ALLOWAY Method Outline Standard Laboratory Method: SM4500-F - B and SM4500-F-C Parameter: Total Fluoride via Distillation Method: Distillation then Specific Ion Date Issued: 01/04/82 Date Revised: 04/09/02, 08/12/03, 01/31/05, 04/07/2008 Optimum Concentration Range: 0.1-10 mg/l Sensitivity: N/A Detection Limit: 0.10 mg/l Reference: Standard Methods 20 th edition, 1998 Alloway Page 1 of 9
Total Fluoride 1.0 Scope and Application: 1.1 This method is applicable to the measurement of fluoride in drinking, surface and saline waters, and domestic and industrial wastes. 1.2 The applicable range of this method is from 0.10 to 10 mg/l. Higher levels may be measured by sample dilution. 2.0 Summary of Method: 2.1 Fluoride is determined potentiometrically using a fluoride electrode in conjunction with a standard single-junction sleeve type reference electrode and a ph meter having an expanded millivolt scale. 2.2 The fluoride elctrode has a laser-type toped lanthanum fluoride crystal across which a potential is established by fluoride solution at different concentrations. The crystal contacts the sample at one face and an internal reference solution at the other. The cell is represented Ag/AgCl, Cl (0.3M), F - (0.001M)\LaF 3 \Test Solution\reference solution. 2.3 The fluoride ion activity depends on total ionic strength and ph of the solution. Fluoride concentration is measured by adding buffer TISABII which provides a nearly uniform ionic background, adjusts ph, and breaks up complexs. 2.4 Distillation will separate fluoride from other nonvolatile constituents in water. 3.0 Definitions 3.1 Accuracy-The degree of agreement between an observed value and an accepted reference value. Accuracy includes a combination of random error (precision) and systematic error (bias) components which are due to sampling and analytical operations; a data quality indicator. 3.2 Aliquot - A portion of the field sample to be processed through the analytical steps 3.3 Analytical Batch Composed of prepared environmental samples (extracts, digestates, or concentrates) which are analyzed together as a group. An analytical batch can include prepared samples originating from various environmental matrices. 3.4 Calibration To determine, by measurement or comparison with a standard, the correct value of each scale reading on a meter, instrument, or other device. The levels of the applied calibration standard must bracket the range of planned or expected sample measurements. 3.5 Calibration Curve The graphical relationship between the known values, such as concentrations, of a series of calibration standards and their instrument response. Alloway Page 2 of 9
3.6 Continuing Calibration Check or Verification Standard - check standard analyzed periodically to evaluate whether the analytical process remains in control. These results are compared to the initial calibration. Noted as ICV for initial and CCV for continuing check. 3.7 Duplicate Analyses- The analyses or measurements of the variable of interest performed identically on two sub-samples of the same sample. The results from duplicate analyses are used to evaluate analytical or measurement precision but not the precision of sampling, preservation or storage internal to the laboratory. 3.8 Homogeneous Sample - A sample which has an even distribution of material. 3.9 Instrument Detection Limit - The minimum concentration of an analyte that can be measured with 99% confidence that the analyte concentration is greater than zero. Determine the IDL with seven replicates of standard solution at the instrument with no specific analytical preparation. 3.10 Method Detection Limit - The minimum concentration of an analyte that can be measured with 99% confidence that the analyte concentration is greater than zero. Determine the MDL with seven replicates of standard solution taken through the preparative and analytical procedures. 3.11 Initial Calibration - A series of standards analyzed to produce a calibration curve in order to develop a linear system. 3.12 Internal Standard A known amount of standard added to a test portion of a sample as a reference for evaluating and controlling the precision and bias of the applied analytical method. 3.13 Laboratory Control Sample A sample matrix, free from the analytes of interest, spiked with verified known amounts of analytes from a source independent of the calibration standards or a material containing known and verified amounts of analytes. It is generally used to establish intra-laboratory or analyst/technician specific precision and bias or to assess the performance of all or a portion of the measurement system. LCSA denotes aqueous samples and LCSS denotes solid samples. 3.14 Matrix- The component or substrate that contains the analyte of interest. 3.15 Matrix Spike A sample prepared by adding a known mass of target analyte to a specified amount of matrix sample for which an independent estimate of target analyte is available. Matrix spikes are used, for example, to determine the effect of the matrix on a method s recovery efficiency. 3.16 Matrix Spike Duplicate A second replicate matrix spike prepared in the laboratory and analyzed to obtain a measure of the precision of the recovery for each analyte. Alloway Page 3 of 9
