Windward Community College Heeia Stream and Kaneohe Bay Water Quality Assessment Project 2004-2005 (NODC Accession 0002449)

Determination of Nitrite, Nitrate and Phosphate Summary of Method. Water samples are filtered and analyzed by ionchromatography (IC). Each analytical batch consists of a blank, 5 external calibration standards and a calibration check for every 8 samples. The method detection limits (MDL) are as follows: 0.1 mg/L for phosphate, and0.05 mg/L for nitrite and nitrate. Preparation of IC samples. Water samples are pre-filtered before analysis inthe Dionex ICS-90 ion chromatography system. Fresh water samples (5 mL) are filtered through 0.20 mm IC Millex syringe filters (for freshwater samples) while saltwater samples are filtered through the Dionex Ag/H cartridges and diluted 50:50 using deionized distilled water. Preparation of IC calibration standards. The following calibration standards are prepared.(1) 0.1 mg/L of phosphate, 0.05 mg/L of nitrite and 0.05 mg/L nitrate(2) 0.2 mg/L phosphate and 0.1 mg/L nitrite and 0.1 mg/L nitrate(3) 1.0 mg/L phosphate and 0.5 mg/L nitrite and 0.5 mg/L nitrate(4) 2.0 mg/L phosphate and 1.0 mg/L nitrite and 1.0 mg/L nitrate(5) 10.0 mg/L phosphate and 5.0 mg/L nitrite and 5.0 mg/L nitrate Calibration. The calibration curve must consist of at least three datapoints. The response of each calibrator must be within 10%, otherwise, it does not meet method criteria and must be removed from the working calibration curve.Final data are summarized in Excel worksheets. The nitrite as N (mg/L) is calculated by multiplying the nitrite (mg/L) with 0.304 (factor). Likewise, the nitrate as N (mg/L) content is calculated by multiplying the nitrate(mg/L) content with 0.226 (factor). The phosphate (mg/L) content is converted to phosphorus (mg/L) by using the factor of 0.326. Determination of Total Nitrogen and Total Phosphorus Summary of Method. To analyze the total N and total P content, all phosphorus-and nitrogen-containing substances in the water sample are first converted to inorganic nitrates and phosphates by photo-oxidation. After photo-oxidation, the samples are analyzed as described above. Photo-oxidation. Water samples (100 mL) added with 2 drops of 30% H2O2, arephoto-oxidized using Ace-Hanovia photooxidation apparatus (Department ofHealth State Laboratory) for four (4) hours to hydrolyze all phosphorus-containing substances into phosphates, and all nitrogen-containing substances into nitrates.