TROUBLESHOOTING GUIDE
Contents
1. Symptom Possible Cause Remedy Symptom No 14 cont d 6 Air peaks or H20 peaks 6 This is not a trouble symptom but normal with TCD using syringe injection or an aqueous sample 7 Multiple or incomplete deriva 7 Re evaluate derivatization proce tives formed in sample work up dure 8 Sample decomposition 8 Try lower temperature and or dif ferent column Problem Problem Symptom No 15 Tailing Peaks 1 Column or injection port temper 1 Increase temperature do not ex ature too low ceed maximum temperature for column 2 Column deteriorating 2 If peaks tail on old column but re tention times have not changed from what they were when col umn was new replacing first 6 of packing or replacing the pre column may help If retention Normal times have changed column prob ably should be replaced 3 Active sample adsorbing on injec 3 Use more inert system all glass tion port transfer lines column or Teflon specially designed pack or glass wool ing on column injection and proper glass wool type 4 Two compounds eluting 4 Increase sensitivity and reduce sample size Reduce temperature approximately 20 C and look for partial separation Problem 5 Needle hitting and breaking pack 5 Remove some packing so needle ing in column inlet won t penetrate it Symptom No 16 Leading Peaks 1 Column overload i 1 Decrease sample size 2 Two components eluting 2 Decrease sample size i2. NOTE If your instrument is equipped with dual channels detector electrometer record er etc see paragraph c a Check the recorder by setting the gas chromatograph s attenuation to infinity The recorder pen should go to electronic zero If the symptom baseline drift noise etc disappears the recorder is not the problem If the symptom continues refer to the recorder instruction manual b To isolate the detector FID as the source of trouble turn off the instrument and disconnect the cable at the detector end from the detector to the electrometer Note To prevent inducing extraneous noise onto the cable it may be necessary to install a coaxial cap on the free end If the symptom disappears when power is on the problem is the detector If the symptom con tinues disconnect the same cable at the electrometer If the symptom now disappears the cable is defective Replace it If the symptom still continues refer to the electrometer instrument manual c If your chromatograph is equipped with dual detector channels you have a simple but effective alternate means of identifying the problem source using the sec ond or parallel detector and electrometer If the symp tom occurs in channel A disconnect at the detectors shown below the cables which connect channels A and B detector outputs to channels A and B electrometer inputs Reconnect the cable from electrometer B input to the output of detector A This
3. high pressure drop 2 Insufficient carrier gas source pres 2 Increase gauge pressure by 10psig sure 3 Insufficient source pressure for 3 Flow control must have 10 15psig temperature program higher than maximum pressure reached at maximum tempera ture to function properly 4 Plugged injection port carrier gas 4 Replace tubing or gas purifiers as line or gas purifiers required 5 Column over packed or glass wool 5 Increase carrier gas pressure too tight Note not all packings have same Pressure drop If flow is still in sufficient install another column If flow is okay column was the problem If not check plumbing system for flow restrictions e g plugged detector plugged gas fil ters etc 19 Symptom Possible Cause Remedy Symptom No 33 Column deteriorates too soon after installation peaks tail are poorly resolved etc NE h Normal L Problem 1 Operating column near or above maximum temperature limit of packing 2 Water or O in carrier gas is con taminating column 3 O contamination due to column leaks 4 Aqueous samples serum plasma and other complex samples Use higher temperature phase b Use shorter column and lower temperature if possible c Reduce temperature when col umn is not in use d Remove column when another column is used at higher tem perature 2 Use carrier gas purifi
4. AMINES Bulletin Number Acylation 721 Aliphatic and Aromatic Amines acylation columns separations 737 Nitrosamine Priority Pollutants 775 N Nitrosamines contaminants in foods or wastewater 791 Phenylenediamines GC HPLC 805 AMINO ACIDS PROTEINS Homologs and Polymers separation by size exclusion HPLC HPLC 796 Proteins HPLC 795 APPARATUS Capillary Column Butt Connector 801 Glass GC Columns of Consistent Dimensions 804
5. and con or cables nections per instrument manual 10 Bad connection between FID col 10 Check collector spring clip con lector and voltage source nection Symptom No 2 Solvent peak only or missing 1 Sample too dilute 1 Check system by injecting with peak known standard If okay increase sensitivity or inject larger or more concentrated sample 2 Column or septum leak 2 Check for leaks see page 4 Tighten connections Replace septum 3 Incorrect temperatures 3 a Injection port or column a Ensure that the selected col temperature too low sam umn temperature setting is Normal ple not vaporized correct for column being used and the sample being analyzed Then verify that the oven is operating at the selected temperature In crease the temperature as re quired b Injection port temperature b Decrease injection port tem too high for thermally labile perature Ee compounds Problem c Column temperature too c Decrease column tempera high sample eluting in sol ture vent peak Flow rate incorrect 4 Measure column flow rate and ad just if necessary see page 3 5 Sample adsorption by column 5 Inject standard on known good or glass wool column If okay original column is bad Use properly treated glass wool Problem ie H3PO4 for free acid analysi silicone treated for other com pounds If sample has never been analyzed and is active chemically you may need a special column 6
