2.1. Although methods have been reported for the analysis of solids by atomic absorption spectrophotometry, the technique generally is limited to metals in
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7010 – 1Revision 0 February 2007METHOD 7010GRAPHITE FURNACE ATOMIC ABSORPTION SPECTROPHOTOMETRY SW-846 is not intended to be an analytical training manual. Therefore, method procedures are written based on the assumption that they will be performed by analysts who are formally trained in at least the basic principles of chemical analysis and in the use of the subjecttechnology.In addition, SW-846 methods, with the exception of required method use for the analysisof method-defined parameters, are intended to be guidance methods which contain general information on how to perform an analytical procedure or technique which a laboratory can use as a basic starting point for generating its own detailed Standard Operating Procedure (SOP), either for its own general use or for a specific project application. The performance data included in this method are for guidance purposes only, and are not intended to be and must not be used as absolute QC acceptance criteria for purposes of laboratory accreditation.1.0SCOPE AND APPLICATION 1.1Metals in solution may be readily determined by graphite furnace atomic absorption spectrophotometry (GFAA). The method is simple, quick, and applicable to a large number of metals in environmental samples including, but not limited to, ground water, domesticand industrial wastes, extracts, soils, sludges, sediments, and similar wastes. With the exception of the analyses for dissolved constituents, all samples require digestion prior to analysis. Analysis for dissolved elements does not require digestion if the sample has been filtered and then acidified. NOTE: Organo-metallic species may not be detected if the sample is not digested. This method is applicable to the following elements:Element CASRN a Antimony(Sb)7440-36-0 Arsenic(As)7440-38-2 Barium(Ba)7440-39-3 Beryllium(Be)7440-41-7 Cadmium(Cd)7440-43-9 Chromium(Cr)7440-47-3 Cobalt(Co)7440-48-4 Copper(Cu)7440-50-8 Iron(Fe)7439-89-6 Lead(Pb)7439-92-1 Manganese(Mn)7439-96-5 Molybdenum(Mo)7439-98-7 Nickel(Ni)7440-02-0 Selenium(Se)7782-49-2 Silver(Ag)7440-22-4 Thallium(Tl)7440-28-0 Vanadium(V)7440-62-2 Zinc(Zn)7440-66-6 aChemical Abstract Service Registry Number

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7010 – 2Revision 0 February 20071.2Lower limits of quantitation and optimum ranges of the metals will vary with the matrices and models of atomic absorption spectrophotometers. The data shown in Table 1 provide some indication of the lower limits of quantitation obtainable by the furnace technique. The limits given in Table 1 are somewhat dependent on equipment (such as the type of spectrophotometer and furnace accessory, the energy source, the degree of electrical expansion of the output signal), and are greatly dependent on sample matrix. 1.3Users of this method should state the data quality objectives prior to analysis and must document and have on file the required initial demonstration performance data described in the following sections prior to using the method for analysis. When using furnace techniques, the analyst should be cautioned as to possible chemical reactions occurring at elevated temperatures which may result in either suppression or enhancement of the analysis element (see Sec. 4.0). To ensure valid data with furnace techniques, the analyst must examine each sample for interference effects (see Sec. 9.0) and, if detected, treat them accordingly, using either successive dilution, matrix modification, or the method of standard additions (see Sec.9.10). 1.4 Other elements and matrices may be analyzed by this method as long as the method performance is demonstrated for these additional elements of interest, in the additional matrices of interest, at the concentration levels of interest in the same manner as the listed elements and matrices (see Sec. 9.0).1.5 Prior to employing this method, analysts are advised to consult each type of procedure (e.g., sample preparation methods) that may be employed in the overall analysis for additional information on quality control procedures, development of QA acceptance criteria, calculations, and general guidance. Analysts should consult the disclaimer statement at the front of the manual and the information in Chapter Two for guidance on the intended