SnifProbe: new method and device for vapor and gas sampling

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Abstract

SnifProbe is based on the use of 15 mm short pieces of standard 0.53 mm I.D. capillary or porous layer open tubular columns for sampling airborne, headspace, aroma or air pollution samples. A miniaturized frit-bottomed packed vial named MicroSPE was also prepared which served for the sampling of solvent vapors and gases as well as liquid water. The short (15 mm) trapping column is inserted into the SnifProbe easy-insertion-port and the SnifProbe is located or aimed at the sample environment. A miniature pump is operated for pumping 10–60 ml/min of the air sample through the short piece of column to collect the sample. After a few seconds up to a few minutes of pumping, the short column is removed from the SnifProbe with tweezers (or gloved hands) and placed inside a glass vial of a direct sample introduction device (ChromatoProbe) having a 0.5 mm hole at its bottom. The ChromatoProbe sample holder with its glass vial and sample in the short column are introduced into the GC injector as usual. The sample is then quickly and efficiently desorbed from the short sample column and is transferred into the analytical column for conventional GC and/or GC–MS analysis. We have explored the various characteristics of SnifProbe and demonstrated its applicability and effectiveness in many applications. These applications include: the analysis of benzene, toluene and o-xylene in air, SO2 in air, perfume aroma on hand, beer headspace, wine aroma, coffee aroma, cigarette smoke, trace chemical warfare agent simulants, explosives vapors, ethanol in human breath and odorants in domestic cooking gas. SnifProbe can be operated in the field or at a chemical process. The sample columns can be plugged and stored in a small union storage device, placed in a small plastic bag, marked and brought to the laboratory for analysis with the full power of GC and/or GC–MS. Accordingly, we feel that the major and most significant feature of SnifProbe is that it brings the field and process to the laboratory. Thus, SnifProbe can extend the “arm” of the GC and GC–MS laboratory and enable high-quality field and process analysis.

Introduction

Gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS) are central analytical techniques for the analysis of a broad range of compounds that can be vaporized. Currently, most analyses are performed in the laboratory whereby samples are brought from the field or other origins into the laboratory for further sample preparation and final chromatographic analysis. Since most samples originate outside the laboratory, the area of field portable GC and GC–MS has been a perpetual need [1], [2]. However, field portable instrumentation usually performs worse than its laboratory-based equivalent. Accordingly, there is a continued and growing need to find better methods and devices that will enable fast sampling in the field combined with easy transportation for effective analysis in the laboratory.

Airborne samples originate from a variety of sources including: air pollution, food and beverage aromas, perfumes and cosmetics, solvent, chemical processes, gas leaks, cigarette smoke, off gases of processed materials, odorants, hidden explosives or drugs of abuse and chemical warfare agents.

Currently these airborne samples are sometimes collected in air bags and brought to the laboratory for analysis [3]. One of the problems with this approach is that semi-volatile compounds may irreversibly adsorb onto the bag walls. It is also costly and bulky. Alternatively, solid-phase extraction (SPE) cartridges are brought to the field for air sampling followed by thermal desorption into the GC inlet performed in the laboratory [4], [5]. This approach can be very effective and enables low detection limits due to the large sample volumes, but it is limited in its applicability to semi-volatile compounds that may not be effectively desorbed. Furthermore, analyte degradation, memory and matrix effects can also pose some problems. In addition, it requires expensive thermal desorption instrumentation that is external to the GC system. The adsorption sample containers are also not as small as desirable for certain applications.

Solid-phase microextraction (SPME) [6], [7], [8] is another approach that finds growing use recently, and was adopted for field sampling [9], [10]. However, the SPME sample collection kit is not inexpensive and the samples suffer losses during transportation if not cooled. In addition, SPME sampling can be time consuming and may suffer from limited sensitivity.

Recently, we have developed a new GC sample introduction device termed Direct/dirty sample introduction device (DSI) [11], [12]. A DSI device is available from Varian called ChromatoProbe. Sampling with the DSI device is based on sample introduction in a micro-vial that is directly inserted into the GC injector. Thus, a micro-vial replaces the standard syringe-based injections of liquids or gases. Previously, this device has been shown to be useful for two different major applications, each with several advantages listed as follows:

(A) Sample introduction for mass spectrometry – a cost effective probe. The DSI device, followed by a short (2 m×0.1 mm I.D.) capillary column, effectively transforms a conventional GC injector into a cost-effective alternative to the standard direct insertion probe. As a sample introduction device for MS and MS–MS studies the DSI is characterized by low cost as well as fast and easy operation and DSI to GC–MS interchange. Furthermore, it is inherently immune against leaks and thus can be operated by untrained personnel.

(B) Extract-free dirty sample introduction for GC and GC–MS analysis. In this approach, sampling is performed in a small disposable vial that retains the contaminating non-volatile matrix residue of real world samples and thus eliminates the need for further sample clean-up. Each analysis begins with gentle solvent vaporization, followed by brief heating of the injector to the desired temperature required for achieving intra-injector thermal extraction and sample compound vaporization. The semi-volatile compounds from the sample are cryo-focused on the early portion of the column and analyzed as usual. The DSI is a low-cost device that can reduce the analysis time and cost by reducing sample preparation, and it enables analysis of complex small solids or sludge samples. It also enables efficient thermal extraction combined with excellent GC integrity and may provide higher sensitivity through large-volume injection of concentrated extract. The dirty sample analysis capability of the DSI was demonstrated in the analysis of drugs in raw urine [11], [12], cocaine and heroin in a single hair [13] and pesticides in mixed/blended fruit and vegetables [14], [15], [16]. Recently, Lehotay explored the quantitative aspects of pesticide analysis in agricultural products with the DSI [16].

