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beaker with a watch glass and heat gently The wam aCId will soon dis- solve the membrane 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 conc HNOa Cover and continue heating untIl the dIgestIon IS complete generally indi- cated by a lIght colored dlgestate Evaporate to near dryness (2 mL), cool add 10 mL HCI (1+1) and 15 mL deIonIzed distIlled water per 100 mL dilutIon and warm the beaker gently for 15 min to dissolve any precipi- tated 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 4) Adjust the volume based on the expected con- centrations of elements present ThIS volume wIll vary depending on the elements to be determined (See Note 6) The sample IS now ready for analysIs ConcentratIons so determined shall be reported as suspended NOTE 4 In place of fIltering, the sample after diluting and mixing may be centrifuged or allowed to settle by gravIty overnight to remove Insoluble material 9 3 For the determination of total elements, 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 5) Add 3 mL of conc HNOa Place the beaker on a hot plate and evaporate to near dry- ness 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 conc HNOa 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 addI- tIonal aCId as necessary, until the digestIon IS complete (generally indI- cated when the dlgestate IS light In color or does not change In appear- ance With continued refluxlng ) Again evaporate to near dryness and cool the beaker Add 10 mL of 1+1 Hel and 15 mL of deIonized distilled water per 100 mL of fmal solutIon and warm the beaker gently for 15 min to dIssolve any preCipItate or reSIdue resulting from evaporation Allow to cool, wash down the beaker walls and watch glass WIth deionIzed dIstilled water and filter the sample to remove Insoluble material that could clog the nebulizer (See Note 4) Adjust the sample to a predetermined volume based on the expected concentrations of elements present The sample IS now ready for analySIS (See Note 6) ConcentratIons so determined shall be reported as total NOTE 5 If low determinations of boron are CritIcal, quartz glassware should be use NOTE 6 If the sample analYSIS solution has a dIfferent aCid concentratIon from that given In 94, but does not Introduce a phYSIcal Interference or affect the analytical result the same caIIbratlon standards may be used 9 4 For the determination of total recoverable elements choose a mea- sured volume of a well mixed, aCId preserved sample appropriate for the expected level of elements and trans- fer to a Griffin beaker (See Note 5 ) Add 2 mL of (1+1) HNOaand 10 mL of (1+1) HCI 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 inSO- luble matenal that could clog the nebulizer (See Note 4 ) Adjust the volume to 100 mL and mix The sample IS now ready for analySIS Concentra- tIons so determined shall be reported sample ConcentratIOn values obtamed should not deViate from the actual values by more than ± 5 percent (or the established control limIts whIchever IS lower) If they do, follow the recommendatIons of the instru- ment manufacturer to correct for thIS condition 10 5 Begm the sample run flushing the system With the calibration blank solutIon (75 1) between each sample (See Note 7 ) Analyze the Instrument check standard (76 1) and the calibra- tIon blank (7 5 1) each 10 samples 10 6 If It has been found that method of standard addItion are required, the follOWing procedure IS recommended 10 6 1 The standard addition tech- nique (142) Involves prepanng new standards In the sample matnx by adding known amounts of standard to one or more allquots of the processed sample solutIon ThiS technIque com- pensates for a sample constItuent that enhances or depresses the analyte SIgnal thus prodUCing a different slope from that of the calibratIOn standards It WIll not correct for additive inter- ference which causes a baselme shIft The SImplest version of thIS technique IS the Single-addItion method The procedure IS as follows Two Identical allquots 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 analy- tical SIgnals of A and B are measured and corrected for nonanalyte SIgnals The unknown sample concentration Cx IS calculated total Procedure 10 1 operating parameters established In 6 2 The Instrument must be allowed to become thermally stable before be- ginning ThIS usually reqUIres at least 30 min of operatIon pnor to calibra- tion as 10 Set up Instrument With proper 10 2 configuratIon of computer Initiate appropnate operating Cx = 10 3 ProfIle and calibrate instru- ment according to Instrument manufacturer s recommended procedures, uSing the typical mIxed calibratIon standard solutions descnbed In 7 4 Flush the system With the calibration blank (7 5 1) between each standard (See Note 7 ) (The use of the average intensity of multIple exposures for both standardization and sample analYSIS has been found to reduce random error) NOTE 7 For boron concentrations greater than 500 pg/L extended flush tImes of 1 to 2 min may be requIred 10 4 Before beginning the sample run reanalyze the highest mIxed calibration standard as If It were a SaVscs (SA - Sa) V x Cee 1982 Metals-25 where SA and Sa are the analytIcal Signals (corrected for the blank) of solutIons A and B respectively Vs and Cs should be chosen so that SA IS roughly tWIce Sa on the average 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 carned through the entire procedure For the results from thiS technIque to be valid, the followmg limitatIons must be taken mto consIderatIOn 1 The analytical curve must be linear 2 The chemIcal form of the analyte added must respond the same as the analyte m the samplePDF Image | Methods for Chemical Analysis of Water and Wastes
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