EPA-NERL: 353.4: Nitrate and Nitrite in Estuarine and Coastal Waters by Automated Colorimetry

Summary
Analytes
Revision
Data and Sites

Official Method Name

Determination of Nitrate and Nitrite in Estuarine and Coastal Waters by Gas Segmented Continuous Flow Colorimetric Analysis

Current Revision

Revision 2.0, September 1997

Media

WATER

Instrumentation

Automated Spectrophotometer

Method Subcategory

Inorganic

Method Source

EPA-NERL

Citation

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

Brief Method 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 and Application

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

Applicable Concentration Range

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

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.

Quality Control 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.

Sample Handling

Samples are normally collected using hydrocast or submersible pump systems as described in the method. Samples should be stored in high density polyethylene bottles in the dark at 4^oC until analysis can be performed. Samples with low concentrations of nitrite (common) must be analyzed within 3 hours to obtain reliable nitrite measurements. Samples with high ammonia or nitrite can convert to nitrate due to microbial oxidation, and should be analyzed as soon as possible. Samples containing <10 % of nitrate and ammonia can be preserved for nitrate by freezing for up to a month.

Maximum Holding Time

3 hours; One month for preserved estuarine and coastal water samples

Relative Cost

Less than $50

Sample Preparation Methods

This method has 2 analytes associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Nitrate(14797-55-8) Nitrate Nitrate ion Nitrate-N Nitrates/nitrites Nitrogen, nitrate	0.075 ug/L	106% Rec (SL)	1.50 % RSD (SL)			139.94 ug/L
Nitrite(14797-65-0) Nitrite Nitrite (as ion) Nitrite nitrogen Nitrite-N Nitrites Nitrogen, nitrite	N/A	N/A	N/A

Precision Descriptor Notes:	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 Level Note:	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

Precision Descriptor Notes:

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 Level Note:

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	PDF/Link
Revision 2.0, September 1997

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EPA-NERL: 353.4: Nitrate and Nitrite in Estuarine and Coastal Waters by Automated Colorimetry

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