6. ap propriate Glasrench for the ferrule you are using The Supelco septum nut torque wrench ensures that the cor rect torque is consistently applied when installing septum nuts SAMPLE INJECTION Improper sample injection can cause many problems in gas chromatography To ensure that your injections are accurate and reproducible the following general guidelines and procedures are recommended A Syringe Size Always use a syringe large enough that the desired sample volume does not fill it to capacity and small enough that the sample volume is not less than approx imately 10 of its capacity B Injection Technique Sample injection should be smooth and rapid with quick removal of the syringe after injection in order to avoid peak broadening C Sample Size Reproducibility Many problems in chroma tography result from difficulties in reproducing the size of a sample Some techniques which will help ensure repro ducible samples are discussed below 1 Automatic Injectors These devices improve sample reproducibility by virtue of consistent mechanical opera tion Each step syringe cleaning sampling and sam ple injection is repeated precisely Sampling Valve Injection Sample reproducibility is im proved because chances for variability are greatly re duced Sample size is determined solely by sample loop size and injection is rapid and precise Solvent Flush Technique The following technique is recommended to reduce th
7. applies the signal from the detector output of channel A to the electrometer in put and recorder of channel B If the symptom does not appear on recorder channel B after this cable change then either the electrometer recorder or cables of chan nel A are defective If the symptom is not eliminated the detector of channel A is the problem source aae l ECAN y ane Sec fk 7 Check the carrier gas system for possible problems Refer to the following section Checking the Carrier Gas System g J CHECKING THE CARRIER GAS SYSTEM Atypical carrier gas system is illustrated at the bottom of this page The most common problem within this system is insuffi cient carrier gas flow through the chromatographic column This is generally caused by 1 insufficient source pressure 2 leaks and or 3 an unusually large pressure drop across one of the components in the system Verify the column carrier gas flow at the detector exit using a soap bubble flow meter and a stopwatch We do not recom mend using rotameters for measuring gas flow because specific rotameters are required for each type of gas used and they pos sess a definite linear response range with pressure changes To verify that the carrier gas flow rate is properly adjusted the time required for the soap bubble to travel a specified distance at the desired flow rate should be calculated as follows Time sec Volume Observed cc x 60 sec min Desired
8. smooth rapid injection Repack first 6 of column or re place column a Unresolved peaks after previous column of the same composition produced good results Normal 1 Column too long too short 2 More less packing in column due to a change in support density b packed more tightly loose ly c column inner diameter dif ferent 3 Percent coating increased de creased either due to different manufacturing procedures or er rors 4 Different stationary phase used or slight variation in phase compo sition particularly commercial chemicals not manufactured for GC Different support type Each of these problem sources can be remedied by using pre tested standardized columns and packing materials Symptom Possible Cause Remedy Symptom No 30 Large gaps appear in Improperly packed column Add enough packing to fill in voids packing in glass column then gently vibrate until smooth If this does not solve the problem col umn should be repacked L d Symptom No 31 Packing compacting or 1 Slight compacting may occur 1 You can use this column Shifts shrinking after conditioning when packings are exposed to are not normally a problem pressure Large shift 3 or greater 2 Column may not be properly packed Add more packing Symptom No 32 Low carrier gas flow and 1 Overtightened septum 1 Loosen septum
