•O3 sensors were employed in the development of a miniaturised O3 measurement device combined with LabJack and Labview data acquisition.•The O3 sensor device was firstly applied in the laboratory experiment and also in air quality monitoring.•The influences relative humidity and gas flow rate on sensor signals were investigated independently.Ozone (O3) measurements are a critical component of air quality management and many atmospheric chemistry laboratory experiments. Conventional ozone monitoring devices based on UV absorption are relatively cumbersome and expensive, and have a relative high power consumption that limits their use to fixed sites. In this study electrochemical O3 sensors (OXB421, Alphasense) were used in a miniaturised O3 measurement device combined with LabJack and Labview data acquisition (DAQ). The device required a power supply of 5 V direct current (VDC) with a total power consumption of approximately 5 W. Total weight was less than 0.5 kg, low enough for portable in situ field deployment. The electrochemical O3 sensors produced a voltage signal positively proportional to O3 concentrations over the range of 5 ppb–10 ppm. There was excellent agreement between the performances of two O3 sensors with a good linear coefficient (R2 = 0.9995). The influences of relative humidity (RH) and gas sample flow rate on sensor calibrations and sensitivities have been investigated separately. Coincident calibration curves indicate that sensor performances were almost identical even at different RHs and flow rates after a re-zeroing process to offset the sensor baseline drifts. Rapid RH changes (∼20%/min) generate significant and instant changes in sensor signal, and the sensors consistently take up to 40 min to recover their original values after such a rapid RH change. In contrast, slow RH changes (∼0.1%/min) had little effect on sensor response. To test the performance of the miniaturised O3 device for real-world applications, the O3 sensors were employed for (i) laboratory experiments to measure O3 loss by seawater uptake and (ii) air quality monitoring over an 18-day period. It was found that ozone uptake by seawater was linear to the volume of linoleic acid on a sea surface microlayer and the calculated uptake coefficients based on sensor measurements were close to those from previous studies. For the 18-day period of air quality monitoring the corrected data from the O3 sensor was in a good agreement with those obtained by reference UV O3 analyser with an r2 of 0.83 (n = 8502). The novelty of this study is that the electrochemical O3 sensor was comprehensively investigated in O3 measurements in both laboratory and ambient air quality monitoring and it can to be a miniaturised alternative for conventional O3 monitoring devices due to its low cost, low power-consumption, portable and simple-conduction properties.Download high-res image (225KB)Download full-size image

•Microfluidic derivatization lab-on-a-chip integrates chemical reactor, heater, and evaporator functions with high derivatization efficiency.•Microfluidic derivatization reduces sampling preparation and produces a solution ready for GC analysis without any further treatment.•Microfluidic lab-on-a-chip derivatization technique has been employed in gaseous carbonyl analyses.We present a microfluidic lab-on-a-chip derivatization technique for the analysis of gaseous carbonyl compounds using O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA) as the derivatizing reagent. The novel microfluidic lab-on-a-chip derivatization technique has been developed to measure nmol per mole (ppbv) mixing ratios of gaseous carbonyl compounds, which are of particular importance to atmospheric chemistry. The technique utilised a planar glass microreactor comprising three inlets and one outlet, gas and fluid splitting and combining channels, mixing junctions, and a 2.0 m long, 620 μm internal diameter reaction microchannel. The microreactor integrated three functions, providing: (1) a gas and liquid mixer and reactor, (2) reagent heating, and (3) sample pre-concentration. The concentration of derivatization solution, the volumetric flow rates of the incoming gas sample and PFBHA solution, and the temperature of the microreactor were optimised to achieve a near real-time measurement. The enhanced phase contact area-to-volume ratio and the high heat transfer rate in the microreactor resulted in a fast and high efficiency derivatization reaction, generating an effluent stream which was ready for direct introduction to GC–MS. Good linearity was observed for eight carbonyl compounds over the measurement ranges of 1–500 ppbv when they were derivatized under optimal reaction conditions. The method detection limits (MDLs) were below 0.10 nmol mol−1 for most carbonyls in this study, which is below or close to their typical concentrations in clean ambient air. The performance of the technique was assessed by applying the methodology to the quantification of glyoxal (GLY) and methylglyoxal (MGLY) formed during isoprene photo-oxidation in an outdoor photoreactor chamber (EUPHORE). Good agreements between GLY and MGLY measurements were obtained comparing this new technique with Fourier Transform InfraRed (FTIR), which provides support for the potential effectiveness of the microfluidic technique for gaseous measurements.

