A new reagent system for the determination of formic acid

A spectrophotometric method using phloroglucinol is described for the deter mination of formic acid at ppm level. The method involves the reduction of formic acid by hydrochloric acid and magnesium powder, The formaldehyde so formed is treated with phloroglucinol to give an orange-red coloured dye wi th lambda(max) at 475 nm. Beer's law is obeyed in the concentration range 2 -15 mu g of formic acid per 25 ml of the final solution. The molar absorpti vity of the colour system is 6.1 x 10(4) dm(3) mol(-1) cm(-1). The method h as been applied to the determination of formic acid in biological samples.