Towards smaller and faster gas chromatography-mass spectrometry systems for field chemical detection

Gas chromatography-mass spectrometry (GC-MS) is already an important laboratory method, but new sampling techniques and column heating approaches will expand and improve its usefulness for detection and identification of unknown chemicals in field settings. In order to demonstrate commercially-available technical advances for both sampling and column heating, we used solid phase microextraction (SPME) sampling of both water and air systems, followed by immediate analysis with a resistively heated analytical column and mass spectrometric detection. High-concern compounds ranging from 140 to 466 amu were analyzed to show the applicability of these techniques to emergency situations impacting public health. A field portable (about 35 kg) GC-MS system was used for analysis of water samples with a resistively heated analytical column externally mounted as a retrofit using the air bath oven of the original instrument design to heat transfer lines. The system used to analyze air samples included a laboratory mass spectrometer with a dedicated resistive column heating arrangement (no legacy air bath column oven). The combined sampling and analysis time was less than 10 min for both air and water sample types. By combining dedicated resistive column heating with smaller mass spectrometry systems designed specificallyfor use in the field, substantially smaller high performance field-portable instrumentation will be possible.     

Resistively heated temperature programmable silicon micromachined gas chromatography with differential mobility spectrometry

A microfabricated electromechanical system based on radio frequency modulated ion mobility spectrometry (MEMS-RFIMS), also known as differential ion mobility spectrometry (DMS) has been successfully interfaced to a custom-fabricated resistively heated temperature programmable micromachined gas chromatograph. In contrast to a conventional time-of-flight ion mobility spectrometer, the DMS uses the non-linear mobility dependence in strong radio frequency electric fields for ion filtering. Selective and sensitive detection of targeted analytes of interest can be achieved by using different transport gases, radio frequencies, and associated compensation voltages. In addition, the detection of both positive and negative ions, depending on the ionization mechanism favorable to the analytes involved is achieved. When compared to a stand-alone GC with a non spectrometric detector or a stand-alone DMS, GC-DMS as a hyphenated technique offers two competitive advantages; two orthogonal separating methods in a single analytical system and the resolving power of gas chromatography to minimize charge exchange in the ionization chamber of the detector. In this article, a portable, resistively heated temperature programmable silicon machined gas chromatograph with differential mobility detection is introduced. The performance of the instrument is illustrated with examples of difficult industrial applications.     

Rapid column heating method for subcritical water chromatography

A novel resistive heating method is presented for subcritical water chromatography (SWC) that provides higher column heating rates than those conventionally obtained from temperature-programmed gas chromatography (GC) convection ovens. Since the polarity of water reduces dramatically with increasing temperature, SWC employs column heating to achieve gradient elution. As such, the rate at which the mobile phase is heated directly impacts the magnitude of such gradients applied in SWC. Data from the current study demonstrate that the maximum column heating rate attainable in a typical SWC apparatus (i.e. using a GC convection oven) is around 10 degrees C/min, even at instrument oven settings of over three times this value. Conversely, by wrapping the separation column with ceramic insulation and a resistively heated wire, the column heating rates are increased five-fold. As a result, elution times can be greatly decreased in SWC employing gradients. Separations of standard alcohol test mixtures demonstrate that the retention time of the latest eluting component decreases by 35 to 50% using the prototype method. Additionally, solute retention times in this mode deviate by less than 1% RSD over several trials, which compares very well to those obtained using a conventional GC convection oven. Results suggest that the developed method can be a useful alternative heating technique in SWC.     

Gas chromatography using a resistively heated column with mass spectrometric detection for rapid analysis of pyridine released from Bacillus spores

Gas chromatography using a resistively heated analytical column with full scan electron impact mass spectrometry (EI-MS) was used to detect pyridine generated from heating Bacillus spores in a custom designed furnace inlet, along with gasoline range aromatic (GRA) hydrocarbons representing an environmental contaminant that could interfere with detection of the biologically-derived compound. Gas phase materials from the furnace inlet were collected onto a section of cooled open tubular column, and carrier gas flow was then routed through the trapping column onto the analytical column. Both sections of column were contained within low thermal mass tubular metal sheaths, with each independently and resistively heated allowing rapid temperature ramps and cooling. An analysis time of 2 min resolved spore-derived pyridine from the other organics, and allowed identification by mass spectrum match. Throughput of 20 analyses per hour was shown to be possible with a 1-min column cool-down time between analyses.     

