NUTRIENT
ANALYSIS METHODS MANUAL
FOR HUMIC-CONTAINING ESTUARINE WATERS
AUTHORS/CONTACTS:
Joan E. Sheldon and
Dr. William J.
Wiebe
Revision Date: June 7, 1997
PROBLEMS COMMON TO MANY OR ALL ANALYSES
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.
METHODS COMMON TO ALL PROTOCOLS
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.
Glassware: 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.
Plasticware: 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.
Water: 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
PROBLEMS COMMON TO MANY OR ALL ANALYSES
- 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.
METHODS COMMON TO ALL PROTOCOLS
- 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.
- Glassware:
- 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.
- Plasticware:
- 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.
- Water:
- 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
