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NITROGEN, NITRATE Method 352.1 (Colorimetric, Brucine) STORET NO. Total 00620 I Scope and Apphcatton II Thls method lS apphcable to the analysls of dnnkmg, surface and sahne waters, domestlc andmdustnalwastes Modlficattoncanbemadetoremoveorcorrectforturbldlty,color, sahmty, or dlssolved orgamc compounds m the sample 12 TheapphcablerangeofconcentratlOnslS0 1to2mgN03-N/hter 2 Summary of Method 2 1 ThlS method lS based upon the reactIOn of the mtrate lon wlth brucme sulfate m a 13 N H2S04 solutlOn at a temperature of 100°C The color ofthe resultmg complex lS measured at410nm TemperaturecontrolofthecolorreactlonlSextremelycntical 3 Sample Handhng and Preservation 3 1 Analysls should be made as soon as posslble If analysls can be made wlthm 24 hours, the sample should be preserved by refngeratlOn at 4°C When samples must be stored for more than 24 hours, they should be preserved wlth sulfunc aCld (2 ml conc H2S04 per hter) and refngeratlOn 4 Interferences 41 Dlssolvedorgamcmatterw111causeanoffcolorm 13N H2S04 andmustbecompensated for by addlttonS of all reagents except the brucme-sulfamhc aCld reagent Thls also apphes to natural color present not due to dlssolved orgamcs 42 The effect ofsahmty lS ehmmated by addltion ofsodlUm chlonde to the blanks, standards and samples 43 All strong oXldlZmg or reducmg agents mterfere The presence of oXldlzmg agents may be determmed wlth a total resldual chlonne test klt 44 ResldualchlonnemterferencelSehmmatedbytheaddltlOnofsodmmarsemte 45 Ferrous and fernc lron and quadnvalent manganese glVe shght posltlve mterferences, but m concentratlOns less than I mg/1 these are neghglble 46 Uneven heatmg of the samples and standards dunng the reactlOn time w111 result m erratlc values The necesslty for absolute control of temperature durmg the cntical color development penod cannot be too strongly emphaslzed 5 Apparatus 51 Spectrophotometer or filter photometer sUltable for measunng absorbance at 410 nm 52 Sufficlent number of 40-50 ml glass sample tubes for reagent blanks, standards and samples 53 Neoprene coated Wlre racks to hold sample tubes 54 Water bath sUltable for use at 100°C Thls bath should contam a stunng mechamsm so that all tubes are at the same temperature and should be of sufficlent capaclty to accept Approved for NPDES and SDWA Issued 1971 352 1-1PDF Image | Methods for Chemical Analysis of Water and Wastes
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