Fluoride in Drinking Water
Contents
1. 14 Remove the electrode after reading the last sample Rinse the electrode Store in a fluoride standard of similar concentration to the sample that will be analyzed next Refer to the electrode manual for more information on electrode storage 11 Add 5 mL concentrated liquid TISAB to the sample Stir to mix 12 After the measurement is stable record or store the measurement value Fluoride in Drinking Water Page 5 of 10 Fluoride in Drinking Water Electrode assembly 1 Remove the cap from the electrolyte cartridge 2 Visually inspect the Luer tip of the electrolyte cartridge If air is present rotate the feed screw counter clockwise until gel expels the air and fills the tip 3 Fit the cartridge outlet tube firmly onto the inlet tube of the electrode body Figure 28 Figure 28 Attach the outlet tube 4 Place the dispenser unit over the electrolyte cartridge Screw the dispenser unit onto the electrode body until reaching the stop Do not over tighten 5 Dispense the electrolyte gel by pressing the pump button Repeat this procedure until gel is visible at the reference outlet Figure 29 Figure 29 Dispense the electrolyte gel 6 Rinse the electrode with deionized water Do not scratch the crystal 7 To remove an empty cartridge unscrew the dispenser unit and rotate the cartridge counterclockwise while gently pulling it out of the electrode Fluoride in Drinking Water Page 6 of 10 F2. Fluoride in Drinking Water DOC316 53 01237 USEPA Direct Measurement ISE Method Method 8323 0 1 to 10 0 mg L F Powder Pillow or TISAB Solution Scope and Application Drinking water 1 USEPA equivalent method Test preparation How to use instrument specific information The nstrument specific information table displays requirements that may vary between instruments To use this table select an instrument then read across to find the corresponding information required to perform this test Table 447 Instrument specific information Electrode sensiOn 4 meters 5192800 sensiOn 2 meters 5192800 1 The user must construct the calibration curve with the sens On 2 meter Before starting the test Refer to the meter user manual for meter operation Refer to electrode manual for electrode maintenance and care For USEPA reporting replace the standards in step 1 with a 0 5 mg L 1 0 mg L and 2 0 mg L fluoride standard solution to calibrate the electrode Prepare the electrode Refer to Electrode assembly and Condition the electrode in this procedure Collect the following items Description Quantity Fluoride ISA buffer pillows TISAB OR Fluoride ISA solution concentrated TISAB 5 0 mL Sodium acetate ACS varies Fluoride standard solutions 1 00 mg L F varies 2 00 mg L F or varies 0 5 mg L F USEPA varies Potassium chloride reference electrolyte gel cartridges varies Water deionized varies
3. Set 4 Place the beaker with prepare two 25 mL mL concentrated Fluoride the electrode type to BNC the 1 mg L standard ona standard solutions of Total lonic Strength Set the units to mg L magnetic stirrer Stir at a 1 mg L and 10 mg L F Adjustment Buffer TISAB Press CAL moderate rate per 25 mL of standard Stir Rater to the meter user to mix manual for details GD sensio GD sensio Standard Stabilizing Repeat 4 7 5 Place the electrode 6 Edit the display to 7 The display willshow 8 Repeat steps 4 7 for into the standard show the concentration of Stabilizing until the the 10 mg L standard the standard measurement is complete After the last standard is Accept the concentration Remove the electrode measured store the from the standard solution calibration in the meter Rinse with deionized water Refer to the meter user and blot dry manual for details Fluoride in Drinking Water Page 4 of 10 Fluoride in Drinking Water Fluoride in drinking water liquid TISAB solution method continued 9 Transfer 25 mL of the sample to a 50 mL beaker Add a stir bar to the beaker Place the beaker on a magnetic stirrer and stir at a moderate rate Repeat 9 12 13 Repeat steps 9 through 12 for each sample 10 Remove the electrode from the standard solution Rinse it with deionized water and blot dry Place it into the sample The sample should be the same temperature as the standards 1 C
