EPA Method 353.4


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EPA Method 353.4:
Nitrate and Nitrite in Estuarine and Coastal Waters by Automated Colorimetry. Official Name: Determination of Nitrate and Nitrite in Estuarine and Coastal Waters by Gas Segmented Continuous Flow Colorimetric Analysis

Summary:
The methods uses an automated gas segmented continuous flow colorimetric system to determine nitrate and nitrite.Nitrate and nitrite: A sample is passed through a column containing granulated copper-cadmium to reduce nitrate to nitrite. The nitrite (originally in the sample and reduced nitrate) is determined by diazotizing with sulfanilamide and coupling with N-(1-naphthyl)-ethylenediamine dihydrochloride to form a highly colored azo dye, which is measured with a spectrometer.Nitrite alone: The procedure is the same except that the cadmium column is bypassed.Nitrate alone: Subtract "Nitrite" from "Nitrate and Nitrite."

Scope:
This method determines nitrate and nitrite in estuarine and coastal waters.

Citation:
Methods for Determination of Chemical Substances in Marine and Estuarine Matrices - 2nd Edition (EPA/600/R-97/072)

Interferences:
(A) Hydrogen sulfide: Hydrogen Sulfide above 0.1 mg-sulfide/L can interfere with analysis by precipitating on the cadmium column. Remove hydrogen sulfide by precipitation with cadmium or copper salt.(B)Heavy metals: Iron, copper and other heavy metals at concentrations > 1 mg/L alter the reduction efficiency of the cadmium complex. EDTA is added to complex metal ions, removing this interference.(C) Phosphate: Phosphate at a concentration > 0.1 mg/L decreases reduction efficiency of cadmium. Dilute samples if possible or remove phosphate with ferric hydroxide prior to analysis.(D) Particulates: Filter out particulates after sample collection.(E) Refractive index: The method corrects for refractive index interferences due to a mismatch in the salinity of standards and samples.

QC Requirements:
Each laboratory using this method is required to implement a formal quality control program. The minimum requirements of this program consist of an initial demonstration of performance, continued analysis of laboratory reagent blanks, laboratory duplicates, and laboratory fortified blanks with each set of samples as a continuing check on performance.

Maximum Holding Time:
3 hours; One month for preserved estuarine and coastal water samples

Media:
WATER

Subcategory:
Inorganic

Concentration:
0.075 ug-N/L to 5.0 mg-N/L.

Precision:
A sample with a salinity of 32.623% and ambient nitrate concentration of 48.22 ug-N/L were fortified with 139.94 ug-N/L (see Section 13 of the method). Seven replicates of the sample were analyzed to generate precision and accuracy. Additional data generated at different salinities and ambient nitrate concentrations are available in the method. Note: It appeared from the method that the analyte being measured was nitrate. However, the measurement of nitrite should yield similar results, with differences due to the efficiency of cadmium column reduction.

Detection:
An MDL was determined by one laboratory using nitrate-fortified low nutrient sea water at five different salinities, according to the MDL procedure at 40 CFR part 136, Appendix B. The procedure also is detailed in Section 9.2.2

Revision Number:
Revision 2.0, September 1997

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