9. standard technique d Inconsistent quantitation for same sample on successive analyses e Low values for minor com pounds f Increased peak response with successive injections b 1 Differing detector response for different components 2 Adsorption of components by packing glass wool tub ing or transfer lines Internal standard not com pensating for all components in sample 2 Slope sensitivity of integra tion not high enough for late eluters Insufficient resolution of peaks or peak tailing Sample size too small for ac curate counting by integrator Adsorption of components and saturation of active sites with sample priming the column b 1 Determine correction fac tors and or use internal standards techniques 2 Use deactivated system c 1 Use multiple internal stan dards 2 Use multiple internal stan dards d Modify operating parameters or replace column to improve resolution and eliminate tailing e Increase sample size or elec trometer range setting f Use deactivated system Symptom No 6 Baseline off scale cannot zero 100 A E Normal w p A o lt Problem i Column not conditioned properly T contaminated column or temper ature too high Recorder problem Septum leak Wrong gases e g argon methane with flame Contamination Too much or too little gas flow Imbalance in column flow if using T
10. that you first turn off the chromatograph oven and allow the column to cool for 10 to 15 minutes then turn off the carrier gas Cooling the column and turning off the carrier gas protects your column in two ways allowing the column to cool prevents oxidation of the column packing which can occur when a hot column is exposed to oxygen in the air Allowing the column pressure to drop to am bient pressure prevents the packing from popping or blowing out of the column ends A sudden change in pressure when a col umn or a septum is removed with the carrier gas flowing can blow packing from the column NOTE When storing columns cap the ends with metal Swagelok caps to prevent diffusion of air and subsequent oxidation into the column Plastic caps do not prevent diffusion of air into the column Improperly installed columns and septa are a frequent source of leaks and are the most common cause of glass column break age Incorrectly tightened septum nuts present problems such as excessive septum bleed premature occurrence of septum leaks and low carrier gas flow rates Supelco offers two types of torque wrenches to help ensure correct installation of columns and septa The Glasrench used for installing columns is available in two different torque settings to provide the correct torque for the various types of ferrules This saves both analysis time and money by eliminating leaks over tightening and column breakage Select and use the
11. type and repack inlet LJ side of column ne Always use sharp syringe needle formal and inject in same place Use of a needle guide is recommended 4 Column bleed or contamination Replace column with known good column If okay column requires reconditioning I 5 Gas flows not within minimum 5 Measure flows and verify against maximum limits including H2 manual specifications MO and air on FID or poorly regu hit lated flow Ea 6 Insufficient instrument warm up 6 Allow time for instrument to ei time or temperature equilibration equilibrate when changing oper time ating temperature or installing another column 7 Defective electrometer or detector Troubleshoot as in Isolation of Problem Source section 8 Contaminated detector or injec 8 Clean as recommended in instru tion port ment manual Symptom No 8 Irregular or unstable baseline 1 Column bleed or contamination i Check out with good column if okay recondition bad column 2 Contaminated detector or injec 2 Clean detector and or injection tion port port 3 Carrier gas leak 3 Check for and correct septum or _ Normal column leaks see page 4 4 Poor carrier gas regulation 4 Check carrier gas supply for suf ficient pressure Replace tank if it is near empty 5 Gas impurities or contaminated Change gas tank use gas purifier gas line and clean metal tubing Problem ste ae x 6 Gas flows not within minimum Measu
12. use with capillary columns TESTING FOR LEAKS The most common method of leak testing is to apply liquids such as Snoop or HT Leak Detector and then watch for bub bles to appear Exercise care when using these liquids since they can contaminate your chromatographic system causing unstable baselines and ghost peaks in subsequent chromatograms These liquids can enter the GC system through an aspirator effect Several devices are available for leak testing such as ther mal conductivity leak detectors and pressure gauges The lat ter were discussed in the previous section When pressure guage readings indicate a possible leak take the appropriate corrective action such as tightening the fittings which would cause this abnormal pressure reading rather than verifying the leak point with Snoop or HT Leak Detector and possibly contam inating the chromatographic system A specific technique for test ing small septum leaks while avoiding contamination employs the Supelco leak tester a plastic capillary tube with two conical ends One end is dipped into Snoop and capillary action pulls a small amount of Snoop into the tube If a leak is present bub bles appear at this end when the opposite end is pressed against the septum nut P3 Septum TA Injection Port Particle Detector Trap Column PROBLEMS RELATED TO COLUMN amp SEPTUM REMOVAL amp INSTALLATION When changing columns or septa it is important
