Following the discovery of nitrite and nitrate as pro-drugs of the vasorelaxant nitric oxide, many studies have reported enhanced athletic performance following intake of these ions either intravenously or as a food supplement. The primary aim of this study was to develop a new accurate, reliable and robust ion chromatography based method. The newly developed method was applied to selected foodstuffs in powdered and/or juice form to measure levels of nitrate and nitrite. In addition to the commonly used beetroot juice, an initial HPLC-based screen of a range of foods identified spinach powder with very high nitrate and nitrite content. As a result of the initial screening, branded beetroot juice, concentrated beetroot juice and spinach powder were analysed using a new extraction method followed by a newly developed and validated ion chromatographic determination of nitrate and nitrite levels. The new ion chromatography based assay showed higher efficiency and better recovery than the HPLC approach. Significant inter-batch variations were found in levels of nitrate and nitrite in the beetroot juice and concentrated beetroot juice samples tested. In contrast spinach powder could provide a homogenous source of nitrate and nitrate for physiological studies. In summary, the new assay is rapid and efficient facilitating rigorous analyses of nitrate and nitrite levels prior to investigations requiring intake of foodstuffs containing these nitric oxide precursors.
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