In this paper we describe a third usage of the DSI device, in the sampling and analysis of airborne vapor and gas with a separate device named SnifProbe.

SnifProbe is based on the use of a short piece (15 mm) of a standard 0.53 mm I.D. capillary or porous layer open tubular (PLOT) column for sampling airborne samples. A miniature pump samples the air through the short trapping column. The sample column is then removed, placed inside the DSI/ChromatoProbe glass vial and introduced into the GC injector for thermal desorption followed by GC and/or GC–MS analysis. The major goal for developing SnifProbe is to provide an important tool for bringing samples from the field to the laboratory. The compact sample columns can be plugged, marked and brought to the laboratory for analysis with the full power of GC and/or GC–MS.

The idea of air sampling and sample trapping with GC capillary columns is not new. In 1970 Cronin [17] described the use of glass PLOT columns for quantitative sample trapping. In 1985 Grob and Habich [18] described the use of open tubular traps for headspace analysis by capillary GC. A year later, Burger and Munro [19] described the use of fused-silica capillary traps in combination with stainless steel tubes for fast thermal desorption by direct current heating. Lovkvist and Jonsson [20] discussed the theory of such sampling and pre-concentration columns. Bicchi et al. [21] described field sampling of plant volatiles with long (up to 3 m) capillary traps and the use of dual GC for the analysis (one GC for trap thermal desorption and one for the analysis). On-line sample treatment for capillary GC analysis is reviewed by Goosens et al. [22]. Recently, Tuan and co-workers [23], [24] described the use of capillary traps in combination with a portable micro GC system.

The SnifProbe method and device that is described in this paper, although similarly uses capillary columns for sampling, represents a different approach of bringing samples from the field to the laboratory. The sampling capillary or tube is being used in the field for sampling while the analysis is performed in the laboratory with the full power of laboratory GC or GC–MS instrumentation.

Section snippets

The SnifProbe device and instrumentation

The SnifProbe vapor and gas sampling device is shown in Fig. 1 together with enlarged sections of its major components. SnifProbe sampling uses 15-mm long standard 0.53 mm I.D. capillary columns. The use of commercially available GC columns enables low-cost sampling units with a wide range of adsorption materials and film thickness, from thin dimethylsiloxane to various PLOT columns. The 0.53 mm I.D. was chosen because its column O.D. (about 0.7 mm) is compatible with the smallest size (No. 1)

SnifProbe vapor and gas sampling method and features

The SnifProbe sampling method (see Fig. 1) is based on pumping 10–60 ml/min of air sample through the short piece of sample collection column. After a few seconds to a few minutes of pumping, the short column is removed from the SnifProbe head and placed inside a ChromatoProbe glass vial (with a 0.5 mm hole at its bottom). The ChromatoProbe with the sample is then introduced into the GC injector for intra-injector sample thermal vaporization followed by conventional GC and/or GC–MS

SnifProbe applications

SnifProbe can be used for a very broad range of applications in the analysis of airborne, headspace, process environment, food aroma or air pollution samples. In order to better explore the features and capabilities of SnifProbe we tested it in several applications. In this section we demonstrate and describe our results and briefly discuss their implications.

SnifProbe sampling with a MicroSPE tube

In the previous section several SnifProbe analyses of semi-volatile organic compounds were described. Here, we extend the range of SnifProbe applications to include the more volatile range of solvents and permanent gases. For these applications the adsorption power of even the PLOT trapping columns is insufficient and packed column materials need to be used. In the lower right side of Fig. 1 and in Section 3, the MicroSPE tube is described. In essence this is a miniaturized version of the

Discussion and conclusions

SnifProbe is a major new capability and device for the current ChromatoProbe sample introduction device. It extends the DSI/ChromatoProbe range of samples to also include gas phase samples.

The SnifProbe approach is based on the use of the SnifProbe pumping and sample collection unit followed by GC sample introduction of the SnifProbe trapping column or MicroSPE vial with the DSI/ChromatoProbe. Unlike with ChromatoProbe sampling that requires a temperature programmable injector, the SnifProbe

Acknowledgements

The authors thank Mr. Gad Frishman for his help with the experiments and sample preparation. The help of Mr. Peter Hill with beer samples, advice and his available SPME–GC–PFPD results is greatly appreciated. This research was supported in part by grants from the Israel Ministry of the Environment and the James Franck Center for Laser Matter Interaction Research.

References (31)

  • E.B. Overton et al.

    J. Hazard. Mater.

    (1995)
  • J. Dewulf et al.

    Atmos. Environ.

    (1997)
  • S.B. Wainhaus et al.

    J. Am. Soc. Mass. Spectrom

    (1998)
  • A. Amirav et al.

    J. Chromatogr. A

    (1998)
  • D.A. Cronin

    J. Chromatogr.

    (1970)
  • K. Grob et al.

    J. Chromatogr.

    (1985)
  • B.V. Burger et al.

    J. Chromatogr.

    (1986)
  • H.P. Tuan et al.

    J. Chromatogr. A

    (1997)
  • P.G. Hill et al.

    J. Chromatogr. A

    (2000)
  • E.B. Overton et al.

    Field. Anal. Chem. Technol.

    (1996)
  • F.R. Cropper et al.

    Anal. Chem.

    (1963)
  • J.R. Hancock et al.

    J. Chromatogr. Sci.

    (1991)
  • J. Pawliszyn

    Solid Phase Microextraction – Theory and Practice

    (1997)
  • C.L. Arthur et al.

    Anal. Chem.

    (1990)
  • T. Górecki et al.

    Can. J. Chem.

    (1996)
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