Silicon Microfabricated Column with Microfabricated Differential Mobility Spectrometer for GC Analysis of Volatile Organic Compounds

Abstract

A 3.0-m-long, 150-microm-wide, 240-microm-deep channel etched in a 3.2-cm-square silicon chip, covered with a Pyrex wafer, and coated with a dimethyl polysiloxane stationary phase is used for the GC separation of volatile organic compounds. The column, which generates approximately 5500 theoretical plates, is temperature-programmed in a conventional convection oven. The column is connected through a heated transfer line to a microfabricated differential mobility spectrometer. The spectrometer incorporates a 63Ni source for atmospheric-pressure chemical ionization of the analytes. Nitrogen or air transport gas (flow 300 cm(3)/min) drives the analyte ions through the cell. The spectrometer operates with an asymmetric radio frequency (RF) electric field between a pair of electrodes in the detector cell. During each radio frequency cycle, the ion mobility alternates between a high-field and a low-field value (differential mobility). Ions oscillate between the electrodes, and only ions with an appropriate differential mobility reach a pair of biased collectors at the downstream end of the cell. A compensation voltage applied to one of the RF electrodes is scanned to allow ions with different differential mobilities to pass through the cell without being annihilated at the RF electrodes. A unique feature of the device is that both positive and negative ions are detected from a single experiment. The combined microfabricated column and detector is evaluated for the analysis of volatile organic compounds with a variety of functionalities.

Control of dopants/modifiers in differential mobility spectrometry using a piezoelectric injector

“…Halogenated compounds are widely used in explosives detection, and usually these are chlorinates [17]. However chloride clusters are difficult to resolve from oxygen-based negative mode reactant ion signals, and as the dissociative ionisation of bromoalkanes in DMS have been observed to be similar/same as that of chloroalkanes a brominated compound was selected to allow the negative mode ions to be resolved and the operation of the system to be demonstrated in a straightforward way [24].…”

“…The compensation field of the ion cluster observed at a compensation field of -356.2 V cm -1 is thought to be due to a bromide cluster formed through dissociative ionisation [24]. At mass fluxes below 149 ng min -1 ("A" in Figure 5) the loss of oxygen-based reactant ions was inversely proportional to the yield of bromide ions, and this is indicative of charge transfer from the oxygen reactant ions to 1-bromohexane followed by dissociation.…”

A planar micro-concentrator/injector for low power consumption microchromatographic analysis of benzene and 1,3 butadiene

“…Moreover, these systems can provide a selective detection of a wide range of toxic compounds (Terry et al 1979;Reston and Kolesar 1994;Matzke et al 1998;Wiranto et al 1999;Lambertus et al 2005;Lu et al 2006;Zellers et al 2007;Ohira and Toda 2008;Radadia et al 2008;Jin and Zellers 2009;Zhong et al 2009;Kim et al 2009;Serrano et al 2009). …”

Ion mobility spectrometer—field asymmetric ion mobility spectrometer-mass spectrometry

“…The ions exiting the mobility device yield a time-or size-dependent ion mobility spectrum. FAIMS (field asymmetric waveform ion mobility spectrometry) has been described [4,13,16,17,21,22,25,27]. The asymmetric waveform is composed of a high voltage component, lasting for a short period of time and a low voltage component, of opposite polarity, lasting a longer period of time.…”