Garlmer River Data



AUTHORS/CONTACTS: Joan E. Sheldon and Dr. William J. Wiebe

Revision Date: June 7, 1997

Humic Interference:
All the analytical procedures presented here are colorimetric in nature. Substances other than the one of interest, especially colored compounds, may interfere by absorbing at the wavelength used in the analysis. Usually this may be corrected by subtracting the absorbance of the sample (alone or with some of the reagents added) from the absorbance after analytical color development. In addition to its color, humic material seems to interfere in many analyses by lessening analytical color development. During the development of most of the protocols presented here, it was noted that recovery of internal standards from humic- rich river waters (after correction for natural water color) was low. The mechanisms for this are unclear; binding of the analyte of interest or interference in color development reactions are possibilities. Whatever the mechanism, the result is usually that simple subtraction of the sample color from the final color leads to underestimation of nutrient concentrations. Corrections for this, which have been taken from the literature or determined empirically, include sample dilution and modification of analyses to precipitate humics.
Salt Error:
Some nutrient analyses are affected by the salinity of estuarine and marine waters. However, these procedures have been developed for or tested in saline waters, and multiplicative correction factors derived by adding standards to waters of varying salinity are well known.

Container Preparation:
Wash all containers (bottles, tubes, beakers, filter towers, etc., including any caps) in Liquinox® and tap water. Do not use other brands of soap or detergent without testing, as many contain ammonia (Micro®) or phosphates (Alconox®). Rinse thoroughly with distilled or deionized water (not necessarily the best water available). Soak in 10% stock HCl for several hours or overnight. Rinse thoroughly with the best water available (preferably 18 megohm-cm water). Dry in oven or air.
Wash and dry as above, then cover or wrap with aluminum foil and bake (ash) at 500 oC for 2 hours. Cool slowly. Any glass other than Pyrex® may crack.
Wash and dry as above. Since they cannot be baked to reduce possible contaminants, plastics should, if possible, be kept for specific purposes e.g. keep making a reagent in the same bottle. In particular, plastic sample bottles should not be used for anything else.
Use 18 megohm-cm water or the best deionized water available for preparing all standards and reagents.
GF/F filters:
Bake (ash) at 450 oC for 2 hours, not more; otherwise, they tend to get brittle.
Common reagents:
1 N NaOH: 40 g made up to 1 L with water
0.5 N NaOH: 20 g made up to 1 L with water
1 N H2SO4: 28 ml made up to 1 L with water