Abstract
Abstract. A microfluidic lab-on-a-chip derivatisation technique has been developed to measure part per billion (ppbV) mixing ratios of gaseous glyoxal (GLY) and methylglyoxal (MGLY), and the method is compared with other techniques in a smog chamber experiment. The method uses o-(2, 3, 4, 5, 6-pentafluorobenzyl) hydroxylamine (PFBHA) as a derivatisation reagent and a microfabricated planar glass micro-reactor comprising an inlet, gas and fluid splitting and combining channels, mixing junctions, and a heated capillary reaction microchannel. The enhanced phase contact area-to-volume ratio and the high heat transfer rate in the micro-reactor resulted in a fast and highly efficient derivatisation reaction, generating an effluent stream ready for direct introduction to a gas chromatograph-mass spectrometer (GC-MS). A linear response for GLY was observed over a calibration range 0.7 to 400 ppbV, and for MGLY of 1.2 to 300 ppbV, when derivatised under optimal reaction conditions. The analytical performance shows good accuracy (6.6% for GLY and 7.5% for MGLY), suitable precision (<12.0%) with method detection limits (MDLs) of 75 pptV for GLY and 185 pptV for MGLY, with a time resolution of 30 min. These MDLs are below or close to typical concentrations of these compounds observed in ambient air. The feasibility of the technique was assessed by applying the methodology to quantify α-dicarbonyls formed during the photo-oxidation of isoprene in the EUPHORE chamber. Good correlations were found between microfluidic measurements and Fourier Transform InfraRed spectroscopy (FTIR) with a correlation coefficient (r2) of 0.84, Broadband Cavity Enhanced Absorption Spectroscopy (BBCEAS) (r2 = 0.75), solid phase micro extraction (SPME) (r2 = 0.89), and a photochemical chamber box modelling calculation (r2 = 0.79) for GLY measurements. For MGLY measurements, the microfluidic technique showed good agreement with BBCEAS (r2 = 0.87), SPME (r2 = 0.76), and the modeling simulation (r2 = 0.83), FTIR (r2 = 0.72) but displayed a discrepancy with Proton-Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS) with r2 value of 0.39.
Highlights
Glyoxal (GLY, CH(O)CHO) and methylglyoxal (MGLY, CH3C(O)CHO) are the most prevalent α-dicarbonyls in the ambient atmosphere
We have described previously the optimisation process and parameters for formaldehyde measurement (Pang and Lewis, 2012) and have undertaken a similar optimisation here including solvent selection, optimisations of PFBHA concentration, temperature, storage time, gas and solution flows
It is appreciated that the above results are based on a small amount of data from a few experiments but we believe that this study indicates that the microfluidic derivatisation technique is a valuable and feasible analytical method for GLY, MGLY and potentially other trace atmospheric carbonyl compounds in ambient air
Summary
Glyoxal (GLY, CH(O)CHO) and methylglyoxal (MGLY, CH3C(O)CHO) are the most prevalent α-dicarbonyls in the ambient atmosphere. GLY and MGLY have attracted recent attention as potentially important contributors to global secondary organic aerosol (SOA) (Volkamer et al, 2009; Hallquist et al, 2009; Hoffmann et al, 1997), which can significantly impact climate, air quality and human health (Solomon et al, 2007; Mauderly and Chow, 2008). They are highly water-soluble and can form SOA through uptake into the aqueous phase of an aerosol particle or cloud droplet, followed by aqueous-phase reactions that lead to the formation of low-volatility organonitrogen/organosulphate/ oligomeric products (Hamilton et al, 2013; De Haan et al, 2009; Loeffler et al, 2006). GLY was reported to account for up to 15 % of the mass of SOA in Mexico City (Volkamer et al, 2007)
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