Analyte: nitrate

The nitrate ion, NO3, is the base of nitric acid, HNO3, which is a strong acid with a pKa of -1.3, and thus fully dissociated in all aqueous solutions regardless of pH. The nitrate ion is singly charged and carries a hydration layer comprised of 2.0 associated water molecules. Some properties of the nitrate ion are summarized in the table below.

Nitrate analysis

Nitrate is often analysed by ion chromatography (IC), using either carbonate-bicarbonate eluents or hydroxide eluents. Unlike most of the other common inorganic anions, nitrate absorbs ultraviolet (UV) light, and can thus be determined both by suppressed conductivity detection, and by UV spectrometry at wavelengths below 220 nm.

Table of some nitrate ion properties at 25 °C

IonMolecular weight, MMolar conductivity, λ0Diffusion coefficient, DIonic radius, rHydration shell, Δr
(g/mol)(S·cm2/mol)(mm2/ms)(pm)(pm)
Nitrate, NO362.01711.9017944
M, was retrieved from Chemical Aid Molecular Mass Calculator. Values for λ0 & D, are from CRC Handbook of Chemistry and Physics, 75th Ed., D.R. Lide (Ed.), CRC Press Inc. (1994), Boca Raton, pp 5-90 to 5-92. Data for r & Δr, plus the number of water molecules, n, mentioned in the text, are from Y. Marcus, J. Chem. Soc. Faraday Trans., 87 (1991) 2995-2999. The pKa values mentioned in the text are from Organic Chemistry Data pKa compilation.

Learn more

To learn more, browse the application examples below or contact Diduco to discuss your specific analysis.

Illustration of nitrate ion with hydration layer

Applications

To ensure that liquid chromatography analysis methods meet regulatory demands of retention repeatability as dictated by pharmacopoeia and the ICH guidelines, it is important to protect weakly buffered eluents from ambient carbon dioxide. The formation of carbonate species will otherwise change the pH and strength of the eluent, thus shifting retention.
Suppressed ion chromatography with conductivity detection is a powerful and sensitive technique to analyse charged ionic species, especially anions of strong acids. The chemically regenerated membrane suppressor Xenoic® XAMS can enable analysis of such anions down to levels of a few microgram per litre (part per billion, ppb).
Official procedure for quality control of drinking water according to the United States Environmental Protection Agency. This procedure allows quantification of the seven common inorganic anions fluoride, chloride, nitrite, bromide, nitrate, phosphate and sulfate in the ranges recommended by WHO and national authorities.
Many medicines and dietary supplements are bases that carry a positive charge, and consequently these small molecules are accompanied by negatively charged counterions. Such anionic excipients may influence the properties of the pharmaceutical formulation and can also influence the effect of the active ingredient since different ion pairs can have different dissolution rates or abilities to penetrate cell walls.
Gradient elution is a powerful tool when aiming to separate many compounds having a wide range of different chemical characteristics. Hydroxide gradients are the most common in ion chromatography since they can be converted into pure water with nearly zero conductivity.
Many medicines and dietary supplements are bases that carry a positive charge, and consequently these small molecules are accompanied by negatively charged counterions. Such anionic excipients may influence the properties of the pharmaceutical formulation and can also influence the effect of the active ingredient since different ion pairs can have different dissolution rates or abilities to penetrate cell walls.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.
Separation of inorganic anion standards at eluent conditions recommended by the column manufacturer.

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