1、Designation: D 4192 03Standard 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 (e) 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 rang
3、e 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
4、 mg/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
5、 in 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 This standard does not purport to address all of thesafety concerns, if any, associa
6、ted 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 limitations prior to use. For a specificprecautionary statement, see Note 3.2. Referenced Documents2.1 ASTM Standards:D 1066 Pra
7、ctice for Sampling Steam3D 1129 Terminology Relating to Water3D 1192 Specification for Equipment for Sampling Waterand Steam in Closed Conduits3D 1193 Specification for Reagent Water3D 2777 Practice for Determination of Precision and Bias ofApplicable Methods of Committee D-19 on Water3D 3370 Practi
8、ces for Sampling Water from Closed Con-duits3D 5810 Guide for Spiking into Aqueous Samples3D 5847 Practice for the Writing Quality Control Specifica-tions for Standard Test Methods for Water Analysis33. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology
9、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 is not easilysolubil
10、ized; 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 1000 to 2000 mg/L i
11、nstock 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 for allinstrumental pa
12、rameters. 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 ASTM Committee D19 on W
13、aterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Current edition approved Jan. 10, 2003. Published January 2003. Originallyapproved in 1982. Last previous edition approved in 1997 as D 419297.2Platte, J. A., and Marcy, V. M., “A New Tool for the Water Che
14、mist,” IndustrialWater Engineering, May 1965.3Annual Book of ASTM Standards, Vol 11.01.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7.3 Pressure-Reducing ValvesThe
15、supplies of fuel andoxidant shall be maintained at pressures somewhat higher thanthe operating pressure of the instrument by using suitablevalves.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reage
16、nts shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Societywhere such specifications are available.4Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theac
17、curacy of the determination.8.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean reagent water conformingto Specification D 1193, Type I. Other reagent water types maybe used provided it is first ascertained that the water is ofsufficiently high purity to perm
18、it 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.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 ch
19、loride (KCl) in water and diluteto 1 L with water.NOTE 2Certified potassium stock solutions are commercially avail-able through chemical 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
20、passed through a suitablefilter to remove oil, water, and other foreign substances is theusual oxidant.8.6 Fuel: AcetyleneStandard, commercially availableacetylene is the usual fuel. Acetone, always present in acety-lene cylinders can affect analytical results. The cylinder shouldbe replaced at 50 p
21、sig (345 kPa) to avoid acetone carry over.NOTE 3Warning: “Purified” grade acetylene containing a specialproprietary solvent rather than acetone should not be used with poly(vinylchloride) tubing as weakening of the tubing walls can cause a potentiallyhazardous situation.9. Sampling9.1 Collect the sa
22、mples in accordance with the applicableASTM standard as follows: Practices D 3370, Practice D 1066,and Specification D 1192.10. Standardization10.1 Prepare 100 mL each of a blank and at least fourstandard solutions to bracket the expected potassium concen-tration range of the samples to be analyzed
23、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, middle, and maximum points for an analyticalcurve.10.2 Aspirate the blank and the standards and record theinstrument readings. Aspirate water bet
24、ween standards.10.3 Prepare an analytical curve by plotting the absorbanceversus concentration for each standard on linear graph paper.Alternatively, read directly in concentration if this capability isprovided with the instrument.11. Procedure11.1 Aspirate each sample and determine its absorbance o
25、rconcentration. Aspirate water between samples.12. Calculation12.1 Calculate the concentrations of potassium in thesamples, in milligrams per litre, by either referring the absor-bance obtained for each sample to a prepared analytical curve10.3 or reading directly in concentration if the capability
26、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 factor.13. Precision and Bias513.1 The overall and single-operator precision of this testmethod for eight laboratories, which
27、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 Table 1.NOTE 4Only reagent water was used to obtain the precision statementsince this test method is designated for the determina
28、tion 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 Recoveries of known amounts of potassium (frompotassium chloride) in the series of prepared standards for thesame laboratories and
29、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 the allowances made in 1.4 ofPractice D 2777 98, these precision and bias data do meetexisting requirements for interlaboratory
30、 studies of CommitteeD19 test methods.4“Reagent Chemical, American Chemical Society Specifications,” Am. Chemi-cal Soc., Washington, DC. For suggestions on the testing of reagents not listed bythe American Chemical Society see “Analar Standards for Laboratory Chemicals,”BDH Ltd., Poole, Dorset, U.K.
31、, and the “United States Pharmacopeia.”5Supporting data are available from ASTM Headquarters. RequestRR: 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.
32、03 0.179 0.062 + 1.13D419203214. Quality 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 V
33、erification:14.2.1 Analyze at least three 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 th
34、e initialcalibration blank, a calibration 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. T
35、he concentration of a mid-range stan-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
36、change in the measurement system, forexample, 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 o
37、f potassium. The matrix and chem-istry 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. The replicates may beinterspersed with samples.
38、14.3.3 Calculate the mean and standard deviation of theseven values and compare to the 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
39、 5847 for information on applying the F test and t test inevaluating the acceptability 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
40、. If large numbers of samples areanalyzed in the batch, analyze the LCS after every 10 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 pret
41、reatment. 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 halted until the problem is corrected, and either allthe samples in the batch must be reanalyzed, or the results mustbe qualified
42、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 each batch.The concentration of potassium found in the blank should beless than 0.5 times the lowest calibration standard. If theconcentration o
43、f potassium is found above this level, analysisof samples is halted until the contamination 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
44、Spike (MS):14.6.1 To check for interferences in the specific matrixbeing tested, perform 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
45、 concen-tration of potassium must not exceed the high calibrationstandard. The spike 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 t
46、he percent recovery of the spike (P) usingthe following formula:P 5 100 AVs1 V! 2 BVs# / 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 = vo
47、lume (mL) added with spike.14.6.4 The percent recovery of the spike shall fall 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
48、circumstances, one of thefollowing remedies must be employed: the matrix interferencemust 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 crit
49、eria 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 detection limit for the analyte,a matrix spike duplicate (MSD) should be used.14.7.2 Calculate the standard deviation of the duplicatevalues and compare to the precision in the collaborative studyusing an F test. Refer to 6.4.4 of
