1、Designation: D 4192 08Standard Test Method forPotassium in Water by Atomic AbsorptionSpectrophotometry1This standard is issued under the fixed designation D 4192; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev
2、ision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of lowamounts of potassium in waters2having low solids content.The applicable range
3、of this test method is 0.20 to 4.0 mg/Lwhen using the 766.5-nm resonance line. The range may beextended upward by dilution of an appropriate aliquot ofsample or by using the less-sensitive 404.4-nm resonance line.Many workers have found that this test method is reliable forpotassium levels to 0.02 m
4、g/L, but use of this test method atthis low level is dependent on the configuration of the aspiratorand nebulizer systems available in the atomic absorptionspectrophotometer as well as the skill of the analyst. Theprecision and bias data presented are insufficient to justify useof this test method i
5、n the 0.02-mg/L range.1.2 This test method has been used successfully with spikedreagent water. It is the analysts responsibility to ensure thevalidity of this test method to other low dissolved solidsmatrices.1.3 The values stated in SI units are to be regarded asstandard. No other units of measure
6、ment are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limita
7、tions prior to use. For a specificprecautionary statement, see Note 3.2. Referenced Documents2.1 ASTM Standards:3D 1066 Practice for Sampling SteamD 1129 Terminology Relating to WaterD 1193 Specification for Reagent WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Metho
8、ds of Committee D19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 5810 Guide for Spiking into Aqueous SamplesD 5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water Analysis3. Terminology3.1 For definitions of terms used in this test method,
9、refer toTerminology D 1129.4. Summary of Test Method4.1 Potassium is determined by flame atomic absorptionspectrophotometry. The potassium content is determined byaspirating the low solids sample directly with no samplepretreatment.5. Significance and Use5.1 Potassium occurs in rocks in a form that
10、is not easilysolubilized; therefore, the potassium content of natural watersis usually low. Most natural waters contain less than 20 mg/Lof potassium, but waters containing several hundred milli-grams per litre are occasionally found. Potassium is essential toanimal nutrition, but a concentration of
11、 1000 to 2000 mg/L instock water is regarded as the extreme limit permissible.6. Interferences6.1 In the analysis of low-solids water, interferences areusually negligible.7. Apparatus7.1 Atomic Absorption Spectrophotometer for use at 766.5nm.NOTE 1The manufacturers instructions should be followed fo
12、r allinstrumental parameters. Wavelengths other than 766.5 nm may be usedonly if they have been determined to be equally suitable.7.2 Potassium Hollow-Cathode LampsMultielement hol-low cathode lamps are available and also have been foundsatisfactory.1This test method is under the jurisdiction of AST
13、M Committee D19 on Waterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Current edition approved Oct. 1, 2008. Published October 2008. Originallyapproved in 1982. Last previous edition approved in 2003 as D 4192 03.2Platte, J.A., and Marcy, V. M., “ANew Tool
14、 for the Water Chemist,” IndustrialWater Engineering, May 1965 .3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM websi
15、te.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7.3 Pressure-Reducing ValvesThe supplies of fuel andoxidant shall be maintained at pressures somewhat higher thanthe operating pressure of the instrument by using suitablevalves.8. R
16、eagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Societywhere such specifications are availab
17、le.4Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean reagent water conformingto Sp
18、ecification D 1193, Type I. Other reagent water types maybe used provided it is first ascertained that the water is ofsufficiently high purity to permit its use without adverselyaffecting the bias and precision of the test method. Type IIwater was specified at the time of round robin testing of this
19、test method.8.3 Potassium Solution, Stock (1.0 mL = 1.0 mg K)Drypotassium chloride to constant weight at 105C. Dissolve1.907 g of the dry potassium chloride (KCl) in water and diluteto 1 L with water.NOTE 2Certified potassium stock solutions are commercially avail-able through chemical supply vendor