4. 050 On the Worldwide Web www hach com E mail techhelp hach com FAX 970 669 2932 Hach Company 2007 2010 2012 All rights reserved Printed in the U S A Edition 7
5. Fluoride in Drinking Water Page 1 of 10 Fluoride in Drinking Water Collect the following items continued Description Beaker 50 mL polypropylene Bottle wash 500 mL Cylinder graduated 25 mL polypropylene Platinum series fluoride combination electrode BNC sension 2 Portable pH ISE Meter or sens on 4 Laboratory pH ISE Meter Stir Bar 7 8 X 3 16 in 22 2 x 4 8 cm Stirrer electromagnetic with stand and stir bar See Consumables and replacement items for reorder information Fluoride in drinking water powder pillows method Quantity 3 or 4 USEPA 1 3 1 1 2 or 3 USEPA 1 1 In 50 mL beakers prepare two 25 mL standard solutions of 1 mg L and 10 mg L F 5 Place the electrode into the standard Fluoride in Drinking Water Page 2 of 10 2 Add the contents of one Fluoride Total lonic Strength Adjustment Buffer TISAB Powder Pillow to each standard Stir to dissolve Gace sensor Standard 6 Edit the display to show the concentration of the standard Press ENTER to accept the concentration ISE mV 4 3 Turn the meter on Set the electrode type to BNC Set the units to mg L Press CAL Refer to the meter user manual for details Gace senslOIr Stabilizing 7 The display will show Stabilizing until the measurement is complete Remove the electrode from the standard solution Rinse with deionized water and blot dry 4 Place the beak
6. e more basic and increase OH Fluoride in Drinking Water Page 7 of 10 Fluoride in Drinking Water pH Effects In solutions with a pH below 5 hydrogen ion complexes some of the fluoride ions forming the undissociated acid HF and the ion HF Figure 31 shows the proportion of free fluoride ion in acid solutions If the background ionic strength is high and constant in comparison with the ion being measured the activity coefficient is constant and activity is directly proportional to ion concentration Total ionic strength adjustor is added to standards and samples to make the background ionic strength high decomplex fluoride and adjust the solution pH to 5 0 5 5 Figure 31 Ratio of free F in acid solutions Sample collection preservation and storage e Collect samples in plastic bottles e Samples may be stored up to 28 days Accuracy check Checking electrode response To verify measurement accuracy measure the electrode potential of two fluoride standard solutions that are one decade apart in concentration For example use 1 mg L and 10 mg L standards to bracket an expected sample concentration of 3 mg L The two standards should have mV potentials that are 58 3 mV apart at 25 C Both solutions must be greater than 0 2 mg L F Checking calibration accuracy To verify calibration accuracy measure the concentration of a known standard e g 2 00 mg L within the calibration range Checking the accuracy of the sa
7. er with the 1 mg L standard on a magnetic stirrer Stir at a moderate rate Repeat 4 7 8 Repeat steps 4 7 for the 10 mg L and 0 5 mg L USEPA standard After the last standard is measured store the calibration in the meter Refer to the meter user manual for details Fluoride in Drinking Water Fluoride in drinking water powder pillows method continued 9 Transfer 25 mL of the sample to a 50 mL beaker Add a stir bar to the beaker Place the beaker on a magnetic stirrer and stir at a moderate rate Repeat 9 12 13 Repeat steps 9 through 12 for each sample 10 Remove the electrode from the standard solution Rinse it with deionized water and blot dry Place it into the sample The sample should be the same temperature as the standards 1 C 14 Remove the electrode after reading the last sample Rinse the electrode Store in a fluoride standard of similar concentration to the sample that will be analyzed next Refer to the electrode manual for more information on electrode storage L 11 Add the contents of one TISAB Powder Pillow Stir to dissolve per vd g7 12 After the measurement is stable record or store the measurement value Fluoride in Drinking Water Page 3 of 10 Fluoride in Drinking Water Fluoride in drinking water liquid TISAB solution method oul L 1 In 50 mL beakers 2 Addthecontents of 5 3 Turn the meter on
