Catalytic Determination of Trace Formaldehyde with a Flow Injection System Using the Indicator Reaction between Crystal Violet and Bromate

A sensitive flow injection method is proposed for the determination of formaldehyde based on its catalytic action upon the redox reaction between crystal violet and potassium bromate in phosphoric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of crystal violet injected at the maximum absorption wavelength of 600 nm. A calibration graph from 0.018 to 1.400 µg mL−1 is obtained, and the detection limit is 0.007 µg mL−1 in a sample volume of 30 µL. Up to 15 samples can be analyzed per hour with a relative standard deviation of 1.2 and 2.3%, respectively, for the determination of 1.0 and 0.1 µg mL−1 of formaldehyde. The method is free from most interference. This method has been applied to the determination of formaldehyde in air, decoration boards and paints, and the results compare well with those provided by iodimetry.