either case the total dis charge gas flow rate should be the same as specified in Connecting the Discharge Gas to the Detector on page 16 Ar PDPID Changing the discharge gas from helium to a mixture of 2 argon in helium changes the photon energy level from the 17
18. E switch The function of this control is duplicated by an external logic connection see UNATTENUATED OUTPUT below Introduction 8 Display Indicates standing current in the PDHID mode or bias voltage in the PDECD mode auto scaled to the most suitable range In the un zeroed PDHID mode the display indicates the instantaneous signal current in nA After zeroing the display indicates the standing current by which the signal is offset In the PDECD mode the display indicates the controlling bias voltage unless the CURRENT switch or ZERO button is pressed when it indicates the set current ATTENUATED OUTPUT connector Normally connected to a strip chart recorder This output has an unatten uated range of 0 10V and an internal signal reference at zero volts For best noise performance the shield earth and signal reference should not be connected together The signal from this output is scaled by the attenuation factor set on the front panel UNATTENUATED OUTPUT connector Normally connected to a data acquisition system or other recording means For convenience a full scale 0 10V output and a 1 10 scale 0 1V output are provided with an internal signal reference at zero volts For best noise performance the shield earth and signal reference should not be connected together The internal impedance of these outputs is 1000 ohms The connection marked ZERO is a low true 5V logic level input which duplicates t
19. TED OUTPUTS Normally connected to a data acquisition system or other recording means The two unattenuated outputs are 0 10V full scale and O 1V full scale Output are provided with an internal signal reference at zero volts For best noise performance the shield earth and signal reference should not be connected together The internal impedance of these outputs is 1000 ohms ZERO FUNCTION The connection marked ZERO is a low true 5V logic level input which duplicates the function of the front panel ZERO connection of this input to COM through either a relay contact or logic gate is equivalent to pressing the ZERO button Electrical Connections CAUTION Do not use a wrench to tighten the SMC connectors on the bias and electrometer cables Connections should be finger tight only 1 Referring to Figure 10 as necessary connect the bias and electrometer cables as follows the BIAS B cable to the top electrode closest to the discharge electrodes the electrometer cable ELECT to the middle and the BIAS A cable to the bottom electrode This setup is the same for both detector models The bias outputs supply high voltages when power is applied to the unit and caution should be observed when connecting or disconnecting these cables The full scale input current of the electrometer is determined by the RANGE switch Input voltages in excess of 15 VDC may result in damage to the electrometer 2 Connect the high v
20. TTEN ATTENTION UTILISER UN FUSIBLE DE RECHANGE DE M ME TYPE PULSE suppty PULSE UQ SUPPLY Q Q DETECTOR INPUT 15V MAX CAT II ATTENUATED UNATTENUATED OUTPUT OUTPUT ELECTROMETER BIAS B BIAS A Figure 2 Controls and connections on front top and rear panels of the control module Introduction 7 TEMPERATURE control and indicator Sets the temperature C of the detector heater block The indicator is steadily on when maximum power is being applied to the heater steadily off when no power is applied and regularly blinking on off when the set tem perature has been established Note that due to the fail safe mechanism designed into the temperature controller the heater will not operate if mains power is applied before the heater is connected or if the detector is too cold lt 0 C If the heater is disconnected with mains on the unit must first be turned off to restore control of the heater if the unit is operated in a very cold environment the detector should first be gently warmed without power applied The fail safe mechanism will also act under any condition resulting from loss of control e g over heating RTD failure etc If proper procedures have been followed and the controller will not heat the detector there is cause to suspect that the fail safe mechanism has been activated Consult the factory or an authorize