8. ired reagents Description Quantity Test Unit Catalog number Fluoride ISA buffer pillows 1 100 pkg 258999 OR Fluoride ISA solution 5 mL 3 78 L 2829017 Fluoride Standard Solutions 1 00 mg L varies 500 mL 29149 2 00 mg L varies 500 mL 40520 10 0 mg L varies 500 mL 35949 Potassium Chloride Reference Electrolyte Gel Cartridges varies 2 pkg 2546902 Water deionized varies 4L 27256 Fluoride in Drinking Water Page 9 of 10 Fluoride in Drinking Water Required apparatus Description Quantity Test Unit Catalog number Beaker 50 mL polypropylene 3 each 108041 Bottle wash 500 mL 1 each 62011 Cylinder graduated 25 mL poly 3 each 108140 Fluoride Combination Electrode BNC w filling solution 1 each 5192800 sensIOn 2 Portable pH ISE Meter 1 each 5172500 OR sension 4 Laboratory pH ISE Meter 1 each 5177500 Stir Bar 7 8 x 3 16 in 22 2 x 4 8 cm 1 each 4531500 Select one based on available voltage Stirrer electromagnetic 115 VAC with stand and stir bar 1 each 4530001 Stirrer electromagnetic 230 VAC with stand and stir bar 1 each 4530002 Optional apparatus Description Unit Catalog number Electrode Washer each 2704700 Pipet TenSette 0 1 to 1 0 mL each 1970001 Pipet Tips for 19700 01 TenSette Pipet 50 pkg 2185696 Hac In the U S A Call toll free 800 227 4224 WORLD HEADQUARTERS Outside the U S A Contact the HACH office or distributor serving you Telephone 970 669 3
9. luoride in Drinking Water 8 Connect the BNC connector of the electrode to the BNC connector on the meter Figure 30 Figure 30 BNC connector Note One BNC and one 5 pin connector are on the back of the meter Choose the BNC for the fluoride electrode Disconnect the pH electrode from the 5 pin connector when using the BNC connector Condition the electrode Condition and store the electrode in 1 mg L Fluoride standard storage with lonic Strength Adjuster for 15 to 30 minutes For electrode storage procedures refer to the Fluoride Electrode Instruction Manual Clean the Lanthanum Fluoride Crystal It may be necessary to clean the LaF crystal on the sensing tip of the probe if it becomes covered with organic film or buildup 1 1 Put a small amount of fluoride toothpaste on a soft toothbrush or cloth 2 Gently rub the LaF crystal with the toothpaste using a circular motion Rub until the film is removed 3 Thoroughly rinse the probe with deionized water and blot dry Verify the crystal is clean If not repeat cleaning and rinsing until it is clean 4 Ifthe crystal becomes contaminated by oil grease or fingerprints soak for a few minutes in isopropyl alcohol then rinse with deionized water Interferences Table 448 Interfering substances Interfering substance Interference level Cations Do not interfere CI Br SO42 HCO3 Do not interfere PO4 acetate OH Hydroxy ions CO32 or PO 4s Make the sampl
10. mple reading To verify sample measurement accuracy add a spike of standard fluoride solution with a TenSette or volumetric pipet Use the Spike Volumes table and the formulas in Table 449 Spike Volumes Measured sample Volume amp Concentration of F Standard to Add a ee E 3 6 mg L TO mL of 10mg Fluoride in Drinking Water Page 8 of 10 Fluoride in Drinking Water Percent recovery To calculate the percent recovery only applicable if sample volume is 25 mL M Sx25 CxV M E 357V R x 100 Where M calculated mass of fluoride present after the spike micrograms S mg L of F in sample before spike C concentration of standard used for spiking mg L V spike volume from the Spike Volumes table mL E expected concentration after spiking mg L R percent recovery should be 95 100 A actual reading on meter after spike mg L F Method performance Precision Standard 95 Confidence Limits of Distribution sensiond 1 6 mg L 1 595 1 605 mg L Summary of method The fluoride electrode consists of a sensing Lanthanum Fluoride element bonded into an epoxy body When the sensing element contacts fluoride ions in a solution a potential develops across the sensing element The potential is proportional to the level of fluoride ions present The potential is measured against a constant reference potential with a pH mV meter or ISE meter Consumables and replacement items Requ
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