Construction and application of a cold on-column injection system for capillary gas chromatography

A cold on-column injection system for capillary gas chromatography (GC) applications was constructed. It was based upon a conventional split/splitless capillary GC inlet, which in turn was a modification of a conventional packed GC column inlet. The heart of the laboratory constructed cold on-column inlet design was a disposable pyrex micro-sampling pipet, which functioned as a needle guide for sample injection. The sample was injected through a traditional GC septum. Construction of the injection system is described and applications are illustrated by separations of a variety of complex mixtures.     

制备气相色谱仪的改进及应用研究进展

气相色谱已经成为一种常规的分析手段,但以制备为目的的气相色谱的应用还较少.目前尚没有商品化的制备气相色谱仪,需要对传统的分析型气相色谱仪加以改进,以达到高效分离制备目标化合物的目的.本文综述了国内外对制备气相色谱仪改进工作的研究进展,包括汽化室、色谱柱、分流装置、收集系统等的改进.另外,总结了制备气相色谱在各领域的应用...     

Optimization and application of the large volume on-column introduction (LOCI) technique for capillary GC with preliminary on-line capillary solvent distillation/concentration

This report describes an on-line capillary GC injection system which enables on-column injection of a hundred or more microliters, and yields separations comparable with those obtained from on-column injection of 1–2 microliters of solutions a hundred times more concentrated. Precision, carry-over, linearity, and discrimination are comparable with those of classical sample-introduction techniques. A selection of polar and high boiling compounds has been examined, and excellent peak shapes obtained for hundreds of injections. Initial results indicate that maintenance and long-term reproducibility will also be comparable with those of classical techniques. The instrument utilizes a version of the large volume on-column injector with solvent diversion described in an earlier communication, with the addition of a method for independent heating of the retention gap. This modification reduces the effects of activity in the retention gap and improves the capability of the technology to handle complex mixtures. It also increases reliability and system lifetime, fits readily into most GC ovens, is easily automated, and should be compatible with all capillary GC detectors.     

A simple and easily fabricated device for desorbing volatiles from porous polymers and other adsorbents

A device has been developed for the rapid desorption of organic compounds from adsorbent traps. Some advantages over previous devices include its ease of fabrication from inexpensive and readily obtainable materials, and its high portability between instruments. No major modification of the gas chromatograph (GC) inlet system is necessary and in a matter of seconds the desorber can be removed from the injection port for normal syringe injections. The adsorbent tubes can be transported into the field for sampling and returned to the laboratory for desorption and analysis by GC or GC-MS. Additionally, the device is useful for head space analysis, volatile organics analysis in aqueous solutions, and impurities in gaseous feed streams.     

Applications of a GC autosampler modified for headspace sampling

A GC autosampler designed for liquid injection was modified for static headspace sampling. The modification was very simple and involved replacement of the standard 10-μL syringe with a 100-μL gas-tight syringe. Liquid samples (0.2-1.0 mL) were placed in 2-mL vials, normally used for liquid sampling and an aliquot of the head-space above the liquid was withdrawn and injected into the GC. All parts of the sampling system were at ambient temperature. The system was found to be useful for several applications. Among those discussed in this paper are determination of ethanol in the blood or urine of individuals suspected of driving while intoxicated, residual organic solvents in pharmaceuticals, and screening of effluent waters from industrial plants for acrylonitrile.     

Electrochemical Reduction of a Conjugated Cinnamic Acid Diazonium Salt as an Immobilization Matrix for Glucose Biosensor

Initial results on the synthesis of a new conjugated diazonium salt of trans‐4‐cinnamic acid diazonium fluoroborate, which is used for the chemical modification of the glassy carbon (GC) electrode with trans‐4‐cinnamic acid groups through electrochemical reduction, and direct covalent immobilization of glucose oxidase (GOD) on the cinnamic acid groups are presented. The chemically modified GC electrode exhibits a good selectivity relative to the bare GC electrode for the various possible interfering compounds in glucose analysis: namely ascorbic acid and 4‐acetamidophenol. Covalent immobilization of GOD on the chemically modified GC electrode produces a biosensor which responds to glucose concentration changes in the presence of a soluble redox mediator (ferrocenemethanol). The chemical modification of GC by cinnamic acid groups is potentially useful for the attachment of other enzymes and biochemical reagents.     

