FI-Catalytic Photometric Determination of Trace Amounts of Oxalate

In 1.8×10-2mol·L-1 H2SO4 medium and heated at 30 ℃ for 160 s, the color-fading reaction among K2Cr2O7, KI and rhodamine 6G was significantly catalyzed by oxalate. By applying flow-injection technique, a FI-catalytic photometric method for determination of trace amount of oxalate was proposed. Linearity range was kept in the range of 0.10-1.20 mg·L-1, and limit of detection (3s/k) found was 0.03 mg·L-1, when the sampling frequency was 18 times per hour. Precision of the method was tested by addition of standard oxalate solutions with concentration of 0.30 and 0.80 mg·L-1 for 11 determinations, giving values of RSD′s 2.7% and 1.6% respectively. The proposed method was applied to the analysis of samples of spinach and urine, and using these samples as matrixes, recovery was tested by the standard addition method. Values of recovery found were in the range of 93.3%-96.7%.