Direct Current Plasma (DCP) Optical Emission Spectrometric Method for Trace Elemental Analysis of Water & Wastes 1.0 SCOPE AND APPLICATION 1.1 This method may be used for the detemination of dissolved, suspended, or total elements in drinking water, surface water, domestic and industrial wastewaters. 1.2 Dissolved elements are determined in filtered and acidified samples. Appropriate steps must be taken in all analyses to ensure that potential inter- ferences are taken into account. This is especially true when dissolved solids in the total in process sample exceed 5,000 mg/l (See 4.). 1.3 Total elements are determined after appropriate digestion procedures are per- formed. Since digestion techniques increase the dissolved solids content of the samples, appropriate steps must be taken to correct for potential interference effects. (See 4). 1.4 Table 1 lists elements for which this method applies along with recommended wavelengths and typical estimated instrumental detection limits using conventional pneumatic nebulization. Actual working detection limits are sample dependent and as the sample matrix varies, these concentrations may also vary. In time, other elements may be added as more information becomes available and as required. 2.0 SUMMARY OF METHOD 2.1 The method describes a technique for the simultaneous multi-element or se- quential determination of trace elements in solution. The basis of the method is the measurement of atomic emission by an optical spectroscopic technique. Samples are nebulized and the aerosol that is produced is transported to the plasma where excitation occurs. Characteristic atomic-line emission spectra are produced by a direct current plasma (DCP). Spectra are produced by an echelle grating spectro- meter and the intensities of the lines are moitored by photomultiplier tubes. The photocurrents from the photomultiplier tubes are processed and controlled by a computer system. A background correction technique may be required to compensate for variable background contribution to the determination of trace elements. Back- ground must be measured adjacent to analyte lines on samples during analysis. The position selected for the background intensity measurement, on either or both sides of the analytical line, will be determined by the spectrum adjacent to the analyte line. The position used must be free of spectral interference and reflect the same change in background intensity as occurs at the analyte wavelength measured. Background correction is not required in cases of line broadening where a background correction measurement would actually degrade the analytical result. The possibility of additional interferences named in 4.1 (and tests for their presence as described in 4.2) should also be recognized and appropriate corrections made. 3.0 DEFINITIONS 3.1 Dissolved - Those elements which will pass through a 0.45 mm membrane filter 3.2 Suspended - Those elements which are contained by a 0.45 mm membrane filter. 3.3 Total - The concentration determined on an unfiltered sample following vigorous digestion (11.3), or the sum of the dissolved plus suspended concentrations. (11.1 and 11.2) 3.4 Total Recoverable - The concentration determined on an unfiltered sample follow- ing treatment with hot, dilute mineral acid (11.4). 3.5 Instrumental Detection Limit - The concentration equivalent to a signal, due to the analyte, which is equal to three times the standard deviation of a series of ten replicate measurements of a reagent blank signal at the same wavelength. 3.6 Sensitivity - The slope of the analytical curve, i.e., functional relationship between emission intensity and concentration. 3.7 Instrument Check Standard - A multi-element standard of known concentrations prepared by the analyst to monitor and verify instrument performance on a daily basis. (See 7.6.1) 3.8 Interference Check Sample - A solution containing both interfering and analyte elements of known concentration that can be used to verify background and inter- element correction factor. (See 7.6.2) 3.9 Quality Control Sample - A solution obtained from an outside source having known concentration values to be used to verify the calibration standards. (See 7.6.3) 3.10 Calibration Standards - A series of known standard solutions used by the analyst for calibration of the instrument (i.e., prepare analytical curve). (see 7.4) 3.11 Linear Dynamic Range - The concentration range over which the analytical curve remains linear. 3.12 Reagent Blank - A volume of deionized, distilled water containing the same acid matrix as the calibration standards carried through the entire analytical scheme. (See 7.5.2) 3.13 Calibration Blank - A volume of deionized, distilled water acidified with appropriate acids. The acids used should match the acid concentration in the samples. 