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8 Procedure 81 Phosphorus 8 2 8 1 5 Hydrolyzable Phosphorus 8 3 Orthophosphate 8 3 1 The pH ofthe sample must be adjusted to 7±O 2 usmg a pH meter 8 3 2 Add 8 0 ml of combmed reagent (7 5) to sample and mix thoroughly After a mmlmum of ten mInutes, but no longer than thirty mmutes, measure the color absorbance of each sample at 650 or 880 nm With a spectrophotometer, usmg the reagent blank as the reference solutIOn NOTE 1:Ifthe same volume ofsodmm hydrOXide solutIOn IS not used to adjust the pH ofthe standards and samples, a volume correctIOn has to be employed 9 CalculatIOn 9 1 9 2 Prepare a standard curve by plottmg the absorbance values of standards versus the correspondIng phosphorus concentratIOns 9 1 1 Process standards and blank exactly as the samples Run at least a blank and two standards With each senes ofsamples Ifthe standards do not agree wlthm ±2% of the true value, prepare a new cahbratlOn curve Obtam concentratIOn value of sample directly from prepared standard curve Report resultsasP,mg!1 SEENOTE1. 8 1 1 8 1 2 8 1 3 8 1 4 Add 1ml ofHzS04 solutIOn (7 6) to a 50 ml sample m a 125 ml Erlenmeyer flask Add 0 4 g ofammomum persulfate BoIl gently on a pre-heated hot plate for approximately 30-40 mInutes or untll a final volume of about 10 mIlS reached Do not allow sample to go to dryness Alternatively, heat for 30 mInutes In an autoclave at 121°C (15-20 pSI) Cool and dilute the sample to about 30 ml and adjust the pH of the sample to 7 0 ±O 2 With 1 N NaOH (7 10) usmg a pH meter If sample IS not clear at thiS pomt, add2-3dropsofaCid(76)andfilter DIluteto50ml Alternatively, Ifautoclaved see NOTE 1 Determme phosphorus as outhned m 8 J 2 Orthophosphate 82 1 8 2 2 8 2 3 8 2 4 Add1mlofHzS04 solutIOn(76)toa50mlsamplema125mlErlenmeyerflask Boll gently on a pre-heated hot plate for 30-40 mInutes or untll a final volume of about 10 mIlS reached Do not allow sample to go to dryness AlternatIvely, heat for 30mmutesIn an autoclave at 121°C (15-20 pSI) Cool and dllute the sample to about 30 ml and adjust the pH of the sample to 7 0 ±O 2 With NaOH (7 10) usmg a pH meter If sample IS not clear at thiS POInt, add 2-3 drops ofaCid (7 6) and filter Dllute to 50 ml Alternatively, If autoclaved see NOTE 1 The sample IS now ready for determmatlOn of phosphorus as outhned In 8 3 2 Orthophosphate 3652-5PDF Image | Methods for Chemical Analysis of Water and Wastes
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