Fluoride in Acid Solutions
Contents
1. Fluoride in Acid Solutions DOC316 53 01236 Direct Measurement ISE Method Method 8323 0 1 to 100 0 mg L F ISE Electrode Scope and Application For industrial waters solutions below a pH of 5 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 1 Instrument specific information Meter Electrode senslOon 4 meters 5192800 senslOn 2 meters 5192800 1 The user must construct the calibration curve with the sension 2 meter Before starting the test Refer to the meter user manual for meter operation Refer to electrode manual for electrode maintenance and care Prepare the electrode Refer to Electrode assembly and Condition the electrode in this procedure In solutions below a pH of 5 hydrogen ion complexes some of the fluoride ions forming HF or HF which the electrode will not detect To free the complexed fluoride adjust the pH of the solution so it is weakly acidic to weakly basic before analysis Do not use a strong base such as sodium hydroxide for adjustment since the amount of base added will vary from sample to sample Using a strong base can also change the ionic strength of the sample and alter measurement accuracy Dilution of samples and standards with a large e2. L Vu volume of separate portion before spike in mL l ar 100 X X 3 Final calculation plugging in Xu and K Recovery ye Example A sample was analyzed and read 5 0 mg L F As directed in the Spike volumes table a 1 0 mL spike of 100 mg L F standard was added to another 25 mL sample giving a final standard addition result of 8 75 mg L Calculate the percent recovery as follows _ 5 0 mg Li 25 mL 1 Xi a ae oe 4 81 mg L _ 100 mg Li 1 mL _ 2 K smr im 3 85 mg L 100 X X _ 3 R 1001 Xs Xu _ 1001 8 75 4 81 _ 102 3 Recovery K 3 85 Table 3 Spike volumes Measured Sample Concentration Measured Sample Volume Standard Concentration Standard Volume mg L mL mg L mL 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 Fluoride in Acid Solutions Page 7 of 8 Fluoride in Acid Solutions Consumables and replacement items Required reagents Description Quantity Test Unit Catalog number Fluoride Standard Solutions 1 00 mg L F or varies 500 mL 29149 10 00 mg L F or varies 500 mL 40520 100 0 mg L F varies 500 mL 35949 Potass
3. Set the electrode type to BNC Set the units to mg L Press CAL Refer to the meter user manual for details sension Stabilizing Repeat 7 10 11 Repeat steps 7 10 for the 10 mg L and 100 mg L standards 10 The display will show Stabilizing until the measurement is complete After the last standard is measured store the calibration in the meter Refer to the meter user manual for details Remove the electrode from the standard solution Rinse with deionized water and blot dry 15 Rinse the electrode with deionized water and blot dry 14 Place a stir bar in the beaker and set the beaker on a magnetic stirrer Stir at a moderate speed 8 Place the electrode into the standard 12 Measure the sample into 50 mL beakers to measure 25 mL of prepared buffered sample For example measure 3 mL of sample and dilute it with 27 mL of sodium acetate solution Pour 25 mL of this solution into a 50 mL beaker g 16 Place the electrode into the sample When the reading is stable record the value Fluoride in Acid Solutions Page 3 of 8 Fluoride in Acid Solutions 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 bo
4. UARTERS Telephone 970 669 3050 FAX 970 669 2932 Updated March 2011 Edition 5
5. dy Figure 1 Figure 1 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 2 Figure 2 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 Acid Solutions Page 4 of 8 Fluoride in Acid Solutions 8 Connect the BNC connector of the electrode to the BNC connector on the meter Figure 3 Figure 3 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 Puta small amount of fluoride toothpaste on a soft toothb
6. e this solution to prepare the standards If a standard prepared with background solution gives the same reading after sodium acetate dilution as standard prepared with pure sodium acetate it is not necessary to prepare a background solution 3 For calibration prepare fluoride standards by adding fluoride to the background solution Prepare fresh standards every two weeks if standards are less than 10 mg L F When testing with a direct reading fluoride meter use two standards When testing with a pH mV meter use three standards 4 Dilute each standard 10 1 with sodium acetate solution 9 parts sodium acetate solution to 1 part standard to prepare the buffered solution Mix thoroughly For example measure 3 mL of standard with background solution and dilute it with 27 mL of sodium acetate solution Fluoride in Acid Solutions Fluoride in Acid Solutions method continued gt R ee re oe 45 5 Add the contents of one Fluoride Total lonic Strength Adjustment Buffer TISAB Powder Pillow to 25 mL of the prepared buffered sample Stir to dissolve 9 Edit the display to show the concentration of the standard Press ENTER and accept the concentration 13 Dilute each unknown 10 1 with sodium acetate solution before measurement 7 Place the beaker with the 1 mg L prepared buffered standard ona magnetic stirrer Stir at a moderate rate 6 Turn the meter on