flexibility in the choice of methods, apparatus, materials, reagents, and supplies, and on the responsibilities of the analyst for demonstrating that the techniques employed are appropriate for the analytes of interest, in the matrix of interest, and at the levels of concern. In addition, analysts and data users are advised that, except where explicitly specified in aregulation, the use of SW-846 methods is not mandatory in response to Federal testingrequirements. The information contained in this method is provided by EPA as guidance to be used by the analyst and the regulated community in making judgments necessary to generate results that meet the data quality objectives for the intended application.1.6Use of this method is restricted to use by, or under supervision of, properly experienced and trained personnel, including analysts who are knowledgeable in the chemical and physical interferences described in this method. Each analyst must demonstrate the ability to generate acceptable results with this method. 2.0SUMMARY OF THE METHOD 2.1Although methods have been reported for the analysis of solids by atomic absorption spectrophotometry, the technique generally is limited to metals in solution or solubilized through some form of sample processing. Refer to Chapter Three for a description of appropriate digestion methods.2.2 Preliminary treatment of wastes, both solid and aqueous, is always necessary because of the complexity and variability of sample matrix. Solids, slurries, and suspended material must be subjected to a solubilization process before analysis. This process may vary

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7010 – 3Revision 0 February 2007because of the metals to be determined and the nature of the sample being analyzed. Solubili-zation and digestion procedures are presented in Chapter Three.2.3 When using the furnace technique in conjunction with an atomic absorption spectrophotometer, a representative aliquot of a sample is placed in the graphite tube in the furnace, evaporated to dryness, charred, and atomized. As a greater percentage of availableanalyte atoms is vaporized and dissociated for absorption in the tube rather than the flame, the use of smaller sample volumes or quantitation of lower concentrations of elements is possible. The principle is essentially the same as with direct aspiration atomic absorption, except that a furnace, rather than a flame, is used to atomize the sample. Radiation from a given excitedelement is passed through the vapor containing ground-state atoms of that element. The intensity of the transmitted radiation decreases in proportion to the amount of the ground-state element in the vapor. The metal atoms to be measured are placed in the beam of radiation byincreasing the temperature of the furnace, thereby causing the injected specimen to volatilize. A monochromator isolates the characteristic radiation from the hollow cathode lamp or electrodeless discharge lamp, and a photosensitive device measures the attenuated transmitted radiation.3.0DEFINITIONS Refer to Chapter One, Chapter Three, and the manufacturer’s instructions for a definitionsthat may be relevant to this procedure.4.0INTERFERENCES 4.1Solvents, reagents, glassware, and other sample processing hardware may yield artifacts and/or interferences to sample analysis. All of these materials must be demonstrated to be free from interferences under the conditions of the analysis by analyzing method blanks. Specific selection of reagents and purification of solvents by distillation in all-glass systems maybe necessary. Refer to each method to be used for specific guidance on quality control procedures and to Chapter Three for general guidance on the cleaning of glassware. Also refer to Method 7000 for a discussion of interferences.4.2Although the problem of oxide formation is greatly reduced with furnace procedures (because atomization occurs in an inert atmosphere), the technique is still subject to chemical interferences. The composition of the sample matrix can have a major effect on the analysis. It is those effects which must be determined and taken into consideration in the analysis of each different matrix encountered. See Sec. 9.6 for additional guidance.4.3Background correction is important when using flameless atomization, especially below 350 nm. Certain samples, when atomized, may absorb or scatter light from the lamp. This can be caused by the presence of gaseous