A combined sampling and delay unit for flow injection analysis. The automated determination of 2-thiobarbituric acid reactive substances in foods

A new combined sampling and delay unit is described which makes it feasible to utilize slow chemical reactions in flow injection analysis. The unit allows a number of individual samples to “queue up” for a specified time before being transported to the detector. The applicability has been demonstrated in an automated procedure for the determination of 2-thiobarbituric acid (TBA) reactive substances in foods. The procedure has been optimized on 1–10 μM standards of 1,1,3,3-tetraethoxypropane with regard to the concentration of TBA and reaction time. It was found that analytical conditions of 40 mM TBA, 20 min and 60°C in the automated procedure as compared to 20 mM, 40 min and 100 °C in the manual TBA procedure yielded lower absorbance and a comparable reproducibility. The use of the sampling/delay unit for other slow reactions is indicated.