21. VIGI Valco Instruments Co Inc Pulsed Discharge Detector Models D 2 and D 2 I Instruction Manual Rev 2 14 North America South America and Australia Oceania contact Europe Asia and Africa contact Valco Instruments Co Inc VICI AG International 800 367 8424 sales Schenkon Switzerland 713 688 9345 tech Int 41 41 925 6200 phone 713 688 8106 fax Int 41 41 925 6201 fax valco vici com info vici ch This page intentionally left blank for printing purposes Table of Contents Introduction Description and Operating Principles cccceeeeeeeeseeeeeeeeeeeeeeseeeeeseneeeteeees 1 Safety Notes and Information ccccececceeceeeeeeeneeeeeeeeeeeaeeeseeeeseeeeseneeeteaes 3 Symbols Installation Category Safety Maintenance Components of the Detector System cceceeeeeseeeeeeeeeeeeeeeseneeeeeaeeeseneeeteaes 4 Description of Controls erisso einu aana aa aa iaaa 4 SPOCITICATOMS saiscins sss aeae a a a e a EENE 9 System Requirements Components not Included with the Detector System n 10 System PUY sss saoo aaea a ecules wag ceed cay EAE a e aese AE 10 Gas Specifications ersa a ES E N E AES 11 GC ColumM Selecto Mss aianei e e a a dee 12 Installation General Precautions sisien ai e E ai aE i Eaa 13 Mounting the Detector on the GC irssiuves sivuissa enpanada 13 Gas COMME CHONS sesse iai a eaa N AE Ea aa 14 Installing and Purging the Gas Regulator cccccseeeseeeeeeeteeseneeeees 15 Instal
22. d Setup Background bias voltage VO V 104 2 loop Iw 20 nA 27 107 ECD Mode Detector temperature 50C Discharge gas flow rate 32 mL min Iw 20 nA Iw 10 nA 414 0 17 t t t t t t 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 Dopant Flow rate 3 Xe mL min 17 ECD Mode Detector temperature 50C Discharge gas flow rate 32 mL min Sample 50 ppb freon 11 Iw 10 nA a o x x O14 o 0 014 0 001 tN 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 Dopant Flow rate 3 Xe mL min Figure 7 Effect of 3 Xe dopant flow rate on background voltage VO and ECD response Mode Selection and Setup 28 er M P D foe Bias voltage VO V 5 0 50 100 150 200 250 300 Detector temperature C 6 CCl 5 pg non dissociative EC 5 44 CHCl 5 ng dissociative EC Saal 2 234 x oO 2 350 t t t 0 50 100 150 200 250 300 Detector temperature C 1 350 Figure 8 Effect of temperature on background voltage and sensitivity in ECD mode working current 20 nA App endix PD C2 Controller shipping February 2014 HEATER OUTPUT PULSE SUPPLY CONNECTOR If you have been directed to this part of the manual you are probably replacing an older PD C2 controller or have received a new Pulsed Discharge Detector with the latest design If that is the case congratula tions You have the latest and greatest controller as a
23. d representative Note that the maximum temperature for operation of the PD D2 IS is 400 C Heater control may be lost during periods of fast electrical transients The unit will self recover MODE switch Determines the operational mode of the controller and unzeroes the signal output see discussion under ZERO push button This switch changes the bias voltages supplied to the electrodes as required for each detection mode In the PDHID mode the bias voltages are set at 200 and the linearization circuit is inactive in the PDECD mode the bias voltages are internally controlled and the detector output is linearized Note that the D 2 I cannot operate in the PDECD mode RANGE switch Determines the full scale range of the electrometer 100 nA 1X or 10 nA 10X In PDECD mode the high detector background current normally restricts operation to the 1X range CURRENT switch Sets the standing current in PDECD mode Pressing at the top increases the current pressing at the bottom decreases the current ATTENUATION control Determines the attenuation factor for the recorder output ZERO push button Offsets the output signal to zero volts by a measurement of the standing current The offset is applied to the output when the button is released Once set the offset is not changed unless the unit is re zeroed or the mode is changed To remove any applied offset and restore the unit to an un zeroed condition toggle the MODE or RANG