Low thermal mass gas chromatography: principles and applications

In gas chromatography (GC), temperature programming is often considered to be the second most important parameter to control, the first being column selectivity. A radically new GC technology to achieve ultrafast temperature programming with an unprecedented cool down time and low power consumption has recently become available. This technology is referred to as low thermal mass GC (LTMGC). Though the technology has its roots in resistive heating, which forms the basis of principle and design concept, the approach taken to achieve ultrafast heating and cool down time by LTMGC represents a significant break-through in GC. Despite some rectifiable shortcomings, LTMGC has proven to be an ideal methodology to deliver near/real time GC data, high precision, and high throughput applications. It is a new approach for modern high-speed GC. This paper documents the fundamental design principles behind LTMGC, performance data, and examples of applications investigated.     

A novel focusing injection technique for chemiluminescent detection of volatile sulfur compounds separated by HRGC

A one meter stainless steel capillary column coated with a 20μm film of polydimethylsiloxane was used to replace the Teflon gas sampling loop of a HRGC – flameless SCD system. This column trap was equilibrated with the gaseous sample and then purged with carrier gas while being sequentially, resistively heated in ten 10 cm sections. The sequential heating of the 10cm sections was timed such that the velocity of the moving heated zone was approximately the same as the velocity of the carrier gas. The thick stationary phase film served to retard the front end of the injection band while the ballistic heating accelerated the back end. The net result was focusing of the injection, which gave rise to a narrower injection profile than that obtained with the original Teflon loop.     

Innovations in high-pressure liquid injection technique for gas chromatography: pressurized liquid injection system

In gas chromatography (GC), highly volatile liquefied hydrocarbons are commonly injected using devices such as high-pressure syringes, piston valves, liquid rotary sampling valves, or vaporizing regulators. Although these techniques are adequate in some cases, there are known deficiencies. A new generation of sampling valve has been recently innovated and commercialized. Some of the highlights of the pressurized liquid injection system (PLIS) include compact size, the capability to directly couple to an injection port without the need for preinjection vaporization and transfer lines, and sample sizes ranging from 0.2 to 2.0 micro L. Although the valve has a specification of helium leak-free rating of 82.7 bar (1200 psig), the valve passes a hydrostatic pressure test of up to 414 bar (6000 psig). In the unheated version of PLIS, vaporization of solutes occur mainly because of the sheering effect of carrier gas in combination with thermal energy drawn from an injection port or a heated adaptor. This was found to be adequate for solutes with high to medium volatility of up to nC14 hydrocarbon. A higher molecular weight range of up to nC44 hydrocarbon can be achieved with the implementation of a heated version of PLIS, in which the channel of the shaft can be resistively heated at a rate of up to 400 degrees C/s. With its first introduction in May 2002, PLIS has gained acceptance amongst practitioners in GC because it addresses a key unarticulated need in sample introduction/enrichment and by specifically targeting many deficiencies encountered in contemporary high-pressure injection devices. In this paper, the design and performance of the various valve systems of PLIS, as well as industrial chromatographic applications, is presented.     

On-line monitoring of biotechnological processes by gas chromatographic-mass spectrometric analysis of fermentation suspensions

An on-line monitoring system has been developed for the control of a biorreactor for the anaerobic pretreatment of an industrial waste water. The monitoring system is based on a process mass spectrometer with a temperature controlled membrane inlet. The membrane introduction mass spectrometer (MIMS) is coupled with a resistively heated metal gas chromatography capillary column, which serves as a transfer line between the bioreactor and the MIMS. Sampling and injection is performed by means of a pneumatically driven membrane probe, which enables monitoring of soluted and gaseous substances in the fermentation broth. The system can also be coupled to other processes.     

Recent trends and developments in pyrolysis-gas chromatography

Pyrolysis-gas chromatography (Py-GC) has become well established as a simple, quick and reliable analytical technique for a range of applications including the analysis of polymeric materials. Recent developments in Py-GC technology and instrumentation include laser pyrolysis and non-discriminating pyrolysis. Progress has also been made in the detection of low-level polymer additives with the use of novel Py-GC devices. Furthermore, it has been predicted that future advances in separation technology such as the use of comprehensive two-dimensional gas chromatography will further enhance the analytical scope of Py-GC.     