3.14 Method of Standard Addition - The standard addition technique involves the use of the unknown and the unknown plus a known amount of standard. (See 11.6.1) 4.0 INTERFERENCES 4.1 Several types of interference effects may contribute to inaccuracies in the determin- ation of trace elements. They can be summarized as follows: 4.1.1 Spectral interferences can be categorized as: (1) overlap of a spectral line from another element; (2) unresolved overlap of molecular band spectra; (3) background contribution from continuous or recombination phenomena; (4) background contribution from stray light from the line emission of high concentration elements. The first of these effects can be compensated by utilizing a computer correction of the raw data, requiring the monitoring and measurement of the interfering element. The second effect may require selection of an alternate wavelength. The third and fourth effects can usually be compensated by a background correction adjacent to the analyte line. In addition, users of simultaneous multi-element instrumentation must assume the responsibility of verifying the absence of spectra interference from an element that could occur in a sample but for which there is no channel in the instrument array. Listed in Table 2 are some interference effects for the recommended wavelengths given in Table 1. The data in Table 2 is an indication of potential spectral interferences. For this purpose, linear relations between concentration and intensity for the analytes and the interference can be assumed. This interference data is expressed as analytic concentration equivalents arising from 100 mg/L of the interference element. The suggested use of the information is as follows: Assume that aluminum (396.152) is to be determined in a sample containing approxi- mately 10 mg/L of calcium. According to Table 2, 100 mg/L of calcium would yield a false signal for aluminum equivalent to approximately 0.1 mg/L. Therefore, 10 mg/L of calcium would result in a false signal for aluminum equivalent to approximately 0.01 mg/L. The reader is cautioned that other analytical systems may exhibit somewhat differenent levels of interference than those shown in Table 2, and that the interference effects must be evaluated for each individual system. Generally, interferences are discernible if they produce peaks or background shifts corresponding to 10x the analyte detection limit. 4.1.2 Physical interferences are generally considered to be effects associated with the sample nebulization and transport processes. Such properties as change in viscosity and surface tension can cause significant inaccuracies especially in samples which may contain high dissolved solids and/or acid concentrations. The use of a peristaltic pump may lessen these interferences. If these types of interferences are operative, they must be reduced by dilution of the sample and/or utilization of standard addition techniques. Also, it has been reported that better control of the argon flow rate improves instrument performance. This is accomplished with the use of mass flow controllers. 4.1.3 Chemical interferences are characterized by molecular compound formation, ionization effects and solute vaporization effects. Normally these effects are not pronounced with the DCP technique, however, if observed they can be minimized by careful selection of operating conditions (that is, observation position, and so forth), by buffering (4.1.4) of the sample, by matrix matching, and by standard addition pro- cedures. These types of interferences can be highly dependent on matrix type and the specific analyte element. 4.1.4 Elements such as lithium, sodium, potassium, rubidium, cesium, calcium, magnesium, etc. can cause enhancement of the net signl-to-noise ratio for many of the elements in this method. This effect can be both controlled and utilized advan- tageously by the addition of lithium, or cesium at a final concentration of 1,000 mg/L, to the blank, the standards, and the samples. 4.2 It is recommended that whenever a new or unusual sample matrix is encountered, a series of tests be performed prior to reporting concentration data for analyte ele- ments. Theses tests, as outlined in 4.2.1 through 4.2.4 will ensure the analyst that neither positive nor negative interference effects are operative on any of the analyte elements thereby distorting the accuracy of the reported values. 4.2.1. Serial Dilution - If the analyte concentration is sufficiently high (minimally a factor of 10 above the instrumental detection limit after dilution), an analysis of a di- lution should agree within 5% of the original determination (or within some accept- able control limit (14.1) that has been established for that matrix). If not, a chemical or physical interference effect should be suspected. 5.0 SAFETY 5.1 The toxicity or carcinogenicity of each reagent used in this method has not been precisely defined; however, each chemical compound should be treated as a potential health hazard. From this viewpoint, exposure to these chemicals must be reduced to the lowest possible level by whatever means available. The laboratory is responsible for maintaining a current awareness file of OSHA regulations regarding the safe handling of the chemicals specified in this method. A reference file of material data handling sheets should also be made available to all personnel involved in the chemical analysis. Additional references to laboratory safety are available and have been identified in the reference section for the information of the analyst. 