The development of an automated continuous measurement system for the monitoring of HCHO and CH3CHO in the atmosphere by using an annular diffusion scrubber coupled to HPLC

An automated continuous measurement system for the monitoring of formaldehyde (HCHO) and acetaldehyde (CH 3 CHO) in the urban atmosphere was developed by using an annular diffusion scrubber in conjunction with a high-performance liquid chromatograph (HPLC). With this technique, atmospheric HCHO and CH 3 CHO were effectively collected by the annular diffusion scrubber which consists of a porous polytetrafluoroethylene (PTFE) tube disposed concentrically within a Pyrex-glass tube and a scrubbing solution. 2,4-Dinitrophenylhydrazine (DNPH) was selected as the scrubbing solution for collecting HCHO and CH 3 CHO, which are derivatized to 2,4-dinitrophenylhydrazone-formaldehyde (DNPH-HCHO) and 2,4-dinitrophenylhydrazone-acetaldehyde (DNPH-CH 3 CHO), respectively. An aliquot of the sample solution was automatically injected into an HPLC equipped with a semi-micro ODS column and a UV-VIS detector for separating and determining DNPH-HCHO and DNPH-CH 3 CHO. All the operations are sequenced by a programmable controller, and automated continuous measurements are performed with a typical temporal resolution of 1 h. The collection efficiencies of HCHO and CH 3 CHO were about 97% and 93%, respectively, at an air flow rate of 0.2 L/min. The lower detection limits (3σ of the blank hydrazones) of HCHO and CH 3 CHO were 0.05 ppbv and 0.10 ppbv, respectively, in the case of 12-L air sample volume. Analytical response of a standard solution of DNPH-HCHO and DNPH-CH 3 CHO by the HPLC during a 10-day continuous measurement was unchanged and the relative standard deviation (RSD) was < 1.0%. Interferences from O 3 and NO 2 were insignificant in this annular diffusion scrubber method. Both for HCHO and CH 3 CHO measurements, concentrations from this developed system well agreed with those measured by a DNPH Silica cartridge method.