molecular species, salt particles, or smoke in the sample beam. If no correction is made, sample absorbance will be greater than it should be, and the analytical result will be erroneously high. Zeeman background correction is effective in overcoming composition or structured background interferences. It is particularly useful when analyzing for As in the presence of Al and when analyzing for Se in the presence of Fe.4.4Memory effects occur when the analyte is not totally volatilized during atomization. This condition depends on several factors — volatility of the element and its chemical form, whether pyrolytic graphite is used, the rate of atomization, and furnace design. This situation is detected through blank burns. The tube should be cleaned by operating the furnace at full

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7010 – 4Revision 0 February 2007power for the required time period, as needed, at regular intervals during the series ofdeterminations.4.5Gases generated in the furnace during atomization may have molecular absorption bands encompassing the analytical wavelength. When this occurs, use either background correction or choose an alternate wavelength. Background correction may also compensate for nonspecific broad-band absorption interference and light scattering.4.6Continuum background correction cannot correct for all types of background interference. When the background interference cannot be compensated for, chemically remove the analyte or use an alternate form of background correction (see Chapter Two). A single background correction device to be used with this method is not specified; however, it must provide an analytical condition that is not subject to the occurring interelement spectral interferences of palladium on copper, iron on selenium and aluminum on arsenic.4.7Interference from a smoke-producing sample matrix can sometimes be reduced by extending the charring time at a higher temperature or utilizing an ashing cycle in the presence of air. Care must be taken, however, to prevent loss of the analyte.4.8Samples containing large amounts of organic materials should be oxidized by conventional acid digestion before being placed in the furnace. In this way, broad-band absorption will be minimized.4.9Anion interference studies in the graphite furnace indicate that, under conditions other than isothermal, the nitrate anion is preferred. Therefore, nitric acid is preferable for any digestion or solubilization step. When another acid in addition to nitric acid is needed, a minimum amount should be used. This applies particularly to hydrochloric and, to a lesser extent, to sulfuric and phosphoric acids.4.10Carbide formation resulting from the chemical environment of the furnace has beenobserved. Molybdenum may be cited as an example. When carbides form, the metal isreleased very slowly from the resulting metal carbide as atomization continues. Molybdenummay require 30 seconds or more atomization time before the signal returns to baseline levels. Carbide formation is greatly reduced and the sensitivity increased with the use of pyrolyticallycoated graphite. Elements that readily form carbides are noted with the symbol “(p)” in Table 1.4.11Spectral interference can occur when an absorbing wavelength of an element present in the sample, but not being determined, falls within the width of the absorption line of the element of interest. The results of the determination will then be erroneously high, due to the contribution of the interfering element to the atomic absorption signal. Interference can also occur when resonant energy from another element in a multielement lamp, or from a metalimpurity in the lamp cathode, falls within the bandpass of the slit setting when that other metal is present in the sample. This type of interference may sometimes be reduced by narrowing the slit width.4.12It is recommended that all graphite furnace analyses be carried out using an appropriate matrix modifier. The choice of matrix modifier is dependent on analytes, conditions, and instrumentation and should be chosen by the analyst as the situation dictates. Follow the instrument manufacturers instructions for the preferred matrix modifier. Refer to Chapter Twofor additional guidance.4.13It is recommended that a stabilized temperature platform be used to maximize an isothermal environment within the furnace cell to help reduce interferences. Refer to Chapter Two for additional guidance.