24. en if the unit is turned off Turn off both power switches front and back of the controller and allow the detector to cool down naturally before disconnecting or shutting off the discharge gas e Do not cover the unit with materials or devices which would restrict air circulation e Position the controller unit where the mains switch on the rear panel can be reached easily Mounting the Detector on the GC r x DOPANT GAS INLET DISCHARGE Vertical Mounting ECD MODE GAS INLET eee i DOPANT VENT Most GCs have an existing opening which PpD O venr will allow the PDD to sit vertically on top of the column oven with the column inlet manifold PD D2 top or tube PD D2 IS bottom extending into the oven The PD D2 IS vent tube can either extend into the oven or be carefully bent near the base to remain outside the oven If you are replacing an existing detector you can usually just remove it and set the PDD in its place If not use a drill or chassis punch to drill a hole of the proper size and set the detector in position While trying to match the mounting holes of the base plate to every GC on the market is impractical we have located the mounting holes so that at least two of them will coincide with existing holes on the GC If you had to drill a new hole to mount the PDD you will have to drill new mounting holes as well Orient the detector to allow for easy cable and gas connections DZE
25. est it again repeating as necessary until there is no change in the standing current 4 Repeat the test for every fitting in the discharge gas plumbing 5 Reinstall the column according to the instruction on page 17 When the standing current reaches an acceptable level the detector is ready for use Proceed to the next chapter Mode Selection and Setup If the current stays high use this method to check for leaks at the column detector connection Installation 22 Column Bakeout Precautions To prevent detector contamination we strongly recommend disconnecting the column from the detector during column bakeout procedures When the column in reinstalled after bakeout refer to page 17 if necessary the standing current should be at an acceptable level If you have exhausted these troubleshooting methods and the standing current is still high consult the factory Mode Selection and Setup Helium Ionization Mode Since the PDHID mode provides a better indication of the cleanliness and the integrity leak tightness of the system that mode is utilized for initial testing and startup If the system is operating according to the parameters described thus far it is ready for operation in the PDHID mode In the PD D2 IS the column connects directly to the inlet and cannot be adjusted However the PD D2 may require some additional work on the column positioning If the instructions of Step 1 at the top of page 17
26. he combined impurities in and eluting with the carrier gas The smaller the difference the better the quality of the gas exiting the column 10 Set the column oven to the temperature required for the intended analysis When the oven reaches the set temperature read and record the standing current The difference from the previous reading is the ionization of the column bleed The smaller the difference the better the column is conditioned Installation 21 NOTE Some stationary phases will have a higher bleed than others but are still suitable for this detector However the lower the bleed the lower the chances of contaminating the detector cell From this point the standing current should be observed and logged after any system change In addition logging the standing current with and without the column on a regular basis is an effective monitor of system integrity leak tightness and cleanliness We also recommend tracking the internal standard quantity on column area count for sensitivity continuity Troubleshooting High Background Current If the background current does not drop below 2 nA even after a 12 hour bakeout there is either a leak in the system or the column effluent is not clean To see if the high background current is due to the column 1 Make sure the controller is in the un zeroed condition Refer to the discussion about the ZERO push button on page 7 2 For a PD D2 loosen the knurled nut and p
27. he function of the front panel ZERO connection of this input to COM through either a relay contact or logic gate is equivalent to pressing the ZERO button HEATER OUTPUT connector For connection to the detector heating system ELECTROMETER INPUT cable For connection to the collector electrode of the PD detector The full scale input current is determined by the RANGE switch Input voltages in excess of 15 VDC may result in damage to the electrometer BIAS A B OUTPUT cables For connection only to the bias electrodes of the PD detector in the manner described on page 19 under the heading Electrical Connections These outputs supply high voltages when power is applied to the unit and caution should be observed when connecting or disconnecting these cables NOTE These terminals are for connection only to equipment having no accessible live parts Insulation of external circuits to which these are connected must meet the requirements of EN61010 for 220 VDC working voltage Introduction Specifications Mains line Fuse Pressure 9 115 230 V 50 60 Hz 175 VA 2 A time delay 5 x 20 mm 6 9 kPa 1 psi operating 6 9 MPa 1000 psi max working Maximum temperature PD D2 IS PD D2 Heater power Sensitivity 10X range 1X range Range 10X 1X Noise 1X 10X Risetime Output impedance 400 C 400 C 60 W max 48 V PWM 1 0 V nA 0 1 V nA 1 10 nA full scale 100 nA full