13. CD Contaminated detector such as nitrogen phosphorous detector NPD with Snoop or ECD with chlorinated solvents Electrometer or detector problem Verify by reducing column tem perature to ambient If baseline is normal check system with good column If okay recondition bad column 2 Set attenuation to infinity If re corder goes to electrical zero it s okay If it does not go to zero troubleshoot recorder per recor der manual Check septum for leaks and cor rect leaks if required see page 4 Verify gases are correct for instru ment and detector as specified in manual 5 Turn off injection port heat If zeroing capability returns clean injection port liners etc 6 Check and adjust to within manu al specifications 7 Check and adjust as required 8 Avoid sources of contamination ie Don t use Snoop with NPD or chlorinated solvents with ECD 9 Troubleshoot instrument per man ual Tr Symptom Possible Cause Remedy Symptom No 7 Baseline drift te Carrier gas flow changing with temperature during temperature programming 1 Increase carrier gas source pres sure to 15psig above column head pressure to detector wire causes AC noise 2 Septum or column leaks Check and correct as required see page 4 3 Septum bleed or septum fragments Replace septum with higher tem in column perature
14. Column cannot separate compo 6 Change column or solvent Symptom Possible Cause Remedy Symptom No 3 Low response all correct 1 Poor injection technique 1 Use correct syringe size and sol retention time vent flush techniques see pages 4 and 5 2 Wrong sensitivity setting or sam 2 Check and correct if necessary pleisize toosmall Inject standard sample for com parison 3 Defective syringe 3 Use new syringe 4 Septum leak 4 Replace septum 5 Injection port temperature too 5 Increase injection port tempera Normal low for sample ture 6 FID only H3 or air flow incor 6 Measure and correct if necessary rect 7 FID only low Op level in com 7 Replace air tank pressed air 8 FID only faulty connection be 8 Clean collector spring clip with tween FID collector and voltage emory paper source 9 Dirty electron capture detector 9 Clean per instrument manual Problem ECD 10 a Thermal conductivity detec 10 a Measure and adjust carrier tor TCD carrier gas flow gas flow if necessary rate is incorrect b Cell voltage is incorrect b Refer to instrument manual 11 Adsorption of sample by column 11 Use deactivated column materials glass wool tubing etc 12 Flame photometric detector FPD 12 Check with known standard hy only hydrocarbon eluting with drocarbon free and change to col sample causi
15. Flow cc min Where Time Sec time required for the bubble to travel the observed distance Volume Observed volume indicated by the soap bubble flow meter Desired Flow the rate specified by the method being used Example Obtain a flow rate of 20 cc min using a 10cc soap bubble meter Time sec 10cc x 60 sec min 20ce min Time sec 30 sec If the time required is not equal to the calculated time adjust the carrier gas flow rate If sufficient flow cannot be obtained by adjusting the flow control valve the problem is probably due to inadequate source pressure observed at P1 Increasing this pressure will usually provide adequate flow Normally a source pressure of 60psig is sufficient for 6 to 12 foot columns Remem ber increasing the column length oven temperature and or flow rate will require raising the source pressure The source pressure is particularly important if you are using a temperature program since the pressure must be 10 15psig in excess of the column pressure drop at the maximum temperature This pressure dif ference allows the differential flow controller to function proper ly If the correct pressure difference is not maintained carrier gas flow will drop drastically at elevated temperatures Typical Carrier Gas System ad P2 Rotameter Oxygen Trap Molecular Sieve Trap Control Valve Carrier Source Other common causes of inadequate gas flow a
16. LESHOOTING TABLE Symptom Possible Cause Remedy Symptom No 1 No Peaks 1 Detector or electrometer power Check detector electrometer set off or fuse blown ting and fuses 2 Sample injected in wrong col Re inject sample in proper column umn in multiple column chromato graph 3 Flame ionization detector FID Check FID with mirror over ex not lit haust If lit HzO condensates on mirror If not lit light flame Check H3 and air flows Normal 4 No carrier gas flow Measure carrier gas at detector or column exit If no carrier gas flow is present check for leaks or ob p structions at column connection Problem and septum Check for adequate pressure at tank and ensure septum is not over tightened flow cut off by septum obstructing the column 5 Defective syringe Replace syringe r nents from solvent Symptom Possible Cause Remedy Symptom No 1 cont d 6 Column or septum leak 6 Replace the septum Check column connections 7 Injection port temperature too 7 Increase injection port tempera low sample not vaporized when ture but not in excess of liquid analyzing high boilers phase temperature limit or inject sample directly onto column packing 8 Defective recorder 8 Check recorder connections Check recorder zero Troubleshoot recorder according to recorder manual 9 Defective detector electrometer 9 Check collector voltage