Qualitative supercritical fluid extraction coupled to capillary gas chromatography

The usefulness and ease of utilizing supercritical fluid extraction (SFE) directly coupled to capillary gas chromatography (GC) as quantitative or qualitative analytical problem-solving tools will be demonstrated. As an alternative to conventional liquid solvent extractions, SFE presents itself as a means to achieve high extraction efficiencies of different compounds in complex solid matrices in very rapid tims frames. Moreover, SFE has an additional advantage of being able to achieve distinct extraction selectivities as a function of the solubilizing power of the supercritical fluid extracting phase. For on-line SFE/GC, the extraction effluent is directly transferred to the analytical chromatograph. On-line SFE/GC involves the decompression of pressurized extraction effluent directly into a heated, unmodified capillary split injection port of the GC. In this respect, SFE introduction into GC can be used as an alternative means of GC injection, comparable to such modes of injection as pyrolysis and thermal desorption. This paper will show applications of SFE/GC where mass spectrometric detection together with flame ionization detection was used for component identification from environmental, tobacco, and petroleum matrices.     

Achieving high peak capacity production for gas chromatography and comprehensive two-dimensional gas chromatography by minimizing off-column peak broadening

By taking into consideration band broadening theory and using those results to select experimental conditions, and also by reducing the injection pulse width, peak capacity production (i.e., peak capacity per separation time) is substantially improved for one dimensional (1D-GC) and comprehensive two dimensional (GC×GC) gas chromatography. A theoretical framework for determining the optimal linear gas velocity (the linear gas velocity producing the minimum H), from experimental parameters provides an in-depth understanding of the potential for GC separations in the absence of extra-column band broadening. The extra-column band broadening is referred to herein as off-column band broadening since it is additional band broadening not due to the on-column separation processes. The theory provides the basis to experimentally evaluate and improve temperature programmed 1D-GC separations, but in order to do so with a commercial 1D-GC instrument platform, off-column band broadening from injection and detection needed to be significantly reduced. Specifically for injection, a resistively heated transfer line is coupled to a high-speed diaphragm valve to provide a suitable injection pulse width (referred to herein as modified injection). Additionally, flame ionization detection (FID) was modified to provide a data collection rate of 5kHz. The use of long, relatively narrow open tubular capillary columns and a 40°C/min programming rate were explored for 1D-GC, specifically a 40m, 180μm i.d. capillary column operated at or above the optimal average linear gas velocity. Injection using standard auto-injection with a 1:400 split resulted in an average peak width of ～1.5s, hence a peak capacity production of 40peaks/min. In contrast, use of modified injection produced ～500ms peak widths for 1D-GC, i.e., a peak capacity production of 120peaks/min (a 3-fold improvement over standard auto-injection). Implementation of modified injection resulted in retention time, peak width, peak height, and peak area average RSD%'s of 0.006, 0.8, 3.4, and 4.0%, respectively. Modified injection onto the first column of a GC×GC coupled with another high-speed valve injection onto the second column produced an instrument with high peak capacity production (500-800peaks/min), ～5-fold to 8-fold higher than typically reported for GC×GC.     

Simplifying the setup for vacuum‐outlet GC: Using a restriction inside the injection port

The application of vacuum GC has several advantages over pressurized GC. One of the key characteristics is that the optimal gas velocity is very high. Combined with short capillary columns of wide internal diameter, this results in short analysis times using standard GC‐MS equipment. To make vacuum GC possible using a GC‐MS system, a restriction must be positioned at the injection side of the column. This restriction is usually made of deactivated 0.1 mm i.d. fused‐silica tubing which is coupled to the analytical column. Such restrictions will work, but practical challenges are found in coupling, reducing dead volume and robustness. A new way of making restrictions is by incorporating the restriction into the injection port. Using well‐defined short pieces of fused silica with internal diameter of 0.025 mm, one can make a restriction using a Press‐Tight® type connector, and position this inside the injection port. By doing this, the restriction is very short and at high temperature all the time. Activity plays a minimal role, and also leaks will not be an issue as the coupling is in 100% inert gas. Data obtained using this concept is promising as vacuum GC becomes easier and more robust.     