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7010 – 5Revision 0 February 20074.14Cross-contamination and contamination of the sample can be major sources of error because of the extreme sensitivities achieved with the furnace. The sample preparation work area should be kept scrupulously clean. All glassware should be cleaned as directed in Sec. 6.6. Pipet tips are a frequent source of contamination. The analyst should be aware of the potential for the yellow tips to contain cadmium. If suspected, they should be acid soaked with 1:5 nitric acid and rinsed thoroughly with tap and reagent water. The use of a better grade of pipet tip can greatly reduce this problem. Special attention should be given to assessing the contamination in method blanks during the analysis. Pyrolytic graphite, because of the production process and handling, can become contaminated. As many as five to ten high- temperature burns may be needed to clean the tube before use. In addition, auto sampler tips may also be a potential source of contamination. Flushing the tip with a dilute solution of nitric acid between samples can help prevent cross-contamination.4.15Specific interference problems related to individual analytes are located in this section.4.15.1Antimony — High lead concentration may cause a measurable spectralinterference on the 217.6 nm line. Choosing the secondary wavelength or using background correction may correct the problem.4.15.2Arsenic arsenic and many of its compounds are volatile; therefore, samples may be subject to losses of arsenic during sample preparation. Likewise, caution must be employed during the selection of temperature and times for the dry and char (ash) cycles. A matrix modifier such as nickel nitrate or palladium nitrate should be added to all digestates prior to analysis to minimize volatilization losses during drying and ashing. addition to the normal interferences experienced during graphite furnace analysis, arsenic analysis can suffer from severe nonspecific absorption and light scattering caused by matrix components during atomization. Arsenic analysis is particularly susceptible to these problems because of its low analytical wavelength (193.7 nm). Simultaneous background correction must be employed to avoid erroneously high results. Aluminum is a severe positiveinterferant in the analysis of arsenic, especially using D2 arc backgroundcorrection. Although Zeeman background correction is very useful in this situation, use of any appropriate background correction technique is acceptable.4.15.3Barium — Barium can form barium carbide in the furnace, resulting in lesssensitivity and potential memory effects. Because of chemical interaction, nitrogen should not be used as a purge gas and halide acids should not be used.4.15.4Beryllium — Concentrations of aluminum greater than 500 ppm maysuppress beryllium absorbance. The addition of 0.1% fluoride has been found effective in eliminating this interference. High concentrations of magnesium and silicon cause similar problems and require the use of the method of standard additions.4.15.5Cadmium — Cadmium analyses can suffer from severe non-specificabsorption and light scattering caused by matrix components during atomization. Simultaneous background correction is needed to avoid erroneously high results. Excess chloride may cause premature volatilization of cadmium; an ammonium phosphate matrix modifier may minimize this loss.

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7010 – 6Revision 0 February 20074.15.6Chromium — Low concentrations of calcium and/or phosphate may causeinterferences; at concentrations above 200 mg/L, calcium’s effect is constant and eliminates the effect of phosphate. Therefore, add calcium nitrate (calcium nitrate solution: dissolve 11.8 g of calcium nitrate in 1 L reagent water) to ensure a constant effect. Nitrogen should not be used as the purge gas because of a possible CN band interference.4.15.7Cobalt — Since excess chloride may interfere, it is necessary to verify bystandard additions that the interference is absent unless it can be shown that standard additions are not necessary.4.15.8Lead — If poor recoveries are obtained, a matrix modifier may benecessary. Add 10 uL of phosphoric acid to 1 mL of prepared sample.4.15.9Molybdenum — Molybdenum is prone to carbide formation; use apyrolytically coated graphite tube.4.15.10Nickel — Severe memory effects for nickel may occur in graphite furnacetubes used for other GFAA analyses, due to the use of a nickel nitrate matrix modifier in those methods. Use of graphite furnace tubes and contact rings for nickel analysis that are separate from those used for arsenic and selenium analyses is strongly recommended.4.15.11Selenium selenium and many of its compounds are volatile; therefore, samples may be subject to losses of selenium during sample preparation. Likewise, caution must be employed during the selection of temperature and times for the dry and char (ash) cycles. A matrix modifier such as nickel nitrate or palladium nitrate should be added to all digestates prior to analysis to minimize volatilization losses during drying and ashing. addition to the normal interferences experienced during graphite furnace analysis, selenium analysis can suffer from severe nonspecific absorption and light scattering caused by matrix components during atomization. Selenium analysis is particularly susceptible to these problems because of its low analytical wavelength (196.0 nm). Simultaneous background correction must be employed to avoid erroneously high results. High iron levels can give overcorrection with deuterium background. Although Zeeman background correction is very useful in this situation, use of any appropriate background correction technique is acceptable. analysis suffers interference from chlorides (>800 mg/L) and sulfate (>200 mg/L). The addition of nickel nitrate such that the final concentration is 1% nickel will lessen this interference.4.15.12Silver — Silver chloride is insoluble, therefore HCl should be avoidedunless the silver is already in solution as a chloride complex. In addition, it is recommended that the stock standard concentrations be kept below 2 ppm and the chloride content increased to prevent precipitation. If precipitation is occurring, a 5%:2% HCl:HNO3 stock solution may prevent precipitation. Daily standard preparation may alsobe needed to prevent precipitation of silver. Analysts should be aware that this technique may not be the best choice for this analyte and that alternative techniques should be considered.