3.17 Quality Assurance An integrated system of activities involving planning, quality control, quality assessment, reporting and quality improvement to ensure that a product or service meets defined standards of quality with a stated level of confidence. 3.18 Quality Control The overall system of technical activities whose purpose is to measure and control the quality of a product or service so that it meets the needs of users. 3.19 Reagent Blank or Method Blank A sample consisting of reagent(s), without the target analyte or sample matrix, introduced into the analytical procedure at the appropriate point and carried through all subsequent steps to determine the contribution of the reagents and of the involved analytical steps. 3.20 Reporting Limit - The practical quantitation level for an analyte, greater than the MDL, accounting for dilutions and matrix specific concerns. 3.21 Sample Duplicate Two samples taken from and representative of the same population and carried through all steps of the sampling and analytical procedures in an identical manner. Duplicate samples are used to assess variance of the total method including sampling and analysis. 3.22 Reporting Limit Check (RDL) quality control sample analyzed as part of the analytical run at the reporting limit to determine accuracy and precision. 4.0 Interferences 4.1 Extremes of ph interfere; sample ph should be between 5 and 9 s.u.. Polyvalent cations of Si +4, Fe+3, and Al+3 interfere by forming complexes with fluoride. The degree of interference depends upon the concentration of complexing cations, the concentration of fluoride and the ph of the sample. The addition of a ph 5.0 buffer (described below) containing a strong chelating agent preferentially complexes aluminum (the most common interference), silicon and iron and eliminates the ph problem. Adding ph buffer TISAB II elimates most interferences. 4.2 Fluoride forms complexs with several polyvalent cations, especially aluminum and iron. The extent of complexation depends on solution ph, the relative levels of fluoride, and nature of the complexing species. 4.2.1 The ingredient CDTA (Cyclohexylenediaminetetraacetic acid) of the buffer TISAB complexes interfering cations to release free fluoride ions. 4.3 In acidic solutions, the HF HF complex forms. If solution is alkaline the Hydroxide ion interferes with electrode response if the hydroxide concentration is greater than 1/10, the concentration of fluoride. Alloway Page 4 of 9
4.3.1 The TISAB buffer maintains ph between 5 and 9 s.u. so that these interferences do not occur. 5.0 Safety 5.1 The toxicity or carcinogenicity of each chemical and reagent used in this method has not been precisely defined. However, each one must be treated as a potential health hazard, and exposure to these chemicals should be minimized. Each analyst is responsible for adherence to the procedures outlined in the Chemical Hygiene Plan. Material Safety Data Sheets are kept in the laboratory. 5.2 Some method analytes have been tentatively classified as known or suspected human or mammalian carcinogens. Pure standard materials and stock standard solutions of these compounds should be handled with suitable protection to skin, eyes, etc. 5.3 Safety glasses and lab coats must be worn when handling samples and solvents. Safety glasses must be worn when handling glassware. 6.0 Equipment and Supplies 6.1 ph meter with expanded millivolt scale, ph meter with direct concentration reading or a selective ion meter such as the Orion 400 series, or equivalent. 6.2 Fluoride Ion Activity Electrode, such as Orion No. 94-09, or equivalent. 6.3 Reference electrode, single junction, sleeve type, such as Orion No 90-01, or equivalent. Do not use fiber-tip reference electrodes because they behave erractically in very dilute solutions. 6.4 Magnetic stirrer, thermally insulated, and teflon-coated stirring bar. 6.5 Distillation apparatus: A 1-liter round bottom, long-necked pyrex boiling flask, connecting tube, efficient condenser, thermometer adapter and thermometer reading to 200 C. All connections should be ground glass. 