In this paper, we propose for the first time a microinjector based on MEMS technology using monocrystalline silicon as a deformation membrane. This injector integrates six micro-valves and one sample loop. Compared to traditional polymer membranes, monocrystalline silicon is thermally stable and does not deform during the fabrication process. The test results show that the micro-injector achieves the injection of a $1.5 \mu \mathrm{L}$ gas mixture.

In this work, we reported a micro thermal conductivity detector with diffusion channels (mu TCD-D). The hot wires of mu TCD-D are prepared in the diffusion channels to reduce the effect of forced convection and increase the proportion of gas thermal conduction in the total heat dissipation so that the sensitivity of the detector to the low-concentration small molecule gases is improved significantly, which may be found interested by the general readers. Compared to the micro thermal conductivity detector with traditional straight channel design (mu TCD-S), the proportion of gas thermal conduction in the total heat dissipation is increased from 88.23 % to 94.94 % and the proportion of forced convection is decreased from 7.90 % to 0.89 % which leads to a better sensitivity to gas thermal conductivity. Experimental results show that the response of mu TCD-D for propane is increased by 80.84 % with a concentration of 5000 ppm compared to mu TCD-S. mu TCD-D achieve the detection of C2-C4 n-alkanes mixture at concentration as low as 5 ppm indicated that mu TCD-D has ppm level detection limit.

Due to the high conformal films, atomic layer deposition (ALD) alumina has been used as a uniform stationary phase or support layer of stationary phase for micro gas chromatographic column. However, the severe tailing of chromatographic peaks appears when ALD alumina is used as the stationary phase. Recently, an H-diffusion model was proposed to explain the H accumulation phenomenon of ALD alumina films. Compared with the normal-resistance silicon substrates, the ALD alumina films based on low-resistance silicon substrates have fewer H impurities, which may further improve the tailing of chromatographic peaks and the theoretical number of plates. In this paper, a micro gas chromatographic column based on the low-resistance silicon (LR-μGCC) substrate (resistivity, 0.001–0.005 Ω·cm) using alumina deposited by atomic layer deposition as the stationary phase is reported. Compared with normal-resistance silicon substrates (resistivity, 1–10 Ω·cm), the micro gas chromatographic columns (μGCC) prepared on low-resistance silicon substrates have a higher separation performance. The test results showed that the LR-μGCC increased the theoretical plate number of alkane mixtures (n-hexane, n-octane, n-nonane, and n-decane) by 20.9

A micro gas chromatographic column with mesoporous surface micro column array prepared by anodization method was proposed.A porous support layer with a characteristic pore size of about 30 nm inside the chromatographic column was prepared in situ using anodization method,and a uniform alumina stationary phase was deposited on the mesoporous support layer using atom layer deposition(ALD)technique.The existence of a mesoporous support layer increased surface area of the chromatographic column,thereby increasing the total amount of stationary phase loading and enhancing column capacity,which facilitated chromatographic separation.The test results showed that the porous support layer significantly reduced the longitudinal molecular diffusion and mass transfer resistance of the micro gas chromatographic column,and significantly increased the number of theoretical plates(n-nonane increased by 290.2%).Furthermore,column efficiency of the chromatographic column was less affected by flow rate,which was conducive to rapid separation of heavy hydrocarbon mixtures.

In this study, an ON/OFF type micro-valve with a sandwich (glass-silicon-glass) structure was designed and fabricated based on the micro-electro-mechanical system (MEMS) technique. The deformable membrane of this micro-valve was prepared on the silicon on insulator (SOI) substrate and sealed using Si-Si bonding and anodic bonding methods. The micro-valve had high-temperature stability and was suitable for integration with other gas chromatography components. The deformable membrane with a thickness of 10 mu m was processed on the top silicon of the SOI substrate. The flow control of the micro-valve could be achieved by changing the driving pressure applied to the deformable membrane to deform it. Compared with polymer membranes, the deformable membrane prepared on the top layer silicon of SOI had better temperature stability and could be released using the deep reactive ion etching technique after silicon-silicon bonding, avoiding deformation during the preparation process. In addition, due to the small gap between the membrane and the inlet/outlet holes, the dead volume of the microvalve was very small. The test results indicated that the micro-valve achieved flow control and ON/OFF functions with good repeatability.