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7010 – 8Revision 0 February 2007wavelength range of 190 to 800 nm, and provisions for interfacing with a graphical display. Theinstrument must be equipped with an adequate correction device capable of removing undesirable nonspecific absorbance over the spectral region of interest and provide an analytical condition not subject to the occurrence of interelement spectral overlap interferences.6.2Hollow cathode lamps — Single-element lamps are preferred but multielement lamps may be used. Electrodeless discharge lamps may also be used when available. Other types of lamps meeting the performance criteria of this method may be used.6.3Graphite furnace — Any furnace device capable of reaching the specified temperatures is satisfactory. For all instrument parameters (i.e., drying, ashing, atomizing,times and temperatures) follow the specific instrument manufacturers instructions for each element.6.4Data systems recorder — A recorder is recommended for furnace work so that there will be a permanent record and that any problems with the analysis such as drift, incomplete atomization, losses during charring, changes in sensitivity, peak shape, etc., can be easily recognized.6.5Pipets — Microliter, with disposable tips. Sizes can range from 5 to 100 µL as needed. Pipet tips should be checked as a possible source of contamination when contamination is suspected or when a new source or batch of pipet tips is received by thelaboratory. The accuracy of variable pipets must be verified daily. Class A pipets can be used for the measurement of volumes equal to or larger than 1 mL.6.6Glassware — All glassware, polypropylene, or fluorocarbon (PFA or TFE) containers, including sample bottles, flasks and pipets, should be washed in the following sequence — 1:1 hydrochloric acid, tap water, 1:1 nitric acid, tap water, detergent, tap water, and reagent water. Chromic acid should not be used as a cleaning agent for glassware if chromium is to be included in the analytical scheme. If it can be documented through an active analytical quality control program using spiked samples and method blanks that certain steps in the cleaning procedure are not needed for routine samples, those steps may be eliminated from the procedure. Leaching of polypropylene for longer periods at lower acid concentrations is necessary to prevent degradation of the polymer. Alternative cleaning procedures must also be documented. Cleaning for ultra-trace analysis should be reviewed in Chapter Three.6.7Volumetric flasks of suitable precision and accuracy. 7.0REAGENTS AND STANDARDS 7.1Reagent grade or trace metals grade chemicals must be used in all tests. Unless otherwise indicated, it is intended that all reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination. All reagents should be analyzed to demonstrate that the reagents do not contain target analytes at or above the lowest limit of quantitation.7.2Reagent water — All references to water in the method refer to reagent water, unless otherwise specified. Reagent water must be free of interferences.7.3Nitric acid , HNO 3 — Use a spectrograde acid certified for AA use. Prepare a 1:1dilution with water by adding the concentrated acid to an equal volume of water. If the method

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7010 – 9Revision 0 February 2007blank does not contain target analytes at or above the lowest limit of quantitation, then the acidmay be used.7.4Hydrochloric acid (1:1), HCl — Use a spectrograde acid certified for AA use. Prepare a 1:1 dilution with water by adding the concentrated acid to an equal volume of water. If the method blank does not contain target analytes at or above the lowest limit of quantitation, then the acid may be used.7.5Purge gas — A mixture of H 2 (5%) and argon (95%). The argon gas supply must behigh-purity grade, 99.99% or better. If performance can be documented, alternative gases may be used.7.6Stock standard metal solutions — Stock standard solutions are