6.0 APPARATUS 6.1 DC argon plasma spectrometer with a wavelength range from 190 nm to 800 nm. 6.1.1 The manufacturer's operating instruction manual and handbook of spectral lines should be followed for all instrumental parameters and setup. (See Table 4). 6.2 The three electrode DCP jet is hereby specified. 6.2.1 Any two electrode DCP jet must be updated to the three electrode system 6.3 Computer controlled background compensator. 6.4 Peristaltic pump with a pumping rate of about 2 mL/min. 6.5 Support Gas- Argon, either distilled from commercially available liquid, or a "purified" grade cylinder (welding grade or better). 7.0 REAGENTS AND STANDARDS 7.1 Acids used in the preparation of standards and for sample processing must be ultra-high purity grade or equivalent. Redistilled acids are acceptable. 7.1.1 Hydrochloric acid, concentrated (sp gr 1.19). 7.1.2 Hydrochloric acid, (1 + 1): Add 500 mL concentrated HCl (sp gr 1.19) to 400 mL deionized, distilled water and dilute to 1 liter. 7.1.3 Nitric acid, concentrated (sp gr 1.41). 7.1.4 Nitric acid (1+1): Add 500 mL concentrated HNO3 (sp gr 1.41) to 400 mL de- ionized, distilled water and dilute to 1 liter. 7.2 Deionized, distilled water: Prepare by passing distilled water through a mixed bed of cation and anion exchange resins. Use deionized, distilled water for the preparation of all reagents, calibration standards and as dilution water. The purity of this water must be equivalent to ASTM Type II reagent water of specification D 1193 (14.3). 7.3 Standard stock solutions may be pruchased or prepared from ultra high purity grade chemicals or metals. All salts must be dried for 1 hour at 105 degrees C unless otherwise specified. CAUTION: (Many metal salts are extremely toxic and may be fatal if swallowed. Wash hands thoroughly after handling.) Typical stock solution preparation procedures follow: 7.3.1 Aluminum solution, stock, 1 mL = 100 ug Al: Dissolve 0.100 g of aluminum metal in an acid mixture of 4 mL of (1+1) PCl and 1 mL of concentrated HNO3, in a beaker. Warm gently to effect solution. When solution is complete, transfer quan- titatively to a liter flask, add an additional 10 mL of (1+1) HCl and dilute to 1000 mL with deionized, distilled water. 7.3.2 Barium solution, stock, 1 mL - 100 ug Ba: Dissolve 0.1516 g BaCl2 (dried at 250 degrees C for 2 hours) in 10 mL deionized, distilled water with 1 mL (1+1) HCl. Add 10.0 (1+1) HCl and dilute to 1000 mL with deionized, distilled water. 7.3.3 Beryllium solution, stock, 1 ml - 100 ug Be: Do not dry. Dissolve 1.966 g BeSo4 . 4H2O, in deionized, distilled water, and 10.0 mL concentrated HNO3 and dilute to 1000 mL with deionized, distilled water. 7.3.4 Boron solution, stock, 1 mL - 100 ug B: Do not dry. Dissolve 0.5716 g an- hydrous H3BO3 in dionized distilled water, dilute to 1000 mL. Use a reagent meeting ACS specifications, keep the bottle tightly stoppered and store in a disiccator to pre- vent the entrance of atmospheric moisture. 7.3.5 Cadmium solution, stock 1 mL - 100 ug Cd: Dissolve 0.1142 g CdO in a min- imum amount of (1+1) HNO3. Heat to increase rate of dissolution. Add 10.0 mL concentrated HNO3 and dilute to 1000 mL with deionized distilled water. 7.3.6 Calcium solution , stock 1 mL - 100 ug Ca: Suspend 0.2498 g CaCO3 dried at 180 degrees C for 1 hour before weighing in deionized, distilled water and dissolve cautiously with minimum amount of (1+1) HNO3. Add 10.0 mL concentrated HNO3 and dilute to 1000 mL with deionized, distilled water. 7.3.7 Chromium solution, stock, 1 mL - 100 ug Cr: dissolve 0.1923 g of CrO3 in de- ionized, distilled water. When solution is complete, acidify with 10 mL concentrated HNO3 and dilute to 100 mL with deionized, distilled water. 7.3.8 Cobalt solution, stock 1 mL - 100 ug Co: dissolve 0.1000 g of cobalt metal in a minimum amount of (1+1) HNO3. Add 10.0 mL (1+1) HCL and dilute to 1000 mL with deionized, distilled water. 7.3.9 Copper solution, stock, 1 mL - 100 ug Cu: Dissolve 0.1252 g CuO in a minimum amount of (1+1) HNO3. Add 10.0 mL concentrated HNO3 and dilute to 1000 mL with deionized, distilled water. 7.3.10 Iron solution, stock, 1 mL - 100 ug Fe: dissolve 0.1430 g Fe2O3 in a warm mixture of 20 mL (1+1) HCl and 2 mL of concentrated HNO3. Cool, add an add- itional 5 mL of concentrated HNO3 and dilute to 1000 mL with deionized, distilled water. 7.3.11 Lead solution, stock, 1 mL - 100 ug Pb: Dissolve 0.1599 g Pb(NO3)2 in a minimum amount of (1+1) HNO3. Add 10.0 mL concnetrated HNO3 and dilute to 1000 mL with deionized, distilled water. 7.3.12 Magnesium solution, stock, 1 mL - 100 ug Mg: Dissolve 0.1658 g MgO in a minimum amount of (1+1) HNO3. Add 10.0 mL concentrated HNO3 and dilute to 1000 mL with deionized, distilled water. 7.3.13 Manganese solution, stock, 1 mL - 100 ug Mn: Dissolve 0.1000 g of man- ganese metal in the acid mixture 10 mL concentrated HCl and (1+1) concentrated HNO3, and dilute to 1000 mL with deionized, distilled water. 7.3.14 Molybdenum solution, stock, 1 mL - 100 ug Mo: Dissolve 0.2043 g (NH4) MoO4 in deionized, distilled water and dilute to 1000 mL. 7.3.15 Nickel solution, stock, 1 mL - 100 ug Ni: Dissolve 0.1000 g of nickel metal in 10 mL hot concentrated HNO3, cool, and dilute to 1000 mL with deionized, distill- ed water. 