20、s.8.4 Potassium Solution, Standard (1.00 mL = 0.1 mg K)Dilute 100.0 mL of potassium stock solution to 1 L with water.8.5 Oxidant: Air, which has been passed through a suitablefilter to remove oil, water, and other foreign substances is theusual oxidant.8.6 Fuel: AcetyleneStandard, commercially avail
21、ableacetylene is the usual fuel. Acetone, always present in acety-lene cylinders can affect analytical results. The cylinder shouldbe replaced at 50 psig (345 kPa) to avoid acetone carry over.NOTE 3Warning: “Purified” grade acetylene containing a specialproprietary solvent rather than acetone should
22、 not be used with poly(vinylchloride) tubing as weakening of the tubing walls can cause a potentiallyhazardous situation.9. Sampling9.1 Collect the samples in accordance with the applicableASTM standard as follows: Practices D 3370 and PracticeD 1066.10. Standardization10.1 Prepare 100 mL each of a
23、blank and at least fourstandard solutions to bracket the expected potassium concen-tration range of the samples to be analyzed by diluting thestandard potassium solution 8.4 with water. Prepare the stan-dards each time the test is to be performed. Select the standardsto give zero, median, and maximu
24、m points for an analyticalcurve.10.2 Aspirate the blank and the standards and record theinstrument readings. Aspirate water between standards.10.3 Prepare an analytical curve by plotting the absorbanceversus concentration for each standard on linear graph paper.Alternatively, read directly in concen
25、tration if this capability isprovided with the instrument.11. Procedure11.1 Aspirate each sample and determine its absorbance orconcentration. Aspirate water between samples.12. Calculation12.1 Calculate the concentrations of potassium in thesamples, in milligrams per litre, by either referring the
26、absor-bance obtained for each sample to a prepared analytical curve10.3 or reading directly in concentration if the capability isprovided with the instrument.12.2 If an aliquot of diluted sample was analyzed, multiplythe concentration of potassium, in milligrams per litre, by theappropriate dilution
27、 factor.13. Precision and Bias513.1 The overall and single-operator precision of this testmethod for eight laboratories, which included a total of twelveoperators analyzing each sample on three consecutive days,within its range for reagent water varies with the quantity beingmeasured according to Ta
28、ble 1.NOTE 4Only reagent water was used to obtain the precision statementsince this test method is designated for the determination of trace amountsof potassium in low-solids water.13.2 It is the users responsibility to ensure the validity ofthis test method for waters of untested matrices.13.3 Reco
29、veries of known amounts of potassium (frompotassium chloride) in the series of prepared standards for thesame laboratories and operators were as given in Table 1.13.4 Precision and bias for this test method conforms toPractice D 2777 77, which was in place at the time ofcollaborative testing. Under
30、the allowances made in 1.4 ofPractice D 2777 06, these precision and bias data do meetexisting requirements for interlaboratory studies of CommitteeD19 test methods.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing
31、of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.5Supporting data have been filed at ASTM Internation
32、al Headquarters and maybe obtained by requesting Research Report RR: D19-1081.TABLE 1 Determination of Bias for Potassium in Reagent Waterby Atomic AbsorptionAmountAdded,mg/LAmountFound,mg/LStSoBias %0.15 0.164 0.037 0.014 + 9.331.50 1.62 0.085 0.044 + 8.003.00 3.03 0.179 0.062 + 1.13D419208214. Qua
33、lity Control14.1 In order to be certain that analytical values obtainedusing these test methods are valid and accurate within theconfidence limits of the test, the following QC procedures mustbe followed when analyzing potassium .14.2 Calibration and Calibration Verification:14.2.1 Analyze at least
34、four working standards containingconcentrations of potassium that bracket the expected sampleconcentration, prior to analysis of samples, to calibrate theinstrument. The calibration correlation coefficient shall beequal to or greater than 0.990. In addition to the initialcalibration blank, a calibra
35、tion blank shall be analyzed at theend of the batch run to ensure contamination was not a problemduring the batch analysis.14.2.2 Verify instrument calibration after standardization byanalyzing a standard at the concentration of one of thecalibration standards. The concentration of a mid-range stan-
