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Ion chromatographic studies of oxalate: Applications to neonatal parenteral nutrition
The development of nephrocalcinosis, the progressive formation and deposition of oxalate crystals in the kidneys, in premature infants is a relatively common and potentially serious condition. Although hyperoxaluria and hypercalciurea are both associated with the pathogenesis of nephrocalcinosis, it is believed that hyperoxaluria may be more important in enhancing the risk of calcium oxalate precipitation. Therefore, dietary measures to decrease urinary oxalate excretion in preterm infants may lead to decreased incidence of nephrocalcinosis. ^ Total parenteral nutrition (TPN) solutions can act as a direct source of oxalate introduction into premature infants since they contain ascorbic acid (vitamin C) which is known to oxidize to oxalate in-vitro. Since increased urinary oxalate excretion has been reported in infants receiving TPN is was of clinical interest to be able to determine whether the infusion of TPN solutions into premature infants resulted in an unnecessary oxalate burden. ^ A robust ion chromatographic method with suppressed conductivity detection was developed for the reliable determination of oxalate at part-per-million (ppm) levels in TPN solutions. An eluent system based on sodium carbonate and sodium bicarbonate was developed, permitting the separation and selective detection of oxalate from the major anionic components of the TPN matrix. The interference effect of method induced oxalate formation from ascorbate, which is known to hinder the determination of oxalate in TPN by currently available methodologies, was shown to be absent. The application of uncertainty in measurement was applied to ensure that a low level of experimental uncertainty was carried through to the obtained data. ^ The effect of non-linear analyte response that is commonly reported when using carbonate and bicarbonate eluents with suppressed conductivity was evaluated. The deviation of calibration data from a linear response was found to be only very slight over the oxalate concentrations studied (0.2 ppm–30 ppm). ^ The application of the developed method to the preliminary study of oxalate formation in TPN subjected to phototherapy conditions was successfully demonstrated. ^
Nigel Raymond Metcalfe,
"Ion chromatographic studies of oxalate: Applications to neonatal parenteral nutrition"
(January 1, 2003).
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