GC/SAW

Electronic Sensor Technology zNose model 4100/7100 (GC-SAW) www.estcal.com... 

Williams, D., Pappas, G., 1999. Rapid identification of nerve agents sarin (HB) and soman (GD) with the use of a field-portable GC/SAW vapor detector and liquid desorption front-end device. Field Anal. Chem. Technol. 3,45-53. 

Purpose Generate data sets using mixed deterministic/stochastic models with N = 1. .. 1000. These data sets can be used to test programs or to do Monte Carlo studies. Five different models are predefined sine wave, saw tooth, base line, GC-peaks, and step functions. Data file SIMl.dat was... 

R Schiff, P Reddy, M Ahotupa, E Coronado-Heinsohn, M Grim, SG Hilsenbeck, R Lawrence, S Deneke, R Herrera, GC Chamness, SAW Fuqua, PH Brown, CK Osborne. J Natl Cancer Inst 92 1926-1934, 2000. 

McGuire WL, Chamness GC, Fuqua SAW (1991) Estrogen receptor variants and clinical breast cancer. Mol Endocrinol 5 1571... 

Ciocca DR, Oesterreich S, Chamness GC, McGuire WL, Fuqua SAW (1993) Biological and clinical implications of heat shock protein 27000 (Hsp27 a review. J Natl Cancer Inst 85 1558-1570... 

Microsensors have the potential for selective GC detectors and also as remote sensors when combined in arrays often referred to as electronic noses . Promising microsensors include surface acoustic wave (SAW) detectors normally coated with different semi-selective polymeric layers and microelectromechanical systems (MEMS) including microcantilever sensors. The hope is that, in the future, hundreds of such microcantilevers, coated with suitable coatings, may be able to achieve sufficient selectivity to provide a cost-effective platform for detecting explosives in the presence of potentially interfering compounds in real environments. This array of... 

In other GC separations, the differences in vapor pressure, or a combination of the two effects used to produce the desired separation, can be exploited. We saw in Chapter 6 how the members of a homologous series are separated according to differences in boiling points. 

In Chapter 6 we saw that, by itself, chromatography is not well suited to qualitative analysis thus it is often combined with other methods. The most successful combination has been GC with mass spectrometry (MS) GC s ability to separate materials and MS s ability to identify them has made the combination one of the most powerful analytical techniques available today. The other forms of chromatography are also being combined with MS and with infrared spectroscopy (IR). The resulting analytical methods are usually designated by their combined abbreviations (e.g., GC/MS or GC-MS) and are known as hyphenated techniques. The current status of these methods will be described briefly. 

Unfortunately, in many instances the materials employed as sensor coatings are nonvolatile solids (polymers) for which 6 values cannot be calculated directly. Solubility parameters for these materials can be estimated, however, by immersion testing [172b], inverse gas chromatography [173,174] or ftom coated-SAW sensor responses [166]. In inverse chromatography, the polymeric coating material is used as a stationary phase on a GC column, and the specific retention volumes (V ) for several solutes are determined. Since the Vg is directly related to, Kc, the solubility parameter for the polymer coating can be derived from relationships similar to Equation 5.32. A similar approach is used to derive S, from SAW sensor response data [166]. 

SlMl.dat Section 1.4 Five data sets of 200 points each generated by SIM-GAUSS the deterministic time series sine wave, saw tooth, base line, GC-peak, and step function have stochastic (normally distributed) noise superimposed use with SMOOTH to test different filter functions (filer type, window). A comparison between the (residual) standard deviations obtained using SMOOTH respectively HISTO (or MSD) demonstrates that the straight application of the Mean/SD concept to a fundamentally unstable signal gives the wrong impression. 

Let us first demonstrate the source of difficulty by a simple example. Consider an ideal gas in the T, V, N ensemble. In section 2.5, we saw that gc(R) in this case has the form (see also Appendix G)... 

Sensor types ISE, QCM, SAW, single-X spectroscopy sensor arrays (QCM, SAW, ISE) multi-X spectroscopy, mass spectrometry, chromatography GC-MS excitation-emission- fluorescence... 

Table 3. Some commercial companies that manufactured sensor-based electronic noses and related instruments in 2003. Key to sensor technologies MOS - metal oxide sensor, CP -conducting polymer, QMB - quartz crystal microhalance, FET - field effect transistor, SAW - surface acoustic wave key to analytical instruments MS - mass spectrometry, GC - gas chromatography, IMC - ion mobility cell...

Another example of a quasi-electronic nose is the use of a reconfigured GC column. One commercial example is the z-Nose which is a portable instrument based upon a short Im GC column with an uncoated SAW detector. The instrument is calibrated using compounds similar to the target analyte and shows some promise in detecting explosives [7]. 

An example of one of TSA/TSL s R D funded MEMS based project is the Sandia National Laboratories (SNL) MicroHound project. This is based on the SNL Micro Chem Lab on a Chip , illustrated in Figure 1. The original prototype system from SNL was developed for high vapour pressure, chemical weapons (CW) detection, which utilized a MEMS GC separator, with miniature surface acoustic wave (SAW s) based sensors. The system included an inlet, coated pre-concentrators, detectors, and pumps. To make this useful for trace explosives detection, the addition of an alternate front-end sample collection/macro-preconcentrator and MEMS based coated-preconcentrator is necessary, along with the option to utilize or exclude the MEMS GC separator followed by detection by either, or both, SAW s and miniaturized IMS detectors. 

Chapters 15 and 16 continue with a discussion of some of the new types of electronic noses namely a fast GC column with a SAW detector and secondly the use of micromechanical sensors. 

The Model 4300 zNose is a portable GC that can detect and measure levels of many types of vapours, toxins, explosives, narcotics and other compounds. It is the first GC to be based on surface acoustic wave (SAW) technology. The battery pack allows field operation for six hours. Analysis time is between 1-60 seconds and sensitivity is low ppb for most compounds with a precision of 5 % RSD. The combined weight of the sampler, chassis and charger is 14.6 kg. 

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