Quantification of polychlorinated dibenzo-p-dioxins and dibenzofurans by direct injection of sample extract into the comprehensive multidimensional gas chromatograph/high-resolution time-of-flight mass spectrometer

Polychlorinated dibenzo-p-dioxins and dibenzofurans in crude extracts of fly ash and flue gas from municipal waste incinerators were quantified using a comprehensive multidimensional gas chromatograph (GC x GC) coupled to a high-resolution time-of-flight mass spectrometer (HR-TOFMS). For identification and quantification, we developed our own program to prepare 3D chromatograms of selected mass numbers from the data of the GC x GC/HR-TOFMS. Isolation of all congeners with a TCDD toxic equivalency factor from the other isomers by only one injection was confirmed. The instrumental detection limit of TCDD on the GC x GC/HR-TOFMS was 0.9 pg by the relative calibration method. Quantification of these substances in the crude extracts was achieved by direct injection to the GC x GC/HR-TOFMS. The results agree with the values obtained using a generic gas chromatography/high-resolution mass spectrometry (GC/HRMS) system. It was confirmed that measurement by high-resolution TOFMS and GC x GC effectively reduces interference from other chemicals.     

Fast gas chromatography analysis of N-carbamates with cold on-column injection

Direct gas chromatographic (GC) analysis of thermally labile N-carbamates is studied by using fast GC with cold on-column injection. With the greatly reduced injection temperature, short column lengths, high flow rate, and fast temperature-programming rate, the exposure of carbamates to high temperature is reduced and degradation can be avoided. Nine N-carbamates in EPA Method 531 are eluted without thermal decomposition. The relative standard deviation percentage for peak areas average 1.9% for all of the carbamates analyzed. A conventional GC instrument is employed to simplify the experiments. GC-mass spectrometry is used to monitor the decomposition peaks.     

Fast gas chromatography analysis of N-carbamates with cold on-column injection

Direct gas chromatographic (GC) analysis of thermally labile N-carbamates is studied by using fast GC with cold on-column injection. With the greatly reduced injection temperature, short column lengths, high flow rate, and fast temperature-programming rate, the exposure of carbamates to high temperature is reduced and degradation can be avoided. Nine N-carbamates in EPA Method 531 are eluted without thermal decomposition. The relative standard deviation percentage for peak areas average 1.9% for all of the carbamates analyzed. A conventional GC instrument is employed to simplify the experiments. GC-mass spectrometry is used to monitor the decomposition peaks.     

Characterization of a 2‐Benzo[c]cinnoline Modified Glassy Carbon Electrode by Raman Spectroscopy,Electrochemical Impedance Spectroscopy,and Ellipsometry

This work describes the characterization of the grafted 2‐benzo[c]cinnoline (2BCC) molecules at a glassy carbon (GC) electrode surface by voltammetry and spectroscopy. Attachment of the molecule to the carbon substrate was achieved by the electrochemical reduction of 2‐benzo[c]cinnoline diazonium salt (2BCC‐DAS). GC electrode modification was carried out in aprotic solution with 2BCC diazonium salt. Dopamine (DA) and ascorbic acid (AA) were used to prove the surface modification to see the blockage of the electron transfer. The presence of 2BCC at the GC electrode surface was characterized by cyclic voltammetry and Raman spectroscopy. Raman spectroscopy was used to monitor molecular bound properties of the adsorbates at the 2BCC‐GC surface and confirm the attachment of 2BCC molecules onto the GC surface. The thickness of the 2BCC film on GC was also investigated by ellipsometric measurement.     

Optimized pressure-pulse splitless injection and electron-capture, negative ionization detection for the congener specific determination of compounds of technical toxaphene

The goal of the study is the optimization of the congener specific determination of compounds of technical toxaphene (CTTs). For this reason GC/ECNI-MS and CTT standard mixtures are applied. The splitless injection is improved by pressure-pulse injection which yields significantly higher abundance of the CTTs than by the conventional constant flow injection technique. The abundance of low volatile CTTs like B9-1025 (Parlar #62) is increased by factor 3 or more. The pressure-pulse injection can easily be integrated in standard (constant flow splitless injection) methods without influencing the retention times and reproducibility. The GC oven program and the flow are optimized for the separation of CTTs on a non-polar CP-Sil 2 column. Problems caused by oxygen in the ion source are discussed.     