28. ling and Purging the Helium Purifier 16 Connecting the Discharge Gas to the Detector 16 Column COMMBCHION rasins a N E EES 17 TOSUN TOF LEARG sorocaba it a R A 17 Electrical Connections scisisicecgecediceneesec a s asa tabi es aE a Ea eaae 19 Atal IPOWO rp sonsaina a a ydoveceeas ved aeeevdei eneenee es ndaaneteeends 20 Troubleshooting High Background Current cccccceeeeeeeeeeneeeeeeeeeeseeeeteaeees 21 Checking for Leaks in the Discharge Gas Plumbing eceeeee 21 Column Bakeout Precautions cccccceeeeeeeeeeeeeeeeeeeeeeeeseeeeseeeeseeees 22 Mode Selection and Setup Helium lOniZation ModE sossar a 23 Selective Photoionization Mode sssseesseessseesereessrsrnterirssirnsrinrsrnnsrennsrnnnnt 23 Electron Capture Mode s snot aae aoaaa asi a 25 Appendix PD C2 Controller shipping February 2014 Attenuated OUP Uls ecncnianmaia EER 29 Unattonuatod OUtOUtS seuna 30 LOO FUNGON a a oinaudentesapayectcendes 30 Electrical COMMECTIONS Jssinisasisnsii n aia a aaO a 30 Note About Compatibility sssini aa a 31 Wamani ari E E dzet gente tecceeadteeeteaaes 32 Detector Performance LOUren anan EE N 33 This page intentionally left blank for printing purposes Introduction NOTE The contents of this manual apply to either the HID ECD dual mode detection system D 2 or the HID single mode detection system D 2 I In general the manual describes the dual mode detector information which applies specifically t
29. nal helium purifier which must be purged and conditioned in the same manner as the purifier installed on the discharge gas supply If you are using more than one dopant we recommend use of a Valco multiposition stream selection valve so that no fittings have to be disconnected Not only is this convenient it keeps the system closed minimizing chances of contamination When changing from one dopant to another allow at least one hour for the old gas to be purged from the system Mode Selection and Setup 25 Electron Capture Mode PD D2 only Since the PDHID mode provides a better indication of the cleanliness and the integrity leak tightness of the system we utilize that mode for initial testing If the system is operating according to the parameters described thus far it is ready for operation in the PDHID mode To configure the PD D2 to operate in the PDECD mode 1 If the discharge is not already established turn on the MAINS switch and the DISCHARGE switch The discharge should start within five minutes 2 Set the MODE switch on the controller to PDECD 3 Set the detector temperature with the TEMPERATURE control knob 4 Set the electrometer RANGE switch to 1X The high detector back ground current associated with the PDECD mode normally precludes operation in the 10X range Leave the BIAS B cable alone Remove the BIAS A cable and move the ELECTROMETER cable to the bottom electrode Remember that connecti
30. nce of analyte A K is the electron capture coefficient and A is the concentration of A The majority of commercially available ECDs use a variable frequency constant current technique to increase the linear Introduction 3 dynamic range whereas in the D 2 a unique system of feedback to the bias electrode is employed It operates by comparing the detector output current to a reference value and changing the bias voltage to maintain the detector current at the reference value E g in the presence of an electron capturing compound the bias voltage must be raised to maintain constant detector current The bias voltage scaled to an appropriate range is the linearized output signal representing the concentration of the capturing compound This results in a linear dynamic range of more than five orders of magnitude The feedback is incorporated in such a way that it is by passed in the PDHID mode Safety Notes and Information Symbols HIGH VOLTAGE Voltages presenting the risk of electric shock are present in several places in the equipment Avoid contact with hazard ous live parts Do not probe into openings or attempt to defeat safety mechanisms HOT SURFACE The surface of the detector body may be hot while in op eration possibly in excess of 250 C Caution should be observed ATTENTION Refer to the manual PROTECTIVE EARTH This internal connection provides protection against electric shock from mains voltage