Design of platinum hot wire gas sensors

The design characteristics of lower-power platinum gas sensors are studied. These sensors work by the detection of the positive ions produced during the catalytic oxidation of organic vapours on hot platinum wires and ribbons. These sensors are selective to long-chain hydrocarbons. A prototype sensor design is presented, which uses a small piece of platinum ribbon welded to a ceramic header with a wire mesh cathode to collect the positive ions. The ionic current is measured with a battery-run picoammeter circuit biased to float at −120 V. The ribbon is heated resistively with a standad power supply. At the operating temperature of 800 °C, the power consumption is about 2 W. The prototype is capable of detecting iso-octane vapour down to a concentration of 2 ppm. Platinum ribbon was used rather than wire as the wire had a greater tendency to melt due to thermal runaway in the resistive heating process. It was observed that the number of positive ions produced by the catalytic process decreased during long-term measurements. Scanning electron micrographs showed this to be due to facetting of the platinum surface. A few seconds' exposure at 1300 °C restored the surface and the ionic response. Thus periodic thermal cycling is necessary for the prototype sensor.     

Development of a simple gradient LC-IR interface for the detection of terpenoids from the alpha-pinene-ozone reaction

The development of a simple interface between liquid chromatography and infrared spectroscopy (LC-IR) using a coaxial sprayer is described for less volatile analytes. The system consists of a transfer capillary, in which the analytes are transported from the separation column of the gradient-LC to the outlet of the sprayer. This transfer capillary is coaxially surrounded at the outlet by a stainless steel sprayer capillary, which is resistively heated and flushed with nitrogen gas. The samples are sprayed in the manner that the eluent is vaporized by the heated nitrogen when exiting the capillary, while the analytes are deposited on a moving slide made of infrared transparent material (ZnSe or CaF2). Afterwards the deposited compounds are analyzed with an infrared microscope in transmission. First results from reaction products of the gas phase reaction of alpha-pinene with ozone are presented.     

针阱微萃取技术的研究与应用进展

随着检测需求的提高与分析技术的发展,简单、自动化、环保与小型化的微型样品前处理技术越来越受到关注。针阱微萃取(NTME)是在固相微萃取(SPME)技术的理论基础上发展起来的一种新型微型萃取技术,其萃取装置将吸附剂填充到不锈钢针内制得,可避免固相微萃取纤维易碎及涂层脱落的问题,而且通过动态萃取,可使目标物被彻底萃取,具有更好的耐用性和富集能力。近年NTME结合气相色谱法在挥发性和半挥发性有机污染物分析中获得广泛应用,已有诸多关于NTME的研究被报道。吸附剂是影响NTME萃取性能的核心,本文简要概述了近年NTME的吸附剂种类,并综述了其在环境、食品、生物领域的应用进展。     

Principles and Analytical Applications of Heated Electrodes

This article reviews the development of the various heated electrodes, heating devices and their analytical applications which have been published during the last decades. Generally spoken, electrode heating can provide different positive effects on electrochemical measurements: mass transport enhancement, reaction kinetics acceleration and the removal of deposited substances from the electrode surface. This often leads to remarkably improved signal-to-noise characteristics in electroanalytical chemistry. Short heat pulses or direct heating of very small electrolyte compartments allow for temperatures far above the boiling point of the solution. Major application fields include trace metal and nucleic acids analysis. Future development will result in miniaturized selectively heated electrode arrays.     

Adding a new separation dimension to MS and LC–MS: What is the utility of ion mobility spectrometry?

Ion mobility spectrometry is an analytical technique known for more than 100 years, which entails separating ions in the gas phase based on their size, shape, and charge. While ion mobility spectrometry alone can be useful for some applications (mostly security analysis for detecting certain classes of narcotics and explosives), it becomes even more powerful in combination with mass spectrometry and high‐performance liquid chromatography. Indeed, the limited resolving power of ion mobility spectrometry alone can be tackled when combining this analytical strategy with mass spectrometry or liquid chromatography with mass spectrometry. Over the last few years, the hyphenation of ion mobility spectrometry to mass spectrometry or liquid chromatography with mass spectrometry has attracted more and more interest, with significant progresses in both technical advances and pioneering applications. This review describes the theoretical background, available technologies, and future capabilities of these techniques. It also highlights a wide range of applications, from small molecules (natural products, metabolites, glycans, lipids) to large biomolecules (proteins, protein complexes, biopharmaceuticals, oligonucleotides).     

Gas chromatography with spectroscopic detectors.

