Miniaturized micromachined gas chromatography with universal and selective detectors for targeted volatile compounds analysis

doi:10.1016/j.chroma.2018.08.064

Journal of Chromatography A

Volume 1573, 26 October 2018, Pages 151-155

https://doi.org/10.1016/j.chroma.2018.08.064 Get rights and content

Highlights

•
Compact, transportable analytical system comprising three detectors coupled to a micromachined gas chromatograph.
•
Universal and selective detectors provide enhanced selectivity, sensitivity, and confirmatory capability.
•
Relevant and difficult analyses of volatile organic compounds are demonstrated.

Abstract

An effective analytical strategy for targeted analysis of volatile organic compounds which combines two orthogonal separation mechanisms and multiple tunable detection in a compact transportable analytical system is introduced. This strategy uses a commercially available micromachined gas chromatograph comprising a micromachined on-board thermal conductivity detector. The chromatograph capability is enhanced by incorporating a modified diode array detector and a radio frequency modulated ion mobility spectrometry microfabricated electromechanical system. The analytical platform offers powerful detection capabilities of individual compounds and various classes of volatile organic compounds with improved provisional confirmatory capability. The transportable micromachined gas chromatograph employs field replaceable conventional capillary columns for the separation of analytes. The use of a silicon micromachined sample introduction device affords fast injection to minimize band broadening with fast chromatographic separation rendered in the order of minutes. Advantaged synergy also includes leveraging the resolving power of gas chromatography to minimize charge exchange in the ionization chamber of the differential mobility spectrometer for improved detector performance. Performance of this scalable and transportable analytical system is demonstrated with relevant volatile compounds such as acetaldehyde, acetone, carbon disulfide, benzene, and ethyl butyrate having a day-to-day variability less than 5% and with a high degree of reliability.

Introduction

Quantitative analysis of targeted analytes in complex matrices using chromatographic techniques is problematic unless the technique is selective enough to provide sufficient analytical resolution to allow determination of compounds of interest. Although multidimensional gas chromatography offers very high chromatographic selectivity, such approaches often require specialized skills for method development, operation, and maintenance [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]]. Detection systems for GC were first conceived with the single purpose of monitoring column effluent to determine presence and amount of solute eluted from the column. For instance, a thermal conductivity detector (TCD) responds to virtually all compounds, and a flame ionization detector (FID) simply measures ions generated in a flame. An effective approach to tackle the need for trace analysis in a complex matrix is the use of detectors that are capable of providing specific analyte properties [[11], [12], [13], [14], [15]].

Over the last decades, miniaturization is a key and sustained theme for analytical instrument development to address crowded laboratories, bench space, or to enable field, near-line, and at-line deployments. While this effort is purposeful and relevant, more often than not, miniaturization has resulted in degraded analytical capabilities or reduced flexibility of an analytical platform for broad spectrum applications [16,17].

A highly capable, scalable, and portable analytical platform is introduced here which achieves universal detection along with sequential tuneable selective detection in a miniaturized readily transportable platform footprint. The system comprises the following elements and features:

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Micromachined gas chromatograph described elsewhere provides a minimal footprint [[18], [19], [20]].
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Micromachined thermal conductivity detector provides a universal response to virtually all analytes in addition to extending compound linear range for target compounds when compared to popular portable detectors such as the photoionization detector.
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Microelectromechanical systems (MEMS)-based radio frequency modulated ion mobility spectrometry (differential mobility spectrometry; μDMS), which uses the non-linear mobility dependence in strong radio frequency electric fields to filter positive and negative ions generated in a Ni⁶³ ionization source [[21], [22], [23], [24], [25], [26], [27]].
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Diode array detector (DAD) designed for liquid chromatography; repurposed for use with contemporary capillary gas chromatography for selective detection of compounds with chromophores [[28], [29], [30], [31], [32], [33]].

Confirmatory detection can be realized if the target compounds are detected by both selective detectors, and by three detectors if the analyte’s concentration is sufficiently high. With this approach, the goals of transportability and platform scalability are achieved, without compromising analytical capability or system flexibility. Temporal and spatial separation mechanisms are realized in a single transportable analytical system. Advantaged synergy also includes leveraging the resolving power of gas chromatography to minimize charge exchange in the ionization chamber of the differential mobility spectrometer for improved detector performance. The incorporation of three atmospheric pressure detectors affords fast system start up and ease of maintenance. We prove the performance of this novel transportable analytical system to be highly reliable and useful with relevant compounds and with examples of practical applications.

Section snippets

Experimental

An Agilent CP-4900 micromachined gas chromatograph (Agilent Technologies, Middelburg, the Netherlands) was used as the analytical platform. A column module comprising an 8 m × 0.25 mm−i.d. × 1 μm column coated with 5% phenyl methyl polydimethylsiloxane stationary phase (VF-5 ms, Agilent Technologies) was employed. The column was interfaced with a micromachined silicon injector (Agilent Technologies). The inlet temperature was operated at 100 °C and an injection time of 300 ms was used

Results and discussion

Injection bandwidths are a critical optimization parameter for high-speed and miniaturized chromatography systems. The commercially available micromachined injector is a time-based injector with its design traced back to the seminal work of Terry et al. [18,19]. To ensure the performance of the injector was not compromised due to the substantial addition of hardware and modifications made downstream from the injector, an injection profile study was conducted. The model compounds chosen for

Conclusions

A highly flexible, scalable, and transportable analytical platform suitable for a broad suite of applications was constructed and its performance has been probed using a range of volatile compounds. The strategy of combining universal and selective detectors in a micromachined GC platform to enhance system applicability and asset utilization is a highly beneficial one. This strategy demonstrated miniaturization can take place without compromising system capability and performance. The

Acknowledgments

The authors would like to acknowledge Prof Paul Haddad, of the Australian Centre for Research on Separation Science (ACROSS) for his support and guidance. Special thanks to Dr Tonya Stockman, Dr Wayde Konze of Dow Chemical, Ms Shanya Kane and Mr Dave Judd for their support and encouragement. Dr Rannan Miller, of MIT and Dr Erkinjon Nazarov of Draper Laboratories are acknowledged for their fruitful discussions on μDMS. Dr Jos Curvers is recognized for his valuable advice on micromachined silicon

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Miniaturized micromachined gas chromatography with universal and selective detectors for targeted volatile compounds analysis☆

Highlights

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgments

Anal. Chim. Acta

J. Chromatogr. A

Trends Analyt. Chem.

J. Chromatogr. A

J. Chromatogr. A

J. Chromatogr. A

J. Chromatogr. A

J. Chromatogr. A

Multidimensional gas chromatography: advances in instrumentation, chemometrics, and applications

Anal. Chem.

A simplified approach in flow controlled multidimensional gas chromatography

Anal. Methods

Multidimensional Chromatography

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Anal. Chem.

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J. Sep. Sci.

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Anal. Methods

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A review: GC method development and validation

Int. J. Anal. Bioanal. Chem