7. ium Chloride Reference Electrolyte Gel Cartridges varies 2 pkg 2546902 Sodium Acetate ACS varies 454 g 17801H Water deionized varies 4L 27256 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 senson 4 Laboratory pH ISE Meter 1 each 5177500 Stir Bar 7 8 x 3 16 in 22 2 x 4 8 cm 4 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 Tensette pipet 1 0 10 0 mL 1 each 1970010 Class A 25 mL volumetric pipet 1 each 1451540 Safety bulb pipet filler 1 each 1418900 Class A 1000 mL volumetric flask 1 each 1457453 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 D FOR TECHNICAL ASSISTANCE PRICE INFORMATION AND ORDERING In the U S A Call toll free 800 227 4224 Outside the U S A Contact the HACH office or distributor serving you On the Worldwide Web www hach com E mail techhelp hach com Hach Company 2007 All rights reserved Printed in the U S A HACH COMPANY WORLD HEADQ
8. just the solution pH to 5 0 5 5 Figure 4 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 Standard additions method sample spike To verify measurement accuracy perform a standard addition spike on the sample The spike should roughly double the measured concentration without significantly diluting the sample To perform a standard addition sample 1 Use the Spike volumes table to determine the concentration and volume of standard to spike the sample The volume of sample transferred must be accurate 2 Add the amount and concentration specified in the Spike volumes table to the sample 3 After adding the standard proceed with the calculations Results from 90 110 recovery are considered acceptable Calculate percent recovery as follows 100 X X Recovery K Where Xs measured value for spiked sample in mg L Xy measured value for unspiked sample adjusted for dilution by the spike in mg L K known value of the spike in the sample in mg L Calculations X V _ u 1 X ysy Fluoride in Acid Solutions Page 6 of 8 Fluoride in Acid Solutions Where X measured value of unspiked sample in mg L Vu volume of separate unspiked portion in mL V volume of spike in mL _ Civ 2 k Va V Where C concentration of standard used in spike in mg L V volume of spike in m
9. rush 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 2 Interfering substances Interfering substance Interference level Cr Br S042 HCO37 Do not interfere PO4 acetate Interferes refer to pH Effects Some ions such as CO32 or PO4 make the sample more OH Hydroxyl ions basic which increases OH interference but do not directly interfere with the electrode operation CO32 or PO 3 Can make the sample more basic and increase OH Fluoride in Acid Solutions Page 5 of 8 Fluoride in Acid Solutions 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 4 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 ad
10. xcess of sodium acetate will buffer the pH and help adjust the total ionic strength of samples and standards to the same level Collect the following items Description Quantity Fluoride ISA buffer pillows TISAB 1 mL Sodium acetate ACS varies Fluoride standard solutions 10 00 mg L F or varies 2 00 mg L F or varies 100 0 mg L F varies Potassium Chloride Reference Electrolyte Gel Cartridges 1 Water deionized varies Fluoride in Acid Solutions Page 1 of 8 Fluoride in Acid Solutions Collect the following items continued Description Beaker 50 mL polypropylene Tensette pipet 1 0 10 0 mL or 25 mL Class A volumetric pipet Class A 1000 mL volumetric Bottle wash 500 mL Cylinder graduated 25 mL poly Platinum Series Fluoride Combination Electrode BNC sension 2 Portable pH ISE Meter OR sension 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 Acid Solutions method Quantity 1 Prepare a 15 sodium acetate solution by dissolving 150 g of reagent grade sodium acetate in 1000 mL of deionized water Prepare enough solution to dilute all the samples and standards Fluoride in Acid Solutions Page 2 of 8 2 Using deionized water prepare a background solution containing all the sample matrix components except fluoride Us
Download Pdf Manuals
Related Search