High Performance Ion Chromatography Determination of Nitrite and Nitrate in Foodstuffs

Simultaneous determination of nitrate and nitrite in saliva and foodstuffs by non-suppressed ion chromatography with bulk acoustic wave detector

In the present paper, nitrate and nitrite in foodstuffs and saliva were simultaneously determined using a non-suppressed ion chromatography (IC) method with a bulk acoustic wave sensor (BAW) as detector, and 1.5 mmol/L potassium hydrogenphthalate (KHP) as mobile phase. The IC-BAW method is simple, rapid and accurate. The determination limits for nitrite and nitrate are 0.20 and 0.30 mg/L, respectively. The IC-BAW is comparable and agrees with the conventional spectrophotometric method for nitrite and nitrate determination.

Bacterial sulfate production by biodesulfurization of aromatic hydrocarbons, determined by ion chromatography

The use of bacteria to remove sulfur from crude oil or petroleum distillates is a novel concept that presents an alternative biotechnology to the current technology of hydrodesulfurization (HDS). Sulfur must be removed from crude oils prior use. The burning of fossil fuels containing sulfur releases sulfur dioxide into the atmosphere causing acid rain. The aim of this work is to determine the sulfate concentration by ion chromatography (IC), and calculate the percentage of transformation of organic bound sulfur, that is converted to sulfate, and estimate the efficiency of bacteria in desulfurization. IC is a suitable method for sulfate concentration determination. However, when chloride concentrations are significantly high, interference of the sulfate signal does occur. In this case, it could be avoided by diluting samples. A Dionex Model 2000i/SP IC system, with an anionic pre-column (Dionex AG4A), an anion separator column (Dionex AS4A), a suppressor column (Dionex AMMS-II), and a conductivity detector was used. The eluent (21 mM NaOH) and regenerant (electrolyzed 18 M omega/cm water) flow-rates were 1.0 and 2.0 ml/min, respectively. The sample loop volume was 10 microliters and the conductivity sensitivity was 30 muS. The diluted samples were filtered through a 0.45-micron filter before injection. The highest sulfate concentration detected was 24.10 mg/l, corresponding to a maximal conversion rate of 10% in a month. Sulfate ions were not detected in control samples. The correlation coefficient for a linear least squares fit was 0.99 (p < 0.001). The minimal concentration that we can read was 0.02 mg/l and this concentration corresponded to the limit of detection obtained under the conditions employed in this study. IC is an economical, sensitive and accurate way to estimate the sulfate concentrations in microbiological samples.

Nitrite and nitrate analyses: a clinical biochemistry perspective

OBJECTIVE

To review the assays available for measurement of nitrite and nitrate ions in body fluids and their clinical applications.

DESIGN AND METHODS

Literature searches were done of Medline and Current Contents to November 1997.

RESULTS

The influence of dietary nitrite and nitrate on the concentrations of these ions in various body fluids is reviewed. An overview is presented of the metabolism of nitric oxide (which is converted to nitrite and nitrate). Methods for measurement of the ions are reviewed. Reference values are summarized and the changes reported in various clinical conditions. These include: infection, gastroenterological conditions, hypertension, renal and cardiac disease, inflammatory diseases, transplant rejection, diseases of the central nervous system, and others. Possible effects of environmental nitrite and nitrate on disease incidence are reviewed.

CONCLUSIONS

Most studies of changes in human disease have been descriptive. Diagnostic utility is limited because the concentrations in a significant proportion of affected individuals overlap with those in controls. Changes in concentration may also be caused by diet, outside the clinical investigational setting. The role of nitrite and nitrate assays (alongside direct measurements of nitric oxide in breath) may be restricted to the monitoring of disease progression, or response to therapy in individual patients or subgroups. Associations between disease incidence and drinking water nitrate content are controversial (except for methemoglobinemia in infants).

State-of-the-art ion chromatographic determination of inorganic ions in food

A review of the applications of ion chromatography (IC) to the determination of inorganic ions in food is presented. The most promising sample preparation techniques, such as accelerated solvent extraction, supercritical fluid extraction, solid-phase extraction, UV photolysis, microwave-oven digestion and pyrohydrolysis are discussed. Among the various inorganic anions, nitrogen, sulphur and phosphorus species and halides are widely determined in foods and to a lesser extent only, cyanide, carbonate, arsenic and selenium species are considered. IC determination of inorganic cations deals with ammonium ion, alkali, alkaline-earth, heavy and transition metals particularly and only a small amount of literature is found on the other ones, like aluminium and plantinum. A particular advantage of IC over traditional techniques is the simultaneous determination of several species.

Simultaneous determination of nitrite and nitrate anions in plasma, urine and cell culture supernatants by high-performance liquid chromatography with post-column reactions

A high-performance liquid chromatographic method for the determination of nitrite and nitrate anions derived from nitric oxide in biological fluids is presented. After separation on a strong anion-exchange column (Spherisorb SAX, 250 x 4.6 mm I.D., 5 microns), two on-line post-column reactions occur. The first involves nitrate reduction to nitrite on a copper-plated cadmium-filled column. In the second, the diazotization-coupling reaction between nitrite and the Griess reagent (0.05% naphtylethylendiamine dihydrochloride plus 0.5% sulphanilamide in 5% phosphoric acid) takes place, and the absorbance of the chromophore is read at 540 nm. This methodology was applied to biological fluids. Before injection into the chromatographic system, the samples were diluted and submitted to suitable clean-up procedures (urine and cell culture supernatant samples are passed through C18 cartridges, and serum samples were deproteinized by ultrafiltration through membranes with a molecular mass cut-off of 3000). The method has a sensitivity of 30 pmol for both anions, as little as 0.05-0.1 ml sample volume is required and linearity is observed up to 60 nmol for each anion.

Rapid and sensitive determination of nitrite in foods and biological materials by flow injection or high-performance liquid chromatography with chemiluminescence detection

A method is described for the determination of nitrite that is based on reduction of nitrite with potassium iodide followed by chemiluminescence detection of the liberated NO using a thermal energy analyzer. The method worked well both in the flow injection mode and upon interfacing with a reversed-phase high-performance liquid chromatography system. Limited data available indicated a good agreement between results obtained by the chemiluminescence method and those obtained by using a well established colorimetric procedure when they were applied for the determination of nitrite in a number of cured meats, human saliva, and baby foods. The chemiluminescence method is, however, much superior to the colorimetric one in its speed, versatility, as well as sensitivity (200 times more), and requires only a minimum of sample preparation. The detection limit of the new method is about 0.1 ng NaNO2 per injection or 5 micrograms/kg in cured meats and other substrates analyzed.