17. TROUBLESHOOTING GUIDE A feat 1 System Za OSS gt SUPELCO A ROHM AND HAAS COM SUPELCO INC Supelco Park Bellefonte PA 16t Phone 814 359 3441 and 814 359 344 TWX 510 670 3800 FAX 814 359 3044 Copyright 1983 Supelco Inc Bellei ALL RIGHTS RESERVED Changing Column and Septu Guide 792C SUPPLIED BY SUPELCHEM How to Locate Gas Chromatography Problems and Solve Them Yourself By applying a systematic approach to trouble shooting you can solve many of your own GC prob lems The real task is identifying the cause of a prob lem in the shortest possible time This guide outlines techniques that will enable you to troubleshoot your gas chromatography step by step You ll reduce re pair costs and instrument downtime Suggestions for Effective Troubleshooting Certain basic procedures make troubleshooting faster and easier Most important are close observation of operating Parameters and a good record keeping system temperatures flow rates chart speeds column type stationary phase type and amount solid support type and mesh size etc Also of Primary importance is a reference standard containing known concentrations of the components in your sample The refer ence standard should contain no extraneous unknown components Many hours can be wasted hunting problems within an instrument or column when the problem is in fact t
18. column materials i e tubing packing and glass wool 3 Use glass lined stainless steel for transfer lines Symptom No 14 Extra peaks unlike sample chromatogram 1 Septum bleed particularly in tem perature program R 2 Peaks from previous runs particu larly if very broad with short re 1 Turn off injector heater If ghost peaks disappear operate at lower injector temperatures or use high temperature septum 2 Let analysis run longer and then repeat tention time 3 Impurities from sample solvent 3 Run solvent blank with clean sy sample container e g plasticizer ringe If extra peaks appear change from cap liners or contaminated solvent if no extra peaks appear glassware labware and reagents run solvent blank through entire Normal used in sample preparation parti sample work up without sample cularly when excess reagents are If no extra peaks appear impuri concentrated in work up ties are from sample If extra peaks appear repeat solvent blank from each step of work up to iso late source 4 Condensed carrier gas impurities 4 Install or replace carrier gas puri eluting during temperature pro fier gramming R 5 Verify by analyzing lab environ Problem 5 Trace impurities in lab atmosphere ment Take corrective action as Q necessary Gotu wn Lires led mar Aue Cmar 875 NE STE GK Eo On s he sy stom Fuad artes Caan nok as
19. e problem of irreproducible injection volumes when making syringe injections by hand 2 3 Air Plunger Solvent Air Air Plunger annie 4 Sample Solvent a Eliminate sample hang up in the needle by first cleaning the syringe then drawing in a small aliquot of solvent b Remove the syringe from the solvent and draw in a small amount of air c Draw in the desired amount of sample d Remove the syringe from the sample and draw in a little more air e Verify the amount of sample in the syringe barrel This is only possible with syringes that do not have plungers in the needle f Quickly and smoothly inject sample into the chro matograph 4 Syringes With Needle Plungers Improve sample reproducibility by using a syringe with a plunger in the needle This eliminates sample retention in the needle dead volume The solvent flush technique 3 above may be useful since a small amount of sample hang up can still occur OTHER USEFUL PUBLICATIONS In addition to information presented in this guide more helpful tips are available to save time and money in chromatography Some of this information is provided FREE upon request in the following Supelco technical bulletins Bulletin739 Reviews problems caused by using im pure carrier gas and methods of extend ing column life Bulletin 780 Discusses the selection of a septum which will resist leaks and exhibit low bleed at high operating
20. er and appro priate grades of gases Replace tanks before pressure becomes too low 300psig 3 Check for leaks prior to use Al low columns to cool before re moving from GC to prevent col umn exposure to air while hot 4 These samples can 1 strip phase from support 2 chemically react with phase 3 build up on col umn and possibly destroy the col umn injection side first Use of pre column or repacking the inlet will extend column life List of Bulletins by Subject Analyses are by GC unless otherwise indicated FREE Technical Literature to Help You Select the Right Column for Your Analysis Consistent and accurate chromatographic analyses are dependent not only on proper system operation but also on packing materials and analysis techniques Examine the following list of Supelco Bulletins Select the right one or more to help you perform your particular analysis Bulletin ACIDS ORGANIC cutee Dibasic Dicarboxylic Acid Methyl Esters up to C10 762 Elaidate Oleate separation of cis trans isomers 752 Fatty Acids Free C1 4 C20 727 Fatty Acid Methyl Esters C14 C24 746 Fatty Acid Methyl Esters postional cis trans isomers 822 Fatty Acids Volatile C2 C5 at ppm levels in water 751 Fatty Acids Volatile and Nonvolatile esterification and separation 721 ALCOHOLS also see SOLVENTS Acylation 721 Alcoholic Beverage Analyses 790 Blood Alcohols GC HPLC 810