Exhaled gas detection offers a safe, convenient, and non-invasive clinical diagnostic method for preventing the progression of diabetes to complications. In this study, gas chromatography-mass spectrometry (GC-MS) analysis and statistical methods were employed to identify four volatile organic compounds (VOCs) that exhibit significant differences between patients with Type 2 Diabetes Mellitus (T2DM) and those with Diabetic Complications (DC). Compared with those in DC patients, the concentrations of isoprene, acetone, and isopropanol were found to be higher in T2DM patients, whereas the concentrations of tetradecane were lower. Based on the sets of these four VOCs, a voting classifier was constructed using three machine learning methods-Support Vector Machine (SVM), Random Forest (RF) and K-Nearest Neighbors (KNN). The accuracy, sensitivity, specificity, F1 score, and AUC value of the voting classifier are 90.8%, 92.1%, 89.5%, 0.909, and 0.988, respectively, in distinguishing between T2DM and DC. This diagnostic method of exhaled gas detection provides an important foundation for preventing DC and monitoring disease progression of DM.

A monolithic integrated gas chromatography chip, consisting of a micro gas chromatography column (mu GCC) and a micro helium discharge ionization detector (mu HDID) was proposed. The chip was fabricated using micro electromechanical system (MEMS) technique, and its sensitivity was improved from two aspects. On one hand, open tubular column was selected as the separation device, and the auxiliary helium channel width of mu HDID was modulated based on the microchannel width of the mu GCC to match the flow rates of mu HDID and mu GCC. On the other hand, the electrode structure inside the mu HDID collection zone was optimized, a bias electrode group around the collection electrode was constructed, and the ion collection efficiency was improved. After coating HKUST-1 as the stationary phase, the monolithic integrated gas chromatography chip could achieve baseline separation and detection of light hydrocarbon gas mixture (methane, ethane, propane, and n-butane), with a detection limit for propane as low as 25 pg. The chip could carried out test under temperature-programmed conditions, with a resolution of 9.24 for ethane and propane.

Background: As a universal gas detector, helium discharge ionization detector (HDID) can detect almost all components of interest. And due to the high ionization energy of helium and low detection limit, the combination of HDID and gas chromatography has broad application prospects in real-time monitoring. However, its application is currently limited by large volume, high power, and large helium consumption. Microminiaturized HDID can solve the problems. But the decreased zone volume will affect the sensitivity, resulting in a poor detection limit compared to the commercial HDID. Optimizing the electrode structure in the collection zone may be a feasible way. Results: In this paper, a micro helium discharge ionization detector (mu HDID) with 3D bias electrodes was fabricated by micro-electro-mechanical system (MEMS) technique. The 3D bias electrode means the mu HDID has one collection electrode and three bias electrodes in the collection zone. This design creates equipotential surfaces around the collection electrode, significantly enhancing particle collection efficiency. At the same time, the detector uses bulk excitation electrodes in the discharge zone, which has good stability and good baseline noise of 3 mu V. Testing has demonstrated the reliability of the detector, with good time repeatability and good repeatability across different chips. Additionally, the device has good linearity, with a linear dynamic range close to 5 orders of magnitude. Therefore, this is a micro detector suitable for detecting trace small molecule gases. Significance: This paper proposed the 3D bias electrodes for the first time. Compared with the 2D bias electrode, the 3D bias electrode structure makes the electric field lines point directly towards the collection electrode along the direction perpendicular to the equipotential surfaces. This electric field provides charged analytes with greater acceleration and shorter paths, making them reach the collection electrode faster. Therefore, the electrode structure has better collection efficiency, making the mu HDID has high sensitivity.

This paper reports a micro gas chromatographic column (μGCC) with in-situ growing macro-porous silicon as the stationary phase support layer. The macro-porous silicon stationary phase support layer (MPSL) with uniform thickness was fabricated in-situ on the inner surface of the μGCC channels by metal-assisted chemical etching. In order to avoid the negative effect of uneven thickness of the stationary phase, a 10 nm alumina film was deposited as the stationary phase on the MPSL using the atomic layer deposition technique. The macro-porous structure and high specific surface area of the MPSL provide longer diffusion paths and larger mass transfer interfaces for the analytes, which reduces the longitudinal gas diffusion and mass transfer resistance, thus improving the column efficiency. The μGCC with the MPSL achieved a 1306.7 % increase in the theoretical plate number and a 195.0 % improvement in the resolution for n-nonane compared with the μGCC without the MPSL.