7.3.16 Silver solution, stock, 1 mL - 100 ug Ag: Dissolve 0.1575 g AgNO3 in 100 mL of deionized, distilled water and 10 mL concentrated HNO3. Dilute to 1000 mL with deionized distilled water. 7.3.17 Sodium solution, stock, 1 mL - 100 ug Na: Dissolve 0.2542 g NaCl in deionized, distilled water. Add 10.0 mL concentrated HNO3 and dilute to 1000 mL with deionized, distilled water. 7.3.18 Vanadium solution, stock, 1 mL - 100 ug V: Dissolve 0.2297 g NH4VO3 in a minimum amount of concentrated HNO3. Heat to increase rate of dissolution. Add 10.0 mL concentrated HNO3 and dilute to 1000 mL with deionized, distilled water. 7.3.19 Zinc solution, stock, 1 mL - 100ug Zn: Dissolve 0.1245 g ZnO in a minimum amount of dlute HNO3. Add 10.0 mL concentrated HNO3 and dilute to 1000 mL with deionized, distilled water. 7.3.20 Gold solution, stock, 1 mL - 100 ug Au: Weigh 0.1000 g of high purity gold shot or powder and transfer to a Teflon (14.8) beaker. Add 25 mL of concentrated HNO and 75 mL of concentrated HCl. Heat gently until the metal dissolves and the solution volume is reduced to about 25 mL. Add another 100 mL of concentrated HCl and heat until brown fumes no longer evolve. Cool and dilute to l liter with de- ionized water. Store in a plastic bottle that has been presoaked in dilute HNO3 to prevent reduction of gold on the container walls. 7.3.21 Palladium solution, stock 1 mL - 100 ug Pd: Weigh 0.1000 g of high purity palladium sponge and transfer to a Teflon (14.8) beaker. Add 50 mL concentrated HCl plus 10 mL of concentrated HNO3 and warm until dissolution is complete. Evaporate to a syrup and add another 100 mL of concentrated HCl. Continue heating until brown fumes of NO2 cease to evolve. Cook, transfer to a l liter volumetric flask, and dilute to volume with deionized water. Store in a plastic bottle that has been presoaked in dilute HCl. 7.3.22 Platinum solution, stock, 1 mL - 100 ug Pt: Weigh 0.1000 g of high purity platinum sponge and transfer to a Teflon (14.8) beaker. Add 50 mL of concentrated HCl plus 10 mL of concentrated HNO3 and warm until dissolution is complete. Evaporate to a syrup and add another 100 mL of concentrated HCl. Continue heating until brown fumes of NO2 cease to evolve. Cool, transfer to a l liter volumetric flask, and dilute to volume with deionized water. Store in a plastic bottle that has been presoaked in dilute HCl. 7.3.23 Titanium solution, stock, 1 mL - 100 ug of Ti: Weigh 0.6138 g of titanium as high purity (NH4)2 TiO (C2O4)2.H2O and transfer to a 1 liter volumetric flask. Add 100 mL of deionized water and 1 g of oxalic acid. After dissolution, dilute to 1 liter with deionized water. Store in a plastic bottle that has been presoaked in dilute oxalic acid. 7.3.24 Lithium solution, stock, 1 mL - 20,000 ug Li: Weigh 106.481 g of high purity Li2CO3 and transfer to a l L volumetric flask. Slowly add 200 mL concentrated HNO3. Dilute to l L with deionized water. Store in a plastic bottle that has been presoaked in (1+1) HNO3. 7.3.25 Cesium solution, stock, 1 mL - 20,000 ug Cs: Weigh 24.5143 g of high purity Cs2CO3 and transfer to a a 1 L volumetric flask. Slowly add 200 mL of concentrated HNO3. Dilute to 1 L with deionized water. Store in a plastic bottle that has been presoaked in (1+1) HNO3. 7.4 Calibration standard solutions - Prepare calibration standard solution by diluting appropriate volumes as aliquots, of the stock solutions in volumetric flasks. Take proper precautions to ensure acid matrix and concentrations are compatible and like those of the sample as ready for analysis. The addition of the lithium (7.3.24) or cesium (7.3.25) stock solution should be performed rendering a 1000 mg/L concentration in the final diluted standard. When considering final diluted concentration of the calibrating standards, criteria such as the linear dynamic range of the analyte wavelength and the expected concentration range of the analyte in the sample are important. Transfer the solutions to an appropriate presoaked bottle for storage. Fresh standards should be prepared as needed as shelf-life is limited. Calibration standard solutions must be initially verified using a quality control sample and monitored weekly for stability (See 7.6.3). NOTE: Calibration standards can be mixed under the following conditions: 1. Prior to preparing any combinations, each stock solution has to be analyzed for the presence of impurities and its possible spectral interference on any of the other concomitant elements. 2. Any combination of elements proposed must be verified for chemical compatibility to ensure stability. 3. Actual preparation methodology must consider the final acid concentration of the samples which are being analyzed. Matching acid concentration between standards and sample should be conducted. 7.5 Two types of blanks are required for the analysis. The calibration blank (3.13) is used in establishing the analytical curve while the reagent blank (3.12) is used to correct for possible contamination resulting from varying amount of the acids used in the sample processing. 7.5.1 The calibration blank is prepared by mixing the appropriate acid and deionized distilled water to match the type of acid and concentration of acid used in a specific sample prepartation. Refer to one of the three peparations covered in Section 11. It is important to match the calibration blank with the correct sample procedure. Lithium or cesium stock solution should be added to blank to render a 1000 mg/l concentration in the final solution. 