Among a number of gas analyzers, portable gas chromatography (GC) systems created by the integration of microfabricated components are promising candidates for rapid and on-site analysis of a number of complex chemical mixtures. This Feature provides a snapshot of the progress made in developing micro gas chromatography (μGC) systems in the last 4 decades. In particular, we discuss the development of microfabricated preconcentrators, separation columns, and detectors. Furthermore, we review different stationary phase materials used to coat the separation columns and the major efforts toward the development of an integrated μGC.

Micro Gas Chromatography: An Overview of Critical Components and Their Integration

In recent years, the need for measurement and detection of samples in situ or with very small volume and low concentration (low and sub-parts per billion) is a cause for miniaturizing systems via microelectromechanical system (MEMS) technology. Gas chromatography (GC) is a common technique that is widely used for separating and measuring semi-volatile and volatile compounds. Conventional GCs are bulky and cannot be used for in situ analysis, hence in the past decades many studies have been reported with the aim of designing and developing chip-based GC. The focus of this review is to follow and investigate the development and the achievements in the field of chip-based GC and its components from the beginning up to the present.

Through the years with on-a-chip gas chromatography: a review

This paper reports a unique GC-on-chip module comprising a monolithically integrated semi-packed micro separation column (μSC) and a highly sensitive micro helium discharge photoionization detector (μDPID). While semi-packed μSC with atomic layer deposited (ALD) alumina as a stationary phase provides high separation performance, the μDPID implemented for the first time in a silicon–glass architecture inherits the desirable features of being universal, non-destructive, low power consumption (1.4 mW), and responsive. The integrated chip is 1.5 cm × 3 cm in size and requires a two-mask fabrication process. Monolithic integration alleviates the need for transfer lines between the column and the detector which improves the performance of the individual components with overall reduced fabrication and implementation costs. The chip is capable of operating under the isothermal as well as temperature and flow programming conditions to achieve rapid chromatographic analysis. The chip performance was investigated with two samples: 1) a multi-analyte gas mixture consisting of eight compounds ranging from 98 °C to 174 °C in boiling point and 2) a mixture containing higher alkanes (C9–C12). Our experiments indicate that the chip is capable of providing rapid chromatographic separation and detection of these compounds (<1 min) through the optimization of flow and temperature programming conditions. The GC-on-chip demonstrated a minimum detection limit of ~10 pg which is on a par with the widely used destructive flame ionization detector (FID).

/pdf/gc-on-chip-integrated-column-and-photoionization-detector-5ujop4d2q8.pdf

GC-on-chip: integrated column and photoionization detector

Miniaturized gas chromatography (µGC) systems hold potential for the rapid analysis of volatile organic compounds (VOCs) in an extremely compact and low-power enabled platform. Here, we utilize microfabrication technology to demonstrate the single chip integration of the key components of a µGC system in a two-step planar fabrication process. The 1.5 × 3 cm microfluidic platform includes a sample injection unit, a micromachined semi-packed separation column (µSC) and a micro-helium discharge photoionization detector (µDPID). The sample injection unit consists of a T-shaped channel operated with an equally simple setup involving a single three-way fluidic valve, a micropump for sample loading and a carrier gas supply for subsequent analysis of the VOCs. The innovative sample injection technique described herein requires a loading time of only a few seconds and produces sharp and repeatable sample pulses (full width at half maximum of approximately 200 ms) at a carrier gas flow rate that is compatible with efficient chromatographic separation. Furthermore, our comprehensive characterization of the chip reveals that a wide variety of VOCs with boiling points in the range of 110–216 °C can be analyzed in less than 1 min by optimizing the flow and temperature programming conditions. Moreover, the analysis of four VOCs at the concentration level of one part per million in an aqueous sample (which corresponds to a headspace concentration in the lower parts-per-billion regime) was performed with a sampling time of only 6 s. The µDPID has demonstrated a linear dynamic range over three orders of magnitude. The system presented here could potentially be used to monitor hazardous VOCs in real time in industrial workplaces and residential settings. A chip-sized gas chromatograph can detect hazardous volatile organic compounds in seconds. To avoid thermal crosstalk, the three main components of a microscale gas chromatograph—injector, separation column and mass detector—are normally placed on separate chips. Dr. Masoud Agah and co-workers from Virginia Polytechnic Institute and State University, United States, have combined these components onto a single chip using an innovative setup. The team fabricated a microfluidic injector and alumina-based column in close proximity to reduce analysis time. As samples elute from the column, they are photoionized by a helium-based detector that spots picograms of organic molecules without relying on thermal pre-concentration. The integrated device detects contaminants such as chlorobenzene and xylene with an extremely sharp chromatographic peak—indicating that thermal effects are minimized—and at speeds that allow real-time monitoring of liquids and air.

