Smart three-dimensional gas chromatography

Ionic Liquid-Based Hybrid Gel Microcolumns for Enhanced Narcotic Detection in Portable Micro-Gas Chromatography

As the societal issue of increasing global illicit drug usage emerges, there is a growing demand for more portable and versatile drug detectors. Traditional drug analysis techniques such as gas chromatography (GC), liquid chromatography (LC), and Fourier transform infrared spectroscopy (FTIR) face significant challenges in adapting to diverse real-world applications due to their size, cost, and power requirements. While advancements have been made in the development of on-site drug detection methods such as fluorescence, stereoresonance energy transfer (FRET), colorimetric, electrochemical sensing, and lateral flow assays (LFAs), their reliance on specific reactive materials poses limitations in effectively detecting a wide range of narcotics. Therefore, this study proposes the development of specialized microcolumns with optimized stationary phases for next-generation portable microfabricated GC-based narcotic detectors. The stationary phase consists of a hybrid gel incorporating the ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and OV-1. The stationary phase not only enhances interactions between drug analytes but also demonstrates improved separation characteristics among various narcotic substances. Additionally, the principles of the separation results were validated through density functional theory (DFT) analysis, and the effective separation of over seven types of narcotics was demonstrated through temperature optimization. This research lays the groundwork for the advancement of next-generation portable drug analyzers, offering significant potential in the field.

In-Line Detection with Microfluidic Bulk Acoustic Wave Resonator Gas Sensor for Gas Chromatography

A microfluidic film bulk acoustic wave resonator gas sensor (mFBAR) adapted specifically as an in-line detector in gas chromatography was described. This miniaturized vapor sensor was a non-destructive detector with very low dead volume (0.02 μL). It was prepared by enclosing the resonator in a microfluidic channel on a chip with dimensions of only 15 mm × 15 mm × 1 mm. The device with polymer coating showed satisfactory performance in the detection of organophosphorus compound, demonstrating a very low detection limit (a dozen parts per billion) with relatively short response time (about fifteen seconds) toward the simulant of chemical warfare agent, dimethyl methylphosphonate. The in-line detection of the mFBAR sensor with FID was constructed and employed to directly measure the concentration profile on the solid surface by the mFBAR with the controlled concentration profile in the mobile phase at the same time. The difference of peak-maximum position between mobile phase and solid phase could be a convenient indicator to measure mass transfer rate. With the response of the mFBAR and FID obtained in one injection, an injection mass-independent parameter can be calculated and used to identify the analyte of interest.

Latest Trends on the Future of Three-Dimensional Separations in Chromatography

Separation and characterization of complex mixtures are of crucial importance in many fields, where extremely high separation power is required. Three-dimensional separation techniques can offer a path toward achieving high peak capacities. In this Review, online three-dimensional separation systems are discussed, including three-dimensional gas chromatography, and hyphenated combinations of two-dimensional gas chromatography with liquid chromatography or supercritical-fluid chromatography. Online comprehensive two-dimensional liquid chromatography provides detailed information on complex samples and the need for higher peak capacities is pushing researchers toward online three-dimensional liquid chromatography. In this review, an overview of the various combinations are provided and we discuss and compare their potential performance, advantages, perspectives, and results obtained during the most recent 10-15 years. Finally, the Review will discuss a novel approach of spatial three-dimensional liquid separation to increase peak capacity.

Progressive Cellular Architecture in Microscale Gas Chromatography for Broad Chemical Analyses

Gas chromatography is widely used to identify and quantify volatile organic compounds for applications ranging from environmental monitoring to homeland security. We investigate a new architecture for microfabricated gas chromatography systems that can significantly improve the range, speed, and efficiency of such systems. By using a cellular approach, it performs a partial separation of analytes even as the sampling is being performed. The subsequent separation step is then rapidly performed within each cell. The cells, each of which contains a preconcentrator and separation column, are arranged in progression of retentiveness. While accommodating a wide range of analytes, this progressive cellular architecture (PCA) also provides a pathway to improving energy efficiency and lifetime by reducing the need for heating the separation columns. As a proof of concept, a three-cell subsystem (PCA3mv) has been built; it incorporates a number of microfabricated components, including preconcentrators, separation columns, valves, connectors, and a carrier gas filter. The preconcentrator and separation column of each cell are monolithically implemented as a single chip that has a footprint of 1.8 × 5.2 cm2. This subsystem also incorporates two manifold arrays of microfabricated valves, each of which has a footprint of 1.3 × 1.4 cm2. Operated together with a commercial flame ionization detector, the subsystem has been tested against polar and nonpolar analytes (including alkanes, alcohols, aromatics, and phosphonate esters) over a molecular weight range of 32-212 g/mol and a vapor pressure range of 0.005-231 mmHg. The separations require an average column temperature of 63-68 °C within a duration of 12 min, and provide separation resolutions >2 for any two homologues that differ by one methyl group.

A miniature closed-loop gas chromatography system

This paper reports the characterization of a miniaturized circulatory column system that is capable of magnifying the effective column length by forming a circulatory loop with chip-scale columns, thus ultimately achieving high-efficiency target separation. The circulatory column system is composed of a tandem of 25 cm microcolumns and six valves for fluidic flow control in order to enable chromatographic separation in circulatory motions while requiring only 5.5 kPa of pressure, which current micropumps are currently capable of supplying. The developed column system (1) successfully demonstrated 16 times elongation of a virtual column length up to 800 cm by only utilizing two 25 cm microcolumns, which is the longest column length reported by any MEMS-scale functioning GC column, (2) achieved a high theoretical plate number of 68,696 with pentane circulating after 15.5 circulatory cycles, which corresponds to the plate number per length-pressure of 1611 plate m(-1) kPa(-1), the highest record reported yet, and (3) demonstrated successful separation of target molecules during circulation by utilizing a pentane/hexane mixture, resulting in magnification of the two corresponding peaks via circulation.

A Microfluidic-Based Fabry-Pérot Gas Sensor

We developed a micro-gas detector based on a Fabry-Pérot (FP) cavity embedded in a microfluidic channel. The detector was fabricated in two steps: a silicon substrate was bonded to a glass slide curved with a micro-groove, forming a microfluidic FP cavity; then an optical fiber was inserted through a hole drilled at the center of the groove into the microfluidic FP cavity, forming an FP cavity. The light is partially reflected at the optical fiber endface and the silicon surface, respectively, generating an interference spectrum. The detection is implemented by monitoring the interference spectrum shift caused by the refractive index change of the FP cavity when a gas analyte passes through. This detection mechanism (1) enables detecting a wide range of analytes, including both organic and inorganic (inertia) gases, significantly enhancing its versatility; (2) does not disturb any gas flow so that it can collaborate with other detectors to improve sensing performances; and (3) ensures a fast sensing response for potential applications in gas chromatography systems. In the experiments, we used various gases to demonstrate the sensing capability of the detector and observed drastically different sensor responses. The estimated sensitivity of the detector is 812.5 nm/refractive index unit (RIU) with a detection limit of 1.2 × 10⁻⁶ RIU assuming a 1 pm minimum resolvable wavelength shift.