31. o the 1 4 3 4 MPa 200 500 psi range open the cylinder on off valve slightly and quickly close it again Repeat Step 5 eight or ten times to be certain that all the air is purged On the final purge tighten the regulator connecting nut very securely as the pressure approaches the 2 1 3 4 MPa 300 500 psi range Open the cylinder valve to pressurize the regulator once again Close the valve and observe the needle of the high pressure gauge for 15 minutes If it doesn t move there is no critical leak on the high pressure side of the regulator CAUTION Never use leak detecting fluids on any part of this system Installation 16 Installing and Purging the Helium Purifier 1 If the pressure regulator has a 1 8 male cone type outlet port install the Valco 1 8 external to 1 16 internal reducer EZR21 if it has a 1 4 male cone type outlet port install the Valco 1 4 external to 1 16 internal reducer EZR41 For other regulator outlet fittings a wide variety of Valco adapters are available Remove the cap from the inlet tube of the Valco helium purifier and insert the tube fitting into the 1 16 reducer port Keep the outlet tube capped Use a 1 4 wrench to turn the nut one quarter turn past the point where the ferrule first starts to grab the tubing Do not remove the fitting When made up properly it should be leak tight Turn the output pressure regulating knob clockwise until
32. o the single mode detector is so indicated Description and Operating Principle The pulsed discharge detector is a non radioactive universal detector which can easily be configured to function as a helium ionization detector HID photoionization detector PID or electron capture detector ECD A schematic representation of the two configurations is shown in Figure 1 As the name implies a stable low power pulsed DC discharge in helium is utilized as the ionization source Elutants from the column flowing counter to the flow of helium from the discharge zone are ionized by photons from the helium discharge above Resulting electrons are focused toward the collector electrode by the two bias electrodes The principal mode of ionization is photoionization by radiation arising from the transition of diatomic helium He A di to the dissociative 2He 1S ground state This is the well known Hopfield emission The photon energy from the He continuum is in the range of 13 5 eV to 17 7 eV HELIUM INLET HELIUM INLET DISCHARGE ZONE DISCHARGE ZONE SPRING WASHERS SPRING WASHERS DISCHARGE ELECTRODES QUARTZ QUARTZ INSULATOR GROUND GROUND INSULATOR DOPANT INLET i BIAS ELECTRODE BIAS ELECTRODE A JES COLLECTOR ELECTRODE COLLECTOR ELECTRODE BIAS ELECTRODE SAPPHIRE SAPPHIRE INSULATORS INSULATORS
33. oltage cable from the detector to the pulse supply and connect the pulse supply cable between the back of the controller and the pulse supply 3 Connect the heater cable from the detector to the back of the controller This connector is identical in function to the one on previous controllers so that detectors can interchange between revisions of controllers how ever the location has moved inline with other connectors in the newest version of the controller NOTE These terminals are for connection only to equipment having no accessible live parts Insulation of external circuits to which these are connected must meet the requirements of EN61010 for 220 VDC working voltage Appendix DETECTOR VOLTAGE ECD MODE BIAS B GROUND 31 HIGH D ELECTROMETER BIAS B BIAS A HID MODE _BIAS B DISCHARGE MODULE HEATER CABLE FROM DETECTOR CONTROLLER Rear panel E AAs CG ae 10 V out BLACK Signal common WHITE 1V out GREEN Attenuated out BROWN Common BLUE Zero ORANGE 4 15 VDC YELLOW 15 VDC Figure 10 Electrical connections Note About Compatibility Obsolescence planning is a significant portion of manufacturing control as the speed at which electronic components come to market and reach end of life continues to increase While each revision of