Pulsed flow modulation comprehensive two-dimensional gas chromatography

Pulsed flow modulation (PFM) is based on higher flow rate time compression of the first GC column effluent, which prior to the injection into the second column is stored for a few seconds in a standard fused silica wide bore transfer line. We constructed the PFM device with two standard 1/16 in. brass compression fittings with the insertion of the two columns inside the wide bore 0.53 mm i.d. fused silica storage transfer line for the elimination of dead volumes. This simple arrangement provides a combination of flexibility in the length of the sample storage transfer line hence comprehensive two-dimensional gas chromatography (GC x GC) cycle time, inert sample path and full elimination of cooling gas consumption. A record short second column injection time of 20 ms is demonstrated. Practical injection times are the sample collection time (such as 4s) divided by the second to first column flow rate ratio (such as 20/0.7), which is typically around 150 ms. Due to the low cost of the device it can also be considered for use with non comprehensive time segmented GC x GC to remove a few accidental coelutions. PFM-GCxGC excels with high second column capacity due to the use of 0.32 mm i.d. columns with high flow rates as the second dimension GC x GC column. As a result, PFM-GCxGC can have up to two orders of magnitude higher second column sample capacity and linear dynamic range for improved reduction of adverse matrix interference effects due to column overloading.     

Fused silica capillary GC/MS coupling: A new,innovative approach

A novel fused silica capillary GC/MS direct coupling is described which ensures quantitative transfer of sample from the point of injection to the ion source of a mass spectrometer without contacting any surfaces other than the column wall. This device permits GC analysis of highly labile substances. Aflatoxin B₁, previously considered unassayable by GC, can now be determined by GC/MS.     

纳米金/碳纳米管复合材料修饰电极催化鲁米诺电致发光体系的研究

制备了纳米金/多壁碳纳米管(MWNT)复合材料修饰电极,并将此电极应用于鲁米诺电化学发光体系.电化学发光实验表明,此复合材料修饰电极同时具备了纳米金和碳纳米管的催化性能.此外通过电极活性表面积测算、电化学交流阻抗实验等方法研究了纳米金和碳纳米管在此体系催化过程中的作用.纳米金/碳纳米管修饰电极具有良好的重现性,可以广泛应用于鲁米诺电化学发光测定体系.     

A Comparative Study of the Modification of Gold and Glassy Carbon Surfaces with Mixed Layers of In Situ Generated Aryl Diazonium Compounds

In situ generated aryl diazonium cations were synthesized in the electrochemical cell by reaction of the corresponding amines with NaNO₂ in aqueous HCl. This paper reports a study of the formation of mixed layers from in situ generated aryl diazonium cations. Firstly, glassy carbon (GC) and gold electrode surfaces were modified with five single in situ generated aryl diazonium salts to obtain their corresponding reductive potential followed by the modification of GC and gold surfaces with eight binary mixed layers of in situ generated aryl diazonium salts. The difference between GC and gold surfaces in terms of in situ formation of two‐component aryl diazonium salt films was compared. The behavior of the mixed layers formed from in situ generated aryl diazonium salts relative to diazonium salts that were pre‐synthesized prior to surface modification was also investigated. Cyclic voltammetry and X‐ray photoelectron spectroscopy were used to characterize the resulting modified GC and gold surfaces. It is found that for some aryl diazonium salts the potential at which reductive adsorption is achieved on gold and GC surfaces is significantly different. For the eight sets of binary mixed layers, the species with more anodic potential are more difficult to attach to the both GC and gold surfaces. The behavior of the mixed layers formed from in situ generated aryl diazonium salts and the pre‐synthesized diazonium salts is similar; which emphasizes the advantage of the in situ approach without any apparent difference in behavior to the presynthesized diazonium salts.     

Gas chromatography—Fourier transform infrared spectroscopy—mass spectrometry. A powerful tool for component identification in complex organic mixtures

Fourier transform infrared spectrometry (FTIR) and mass spectrometry (MS) have been combined with gas chromatography (GC) for the identification of eluted components in a complex mixture. The combined technique, GC—FTIR—MS, provides simultaneous GC—FTIR and GC—MS data from a single injection.     

聚邻苯二胺/镍氢氧化物修饰电极的研究

采用循环伏安法(CV)在聚邻苯二胺修饰玻碳电极表面络合Ni2+,然后将其置于NaOH溶液中CV扫描成功制备了镍氢氧化物/聚邻苯二胺/玻碳修饰电极(Ni(OH)2/PoPD/GC).通过CV探讨了聚合和负载机理,电化学交流阻抗谱(EIS)表征了电极修饰过程中界面阻抗变化,扫描电镜表征了PoPD膜负载Ni(OH)2后的形态...