prepared from analytical reagent grade high purity metals, oxides, or nonhygroscopic salts using reagent water and redistilled nitric or hydrochloric acids. (See individual methods for specific instructions.) Sulfuric or phosphoric acids should be avoided as they produce an adverse effect on manyelements. The stock solutions are prepared at concentrations of 1,000 mg of the metal per liter.Commercially available standard solutions may also be used. When using pure metals (especially wire) for standards preparation, cleaning procedures, as detailed in Chapter Three, should be used to ensure that the solutions are not compromised. Examples of appropriate standard preparations can be found in Secs. 7.6.1 through 7.6.18. 7.6.1Antimony — Carefully weigh 2.743 g of antimony potassium tartrate,K(SbO)C4H4O61/2H2O, and dissolve in reagent water. Dilute to 1 L with reagent water; 7.6.2Arsenic — Dissolve 1.320 g of arsenic trioxide, As2O3, or equivalent in 100mL of reagent water containing 4 g NaOH. Acidify the solution with 20 mL conc. HNO3and dilute to 1 L with reagent water.7.6.3Barium — Dissolve 1.779 g of barium chloride, BaCl22H2O, in reagentwater and dilute to 1 L with reagent water.7.6.4Beryllium — Dissolve 11.659 g of beryllium sulfate, BeSO4, in reagentwater containing 2 mL of nitric acid (conc.) and dilute to 1 L with reagent water. 7.6.5Cadmium — Dissolve 1.000 g of cadmium metal in 20 mL of 1:1 HNO3 anddilute to 1 L with reagent water.7.6.6Chromium — Dissolve 1.923 g of chromium trioxide, CrO3, in reagentwater, acidify with redistilled HNO3, and dilute to 1 L with reagent water.7.6.7Cobalt — Dissolve 1.000 g of cobalt metal in 20 mL of 1:1 HNO3 anddilute to 1 L with reagent water. Chloride or nitrate salts of cobalt(II) may be used. Although numerous hydrated forms exist, they are not recommended, unless the exactcomposition of the compound is known.7.6.8Copper — Dissolve 1.000 g of electrolytic copper in 5 mL of redistilledHNO3 and dilute to 1 L with reagent water. 7.6.9Iron — Dissolve 1.000 g of iron wire in 10 mL of redistilled HNO3 andreagent water and dilute to 1 L with reagent water. Note that iron passivates in conc. HNO3, and therefore some water should be present.

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7010 – 10Revision 0 February 20077.6.10Lead — Dissolve 1.599 g of lead nitrate, Pb(NO3)2, in reagent water,acidify with 10 mL of redistilled HNO3, and dilute to 1 L with reagent water.7.6.11Manganese — Dissolve 1.000 g of manganese metal in 10 mL ofredistilled HNO3 and dilute to 1 L with reagent water.7.6.12Molybdenum — Dissolve 1.840 g of ammonium molybdate,(NH4)6Mo7O244H2O, and dilute to 1 L with reagent water.7.6.13Nickel — Dissolve 1.000 g of nickel metal or 4.953 g of nickel nitrate,Ni(NO3)26H2O in 10 mL of HNO3 and dilute to 1 L with reagent water.7.6.14Selenium :Dissolve 0.345 g of selenious acid (actual assay 94.6% H2SeO3) or equivalent and dilute to 200 mL with reagent water. NOTE: Due to the high toxicity of selenium, preparation of a small volume of reagent is described. Larger volumes may be prepared if needed.7.6.15Silver — Dissolve 1.575 g of anhydrous silver nitrate, AgNO3, in reagentwater. Add 10 mL of HNO3 (conc.) and dilute to 1 L with reagent water. Because thisstandard is light sensitive, store in a amber glass bottle in a refrigerator.7.6.16Thallium — Dissolve 1.303 g of thallium nitrate, TlNO3 , in reagent water,acidify with 10 mL of conc. HNO3, and dilute to 1 L with reagent water.7.6.17Vanadium — Dissolve 1.785 g of vanadium pentoxide, V2O5 , in 10 mL ofconc. HNO3 and dilute to 1 L with reagent water.7.6.18Zinc — Dissolve 1.000 g of zinc metal in 10 mL of conc. HNO3 and diluteto 1 L with reagent water.7.7Common matrix modifiers — The use of a palladium modifier is strongly recommended for the determination of all analytes. This will correct for general chemical interferences as well as allow for higher char and atomization temperatures without allowing the premature liberation of analyte. Other matrix modifiers may also be used as recommended by the instrument manufacturer or when an interference is evident. 