Continuous automated measurement of hexavalent chromium in airborne particulate matter

An automated continuous instrument for the collection and measurement of aerosol Cr(VI) is described. The system alternately collects the sample on one of two glass fiber filters. After 15-min sample collection on one filter, the sampling switches over to the second filter. The freshly sampled filter is washed for 8.5 min, and the washings are preconcentrated on a minicolumn packed with anion exchange resin. The washed filter is dried with filtered hot air for the next 6.5 min so that it is ready for sampling at the end of the 15-min cycle. The preconcentrated Cr(VI) on the column is eluted with 0.1 M sodium perchlorate and then reacted with sym-1,5-diphenylcarbazide prior to absorbance detection with a light emitting diode-based dedicated flow-through absorbance detector. The detection limit (S/N = 3) is 5 ng of Cr(VI)/m3, orders of magnitude lower than current regulatory requirements. The instrument operates unattended over long periods. In continuous round-the-clock operation, filter replacement frequency is every 24-72 h, depending on dust loading. The system is portable for facile field deployment and permits fully automated rapid determinations at a very low analysis cost per sample.