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

Ion	Molecular weight, M	Molar conductivity, λ₀	Diffusion coefficient, D	Ionic radius, r	Hydration shell, Δr
	(g/mol)	(S·cm²/mol)	(mm²/ms)	(pm)	(pm)
Nitrate, NO₃^–	62.01	71	1.90	179	44
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, return to the knowledge overview, or contact Diduco to discuss your specific analysis.

Applications

ion chromatography

Preserving eluent quality with dedicated storage protected from ambient carbon dioxide

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.

ion chromatography

Comparing suppressed and non-suppressed ion chromatography

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).

ion chromatography

Quantification of anions in water using an improved ion chromatography system

Anion analysis can be performed at several conditions, using various columns on different systems and still be able to meet official requirements. A common approach is isocratic separation with carbonate-bicarbonate eluents, and this example showcase how such analyses can be improved and streamlined with autosampler injections, continuous suppression and protected eluents.

ion chromatography

Published routine method for quantification of anions in tap water and natural waters

Quantification of the seven common anions is an important part of water quality control. This published ion chromatography method is from a scientific paper that presents full validation data according to the ICH guidelines to meet the requirements of laboratories acting under the ISO 17025 accreditation.

ion chromatography

Quantification of common anions in bottled drinking water according to EPA method 300.1A

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.

ion chromatography

Generic method for isocratic separation of fifteen common pharmaceutical counterions

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.

ion chromatography

Hydroxide gradient elution of organic acids and inorganic anions

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 approach in ion chromatography since they can be converted into pure water with nearly zero conductivity.

ion chromatography