21. he sample being analyzed If your chromatographic system separates the reference standard well and reproducibly any existing problem is most likely related to the sample Your troubleshooting will progress more smoothly if you have on hand 1 A duplicate analytical column one you know will provide acceptable separation under proper condi tions Try this duplicate column in your malfunc tioning system If it corrects your problem the prob lem is related to the original column 2 A new syringe to help isolate the source of ghost peaks Repeat the analysis with a new clean syr inge If your trouble disappears the problem has been isolated to a defective or dirty syringe used during the original analysis 3 Snoop or other leak detection aids Use these to ensure that your entire system is free of leaks manda tory for proper operation NOTE Don t use these liquids with capillary columns 4 Spare septa and high temperature septa These help to identify problems with reproducibility or ghosts caused by leaking or bleeding septa Simply replace your septum with a new duplicate septum or with a higher temperature septum If the symptom disappears the trouble was a leaking or bleeding septum 5 Detector cleaner A dirty detector creates noisy baselines Flame ionization detectors FIDs may be cleaned using either Freon TF an in place cleaner or an ultrasonic bath filled with an immersion cleaner 6 Ther
22. ion etc 3 Check for a sample problem by injecting a reference stan dard If you get a good chromatogram the problem is most likely sample related If not the problem is probably col umn or instrument related 4 Check for a column problem by replacing the column with a duplicate column one known to provide good results under proper conditions If good results are obtained the problem is related to the original column If the symptom persists the problem is related to the instrument Isolate equipment related problems by listing the equipment systems which can cause the observed symptoms e g for broad peaks with long retention times 1 carrier gas sys tem 2 column heating system and 3 injection port heat ing system Next isolate the problem within the suspected systems a Trademarks Dexsil Dexsil Chemical Corporation Freon E I du Pont de Nemours amp Co Inc Glasrench Supelco inc Graphiok Scientific Glass Engineering Party Ltd Australia Shoop Nupro Company Supeltex Supelco inc Crawford Fitting Co Bienen E du Pont de Nemours amp Co Inc VESPEL E El inde Bom de Ne Nemours amp Co Inc For current product prices and a complete explanation of Supelco s limited warranty please see our most recent catalog 6 Isolate possible electronic system malfunctions detector electrometer recorder and associated wiring by perform ing the following checks
23. mometer To verify the oven temperature ruling out a defective temperature control 7 Spare ferrules Often necessary to eliminate leaks in connections 8 Soap bubble meter To check your gas flow 9 Spare recorder and electrometer cables To elimi nate the recording system as a source of trouble 10 Instrument manual ISOLATING THE PROBLEM SOURCE There are five major sources of problems in gas chromatog raphy 1 the operator 2 the sample 3 the column 4 the electronics and 5 the gas flow system Various problems can stem from any one of these sources Eliminate them one by one to isolate the actual cause of the problem To define your problem first refer to the Troubleshooting Table on page 5 Using the symptoms index at the front of the table locate your trouble symptom If there is more than one symp tom note the possible causes for each If one cause is common to all symptoms this is most likely the source of your problem Note that while the troubleshooting table contains most of the symptoms you will encounter it cannot cover all potential prob lems When you cannot find a rapid solution using the troubleshooting table you must systematically isolate the trouble 1 Carefully note the symptoms e g broad peaks unresolved peaks long retention times 2 Rule out operator error by double checking all operating parameters such as temperature carrier gas flow column descript
24. ncrease sen sitivity and decrease temperature by 20 C Look for partial separa tion 3 Sample condensation 3 Check injection port and column temperatures and increase if necessary Normal 4 Sample decomposition 4 Use inert system and deactivated packing Symptom Possible Cause Remedy e Symptom No 17 Split Peaks cm Normal Problem 1 Gross detector overload 2 Sample flashing prior to injec tion simulates two injections 1 Reduce sample size 2 Use syringe with solvent flush technique so that sample is con tained in barrel not in needle Use less volatile solvent Symptom No 18 Square or flat top peaks J Problem 1 Electrometer saturated normal for solvent 2 Defective recorder 1 Reduce sample size 2 Troubleshoot recorder per re corder manual Symptom No 19 E Round top peaks UL Problem 1 Detector overload FID 2 Recorder gain too low 1 Decrease sample size 2 Adjust gain control 13 Possible Cause Remedy Symptom Symptom No 20 Cigar top peak PF Detector overload ECD Reduce sample size Symptom No 21 Clipped peaks column efficiency exceptionally high T Recorder or instrument zero be low minimum moveable range of recorder pen al Shunt recorder leads and
