Methods in Molecular Biology (2020) 1980: 81–86
DOI 10.1007/7651_2019_206
© Springer Science+Business Media New York 2019
Published online: 09 Feburary 2019
Total Nitrogen Determination by a Spectrophotometric
Method
Jaana Koistinen, Mervi Sjo ¨ blom, and Kristian Spilling
Abstract
Being able to measure total nitrogen (TN) is important for following the nitrogen budget. In this chapter,
we present the spectrophotometric method we use for determining TN. The method relies on oxidation
and reduction steps, involving persulfate digestion of nitrogen compounds into nitrate followed by
spectrophotometric determination.
Keywords Nutrient uptake, Total nitrogen
1 Introduction
Total nitrogen (TN) includes all forms of nitrogen (organic and
inorganic) that is found in water, with the exception of the gas
phase (N 2 ), and is defined as the nitrogen that gives rise to nitrite/
nitrate ions. In practice, TN is the sum of nitrite, nitrate, ammonia,
and dissolved and particulate organic nitrogen. TN is an important
variable to measure for keeping track of the nitrogen budget and is
commonly used for monitoring the state of the environment in
lakes and the ocean and also for monitoring waste streams and
cultivations in aquatic environments.
In this chapter, we present the method we use for determining
total nitrogen. The method is based on colorimetric principles,
measuring nitrogen after a persulfate oxidation of nitrogen compounds in alkaline conditions to nitrate, reduction step, and addition of chemicals reacting with the N-containing molecule
[1]. Nitrate formed during the oxidation is reduced to nitrite here
with an acidic vanadium chloride reagent [2], which is simultaneously added with amines forming a colored compound, an azo
dye, that is detectable spectrophotometrically. Total dissolved
nitrogen (TDN) can be determined after filtering the sample,
which excludes the particulate organic carbon (PON). TDN can
be measured together with dissolved organic carbon (DOC) using
81
DOI 10.1007/7651_2019_206
© Springer Science+Business Media New York 2019
Published online: 09 Feburary 2019
Total Nitrogen Determination by a Spectrophotometric
Method
Jaana Koistinen, Mervi Sjo ¨ blom, and Kristian Spilling
Abstract
Being able to measure total nitrogen (TN) is important for following the nitrogen budget. In this chapter,
we present the spectrophotometric method we use for determining TN. The method relies on oxidation
and reduction steps, involving persulfate digestion of nitrogen compounds into nitrate followed by
spectrophotometric determination.
Keywords Nutrient uptake, Total nitrogen
1 Introduction
Total nitrogen (TN) includes all forms of nitrogen (organic and
inorganic) that is found in water, with the exception of the gas
phase (N 2 ), and is defined as the nitrogen that gives rise to nitrite/
nitrate ions. In practice, TN is the sum of nitrite, nitrate, ammonia,
and dissolved and particulate organic nitrogen. TN is an important
variable to measure for keeping track of the nitrogen budget and is
commonly used for monitoring the state of the environment in
lakes and the ocean and also for monitoring waste streams and
cultivations in aquatic environments.
In this chapter, we present the method we use for determining
total nitrogen. The method is based on colorimetric principles,
measuring nitrogen after a persulfate oxidation of nitrogen compounds in alkaline conditions to nitrate, reduction step, and addition of chemicals reacting with the N-containing molecule
[1]. Nitrate formed during the oxidation is reduced to nitrite here
with an acidic vanadium chloride reagent [2], which is simultaneously added with amines forming a colored compound, an azo
dye, that is detectable spectrophotometrically. Total dissolved
nitrogen (TDN) can be determined after filtering the sample,
which excludes the particulate organic carbon (PON). TDN can
be measured together with dissolved organic carbon (DOC) using
81