34. ons should be finger tight only High voltage will be present on the BIAS A cable during operation Cover the end of the cable with tape or otherwise protect the end from accidental contact with persons or equipment Disconnect the column and leave the column inlet open Reinstall the column as indicated in on page 17 The suggested range for the column position is from 99 to 102 mm wherein the detector response not the background current is within 90 of the maximum Since there may be some variation in the flow rate for the different types of capillary columns you may need to optimize the column position within this suggested range With the dopant line still disconnected set the dopant gas 3 xenon in helium flow rate to 5 7 mL min 0 2 mL min In some circumstances methane in helium may be used as the dopant to affect a cost savings Consult the factory for recommendations Remove the plug from the DOPANT port on the detector and replace it with the dopant gas line Check the BIAS B voltage indicated by the controller DISPLAY If the displayed voltage is 0 5 1 V at room temperature the system is ready for operation A bias voltage less than 0 5 V can result in an unstable erratic and noisy system In the PDECD mode the bias voltage is internally controlled to obtain a constant detector current set by means of the CURRENT switch The power up default value for this current is 10 nA at 1X 1 n
35. or the attachment of improper devices to the goods This Limited Warranty does not cover expendable items This warranty is VOID when repairs are performed by a nonauthorized service center or representative For infor mation about authorized service centers or representatives write Customer Repairs Valco Instruments Company Inc P O Box 55603 Houston Texas 77255 or phone 713 688 9345 At Seller s option repairs or replace ments will be made on site or at the factory If repairs or replacements are to be made at the factory Buyer shall return the goods prepaid and bear all the risks of loss until delivered to the factory If Seller returns the goods they will be delivered prepaid and Seller will bear all risks of loss until de livery to Buyer Buyer and Seller agree that this Limited Warranty shall be governed by and construed in accordance with the laws of the State of Texas The warranties contained in this agreement are in lieu of all other warranties expressed or implied including the warranties of merchantability and fitness for a particular purpose This Limited Warranty supercedes all prior proposals or representations oral or written and constitutes the entire understanding regarding the warranties made by Seller to Buyer This Limited Warranty may not be expanded or modified except in writing signed by the parties hereto Detector Performance Log In addition to the occasions indicated in the Comments area of the table
36. rate should not exceed 15 mL min Excessive column flow rates may allow diffusion of the analytes into the discharge region PD D2 IS The PD D2 IS is optimized for 1 8 packed columns The column tubing must be thoroughly cleaned and baked before the column is packed Even when the best care is taken in column tubing cleaning and in the support and stationary phase selection a new column will often bleed compounds resulting in a considerable increase in the detector baseline This initial bleed will usually be reduced to acceptable levels after the column is con ditioned with clean carrier gas flow for several hours at the recommended bakeout temperature The PD D2 IS can also be used with megabore columns Installation The detector is usually mounted on top of the GC column oven The cabling as supplied requires the discharge module to be located within 0 6 m 2 of the detector and the controller to be within 1 m 3 5 of the detector and discharge module The power cord for the controller is 1 8 m 6 long and the signal output cables attenuated and unattenuated are 1 2 m 4 long General Precautions e Do not use plastic polymer or copper tubes for gas handling and interconnectons Use only stainless steel tubing with Valco gold plated ferrules e Do not turn the unit on until the helium discharge gas is flowing through the detector e Do not shut off or disconnect the discharge gas when the detector is hot ev
37. s and should not be removed OPE Installation Category This equipment has been designed for installation category overvoltage category II pollution degree 2 It has been approved for use in heavy industrial environments It has been tested to EN Class A limits and may not be used in residential environments Safety This instrument has been designed and tested in accordance with the product safety standard EN61010 It has left the factory in a safe condition This instruction manual contains important information and warnings which must be followed by the user to insure safe operation and to retain the instrument in a safe condition The case chassis and measuring terminals are connected to the protective earth contact of the mains inlet The instrument operates with a three conductor power cord having a protective earthing conductor and a plug with an earthing contact The Introduction 4 mains line plug shall only be inserted in a socket outlet provided with a protective earth contact The protective action must not be negated by the use of an extension cord without a protective conductor Use only with an approved mains supply cord having a rating of 2A 250V or greater Do not use this equipment in a manner not specified herein CAUTION During normal operation the detector pro duces ultraviolet energy UVA UVB some of which may be emitted Do not watch the arc without eye protection Maintenance The e