BACKGROUND:The micro gas chromatography column (μGCC) is one of the key components of the miniaturized gas chromatography system. However, light alkanes are difficult to be separated by a micro gas chromatography column, especially for methane and ethane, because the length of μGCC is limited by the area of a silicon substrate. More importantly, the heterogeneous microchannel surface formed by silicon glass bonding causes uneven stationary phase coating and the forces between the untreated microchannel surfaces and the stationary phase materials are weak, which will prevent the improvement of separation performance. RESULTS:In this paper, a micro gas chromatography column (μGCC) with uniform HKUST-1 stationary phase is reported. Significantly, an alumina film prepared by the atomic layer deposition (ALD) technique is used to homogenize the heterogeneous microchannels. The alumina is a hydrophilic material and the alumina made by the ALD technique is uniform. The forces between hydrophilic alumina film and HKUST-1 are strong, which can greatly improve the coating uniformity of the hydrophilic stationary phase HKUST-1. The test results show that the μGCC could baseline separate the light alkane mixtures (CH4, C2H6, C3H8, and C4H10) at the high testing temperature of 120 °C. The maximum resolution of the difficult-separated methane and ethane reached 19.2, which is 108 % higher than the μGCC using the same stationary phase without homogenizing the microchannel inner surface. SIGNIFICANCE:The μGCC uses ALD alumina film to homogenize the microchannel inner surface; meanwhile, hydrophilic ALD alumina has a strong electrostatic attraction with the hydrophilic stationary phase HKUST-1. Homogeneous microchannel surface and strong electrostatic attraction are favorable to obtain uniform stationary phase which greatly improves the separation performance, resulting in a large resolution for methane and ethane. The μGCC has broad application prospects in light alkane separation.

In recent years, there has been a significant surge of interest in exploring exhaled gas detection within the context of diabetes research. This burgeoning field has attracted considerable attention due to its potential implications for the early detection and management of diabetes mellitus. Through a comprehensive synthesis of 114 pertinent scholarly works, researchers have delved into the intricate association between diabetes mellitus and exhaled gas detection. Leveraging state-of-the-art detection and analysis methodologies, including gas chromatography, mass spectrometry, spectroscopy, and sensor -based detection systems. This review provides an overview of the composition of some volatile organic compounds and their sources in the exhaled gas of diabetic patients. Furthermore, the application of machine learning -based algorithms has been scrutinized for its potential to facilitate predictive modeling of diabetes risk and associated complications. This comprehensive review also examines the national and international landscape of the development and application of exhaled gas detection methodologies in diabetes research, offering critical insights into current limitations and potential avenues for future research and application.

Foliar application of selenium (Se) is an effective method for biofortification in rice, to ensure that sufficient Se is supplied by the crop to maintain human health. In order to improve Se concentration in rice and meet the daily recommended intake for humans, a foliar Se fertilizer was applied in five regions of Liaoning and Jilin provinces, China, and its effects on rice quality, leaf morphology, and wax characteristics were assessed in field tests. The effects of alkyl polyglycosides (APG) in the Se fertilizer were evaluated, and epicuticular waxes were measured to analyze the effects of the fertilizer on plant water status. The Se fertilizer effectively enhanced organic Se levels in rice (p < 0.05), ranging from 599.8 to 2002.0 mu g kg(-1). An intake of 50 g d(-1) of Se-enriched rice can meet nutritional requirements, with total Se intake ranging from 30.0 to 100.1 mu g d(-1). The Se fertilizer increased the protein content and decreased the proportion of chalky rice (p < 0.05). APG increased the wettability of Se fertilizer on the surface of leaves, so Se could be better absorbed into the leaves and accumulate in rice. The Se fertilizer increased the epicuticular wax so that moisture loss from leaves was reduced. Mean cuticular wax thicknesses were 2.36 and 2.25 mu g cm(2) in Daohuaxiang and Wuyou 4, respectively. These results suggest a link between the quality of rice and epicuticular wax thickness, and the foliar application of Se fertilizer shows promise for increasing Se content in rice grown in Se deficient soils.

The decrease in the stagnation area in semi-packed gas chromatographic columns helps to increase the height and area of chromatographic peaks.