7.5.2 The reagent blank must contain all the reagents and the same volumes as used in the processing of the samples. The reagent blank must be carried through the complete procedure and contain the same acid concentration in the final solution as the sample solution used for analysis. Lithium or cesium stock solution should be added to blanks to render a 1000 mg/l concentration in the final solution. 7.6 In addition to the calibration standards, an instrument check standard (3.7), an interference check sample (3.8) and a quality control sample (3.9) are also required for the analyses. 7.6.1 The instrument check standard is prepared by the analyst by combining com- patible elements at a concentration equivalent to the midpoint of their respective cali- bration curves. 7.6.2 The interference check sample is prepared by the analyst in the following manner. Select a representative sample which contains minimal concentration of the analytes of interest by known concentration of interfering elements that will pro- vide an adequate test of the correction factor. Spike the sample with the elements of interest at the approximate concentration of either 100 ug/L or 5 times the estimated detection limits given in Table 1 (for effluent samples of expected high concentration, spike at a appropriate level.) If the types of samples analyzed are varied, a synthetically prepared sample may be used if the above criteria and intent are met. Lithium or cesium stock solution should be added to render a 1000 mg/L concentration in the final solutin. 7.6.3 The quality control sample should be prepred in the same acid matrix as the calibration standards at a concentration near 1 mg/L and in accordance with the in- structions provided by the supplier. Lithium or cesium stock solution should be added to render a 1000 mg/L concentration in the final solution. 8.0 SAMPLE COLLECTION, RESERVATION, AND STORAGE 8.1 For the determination of trace elements, contamination and loss of reagents, and impurities on a laboratory apparatus which the sample contacts, are all sources of potential contamination. Sample containers can introduce either positive or negative errors in the measurement of trace elements by (a) contamination through leaching or surface desorption and (b) by depleting concentrations through absorption. Thus the collection and treatment of the sample prior to analysis requires particular attention. Laboratory glassware including the sample bottle (whether polyethylene, polypropylene or FEP-flurocarbon) should be throughy washed with detergent and tap water; rinsed with (1+1) nitric acid, tap water, (1+1) hydrochloric acid, tap water and finally deionized, distilled water in that order. (See Note 1 & 2). NOTE 1: Chromic acid may be useful to remove organic deposits from glassware; however, the analyst should be cautioned that the glassware must be thoroughly rinsed with water to remove the last traces or chromium. This is especially important if chromium is to be included in the analytical scheme. A commercial product, NOCHROMIX, available from: Godax Laboratories 6 Varick Street New York, NY 10013 may be used in place of chromic acid. Chromic acid should not be used with plastic bottles. NOTE 2: If it can be documented through an active analytical quality control program using spiked samples and reagent blanks, that certain steps in the cleaning procedure are not required for routine samples, those steps may be eliminated from the procedure. 8.2 Before collection of the sample, a decision must be made as to the type of data desired, that is, dissolved, suspended or total, so that the appropriate preservation and pretreatment steps may be accomplished. Filtration, acid preservation, etc., are to be performed at the time the sample is collected or as soon as possible thereafter. 8.2.1 For the determination of dissolved elements, the sample must be filtered through a 0.45 mm membrane filter as soon as practible after collection. (Glass or plastic filtering appartus are recommended to avoid possible contamination.) Use the first 50-100 mL to rinse the filter flask. Discard this portion and collect the required volume of filtrate. Acidify the filtrate with (1+1) HNO3 to a pH of 2 or less. Normally, 3 mL of (1+1) acid per liter should be sufficient to preserve the sample. 8.2.2 For the determination of suspended elements, a measured volume of unpreserved sample must be filtered through a 0.45 mm membrane filter as soon as practical after collection. The filter plus suspended material should be transferred to a suitable con- tainer for storage and/or shipment. No preservative is required. 8.2.3 For the determination of total or total recoverable elements, the sample is acidified with (1+1) HNO3 to pH 2 or less as soon as possible, preferably at the time of collection. The sample is not filtered before processing. 9.0 CALIBRATION AND STANDARDIZATION 9.1 Setup instrument with proper operating parameter. The instrument must be allowed to become thermally stable before beginning. This usually requires at least 30 minutes of operation prior to calibration. 