36、dard should fall within 615 % of the known concentration.14.2.3 If calibration cannot be verified, recalibrate theinstrument.14.3 Initial Demonstration of Laboratory Capability:14.3.1 If a laboratory has not performed the test before, or ifthere has been a major change in the measurement system, for
37、example, new analyst, new instrument, etc., a precision andbias study must be performed to demonstrate laboratorycapability.14.3.2 Analyze seven replicates of a standard solutionprepared from an Independent Reference Material containing amid-range concentration of potassium. The matrix and chem-istr
38、y of the solution should be equivalent to the solution usedin the collaborative study. Each replicate must be taken throughthe complete analytical test method including any samplepreservation and pretreatment steps.14.3.3 Calculate the mean and standard deviation of theseven values and compare to th
39、e acceptable ranges of bias inTable 1. This study should be repeated until the recoveries arewithin the limits given in Table 1. If a concentration other thanthe recommended concentration is used, refer to PracticeD 5847 for information on applying the F test and t test inevaluating the acceptabilit
40、y of the mean and standard devia-tion.14.4 Laboratory Control Sample (LCS):14.4.1 To ensure that the test method is in control, analyzea LCS containing a known concentration of potassium witheach batch or 10 samples. If large numbers of samples areanalyzed in the batch, analyze the LCS after every 1
41、0 samples.The laboratory control samples for a large batch should coverthe analytical range when possible. The LCS must be takenthrough all of the steps of the analytical method includingsample preservation and pretreatment. The result obtained fora mid-range LCS shall fall within 615 % of the known
42、concentration.14.4.2 If the result is not within these limits, analysis ofsamples is halted until the problem is corrected, and either allthe samples in the batch must be reanalyzed, or the results mustbe qualified with an indication that they do not fall within theperformance criteria of the test m
43、ethod.14.5 Method Blank:14.5.1 Analyze a reagent water test blank with each batch.The concentration of potassium found in the blank should beless than 0.5 times the lowest calibration standard. If theconcentration of potassium is found above this level, analysisof samples is halted until the contami
44、nation is eliminated, anda blank shows no contamination at or above this level, or theresults must be qualified with an indication that they do not fallwithin the performance criteria of the test method.14.6 Matrix Spike (MS):14.6.1 To check for interferences in the specific matrixbeing tested, perf
45、orm a MS on at least one sample from eachbatch by spiking an aliquot of the sample with a knownconcentration of potassium and taking it through the analyticalmethod.14.6.2 The spike concentration plus the background concen-tration of potassium must not exceed the high calibrationstandard. The spike
46、must produce a concentration in the spikedsample that is 2 to 5 times the analyte concentration in theunspiked sample, or 10 to 50 times the detection limit of thetest method, whichever is greater.14.6.3 Calculate the percent recovery of the spike (P) usingthe following formula:P 5 100 AVs1 V! 2 BVs
47、# / CV (1)where:A = analyte concentration (mg/L) in spiked sample,B = analyte concentration (mg/L) in unspiked sample,C = concentration (mg/L) of analyte in spiking solution,Vs= volume (mL) of sample used, andV = volume (mL) of spiking solution added.14.6.4 The percent recovery of the spike shall fa
48、ll within thelimits, based on the analyte concentration, listed in GuideD 5810, Table 1. If the percent recovery is not within theselimits, a matrix interference may be present in the sampleselected for spiking. Under these circumstances, one of thefollowing remedies must be employed: the matrix int
49、erferencemust be removed, all samples in the batch must be analyzed bya test method not affected by the matrix interference, or theresults must be qualified with an indication that they do not fallwithin the performance criteria of the test method.NOTE 5Acceptable spike recoveries are dependent on the concentra-tion of the component of interest. See Guide D 5810 for additionalinformation.14.7 Duplicate:14.7.1 To check the precision of sample analyses, analyze asample in duplicate with each batch. If the concentration of theanalyte is less than five times the det
