Spectrophotometric Determination of Oxalic Acid in Dietary Sources Through Catalytic Titration with Hexavalent Chromium

Abstract

Excess oxalic acid is thought to be a key factor of kidney stone formation in humans. Thus its level in food stuffs should be monitored. In this study, a new spectrophotometric titration method was developed for the determination of oxalic acid (OA) in dietary sources through reaction with hexavalent chromium in presence of Mn (II) as a catalyst. Cr (VI) was used as UV-active material and the determination of OA was based on the decrease in absorbance of the Cr (VI) solution as a result of its reaction with OA. Factors influencing the reduction of Cr (VI), including incubation time, solution pH and background concentration ratio have been optimized. The results showed that the amount of oxalic acid (mg/g) in vegetable samples of Ethiopian collared green (raw and cooked), cabbage (raw and cooked), lettuce (raw),beetroot (raw), pineapple  (before ripe and fully ripe) and mango (before ripe and fully ripe) were 24.15 ± 0.565 and 12.05 ± 0.183, 16.72 ± 0.388 and 9.50 ± 0.424, 14.44 ± 0.183, 15.77 ± 0.175, 23.08 ± 0.212 and 18.31 ± 0.424, 6.75 ± 0.212 and 1.18 ± 0.169 respectively. Ethiopian collared green (Brassica oleraceavar. acephala) contained highest concentration of oxalate, but it was reduced by 50 % after boiling for ten minute. The level of oxalate content in the analyzed fruit samples was found to decrease with increasing growing stage or state of ripeness. All studied food samples contained relatively moderate amounts of total oxalate (< 25 mg/g dry weight) and are safe for human consumption especially when cooked or fully ripe. A very good correlation was observed when the results from the current method and standard method (HPLC) were compared. In conclusion, the current method can successfully be used for determination of OA in fruit and vegetable samples.

Keywords: Spectrophotometric titration, Hexavalent Chromium, Oxalic acid, HPLC.

DOI: 10.7176/FSQM/83-04