25. ng diminished re umn that will separate hydrocar sponse due to quenching effect bons from components of interest Symptom No 4 Low response long retention 1 Low carrier gas flow rate 1 Measure and adjust carrier gas flow time rate if necessary see page 3 2 Carrier gas leak at septum or col 2 Check for leaks and correct if nec umn connections essary see page 4 3 Column temperature too low 3 Increase column temperature 4 Column worn out or conditioned 4 Verify column temperature and at too high a temperature stationary phase temperature li zal mits Normal Check sample with known good column Repack first 6 of column or re place column Problem Symptom No 5 Quantitation not reproducible a Retention time okay Compo nents with longest retention time show using L niques low value when normalization tech 1 Sample incorrect a 1 Incomplete sample injection 2 Injection port or column temperature too low 3 Incorrect slope sensitivity with electronic integrator Ta Verify using known standard a 1 Use solvent flush techniques 2 Increase temperature see page 4 3 Adjust slope sensitivity Symptom Possible Cause Remedy Symptom No 5 cont d b Retention time okay Different components not yielding simi lar peak areas for same amount c Quantitation varies for one component eluting over wide time span even using internal
26. r re place column Check recorder chart speed Reduce sample size Retention time on new column is longer or shorter than on previ ous column of the same composi 1 Column too long too short 2 More less packing in column due to a Support density greater less than previously used b Column packed more tight ly loosely c Column inside diameter greater smaller 3 Percent coating of stationary phase on support is too high low due either to different manufactur ing procedures or errors 4 Different stationary phase used or slight variation in phase com position particularly commercial chemicals not manufactured for GC Problem 5 Different support type Problem This problem can be remedied by using pretested standardized col umns and packing materials Symptom Possible Cause Remedy Symptom No 29 Unresolved peaks on column which previously produced good results J Problem Problem 1 Wrong column temperature 2 Wrong carrier gas flow rate 3 Sample problem a Sample size too large b Sample concentration different than previous analysis causing swamping of minor peak by major peak 4 Poor injection techniques slow 5 Column contaminated or deteri orated Check and adjust temperature 2 Check and adjust flow rate 3 a Reduce sample size b Reduce sample size gt Use
27. re flows and verify against maximum limits including H2 manual specifications and air on FID or poorly regu lated flow 7 Defective electrometer detector Troubleshoot as in Isolation of or cable Problem Source section 8 FID only collector incorrectly 8 Realign as required aligned 9 ECD only heater wire too close 9 Reposition heater wire Symptom Possible Cause Remedy Symptom No 9 Cycling baseline drift Poor instrument location drafts changes in ambient temperature etc Relocate instrument close win dows etc 2 Defective detector or oven tem 2 Replace temperature sensing perature controller probe 3 Defective column oven tempera 3 Replace temperature sensing Normal ture controller probe 4 Carrier gas flow irregular insuf 4 Replace gas tank ficient supply pressure 5 Defective carrier gas regulator 5 Replace regulator er 6 Defective carrier gas flow con 6 Replace flow controller Problem troller 7 Sensitivity too high if using 7 Reduce detector sensitivity or de _pumped gases such as from hy crease output pressure from gener drogen generator ator Symptom No 10 Spikes regular 1 Condensate or dust particles in 1 Clean detector and check ends of FID column to ensure glass wool is in place Normal 2 Contaminated gases 2 Replace gases or insert liquid ni trogen trap in gas line SESaS a 3 Defective electronics or detector 3 Tro
28. re leaks in the system and large pressure drops across one or more of the sys tem components The use of pressure gauges can save con siderable time when isolating these problems Some common leak points are column connections the septum and connec tions for the various valves and gas purifiers A pressure gauge installed between the particle trap and the injection port P3 in the gas system illustration indicates column head pressure A low reading at this point indicates a leak be tween P3 and the detector outlet e g a defective column sep tum etc or a large pressure drop across a previous component e g a plugged oxygen trap A high reading at this point indicates an over tightened septum dirty detector too tightly packed col umn etc Similarly a pressure gauge at P2 will reveal an ex hausted oxygen trap low pressure readings indicate a larger than normal pressure drop across the trap Routine observation of this pressure enables you to determine when the carrier gas purifier should be changed NOTE Many chromatographs have crimps in the carrier gas line between the flow controller and the injection port or employ capillary tubing with a small internal diameter Consequently the pressure reading at point P3 will be dif ferent from the column head pressure reading taken through the septum These restrictions can also make it difficult to obtain sufficient carrier gas flow particularly when convert ing instruments for