In recent years, capillary gas chromatography (GC) with Fourier Transform Infrared (FT-IR) and/or mass spectral (MS) detection has become a primary analytical tool for qualitative and quantitative analysis of complex mixtures. Because of the wide range of applications, the analytical requirements have motivated a variety of chromatographic and detection developments. This review examines those, illustrating with applications that demonstrate the power of GC and multidimensional GC-MS, GC-FT-IR and GC-FT-IR-MS systems for solving a variety of analytical problems. In addition, the article discusses the integrated performance of such analytical systems with the aid of recent sample introduction and computer data analysis advances.     

Pervaporation in chemical analysis

Unlike thermal processes such as distillation, pervaporation relies on the relative rates of solute permeation through a membrane and is a combination of evaporation and gas diffusion. The analytical pervaporation systems consist of a membrane module suitable for liquid sample introduction and a vacuum (or a sweeping gas) on the permeate side. It has been used in a wide range of applications including the analysis of various organic and inorganic compounds, and sample concentration. It has been directly interfaced with gas chromatography, spectrophotometry, capillary electrophoresis, electrochemical detectors, liquid chromatography, and mass spectrometry. A wide range of liquids, slurries, and solids samples has been analyzed using these techniques. This review highlights the basic principles of the pervaporation and the state of its current development as applied to analytical chemistry.     

Separation methods for captopril in pharmaceuticals and biological fluids

Captopril (CAP) is an orally active angiotensin-converting enzyme (ACE) inhibitor and has been widely used for management of hypertension and congestive heart failure. CAP lacks an aromatic chromophore required for facile direct UV detection and also has two chiral centers. These factors can render the determination of CAP in complex matrices challenging. This review covers more than 20 years of analytical research on this drug, focusing mainly on pharmaceutical and biological applications. The primary separation techniques discussed are gas chromatography, liquid chromatography, and capillary electrophoresis. The structures of the CAP derivatizing agents as well as a table summarizing various HPLC methods are provided. A discussion of key recent chromatographic and electrophoretic methods for other ACE inhibitors is also present.     

Temperature pulse modulated amperometry at compact electrochemical sensors

This communication reports about thermal modulation of amperometric signals by short heat pulses applied at directly heated gold electrodes. A gold layer together with a pseudo reference and counter electrode has been printed onto a low temperature cofired ceramic (LTCC) substrate. We chose hexacyanoferrate(II) and picric acid as model analytes in this preliminary study. Peak shaped amperometric signals were formed upon such thermal modulation. The peak current has been taken as the analytical information. Thermal modulation in amperometric measurements activates kinetically inhibited analytes such as picric acid. A linear calibration plot has been obtained ranging from 0.2 to 1 mmol/l. The background contribution was effectively suppressed, even at −0.7 V applied potential at the gold electrode. Convection did not significantly affect the analytical signal. This will be important for applications where convection is pulsating or is otherwise not under control and thus induces disturbances. Future applications include environmental monitoring, flow injection analysis, high performance liquid chromatography and capillary electrophoresis.     

微波辐射用于聚合反应的研究进展

微波辐射在高分子化学研究领域中的应用越来越广泛 ,效果也十分明显 ,与常规加热方式相比 ,微波辐射具有缩短反应时间 ,提高反应产率 ,节省能源损耗 ,制得产物性能好等优点。近年来 ,微波辐射在聚合反应中的应用也越来越多。因此本文对微波辐射在高分子聚合反应中的应用研究进行了综述。     

Fast Capillary Gas Chromatography: Comparison of Different Approaches

Savings in analysis time in capillary GC have always been an important issue for chromatographers since the introduction of capillary columns by Golay in 1958. In laboratories where gas chromatographic techniques are routinely applied as an analytical technique, every reduction of analysis time, without significant loss of resolution, can be translated into a higher sample throughput and hence reduce the laboratory operating costs. In this contribution, three different approaches for obtaining fast GC separations are investigated. First, a narrow-bore column is used under conventional GC operating conditions. Secondly, the same narrow-bore column is used under typical fast GC conditions. Here, a high oven temperature programming rate is used. The third approach uses a recent new development in GC instrumentation: Flash-2D-GC. Here the column is placed inside a metal tube, which is resistively heated. With this system, a temperature programming rate of 100°/s is possible. The results obtained with each of these three approaches are compared with results obtained on a column with conventional dimensions. This comparison takes retention times as well as plate numbers and resolution into consideration.