/pdf/chip-scale-gas-chromatography-from-injection-through-2dfhk34t0a.pdf

Chip-scale gas chromatography: From injection through detection

A controllable and high-yield surface functionalization of silicon microchannels using layer-by-layer (LbL) self-assembly of SiO2 nanoparticles (SNPs) is presented. The application of SNPs (45 nm average diameter) coating as a stationary phase for chromatographic separation is also demonstrated with surface functionalization using chloroalkylsilanes. This method facilitates a simple, low-cost, and parallel processing scheme that also provides homogeneous and stable nanoparticle-based stationary phases with ease of control over the coating thickness. The SNP-functionalized microfabricated columns with either single capillary channels (1 m long, 150 μm wide, 240 μm deep) or very narrow multicapillary channels (25 cm long, 30 μm wide, 240 μm deep, 16 parallel channels) successfully separated a multicomponent gas mixture with a wide range of boiling points with high reproducibility.

/pdf/highly-stable-surface-functionalization-of-microgas-iptwdac3dr.pdf

Highly stable surface functionalization of microgas chromatography columns using layer-by-layer self-assembly of silica nanoparticles.

Silica sputtering as a novel collective stationary phase deposition for microelectromechanical system gas chromatography column: feasibility and first separations.

In a previous study, a new stationary phase deposition technique for micromachined gas chromatography columns was presented. The rerouting of the sputtering technique to this purpose enabled collective and reproducible fabrication of microcolumns in a silicon wafer. Silica-sputtered micromachined columns showed promising separations of light alkanes in isothermal conditions. In order to go beyond the limitations of isothermal separations, the columns were equipped with sputtered platinum filaments to enable high-speed and low-power temperature programming. The separation performances of temperature-programmed silica- or graphite-sputtered microcolumns were investigated: a separation of light alkanes (C1–C5) was completed in 9 s, and heavier alkanes (until C9), cyclic, isomeric, and unsaturated hydrocarbons were also successfully separated. Versatility of these microcolumns was demonstrated with a high-temperature C1–C2 separation and a C1–C5 separation with nitrogen as carrier gas instead of helium. By ma...

Temperature-programmed sputtered micromachined gas chromatography columns: an approach to fast separations in oilfield applications.

In the context of refinery gas testing, we studied the potential of a micro-gas chromatograph (μGC). For this purpose, we fabricated a new type of gas microvalve, based on a polyetheretherketone (PEEK) membrane, which is suitable for the harsh environment of natural gas. Experimental results are presented along with simulations to describe and discuss the static and dynamic behaviors of such a device.

Micro gas chromatograph for harsh refinery gas environment: Microvalves based on PEEK membranes

A first digital microfluidic system has been fabricated that allows to perform programmable and reconfigurable step by step manipulations of gas and volatile compounds. While digital microfluidic platforms have been extensively reported for the manipulation of droplets, such an approach for gaseous samples have not been proposed so far. The programmable system relies on interconnected temperature controlled silicon chips filled with adsorbent that can trap and release analytes. As a proof of concept, all the key elementary operations are demonstrated with alkanes ranging from n-hexane to n-nonane: the trapping, release, moving, adding (mixing) and subtracting (separating) of gaseous analytes. Following the example of digital microfluidic droplet manipulation, such system could open in the future a new field of technologies and applications regarding gas or volatile compounds samples preparation and analysis.

A digital microfluidic platform for gaseous samples : First system and demonstration of elementary operations

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Papers

Silica sputtering as a novel collective stationary phase deposition for microelectromechanical system gas chromatography column: feasibility and first separations.

Temperature-programmed sputtered micromachined gas chromatography columns: an approach to fast separations in oilfield applications.

Micro gas chromatograph for harsh refinery gas environment: Microvalves based on PEEK membranes

A digital microfluidic platform for gaseous samples : First system and demonstration of elementary operations