38. ull the column out 20 mm Secure the nut For a PD D2 IS completely disconnect the column from the column inlet tube leaving the inlet open 3 Watch the detector standing background current indicated in the control ler DISPLAY If the current remains high then either the system has a leak in the discharge gas supply line or the discharge gas has impurities in it Proceed to the next section Checking for Leaks in the Discharge Gas Plumbing If the current decreases dramatically then either the carrier gas supply has leaks and or contaminants or the column is the source of contamination and needs a bakeout Read the Column Bakeout Precautions on the next page before proceeding Checking for Leaks in the Discharge Gas Plumbing Leaks can be detected with hydrogen A small lecture bottle of hydrogen with a regulated flow of 10 15 mL min through a small outlet tube is all that is required This method can only be used to detect leaks on the discharge gas side of the plumbing and between the column and detector inlet 1 Make sure the controller is in its un zeroed condition Refer to the discussion about the ZERO push button on page 7 2 Hold the hydrogen outlet tube at a fitting connection for ten seconds while monitoring the standing current display on the controller 3 If the current remains the same proceed to the next fitting If the current increases there is a leak at that connection Tighten the fitting and t
39. upply and connect the pulse supply cable between the back of the controller and the pulse supply Connect the heater cable from the detector to the back of the controller HIGH DETECTOR VOLTAGE ECD MODE BIAS B D GROUND oy ELECTROMETER HID MODE _BIAS B DISCHARGE MODULE HEATER CABLE FROM DETECTOR If your controller rear panel does not look like this refer to page 31 in the Appendix CONTROLLER Rear panel RED Black 0 10 Common UNATTENUATED ATTENUATED RED WHITE _ 9 4y OUTPUT OUTPUT BLACK GREEN z Shield COMPUTER OR RECORDER lt SHIELD GREEN BROWN _ com AG INTEGRATOR WHITE BLUE gry ETO ORANGE YELLOW Figure 6 Electrical connections Installation 20 Initial Power Up NOTE This section refers to the D 2 operating in the HID mode and to the D 2 I For instructions on using the D 2 in the ECD mode see page 25 However we recommend that D 2 users test system integrity by proceeding with the instructions below before switching to the ECD mode 1 Set the MODE switch on the front of the controller to PDHID 2 Set the discharge gas flow as specified in on page 16 in the section entitled Connecting the Discharge Gas to the Detector CAUTION Always make sure that discharge gas is flow ing before powering up the detector 3 Apply power to the helium purifier
40. urities Gas purity requirements are specified in the next section Tubing Standards of cleanliness that are suitable for many GC applications may be totally inadequate for the sensitive PDHID PDPID PDECD work All surfaces that contact the gas stream must be glass or stainless steel Do not use copper tubing or brass fittings All tubes must be thoroughly cleaned and baked before use Flow Controllers The use of valves or flow controllers in which the gas stream is exposed to any polymer based packing or lubricating material is to be particularly avoided Pressure Regulators We recommend commercial ultra pure grade regulators with stainless steel diaphragms Regulators with diaphragms made of neoprene or other elastomers should never be used System Requirements 11 Gas Specifications For Model D 2 ee reece rane arom voor eroro amoroase tone vom Any gas including He which has an ionization potential greater than 12 eV Any gas including He which has an ionization potential greater than 11 eV The helium purifier HP2 supplied with the system must be used for the discharge gas Purity Specifications e Helium discharge and carrier gas must have a minimum purity of 99 999 with lt 20 ppm Ne impurity For trace analysis of fixed gases we strongly recomment 99 9999 purity He with lt 0 5 ppm Ne e Ar PDPID mode 2 0 3 Ar in 99 999 He balance e Kr PDPID mode 1 5 0 1