7.0 Reagents and Calibration Standards 7.1 Buffer solution, ph 5.0-0-5.5: To approximately 500 ml of distilled water in a 1 liter beaker add 57 ml of glacial acetic acid, 58 g of sodium chloride and 2 g of CDTA (2). Stir to dissolve and cool to room temperature. Adjust ph of solution to between 5.0 and 5.5 with 5 N sodium hydroxide (about 150 ml will be required). Transfer solution to a 1liter volumetric flask and dilute to the mark with distilled water. For work with brines, additional NaCl should be added to raise the chloride level to twice the highest expected level of chloride in the sample. This is generally purchased in concentrated form. (Orion TISAB II). 7.2 Fluoride 100 mg/l - dissolve 0.221 g anhydrous sodium fluoride in distilled water and dilute to 1 liter with distilled water. 7.2.1 10 mg/l std. 10 ml of the 100 mg/l std up to 100 ml in volumetric flask. 7.2.2 1 mg/l std. 10 ml of the 10 mg/l std up to 100 ml in volumetric flask. Alloway Page 5 of 9
7.2.3 0.5 mg/l std. 5 ml of the 10 mg/l std up to 100 ml in volumetric flask. 7.3 Second source fluoride standard (1000 mg/l), purchased from a commercial vendor. 7.3.1 2 mg/l ICV/CCV = 1 ml of the second source standard up to 500 ml 7.4 Sulfuric Acid, concentrated. 8.0 Sample Collection, Preservation, and Handling 8.1 Sample gathered for fluoride procedure can be collected in a plastic or glass non preserved container. 8.2 Sample for fluoride analysis can degrade significantly between collection and analysis. Therefore the sample should be analyzed promptly, and stored at or below 4 o C until analysis is started. 8.3 Holding time is 28 days from date of collection. 9.0 Calibration and Standardization 9.1 From 100 mg/l fluoride standard prepare 10 mg/l, 1 mg/l and 0.5 mg/l for calibration curve. (7.2) 9.2 A second source check standard is prepared from a fluoride standard purchased from a commercial vendor. (7.3) 10.0 Quality Control 10.1 One sample of each batch of ten samples is to be analyzed in duplicate and spiked with a known amount of the fluoride standard. The duplicates must be within 10% of each other and the spikes must be 90-110% of the true value. If the duplicates or spikes fall outside the acceptance range, they must be reanalyzed or flagged with a comment on the report. 10.2 A Initial Calibration Blank (ICB) must be analyzed after the calibration. A Continuing Calibration Blank (CCB) must be analyzed after each batch of ten samples and at the end of the analytical run. The ICB and CCB must read less than the 0.10 mg/l reporting limit. 10.3 A Reporting Detection Limit standard (RDL) must be analyzed following the calibration. The RDL must read 70-130% of the true value. If the RDL falls outside the acceptance range, it must be reanalyzed prior to continuing the run. 10.4 A Initial Calibration Verification standard (ICV) prepared from the second source standard (9.2) must be analyzed following calibration. A Continuing Calibration Verification standard (CCV) prepared from the second source standard (9.2) must be analyzed after each batch of ten samples and at the end of the analytical run. The ICV and CCV must read 90-110% of the true value If the ICV falls outside the acceptance range, the instrument must be recalibrated and the ICV must be reanalyzed prior to analyzing samples. If the CCV falls outside the acceptance range, it must be reanalyzed along with all of the samples analyzed from the last acceptable CCV. 10.5 A Laboratory Control Standard (LCSA) must be analyzed after calibration. Alloway Page 6 of 9
The LCSA must read 90-110% of the true value. If the LCSA falls outside the acceptance range, it must be reanalyzed prior to continuing the analysis. 10.6 The calibration Slope is calculated by the instrument after the calibration is performed. The slope must be 54 to 60 mv/dec. or the instrument must be recalibrated. 10.7 A preparation blank and preparation standard must be prepared with every batch of distillates. 10.8 In addition, a duplicate and spike is prepped with every batch of distillates. 11.0 Analytical Procedures Preliminary Distillation 11.1 Place 400 ml distilled water in the distilling flask. 11.2 Carefully add 200 ml concentrated sulfuric acid and swirl until contents are homogeneous. 11.3 Add glass beads and stir bar; connect the apparatus making sure all joints are tight. 11.4 Turn stir plate on until a continuous slow motion is achieved. 11.5 Turn on the water to the condenser. 11.6 Heat slowly at first, then as rapidly as the efficiency of the condenser will permit until the temperature of the flask contents reaches exactly 175 degrees C. Discard the distillate. This process removes fluoride contamination and adjusts the acid-water ratio for subsequent distillations. 