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Simultaneous determination of total nitrogen and total phosphorus in environmental waters using alkaline persulfate digestion and ion chromatography.

Journal of chromatography. A (2014-12-03)
Brian M De Borba, Richard F Jack, Jeffrey S Rohrer, Joan Wirt, Dongmei Wang
ABSTRACT

An ion chromatography (IC) method was developed for the simultaneous determination of total nitrogen and total phosphorus after alkaline persulfate digestion. This study takes advantage of advances in construction of high-resolution, high-capacity anion-exchange columns that can better tolerate the matrices typically encountered when a determination of total nitrogen and total phosphorous is required. Here, we used an electrolytically generated hydroxide eluent combined with a high-capacity, hydroxide-selective, anion-exchange column for the determination of total nitrogen (as nitrate-N) and total phosphorus (as phosphate-P) in environmental samples by IC. This method yielded LODs for nitrate-N and phosphate-P of 1.0 and 1.3 μg/L, respectively. The LOQs determined for these analytes were 3.4 and 4.2 μg/L, respectively. Due to the dilution factor required and the blank nitrate-N concentration after the persulfate digestion, the quantification limits increased for nitrate-N and phosphate-P to 171 and 63 μg/L, respectively. The suitability of the method was evaluated by determining the nitrogen and phosphorus concentrations from known concentrations of organic-containing nitrogen and phosphorus compounds. In addition, environmental samples consisting of six different wastewaters and 48 reservoir samples were evaluated for total nitrogen and phosphorus. The recoveries of nitrogen and phosphorus from the organic-containing compounds ranged from 93.1 to 100.1% and 85.2 to 97.1%, respectively. In addition, good correlation between results obtained by the colorimetric method and IC was also observed. The linearity, accuracy, and evaluation of potential interferences for determining TN and TP will be discussed.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Sodium hydroxide, reagent grade, ≥98%, pellets (anhydrous)
Sigma-Aldrich
Glycine, suitable for electrophoresis, ≥99%
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Glycine, ReagentPlus®, ≥99% (HPLC)
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Potassium hydroxide, ACS reagent, ≥85%, pellets
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Urea, ACS reagent, 99.0-100.5%
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Urea, powder, BioReagent, for molecular biology, suitable for cell culture
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Sodium hydroxide solution, BioUltra, for molecular biology, 10 M in H2O
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Sodium hydroxide, BioXtra, ≥98% (acidimetric), pellets (anhydrous)
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Sodium hydroxide solution, 1.0 N, BioReagent, suitable for cell culture
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Ammonium chloride, for molecular biology, suitable for cell culture, ≥99.5%
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Potassium hydroxide, reagent grade, 90%, flakes
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Potassium persulfate, ACS reagent, ≥99.0%
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Potassium hydroxide solution, 45 wt. % in H2O
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Glycine, BioUltra, for molecular biology, ≥99.0% (NT)
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Nicotinic acid, ≥98%
Supelco
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Potassium hydroxide solution, volumetric, 8.0 M KOH (8.0N)
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Ammonium chloride, 99.998% trace metals basis
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Urea, 8 M (after reconstitution with 16 mL high purity water)
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Ammonium chloride, ReagentPlus®, ≥99.5%
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Urea solution, BioUltra, ~8 M in H2O