41. were properly executed the column should already be properly positioned at 116 mm 1 mm The suggested range for the column position is between 112 mm and 117 mm wherein the detector response not the background current is within 90 of the maximum Since there may be some variation in the flow rate for the different types of capillary columns the user may want to optimize the column position within this suggested range DO NOT insert the column more than 118 mm With this flow configuration only pure helium passes through the discharge region minimizing the chance of discharge electrode contamination through contact with eluting samples However if very high concentrations of organic compounds are introduced for extended periods of time they could diffuse into the discharge region and contaminate the electrodes Under normal chromatographic use with capillary columns such contamination is negligible even over extended periods Selective Photoionization Mode Since the pulsed discharge detector is essentially a windowless helium photoionization detector changing the discharge gas from pure helium to helium doped with argon krypton or xenon changes the discharge emission profile This results in a change in the photon energy due to additional resonance atomic emissions and diatomic emissions from the rare gas added Thus a single detector can be operated in any of the three photoionization detector PID modes Ar Kr or Xe PID
42. xterior of the instrument should be cleaned regularly with a dusting brush If necessary the casing can be cleaned with a moistened cloth 99 water 1 mild detergent Spirit or petroleum ether can be used to remove greasy dirt Any other cleaning agents can attack the plastic and painted surfaces Under no circumstances should the cleaning fluid get into the instrument Petroleum ether is flammable and care should be taken in its use Under no circumstances should the detector be disassembled for cleaning The components of the detector are assembled with special tooling and held under considerable force Disassembly of the detector may present a safety hazard and will result in its destruction Components of the Detector Systems Components of the detector system are listed in Tables 1 and 2 Check the contents of the packages to verify that everything is present Contact the factory if anything is missing or damaged NOTE damaged shipments must remain with the original packaging for freight company inspection Description of Controls Controls and connectors are indicated in Figure 2 NOTE In early 2014 we began shipping a redesigned controller If the rear panel of your controller does not look like the one in Figure 2 please refer to the appendix on page 29 MAINS switch Controls mains line voltage to the controller unit When this switch is on the unit is operational except for the pulse supply see the next paragraph
43. zation potentials less than or equal to the dopant gas emission energy In this configuration the detector is essentially functioning as a specific photoionization detector for selective determination of aliphatics aromatics and amines as well as other species Since there is no lamp or window sensitivity will not change with time Electron Capture PDECD In the electron capture mode the PDECD is a selective detector for monitoring compounds with high electron affinity such as CFCs chlorinated pesticides and other halogenated compounds The MDQ for this type of compound is at the femtogram 10 level Response characteristics and sensitivity are similar to those of a radioactive Ni ECD In addition to minor configuration changes running in the ECD mode requires the addition of a dopant gas recommended is 3 xenon in helium The dopant gas is first ionized by the photons from the discharge Resulting electrons in the absence of any electron capturing compounds constitute the detector standing current Electron capture processes occur when electron capturing compounds enter the detector resulting in a decrease in the detector standing current which constitutes the PDECD response That the constant potential ECD response is not linear over a wide range is well known The signal from the PDECD is best described by I 1 Ig KA x A where Ip is the detector standing current I is the detector current measured in the prese
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