7.7.1Palladium solution (Pd/Mg) — Dissolve 300 mg of palladium powder in concentrated HNO3 (1 mL of HNO3 , adding 0.1 mL of conc. HCl, if necessary). Dissolve200 mg of Mg(NO3)2 in reagent water. Pour the two solutions together and dilute to 100mL with reagent water.7.7.2Nickel nitrate solution (5%) — Dissolve 25 g of Ni(NO 3)26H2O in reagentwater and dilute to 100 mL.7.7.3Nickel nitrate solution (1%) — Dilute 20 mL of the 5% nickel nitrate solution to 100 mL with reagent water.7.7.4Ammonium phosphate solution (40%) — Dissolve 40 g of ammonium phosphate, (NH4)2HPO4, in reagent water and dilute to 100 mL.7.7.5Palladium chloride — Weigh 0.25 g of PdCl 2 to the nearest 0.0001 g anddissolve in 10 mL of 1:1 HNO3. Dilute to 1 L with reagent water.

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7010 – 11Revision 0 February 20077.8 BlanksTwo types of blanks are required for the analysis of samples prepared by any methodother than Method 3040. The calibration blank is used in establishing the analytical curve and the method blank is used to identify possible contamination resulting from either the reagents (acids) or the equipment used during sample processing including filtration. 7.8.1The calibration blank is prepared by acidifying reagent water to the same concentrations of the acids found in the standards and samples. Prepare a sufficient quantity to flush the system between standards and samples. The calibration blank will also be used for all initial (ICB) and continuing calibration blank (CCB) determinations.7.8.2The method blank must contain all of the reagents in the same volumes as used in the processing of the samples. The method 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 (refer to Sec. 9.5). 7.9The initial calibration verification (ICV) standard is prepared by the analyst (or a purchased second source reference material) by combining compatible elements from a standard source different from that of the calibration standard, and at concentration near the midpoint of the calibration curve (see Sec. 10.2.1 for use). This standard may also be purchased.7.10The continuing calibration verification (CCV) standard should be prepared in the same acid matrix using the same standards used for calibration, at a concentration near the mid-point of the calibration curve (see Sec. 10.2.2 for use).8.0SAMPLE COLLECTION, PRESERVATION, AND STORAGE See the introductory material in Chapter Three, “Inorganic Analytes.”9.0QUALITY CONTROL 9.1Refer to Chapter One for guidance on quality assurance (QA) and quality control (QC) protocols. When inconsistencies exist between QC guidelines, method-specific QC criteria take precedence over both technique-specific criteria and those criteria given in ChapterOne, and technique-specific QC criteria take precedence over the criteria in Chapter One. Anyeffort involving the collection of analytical data should include development of a structured and systematic planning document, such as a Quality Assurance Project Plan (QAPP) or a Sampling and Analysis Plan (SAP), which translates project objectives and specifications into directions for those that will implement the project and assess the results. Each laboratory should maintain a formal quality assurance program. The laboratory should also maintain records to document the quality of the data generated. All data sheets and quality control data should be maintained for reference or inspection. 9.2Refer to a 3000 series method (Method 3015, 3020, 3031, 3050, 3051, or 3052) for appropriate QC procedures to ensure the proper operation of the various sample preparation techniques.9.3Instrument detection limits (IDLs) are a useful tool to evaluate the instrument noise level and response changes over time for each analyte from a series of reagent blank analyses to obtain a calculated concentration. They are not to be confused with the lower limit of

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