Breath analysis may provide a convenient and non-invasive method for clinical monitoring of chronic kidney disease (CKD) progression. However, few breath volatile organic compounds (VOCs) indicating progression of CKD have been reported. In this study, we used gas chromatography-mass spectrometry (GC-MS) for untargeted detection of breath VOCs in stage 1, 3, and 5 CKD patients. The results showed that, the levels of breath 4-heptanone, n-octane, and n-dodecane gradually increased from CKD stage 1 to stage 5, and their increasing rates from CKD stage 3 to stage 5 were higher than those from CKD stage 1 to stage 3. Gender, smoking habits, age, and body mass index (BMI) had insignificant impact on the levels of the three breath VOCs. The accuracies of the polynomial support vector machine (SVM) and K-nearest neighbour (KNN) models based on 4-heptanone + n-octane + n-dodecane combination in distinguishing CKD stages 1, 3, and 5 were 76.3% and 72.8%, respectively. The combination of 4-heptanone + n-octane + n-dodecane was superior to any single component for monitoring CKD progression. These discoveries have valuable implications for long-term clinical monitoring of CKD and improving our understanding of CKD.

A composite material was synthesized at room temperature by performing modification of the copper benzene-1,3,5-tricarboxylate (HKUST-1) metal-organic framework material by multilayer fluorinated graphene (FG). The FG-HKUST-1 composite was used as a stationary phase for a micro gas chromatography column (μGCC) fabricated using micro-electro-mechanical system (MEMS) technology. The separation results showed that the μGCC with the FG-HKUST-1 composite stationary phase achieved a baseline separation of C1-C4 in 8 min. The retention factors for C2-C4 were 2.13, 7.14, and 12.04, respectively. The maximum relative standard deviation (RSD) of the retention times was 0.14 %. The difference in the retention time between methane and ethane was 1.11 min, with a resolution of 9.2 for methane and ethane. The retention factor of ethane and the resolution of methane and ethane were increased by 166 % and 114 %. Therefore, this μGCC is promising for separating light hydrocarbons with widely differing concentrations.

We formulate a local analogue of the ghost conjecture of Bergdall and Pollack, which essentially relies purely on the representation theory of GL_2(Q_p). We further study the combinatorial properties of the ghost series as well as its Newton polygon, in particular, giving a characterization of the vertices of the Newton polygon and proving an integrality result of the slopes. In a forthcoming sequel, we will prove this local ghost conjecture under some mild hypothesis and give arithmetic applications.

A novel micro gas chromatography column (μGCC) with straight-sided elliptic microchannel cross sections was prepared by ultrafast laser-assisted chemical etching inside a glass substrate. The straight-sided elliptic cross sections resulted in a uniform distribution of the flow velocity field. This uniform distribution and the use of a microchannel with a consistent composition led to a uniform stationary phase coating. Upon the separation of a test mixture of C7–C11 alkanes, highly symmetrical chromatographic peaks were obtained. The tailing factors of the chromatographic peaks ranged from 0.95 to 1.05, which satisfies the relevant provisions of Pharmacopoeia of the People's Republic of China (ChP). The test results show that the improvement of the tailing factors is mainly due to the optimization of the cross-section structure rather than the optimization of the test conditions. Notably, due to the simple preparation processes and the low cost of the glass substrate, the total manufacturing cost of this novel μGCC is low.

BACKGROUND:The gas chromatography column is one of the key components of the gas chromatograph and typically be miniaturized using micro-electro-mechanical system (MEMS) technology. Due to the limited area of the Si wafer, the column length of micro gas chromatographic column (μGCC) is usually much smaller than that of commercial chromatographic columns. Therefore, it is always difficult to use μGCCs to separate small molecule gas components such as light hydrocarbons. More importantly, the heterogeneous microchannel surface formed by silicon glass bonding causes uneven stationary phase coating, further preventing the improvement of separation performance. RESULTS:In this paper, a novel all-glass based μGCC with 2 m length for the separation of light hydrocarbons is proposed. The microchannels of the μGCC were directly prepared in the glass substrate by ultrafast laser assisted chemical etching (ULAE). The all-glass microchannels make the coating of the hydrophilic metal-organic frameworks (MOFs) stationary phase continuously because of the homogeneous material composition. Therefore, a widely used copper based hydrophilic MOFs HKUST-1 was used as stationary phase for coating and testing. The test results show that the μGCC which is an open tubular column can realize the baseline separation of light hydrocarbons at 100 °C. And the resolution of difficult separated compounds, methane and ethane, can reach 12.98, which is 201.86 % higher than the silica-based monolithic capillary column in the relevant research. The resolution of ethane and ethylene reaches 6.81 at 120 °C. SIGNIFICANCE:The μGCC fabricated by ULAE method is composed of all-glass and has the uniform stationary phase coating because of the homogeneous microchannel surface which greatly improve the separation performance, resulting in a large resolution for methane and ethane. The all-glass μGCC has broad application prospects in light hydrocarbon separation.