1、Designation: D4192 15Standard Test Method forPotassium in Water by Atomic AbsorptionSpectrophotometry1This standard is issued under the fixed designation D4192; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revis
2、ion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of lowamounts of potassium in waters2having low solids content.The applicable range o
3、f 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 mg
4、/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 in
5、 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. The values given in parent
6、heses are mathematicalconversions to inch-pound units that are provided for informa-tion only and are not considered standard.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 ap
7、pro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For a specificprecautionary statement, see 8.6.2. Referenced Documents2.1 ASTM Standards:3D1066 Practice for Sampling SteamD1129 Terminology Relating to WaterD1193 Specification for Reagen
8、t WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD4841 Practice for Estimation of Holding Time for WaterSamples Containing Organic and Inorganic ConstituentsD5810 Guide for Spiking
9、into Aqueous SamplesD5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water Analysis3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method, referto Terminology D1129.4. Summary of Test Method4.1 Potassium is determined by flame atom
10、ic 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 is not easilysolubilized; therefore, the potassium content of natural watersis usually low. M
11、ost 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 1000 to 2000 mg/L instock water is regarded as the extreme limit permissible.1This test meth
12、od is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Current edition approved Feb. 1, 2015. Published March 2015. Originallyapproved in 1982. Last previous edition approved in 2008 as D4192 08. DOI:10.152
13、0/D4192-15.2Platte, J.A., and Marcy, V. M., “ANew Tool 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 t
14、o the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16. Interferences6.1 In the analysis of low-solids water, interfe
15、rences areusually negligible.7. Apparatus7.1 Atomic Absorption Spectrophotometer for use at 766.5nm.NOTE 1The manufacturers instructions should be followed for allinstrumental parameters. Wavelengths other than 766.5 nm may be usedonly if they have been determined to be equally suitable.7.2 Potassiu
16、m Hollow-Cathode LampsMultielement hol-low cathode lamps are available and also have been foundsatisfactory.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. Reagents an
17、d 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 available.4Other
18、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 Specificatio
19、n D1193, 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 thistest method
20、.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 of appropriate knownpurity are commercially available through chemica
21、l supply vendors.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, com
22、mercially availableacetylene is the usual fuel. Acetone, always present in acety-lene cylinders can affect analytical results. The cylinder shouldbe replaced at 345 kPa (50 psig) to avoid acetone carry over.(Warning“Purified” grade acetylene containing a specialproprietary solvent rather than aceton
23、e should not be used withpoly(vinyl chloride) tubing as weakening of the tubing wallscan cause a potentially hazardous situation.)9. Sampling9.1 Collect the samples in accordance with the applicableASTM standard as follows: Practices D3370 and PracticeD1066.10. Standardization10.1 Prepare 100 mL eac
24、h of a 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 or as determined byPractice D4841. Select the
25、standards to give zero, median, andmaximum points for an analytical curve.10.2 Analyze at least four working standards containingconcentrations of potassium that bracket the expected sampleconcentration, prior to analysis of samples, to calibrate theinstrument. Aspirate the blank and the standards a
26、nd record theinstrument readings. Aspirate water between standards.10.3 Read directly in concentration if this capability isprovided with the instrument or prepare a linear analyticalcurve by plotting the absorbance versus concentration for eachstandard on linear graph paper.11. Procedure11.1 Aspira
27、te 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 reading directly inconcentration if the capability is provided with the instrumentor referring t
28、he absorbance obtained for each sample to aprepared analytical curve (see 10.3).12.2 If an aliquot of diluted sample was analyzed, multiplythe concentration of potassium, in milligrams per litre, by theappropriate dilution factor.13. Precision and Bias513.1 The overall and single-operator precision
29、of this testmethod for eight laboratories, which included a total of twelve4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for Laborator
30、yChemicals, 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 International Headquarters and maybe obtained by requesting Research Report RR:D19-1081. ContactASTM
31、CustomerService at serviceastm.org.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 + 1.13D4192 152operators analyzing each sample on three consecut
32、ive days,within its range for reagent water varies with the quantity beingmeasured according to Table 1.NOTE 3Only 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
33、responsibility to ensure the validity ofthis test method for waters of untested matrices.13.3 Recoveries 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 me
34、thod conforms toPractice D2777 77, which was in place at the time ofcollaborative testing. Under the allowances made in 1.4 ofPractice D2777 13, these precision and bias data do meetexisting requirements for interlaboratory studies of CommitteeD19 test methods.14. Quality Control14.1 In order to be
35、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 four working standards containin
36、gconcentrations of potassium that bracket the expected sampleconcentration, prior to analysis of samples, to calibrate theinstrument (see 10.2). The calibration correlation coefficientshall be equal to or greater than 0.990. In addition to the initialcalibration blank, a calibration blank shall be a
37、nalyzed 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-dard should fall with
38、in 615 % of the known concentration.Analyze a calibration blank to verify system cleanliness.14.2.3 If calibration cannot be verified, recalibrate theinstrument.14.2.4 It is recommended to analyze a continuing calibra-tion blank (CCB) and continuing calibration verification(CCV) at a 10 % frequency.
39、 The results should fall within theexpected precision of the method or 615 % of the knownconcentration.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, forexample, new analyst,
40、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-istry of the solution shou
41、ld 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 the acceptable ranges of
42、 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 PracticeD5847 for information on applying the F test and t test inevaluating the acceptability of the mean and stand
43、ard 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 (laboratory-defined or twenty samples). The labo-ratory control samples for a large batch should cover theanalytical rang
44、e 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 knownconcentration.14.4.2 If the result is not within these limits, analysis ofsamples is halte
45、d 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 method.14.5 Method Blank:14.5.1 Analyze a reagent water test blank with eachlaboratory-defi
46、ned batch. The concentration of potassiumfound in the blank should be less than 0.5 times the lowestcalibration standard. If the concentration of potassium is foundabove this level, analysis of samples is halted until thecontamination is eliminated, and a blank shows no contamina-tion at or above th
47、is level, or the results must be qualified withan indication that they do not fall within the performancecriteria of the test method.14.6 Matrix Spike (MS):14.6.1 To check for interferences in the specific matrixbeing tested, perform a MS on at least one sample from eachlaboratory-defined batch by s
48、piking an aliquot of the samplewith a known concentration of potassium and taking it throughthe analytical method.14.6.2 The spike concentration plus the background concen-tration of potassium must not exceed the high calibrationstandard. The spike must produce a concentration in the spikedsample th
49、at 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 100AVs1V! 2 BVs#/CV (1)where:A = analyte known concentration (mg/L) in spiked sample,B = analyte known concentration (mg/L) in unspikedsample,C = known concentration (mg/L) of analyte in spikingsolution,Vs= volume (mL) of sample used, andV = volume (mL) of spiking solution added.D4192 15314.6.4 The percent recovery of the spike sha
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