9.2 Plasma position should be optimized using the following procedure: A. "Peak" the monochromator on the wavelength of interest. B. Visually set the plasma to the "0" position (See Figure #1). C. Nebulize a standard in the concentration range of 10 to 100 ppm. Adjust the PMT voltage setting to a medium setting. (Approximately 800 V). Re- cord that value. D. Without changing the plasma position, nebulize deionized water and record the digital readout. E. Follow the same procedure for plasma positons +1 and -1 and organize the data as shown in Table 1. For each plasma position, subtract the blank counts from the standard counts to get the net signal. Divide the net signal by the blank count value to obrtain the net signal to blank ratio. The optimum plasma position is where the ratio is the largest figure. In the hypothetical example in Table 3, the maximum ratio is 24 at position 0. 9.3 Initiate appropriate operating configuration of computer. 9.4 Profile and calibrate instrument according to instrument manufacturer's recom- mended procedures, using the typical calibration standard solutions described in (7.4). Flush the system with the calibration blank (7.5.1) between each standard. (The use of the average intensity of multiple exposures for both standardization and sample analysis has been found to reduce random error.). 9.5 Before beginning the sample run, re-analyze the highest calibration standard as if it were a sample. Concentration values obtained should not deviate from the actual values by more than ± 5% (or the established control limits, whichever is lower). If they do, follow the recommendations of the instrument manufacturer to correct for this condition. 9.6 The sensitivity, instrumental detection limit, precision, linear dynamic range, and interference effects must be investigated and established for each individual analyte line on the particular instrument used. It is the responsibility of the anlyst (1) to verify that the instrument configuration and operating conditions used satisfy the analytical require- ments and (2) to maintain quality control data confirming instrument performance and analytical results. 10 QUALITY CONTROL (Instrumental) 10.1 Check the instrument standardization by analyzing appropriate quality control check standards as follows: 10.1.1 Analyze an appropriate instrument check standard (7.6.1) containing the elements of interest at a frequency of 10%. This check standard is used to determine instrument drift. If agreement is not within ± 5% of the expected values or within the established À¨@ «ÀÀßßðñ¸ control. The analysis should be terminated, the problem corrected, and the intrument recalibrated. Analyze the calibration blank (7.5.1) at a frequency of 10%. The result should be within the established control limits to two standard deviations of the mean value. If not, repeat the analysis two more times and average the three results. If the average is not within the control limit, term- inate the analysis, correct the problem and recalibrate the instrument. 10.1.2 To verify interelement and background correction factors analyze the interference check sample (7.6.2) at the beginning, end, and at periodic intervals throughout the sample run. Results should fall within the established control limits of 1.5 times the standard deviation of the mean value. If not, terminate the analysis, correct the problem and recalibrate the instrument. 10.1.3 A quality control sample (7.6.3) obtained from an outside source must first be used for the initial verification of calibration standards. A fresh dilution of this sample shall be analyzed every week thereafter to monitor their stability. If the results are not within ± 5% of the true value listed for the control sample, prepare a new calibration standard and recalibrate the instrument. If this does not correct the problem, prepare a new stock standard and a new calibration standard and repeat the calibration. 11.0 PROCEDURE 11.1 For the determination of dissolved elements, the filtered, preserved sample may often be analyzed as received. The acid matrix and concentration of the samples and calibration standards must be the same. Lithium (7.3.24) or cesium (7.3.25) stock solution should be added to render a 1000 mg/L concentration in the final dilution. If a precipitate forms upon acidification of the sample or during transit or storage, it must be redissolved before the analysis using appropriate total element digestion procedure as described in either 11.3.1, 11.3.2, or 11.3.3. 11.2 For suspended element determination, select from the following the appropriate sample preparation procedure for the element or elements of concern. 11.2.1 For the determination of aluminum, barium, beryllium, boron, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, molybdenum, nickel, silver, sodium, vanadium, and zinc the following sample preparation should be used. Transfer the mebrane filter containing the insoluble material to a 150 mL Griffin beaker and add 4 mL concentrated HNO3. Cover the beaker with the watch glass and heat gently. The warm acid will soon dissolve the membrane. 