Method 1685
Nitrate/Nitrite-N in Water and Biosolids by Automated
Photometry
http://water.epa.gov/scitech/methods/cwa/bioindicators/upload/2008_11_25_methods_method_biological_1685-bio.pdfThis method describes procedures for the determination of nitrate/nitrite-nitrogen, or oxidized
nitrogen, in drinking, ground, and surface water; domestic and industrial waste; and biosolids
(treated municipal sewage sludge). Automated photometry is used to determine the nitrate/nitrite
concentration of the sample. This method is based on U.S. Environmental Protection Agency (EPA)
Method 353.2: Nitrogen, Nitrate-Nitrite (Colorimetric, Automated, Cadmium Reduction)
(Reference 16.1). This method is associated with Method 1691: Municipal Biosolids Sampling
Guidance (Reference 16.2)
2.0 Summary of Method
2.1 Aqueous samples are filtered then passed through a cadmium-copper reduction column prior to
analysis.
2.2 The oxidized nitrogen (the sum of nitrite and nitrate) in solid samples is extracted in reagent water,
filtered, and passed through a cadmium-copper reduction column prior to analysis. The cadmiumcopper
reduction column converts any nitrate present in the samples to nitrite.
2.3 The nitrite concentration of samples (nitite originally present plus reduced nitrate) is determined by
diazotizing with sulfanilimide and coupling with N-(1-naphthyl)ethylenediamine dihydrochloride to
form a highly colored azo dye which is measured by automated colorimetry.
2.4 Quality is assured through calibration and testing of the sample preparation and analytical
instruments.
4.0 Interferences
4.1 Large concentrations of fat, oil and grease (FOG) will coat the cadmium particles used for reduction
of nitrate to nitrite. FOG should be removed by sample extraction with hexane or a 80%/20%
hexane/methyl t-butyl ether mixture prior to passing the sample through the reduction column
(Section 11.2.3).
4.2 Residual chlorine, if present, must be removed by pretreatment of the sample with sodium thiosulfate
before digestion/distillation. Typically, this will be necessary if the sample contains free water or is
aqueous.
4.3 Color present in the sample that absorbs at about 540 nm interferes with the photometry.
4.4 Certain metal ions can interfere with the colorimetry. An ethylenediamine tetraacetate (EDTA)
solution is added to the sample extract to remove these potential interferences.
应该用的是同一个方法。那个检测波长大概是540nm。可见波长。
如果不是记者白吃简化描述了过程，可以肯定所谓的快速检测结果根本不可信。样品只是简单的静置15分钟，根本不能保证别的因素对这吸收检测的影响。至少微乳滴、悬浮物和可能的颜色都会增加实际的数值。对于是否离心机能够出去可能的影响我也表示质疑。
强烈建议山寨版的仪器去检测一下中药水剂。