We describe the development of a compact comprehensive two-dimensional gas chromatograph suitable for the measurement of biogenic VOCs in the atmosphere at part per billion mixing ratios. The design seeks to minimise instrument size and power consumption and maximise portability and autonomy. The instrument concept is to achieve high analyte selectivity for complex VOC mixture analysis using comprehensive two-dimensional GC (GC×GC), rather than hyphenation with larger more expensive detectors such as MS. Key features of the analytical approach are a custom-built miniature thermal desorption trap to collect and concentrate VOCs from the sample gas stream, a copper conducting direct column heating system and a valve-modulated interface to enable GC×GC. The high power and large form-factor turbulent GC oven is replaced by direct column heating (and cooling below ambient) by thermal transfer from copper bobbin holders with heating and cooling input from Peltier devices. The combination of two independent copper bobbins allows for independent control of the two columns needed for comprehensive GC. A heated two position 1/16′′ diaphragm valve is used to enable flow modulation between two columns, with analyte detection at the outlet of the second column using a miniaturised low cost photo-ionisation detector. The instrument sub-components are controlled by a Compact RIO computer (National Instruments) and purpose designed software written in LabVIEW allowing autonomous measurements. The complete system weighs 15 kg, is around the size of a desktop computer and has a mean power demand of 112 W when battery powered. Results on the sensitivity and linearity for isoprene collection and analysis of standard gas mixtures are presented along with a discussion of limiting factors that hinder field device performance.

A microfluidic lab-on-chip derivatisation technique has been optimized to achieve a rapid, automated and sensitive determination of ambient gaseous formaldehyde when used in combination with GC-MS. The method used a Pyrex micro-reactor comprising three inlets and one outlet, gas and fluid splitting and combining channels, mixing junctions, and a 2.0 m long, 620 μm internal diameter reaction micro-channel. The micro-reactor integrated three functions, that of: (1) mixer and reactor, (2) heater, and (3) preconcentrator. The flow rates of the gas sample and derivatisation solution and the temperature of the micro-reactor were optimized to achieve a near real-time measurement with a rapid and high efficiency derivatisation step following gas sampling. The enhanced phase contact area-to-volume ratio and the high heat transfer rate in the micro-reactor resulted in a fast and high efficiency derivatisation reaction. Calibration showed good linearity in the range of 26 to 331 ppb with correlation coefficients R2 = 0.988 and 0.997 for PFPH and PFBHA derivatives. For low gas phase formaldehyde mixing ratios (<26 ppb) the derivatisation solution could be repeatedly recycled through the chip enabling pre-concentration of the derivative – hydrazone. The calibration curves for this recycling approach also showed good linearity from 4.0 to 26 ppb with method detection limits (MDLs) of 2.1 ppb and 1.1 ppb for PFPH and PFBHA derivatives. The feasibility of the technique was assessed using measurements of laboratory ambient air, with formaldehyde the predominant carbonyl compound at a 12.5 ppb level. The proof of principle experiments demonstrated the potential of the approach for on-line measurements of other carbonyls including acetaldehyde, acetone and propionaldehyde.

The classical analytical method for gaseous carbonyl measurements based on solid sorbent coated with 2,4-dinitrophenylhydrazine (DNPH) and analysis by HPLC/UV suffers from limited resolution of carbonyls with similar molecular structures and high molecular weights. In this paper, we report the development of a sensitive and reliable analytical method for simultaneous determination of 21 airborne carbonyls within the C1–C9 range. Carbonyls were collected on a sampling tube filled with 100 mg Tenax TA (60–80 mesh) sorbent coated with 1 μmol pentafluorophenyl hydrazine (PFPH), followed by solvent desorption and analysis by gas chromatography (GC)/mass spectrometry (MS). Common carbonyl gases including formaldehyde, acetaldehyde, butyraldehyde, hexaldehyde and benzaldehyde at ppbv levels were collected with efficiency greater than 90% onto sampling tubes at a flow rate of 100 mL min−1. The limits of detection (LODs, signal/noise = 3) of the tested carbonyls were in the range of 0.08–0.20 ppbv for a sampled volume of 24.0 L. These limits are less than or comparable with those that can be obtained using the DNPH–HPLC method. The method has been field-tested both in ambient air of York and in diluted cigarette smoke. Comparing field tests with the classical DNPH–HPLC method, good agreement was displayed between the two methods for the same carbonyls, but with more carbonyl species detected by the PFPH–GC/MS method. The PFPH–GC/MS method provides better molecular separation for carbonyls with similar structures, is highly sensitivity and gives confirmation of identification by structures when detected using MS.