11.2.2 For the determination of gold, palladium and platinum, the following sample preparation should be used. Transfer the membrane filter containing the insoluble material to a Griffin beaker and add 3 mL of concentrated distilled HNO3. Place the beaker on a steam bath and evaporate to near dryness. Cool the beaker and cautiously add a 5 mL portion of aqua regia. Cover the beaker with a watch glass and return to the steam bath. Continue heating the covered beaker for 30 minutes. Remove cover and evaporate to near dryness. Cool and add (1+1) distilled HNO3 (1 mL per 100 mL dilution). Wash down the beaker walls and watch glass with distilled water and filter the sample to remove silicates and other insoluble material that could clog the nebulizer. Lithium (7.3.24) or cesium (7.3.25) stock solution should be added to render a 1000 mg/L concentration in the final dilution. Adjust the volume to some predetermined value based on the expected metal concentration. The sample is now ready for analysis. 11.2.3 For the determination of titanium, the following sample preparation modification should be used. For processing total and suspended titanium, concentrated H2SO4 (2 mL per 100 mL of final dilution) must be added in additional nitric acid as needed. When solubilization is complete, heat until the appearance of SO3 fumes. Lithium (7.3.24) or cesium (7.3.25) stock solution should be added to render a 1000 mg/L concentration in the final dilution. 11.3 For total element determination, select from the following the appropriate sample preparation procedure for the element or elements of concern. 11.3.1 For the determination of aluminum,, barium, beryllium, boron, cadmium, man- ganese, molybdenum, nickel, silver, sodium, vanadium, and zinc, the following sample preparation should be used. Increase the temperature of the hot plate and digest the material. When the acid has nearly evaporated, cool the beaker and watch glass and add another 3 mL of con- centration HNO3. Cover and continue heating until the digestion is complete, generally indicated by a light colored digestate. Evaporate to near dryness (2 mL), cool, add 10 mL HCL (1+1) and 15 mL deionized, distilled water per 100 mL dilution and warm the beaker gently for 15 minutes to dissolve any precipitated or residue material. Allow to cool, wash down the watch glass and beaker walls with deionized distilled water and filter the sample to remove insoluble material that could clog the nebulizer. (See Note 3.) Lithium (7.3.24) or cesium (7.3.25) stock solution should be added to render a 1000 mg/L concentration in the final dilution. Adjust the volume based on the expected concentration of elements present. This volume will vary depending on the elements to be determined. (See Table 1). The sample is now ready for analysis. Concentrations so determined shall be reported as "Suspended." Note 3: In place of filtering, the sample, after diluting and mixing, may be centrifuged or allowed to settle by gravity overnight to remove insoluble material. Note 4: If low determinations of boron are critical, quartz glassware or Teflon (14.8) should be used. Choose a measured volume of the well mixed acid preserved sample appropriate for the expected level of elements and transfer to a Griffin beaker. (See Note 4). Add 3 mL of concentration HNO3. Place the beaker on a hot plate and evaporate to near dryness cautiously, making certain that the sample does not boil and that no area of the bottom of the beaker is allowed to go dry. Cool the beaker and add another 5 mL portion of concentrated HNO3. Cover the beaker with a watch glass and return to the hot plate. Increase the temperature of the hot plate so that a gentle reflux action occurs. Continue heating, adding additional acid as necessary, until the digestion is complete (generally indicated with the digestate is light in color or does not change in appearance with con- tinued refluxing). Again, evaporate to near dryness and cool the beaker. Add 10 mL of (1+1) HCl and 15 mL of deionized, distilled water per 100 mL of final solution and warm the beaker gently for 15 minutes to dissolve any precipitate or residue resulting from evaporation. Allow to cool, wash down the beaker walls and watch glass with de- ionized, distilled water and filter the sample to remove insoluble material that could clog the nebulizer. (See Note 3). Lithium (7.3.24) or cesium (7.3.25) stock solution should be added to render a 1000 mg/L concentration in the final dilution. Adjust the sample to a predetermined volume based on the expected concentrations of elements present. The sample is now ready for analysis. Concentrations so deter- mined shall be reported as "Total”. 11.3.2 For the determination of gold, palladium and platinum, the following sample preparation should be used. Transfer a representative aliquot of the well mixed sample to a Griffin beaker and add 3 mL of concentrated distilled HNO3. Place the beaker on a steam bath and evaporate to near dryness. Cool the beaker and cautiously add a 5 mL portion of aqua regia. Cover the beaker with a watch glass and return to the steam bath. Continue heating the covered beaker for 30 minutes. Remove cover and evaporate to near dryness. Cool and add (1+1) distilled HNO3 (1 mL per 100 mL dilution). Wash down the beaker walls and watch glass with distilled water and filter the sample to remove silicates and other insoluble material that could clog the nebulizer. Lithium (7.3.24) or cesium (7.3.25) stock solution should be added to render a 1000 mg/L concentration in the final dilution. Adjust the volume to some predetermined value based on the expected metal concentration. The sample is now ready for analysis. 