Determination of atmospheric carbonyls and carboxylic acids by denuder sampling, gradient elution and capillary electrophoresis
DETERMINATION OF ATMOSPHERIC CARBONYLS AND CARBOXYLIC ACIDS BY DENUDER SAMPLING, GRADIENT ELUTION AND CAPILLARY ELECTROPHORESIS
Chan King Yee
for the Degree of Master of Philosophy at The University of Hong Kong
in August 2003
Atmospheric carbonyls and carboxylic acids are semi-volatile orgamc air pollutants that can exist in both the gaseous and particulate phase. The determination of their distribution in gaseous and particulate phases is important due to the ir different adverse effects on the environment and human health. An air sampling system consisting of denuders and filters was developed to collect these pollutants. Gaseous phase pollutants were collected on reagent-coated annular denuders while particulate phase pollutants were passed through the denuders unaffected prior to collection by the downstream filters. The combination of denuders and downstream filters reduces sampling artifacts due to adsorption and volatilization associated with the upstream filters.
A new analytical methodology based on capillary electrophoresis (CE) and
gradient elution technique was developed for the separation and quantification of 16 atmospheric carbonyls which were classified by the Hong Kong Environmental Protection Thpartment as toxic air pollutants. Atmospheric carbonyls collected in the form of carbonyl-hydrazone derivatives were separated by micellar electrokinetic capillary chromatography under a continuously changing gradient of the organic modifiers. The buffer gradient was generated by continuous dynamic mixing of two buffers in the inlet reservoir of the CE setup. Satisfactory separation of 16 carbonyls was achieved by placing 0.1 ml starting buffer in the inlet reservoir containing 20 mM borate, 50 mM SDS and 20 % methanol at pH 8.9 and a subsequent addition of a second buffer containing 20 mM borate, 50 mM SDS and 35 % acetonitrile to the inlet reservoir at a rate of 0.8mllh. The detection limits of the procedure developed for analyzing atmospheric carbonyls using denuder sampling and gradient elution MEKC separation ranged from 0.002 to 1.210 f.lg/nf and working ranges from 0.005 to 43.31 f.lg/nf for 1 to 24- hour sampling at a sampling gas flow rate of 10 Lpm.
Carboxylic acids in the ambient air were collected by chemical conversion into carboxylate anions prior to separation by capillary zone electrophoresis. The coupling of a denuder sampling system with CE using a buffer containing 4 mM 2,6-naphthalenedicarboxylic acid, 14.4 mM Bis- Tris and 0.2 mM tetradecyltrimethylammonium bromide at pH 6.0 allows simultaneous determination of 12 atmospheric carboxylic acids with detection limits ranging from 0.009 to 0.649 f.lg/m3 and working range 0.021 to 106.0 f.lg/nf for sampling from 1 to 24 hours at a sampling gas rate of 10 Lpm.
An applicability study of the new procedures developed for field monitoring was carried out in Hong Kong. The results obtained indicate that a rmjor proportion
of carbonyls sampled were found in the particulate phase whereas most of the carboxylic acids accumulated in the gaseous phase.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:university of hong kong dissertations carbonyl compounds sampling carboxylic acids capillary electrophoresis air apparatus
Date of Publication:01/01/2004