11.7 Cool to 80 degrees C or below. 11.8 Add 200 ml sample or in the case of solid or semi-solid samples, weight 10 g of wet sample and add 100 ml distilled water, mix thoroughly, distill until temperature reaches 175 degrees C but not exceeding 180 degrees C to prevent sulfate carryover. Initial sample volume may need to be adjusted due to total sample volume being limited. 11.9 Use the sulfuric acid solution in the flask repeatedly until the contaminants from the samples accumulate to such an extent that recovery is affected or interferences appear in the distillate. Check periodically by distilling standard fluoride samples. 11.10 High fluoride samples may require that the still be flushed by using distilled water and combining distillates. Analytical Procedure 11.1 Connect fluoride specific ion electrode and a reference electrode to ph meter. (Orion Single Junction reference Electrode and 90-00-01 Filling Station). 11.2 Measure 25 ml of sample or standrds and transfer to disposable beakers. 11.3 Add 25 ml TISAB II into each beaker before analyzing. 11.4 Calibrate meter with BLK, 0.5, 1.0, and 10 mg/l standards. Alloway Page 7 of 9
11.5 For each batch of 10 samples analyze a blank, check standard, duplicate and spiked sample. 12.0 Calculations and Quantitative Analysis 12.1 The electrode output is in concentration units, mg/l. No further calculations are necessary unless accounting for dilutions. The software for the Orion EA 940 converts the concentration in millivolts to mg/l. 12.2 In situations when a result must be generated from the data, the following procedure will be utilized: 1. The template entitled fluoride.xls is used and located in \conifer\excel\template folder 2. Go to the template and put the cursor inside the existing graph, right mouse click to remove the graph. 3. Using column A record the samples IDS for your analytical run. 4. Column B rows 2-4, contain the calibration standard concentrations. 5. In Column C rows 2-4, record the average of the millivolt readings for each calibration standard. 6. Highlight the six cells that contain the calibration standards and the millivolt readings. 7. Click on the Chart Wizard located in the tool bar 8. Highlight XY Scatter 9. Click on NEXT three (3) times. 10. Click on Finish 11. Click on CHART located on the tool bar 12. Scroll down and click on ADD TRENDLINE 13. Click on LOGARITHMIC 14. Click on OPTIONS 15. Click on DISPLAY EQUATION ON CHART 16. Click on OK 17. Enter the millivolt reading for each sample analyzed 12.3 Calculations will need to be added for non-aqueous samples. This results in dividing by the dry weight in the grams of the original sample. 13.0 Data Assessment 13.1 The primary analyst bears the responsibility of producing accurate data. A documented review is performed that includes a check of the following parameters: Calibration verification, QC criteria, calculation checks, Data entry into the LIMS 13.2 The initial data review is documented on the worksheet or benchsheet and dated by the primary analyst. An individual trained in the analytical procedure must perform a secondary review. 13.3 Data qualifiers are used whenever deviations occur while analyzing the samples. The qualifiers are included on the Certificate of Analysis that is presented to the client. Qualifiers include: samples that were not preserved, Alloway Page 8 of 9
failed LFM recovery, qualified due to LRB contamination, estimated or elevated reporting limit due to sample matrix interference, etc. 14.0 Report Generation 14.1 A Certificate of Analysis is generated after each analysis run is complete. The report includes the EPA Method Number, sample identification, date sampled, date logged in to the LIMS, quantitative result, worksheet number, analysis date, and analyst initials. 15.0 Waste Management and Pollution Prevention 15.1 Samples are disposed of according to the SOP on Sample Disposal. For those samples which are deemed to be hazardous materials, these must be lab packed and removed by a third party firm. 15.2 For information about pollution prevention that may be applicable to laboratory practices consult "Less is Better for Laboratory Chemical Management for Waste Reduction" available from the American Chemical Society Department of Government Relations and Science Policy. Address: 1155 16 th St. N.W. Washington, DC 20036. 16.0 Reference: 16.1 US EPA Method 340.2; Measurement of Fluoride by ISE. 16.2 SM 4500 F-B, C Standard Methods 20 th edition, 1998 and previous editions Alloway Page 9 of 9
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