11.3.3 For the determination of titanium, the following sample preparation modification should be used. For processing total and suspended titanium, concentrated H2SO4 (2 mL per 100 mL of final dilution) must be added in addition to the nitric acid. Reflux the sample adding additional nitric acid as needed. When solubilization is complete, heat until the appearance of SO3 fumes. Lithium (7.3.24) or cesium (7.3.25) stock solution should be added to render a 1000 mg/L concentration to the final dilution. 11.4 For total recoverable determination of aluminum, barium, beryllium, boron, cadium, calcium, chromium, cobalt, copper, iron, lead, magnesium, molybdenum, nickel, silver, sodium, vanadium, and zinc, the following sample preparation should be used. Choose a measured volume of a well mixed, acid preserved sample appropriate for the expected level of elements and transfer to a Griffin beaker. (See Note 4). Add 2 mL of (1+1) HNO3 and 10 mL of (1+1) HCl to the sample and heat on a steam bath or hot plate until the volume has been reduced to near 25 mL making certain the sample does not boil. After this treatment, cool the sample and filter to remove insoluble material that could clog the nebulizer. (See Note 3). Lithium (7.3.24) or cesium (7.3.25) stock solution should be added to render a 1000 mg/L concentration in the final dilution. Adjust the volume to 100 mL and mix. The sample is now ready for analysis. Concen- trations so determined shall be reported as "Total." 11.5 Begin the sample run by flushing the system with the calibration blank solution (7.5.1) between each sample. Analyze the instrument check standard (7.6.1) and the calibration blank (7.5.1) each 10 samples. 11.6 If it is found that the method of standard addition is required, the following pro- cedure is recommended. 11.6.1 The standard addition technique involves preparing new standards in the sample matrix by adding known amounts of standard to one or more aliquots of the processed sample solution. This technique compensates for a sample constituent that enhances or depresses the analyte signal thus producing a different slope from that of the cali- bration standards. It will not correct for additive interference which causes a baseline shift. The simplest version of this technique is the single-addition method. The pro- cedure is as follows. Two identical aliquots of the sample solution, each of volume V, are taken. To the first (labeled A) is added a small volume VS of a standard analyte solution of concentration CS. To the second (labeled B) is added the same volume VS of the solvent. The analytical signals of A and B are measured and corrected for nonanalyte signals. The unknown sample concentration Cx is calculated: Cx = SB VS CS — — — (SA - SB) Vx Where SA and SB are the analytical signals (corrected for the blank) of A and B, re- spectively. VS and CS should be chosen so that SA is roughly twice SB of the aver- age. It is best if VS is made much less than VX and thus CS is much greater than CX, to avoid excess dilution of the sample matrix. If a separation or concentration step is used, the additions are best made first and carried through the entire procedure. For the results from this technique to be valid, the following limitations must be taken into consideration: 1. The analytical curve must be linear. 2. The chemical form of the analyte added must respond the same as the analyte in the sample. 3. The interference effect must be constant over the working range of concern 4.The signal must be corrected for any additive interference. 12 CALCULATION 12.1 Reagent blanks (7.5.2) should be subtracted from all samples. This is particularly important for digested samples requiring large quantities of acids to complete the di- gestion. 12.2 If dilutions were performed, the appropriate factor must be applied to sample values. 12.3 Data should be rounded to the thousandth place and all results should be reported in mg/L up the three significant figures. 13.0 PRECISION AND ACCURACY 13.1 Data has been supplied to the EPA for statistical evaluation for all elements listed in Table 1. 14.0 REFERENCES 14.1 Handbook for Analytical Quality Control in Water and Wastewater Laboratories, EPA-600/4-79-019. 14.2 "Methods for Chemical Analysis of Water and Wastes", EPA-600-4-79-020. 14.3 Annual Book of ASTM Standards, Volume 11.01 14.4 "Carcinogens-Working with Carcinogens", Department of Health, Education, and Welfare, Public Health Service, Center for Disease Control., National Institute for Occupational Safety and Health, Publication No. 77-206, August, 1977. 14.5 "OSHA Safety and Health Standards, General Industry:, (29 CFR 1910), Occu- pational safety and Health Administration, OSHA 2206, (Revised, January 1976). 14.6 “Safety in Academic Chemistry Laboratories", American Chemical Society Publi- cation, Committee on Chemical Safety, 3rd Edition, 1979.