The classical analytical method for gaseous carbonyl measurements based on solid sorbent coated with 2,4-dinitrophenylhydrazine (DNPH) and analysis by HPLC/UV suffers from limited resolution of carbonyls with similar molecular structures and high molecular weights. In this paper, we report the development of a sensitive and reliable analytical method for simultaneous determination of 21 airborne carbonyls within the C1–C9 range. Carbonyls were collected on a sampling tube filled with 100 mg Tenax TA (60–80 mesh) sorbent coated with 1 μmol pentafluorophenyl hydrazine (PFPH), followed by solvent desorption and analysis by gas chromatography (GC)/mass spectrometry (MS). Common carbonyl gases including formaldehyde, acetaldehyde, butyraldehyde, hexaldehyde and benzaldehyde at ppbv levels were collected with efficiency greater than 90% onto sampling tubes at a flow rate of 100 mL min−1. The limits of detection (LODs, signal/noise = 3) of the tested carbonyls were in the range of 0.08–0.20 ppbv for a sampled volume of 24.0 L. These limits are less than or comparable with those that can be obtained using the DNPH–HPLC method. The method has been field-tested both in ambient air of York and in diluted cigarette smoke. Comparing field tests with the classical DNPH–HPLC method, good agreement was displayed between the two methods for the same carbonyls, but with more carbonyl species detected by the PFPH–GC/MS method. The PFPH–GC/MS method provides better molecular separation for carbonyls with similar structures, is highly sensitivity and gives confirmation of identification by structures when detected using MS.Download full-size image

We describe the development of a compact comprehensive two-dimensional gas chromatograph suitable for the measurement of biogenic VOCs in the atmosphere at part per billion mixing ratios. The design seeks to minimise instrument size and power consumption and maximise portability and autonomy. The instrument concept is to achieve high analyte selectivity for complex VOC mixture analysis using comprehensive two-dimensional GC (GC×GC), rather than hyphenation with larger more expensive detectors such as MS. Key features of the analytical approach are a custom-built miniature thermal desorption trap to collect and concentrate VOCs from the sample gas stream, a copper conducting direct column heating system and a valve-modulated interface to enable GC×GC. The high power and large form-factor turbulent GC oven is replaced by direct column heating (and cooling below ambient) by thermal transfer from copper bobbin holders with heating and cooling input from Peltier devices. The combination of two independent copper bobbins allows for independent control of the two columns needed for comprehensive GC. A heated two position 1/16′′ diaphragm valve is used to enable flow modulation between two columns, with analyte detection at the outlet of the second column using a miniaturised low cost photo-ionisation detector. The instrument sub-components are controlled by a Compact RIO computer (National Instruments) and purpose designed software written in LabVIEW allowing autonomous measurements. The complete system weighs 15 kg, is around the size of a desktop computer and has a mean power demand of 112 W when battery powered. Results on the sensitivity and linearity for isoprene collection and analysis of standard gas mixtures are presented along with a discussion of limiting factors that hinder field device performance.

A microfluidic lab-on-chip derivatisation technique has been optimized to achieve a rapid, automated and sensitive determination of ambient gaseous formaldehyde when used in combination with GC-MS. The method used a Pyrex micro-reactor comprising three inlets and one outlet, gas and fluid splitting and combining channels, mixing junctions, and a 2.0 m long, 620 μm internal diameter reaction micro-channel. The micro-reactor integrated three functions, that of: (1) mixer and reactor, (2) heater, and (3) preconcentrator. The flow rates of the gas sample and derivatisation solution and the temperature of the micro-reactor were optimized to achieve a near real-time measurement with a rapid and high efficiency derivatisation step following gas sampling. The enhanced phase contact area-to-volume ratio and the high heat transfer rate in the micro-reactor resulted in a fast and high efficiency derivatisation reaction. Calibration showed good linearity in the range of 26 to 331 ppb with correlation coefficients R2 = 0.988 and 0.997 for PFPH and PFBHA derivatives. For low gas phase formaldehyde mixing ratios (<26 ppb) the derivatisation solution could be repeatedly recycled through the chip enabling pre-concentration of the derivative – hydrazone. The calibration curves for this recycling approach also showed good linearity from 4.0 to 26 ppb with method detection limits (MDLs) of 2.1 ppb and 1.1 ppb for PFPH and PFBHA derivatives. The feasibility of the technique was assessed using measurements of laboratory ambient air, with formaldehyde the predominant carbonyl compound at a 12.5 ppb level. The proof of principle experiments demonstrated the potential of the approach for on-line measurements of other carbonyls including acetaldehyde, acetone and propionaldehyde.