29. set re corder baseline adjustment zero to approximately 5 of full scale Problem Symptom No 22 Baseline rise before or after peak Sample decomposition Use inert columns and packings Symptom Possible Cause Symptom No 23 Remedy Baseline change after large peak Problem J Problem FID only flame extinguished Normal Problem Symptom No 24 Baseline drop after peak 1 Sample too large 1 Contamination water or large component is stripping contami nants from column 2 Column not conditioned properly liquid phase being stripped 3 Pressure imbalance when gas sam pling valve activated Repack first 6 of column or re Recondition column Correct pressure imbalance place pre column 2 Incorrect gas flows 3 Flame tip plugged 4 Collector and tip not located properly whistling or humming noise often heard Decrease sample size Check and adjust carrier gas Hz Clean or replace flame tip Adjust collector position and air 15 Symptom Possible Cause Symptom No 25 Remedy Negative dips after peaks Normal Problem 1 Only after large peak such as sol vent sample too large 2 After all peaks with ECD dirty detector cell 1 Decrease sample size 2 Clean detector Sezet No 26 Negati
30. temperatures This bulletin provides test results demonstrating the quality of Ther mogreen LB 1 septa Bulletin 783 Provides information pertaining to dirty flame ionization detectors FIDs and offers hints to help prevent contam ination as well as instructions for cleaning Bulletin 741 Reviews various types of ferrules and methods of preventing problems when connecting glass columns Bulletin 814 Discusses use of wide bore capillary columns in packed column gas chro matographs NPD ABBREVIATIONS ECD Electron Capture Detector FID Flame lonization Detector FPD Flame Photometric Detector GC Gas Chromatography Nitrogen Phosphorous Detector TCD Thermal Conductivity Detector SYMPTOMS INDEX Symptom Symptom Symptom Symptom No Symptom No Symptom No Ha Baseline Detector response low 3 4 Peaks changing 23 missing 2 cycling 9 Ghost peaks negative 12 dip 25 26 random 13 no peaks drift 7 sample memory solvent broad 27 drop 24 peaks 14 unresolved 29 noise 8 off scale Peak shapes incorrect Quantitation zeroing 6 cigar top 20 irreproducible 5 rise 22 clipped 21 PEGA round top 19 Retention time Carrier gas low skewed too long or short 28 flow rate 32 leading edge 16 A i split 17 Spikes Column life short 33 square top 18 irregular 1 tailing 15 regular 10 Column packing compacted 31 gaps in 30 TROUB
31. ubleshoot electronics and de Problem tector as in Isolation of Problem Source section Closely check the recorder cables and detector elec bf tt trometer cables Problem Symptom No 11 Spikes irregular or erratic 1 Defective cable intermittent short 1 Replace cable ing pane 2 ECD heater wires and detector 2 Check wire position and relocate one wire too close or loose if necessary 3 FID insufficient H3 flow 3 Increase H3 flow 4 Electronic interference from ex 4 Relocate instrument and deter Problem ternal source mine possible interference sources e g nearby transmitter site etc Symptom No 12 Negative Peaks 1 Recorder improperly connected 1 Reverse recorder connections or polarity reversed or sample in polarity switch jected into wrong column 2 TCD only impurity in carrier 2 Install or replace carrier gas puri gas fier Problem Symptom Possible Cause Remedy Symptom No 13 Ghost peaks peaks similar to pre vious sample appear when solvent alone is injected Previous Sample Normal solvent injected after sample Problem solvent injected after sample 1 Dirty syringe 2 Column adsorption and subse quent desorption of sample par ticularly in temperature program 3 Adsorption in transfer line 1 Try new syringe with clean sol vent If ghost peaks disappear clean syringes more thoroughly 2 Try more inert
32. ve dip before peak I Normal LL Problem F 1 Pressure imbalance when gas sam pling valve activated 1 Correct pressure imbalance a No 27 Broad solvent peaks gt Dead volume in injection port due to poor column installation 2 Normal with very dilute sample as in trace analysis 3 Poor injection technique 4 Injection port temperature too low 5 Sample solvent interacts with the detector 6 Sample solvent retained by col umn e g methanol by active columns 1 Use on column injection Ensure Proper column connections par ticularly when changing from one column diameter to another OF a 3 Use smooth rapid injection see page 4 4 Increase injection port tempera ture 5 Change sample solvent 6 Change sample solvent MW Symptom Possible Cause Remedy Symptom No 28 Retention time longer or shorter on same column Uh Ill Mh Problem 1 Column temperature too high too low Lad Carrier gas flow rate too low too high 3 Septum or column leak 4 Column contamination or deterio ration 5 Recorder problem 6 Sample overload Check temperature with indepen dent thermometer and adjust temperature as required Measure flow rate with soap bub ble flow meter at column exit and adjust as required Check and correct as required Repack first 6 of column o
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