Bradbury-Nielsen-gate-grid structure for further enhancing the resolution of ion mobility spectrometry.

In our previous work we proposed a three-zone theory for the Bradbury-Nielsen (BN) gate and proved with a grid-BN structure ion mobility drift tube that enhancements of the three-zone features led to higher resolutions and sometimes higher sensitivities. In this work we continued to seek further improvements of the resolution performance by adopting a BN-grid structure in the same drift tube. The postgate grid works both for confinement of the BN gate induced electric field and for isolation of the injection field from the drift field. This makes it possible to obtain better resolutions by further enhancing the compression electric field and lowering the injection field. It was found in the following experiments that reducing the injection field led to higher resolutions yet lower sensitivities. At an injection field of 140 V/cm, the inverse compression coefficient was found to be much larger than that in the grid-BN structure at all gating voltage differences (GVDs). At GVD = 350 V and a gate pulse width of 0.34 ms, the ion mobility spectrometry efficiency R(m)/R(c) reached as high as 221% in the BN-grid structure, presenting a further increase compared to 182% in the grid-BN structure. Finally, two examples are given to show the separation power improvements with good resolutions.

Resolution enhancement of ion mobility spectrometry by improving the three-zone properties of the Bradbury-Nielsen gate.

A simple space compression-dispersion model for ion transport at ambient pressure was mathematically established. On the basis of this model and aided by SIMION simulation, a three-zone theory was proposed to characterize the Bradbury-Nielsen gating electric field features as three zones: the depletion zone, the dispersion zone, and the compression zone. Then, the influences of gating voltage difference increases on the full width at half-maximum of the Cl(-) peak were investigated in detail to verify the theory. For example, at a gating voltage difference of 350 V and a gate pulse width of 0.34 ms, the ion packets injected were reduced to as low as 60% of their original widths, with the peak height increased from 756 to 808 pA and the resolution from 18 to 33, enhanced by 7% and ~80%, respectively. The ion mobility spectrometry (IMS) efficiency ratios, R(m)/R(c) and R(m)/R(p), were also raised above theoretical values and reached about 182% and 175%, respectively. The experimental results were explained using the proposed theory with good consistency. Finally, a compression coefficient was extracted by fitting the experimental data to the applied gate pulse width, presenting a good linearity. All this shows a potential application in improving the performances of ion mobility spectrometry.

Membrane-extraction ion mobility spectrometry for in situ detection of chlorinated hydrocarbons in water.

Membrane-extraction ion mobility spectrometry (ME-IMS) has been developed for in situ sampling and analysis of trace chlorinated hydrocarbons in water in a single procedure. The sampling is configured so that aqueous contaminants permeate through a spiral hollow poly(dimethylsiloxane) (PDMS) membrane and are carried away by a vapor flow through the membrane tube. The extracted analyte flows into an atmospheric-pressure chemical-ionization (APCI) chamber and is analyzed in a specially made IMS analyzer. The PDMS membrane was found to effectively extract chlorinated hydrocarbon solvents from the liquid phase to vapor. The specialized IMS analyzer has measured resolutions of R = 33 and 41, respectively, for negative- and positive-modes and is capable of detecting aqueous tetrachloroethylene (PCE) and trichloroethylene (TCE) as low as 80 and 74 microg/L in the negative ion mode, respectively. The time-dependent characteristics of sampling and detection of TCE are both experimentally and theoretically studied for various concentrations, membrane lengths, and flow rates. These characteristics demonstrate that membrane-extraction IMS is feasible for the continuous monitoring of chlorinated hydrocarbons in water.

Bipolar ionization source for ion mobility spectrometry based on vacuum ultraviolet radiation induced photoemission and photoionization.

A novel bipolar ionization source based on a commercial vacuum-UV Kr lamp has been developed for ion mobility spectrometry (IMS), which can work in both negative and positive ion mode. Its reactant ions formed in negative ion mode were predominantly assigned to be O(3)(-)(H(2)O)(n), which is different from that of the (63)Ni source with purified air as carrier and drift gases. The formation of O(3)(-)(H(2)O)(n) was due to the production of ozone caused by ultraviolet radiation, and the ozone concentration was measured to be about 1700 ppmv by iodometric titration method. Inorganic molecules such as SO(2), CO(2), and H(2)S can be easily detected in negative ion mode, and a linear dynamic range of 3 orders of magnitude and a limit of detection (S/N = 3) of 150 pptv were obtained for SO(2). Its performance as a negative ion source was investigated by the detection of ammonium nitrate fuel oil explosive, N-nitrobis(2-hydroxyethyl)amine dinitrate, cyclo-1,3,5-trimethylene-2,4,6-trinitramine, and pentaerythritol tetranitrate (PETN) at 150 degrees C. The limit of detection was reached at 45 pg for PETN, which was much lower than the 190 pg using (63)Ni ion mobility spectrometry under the same experimental condition. Also, its performance as an ordinary photoionization source was investigated in detecting benzene, toluene, and m-xylene.

On-line measurement of propofol using membrane inlet ion mobility spectrometer.

The concentration of propofol in patient's exhaled air is an indicator of the anesthetic depth. In the present study, a membrane inlet ion mobility spectrometer (MI-IMS) was built for the on-line measurement of propofol. Compared with the direct sample introduction, the membrane inlet could eliminate the interference of moisture and improve the selectivity of propofol. Effects of membrane temperature and carrier gas flow rate on the sensitivity and response time have been investigated experimentally and theoretically. Under the optimized experimental conditions of membrane temperature 100 °C and carrier gas flow rate 200 mL min(-1), the calculated limit of detection (LOD) for propofol was 1 ppbv, and the calibration curve was linear in the range of 10-83 ppbv with a correlation coefficient (R(2)) of 0.993. Finally, the propofol concentration in an anaesthetized mouse exhaled air was monitored continuously to demonstrate the capability of MI-IMS in the on-line measurement of propofol in real samples.

Note: Design and construction of a simple and reliable printed circuit board-substrate Bradbury-Nielsen gate for ion mobility spectrometry.

A less laborious, structure-simple, and performance-reliable printed circuit board (PCB) based Bradbury-Nielsen gate for high-resolution ion mobility spectrometry was introduced and investigated. The gate substrate was manufactured using a PCB etching process with small holes (Φ 0.1 mm) drilled along the gold-plated copper lines. Two interdigitated sets of rigid stainless steel spring wire (Φ 0.1 mm) that stands high temperature and guarantees performance stability were threaded through the holes. Our homebuilt ion mobility spectrometer mounted with the gate gave results of about 40 for resolution while keeping a signal intensity of over 0.5 nano-amperes.

[A novel gas chromatography detector based on ion mobility spectrometry technology and its application].

Ion mobility spectrometry (IMS) is an attractive detector of gas chromatography (GC) due to its high sensitivity, short response time, and comparatively low cost. The hyphenated GC-IMS instrument can simultaneously provide high separation ability of GC and high sensitivity of IMS. In this paper, one setup of a GC-IMS instrument is introduced. The parameters of IMS as the GC detector were evaluated and studied with respect to the resolution and sensitivity including temperature, total voltage and drift gas flow rate. Under the optimal conditions, GC-IMS was used to detect iodomethane, 1,2-dichloroethane, tetrachloromethane and dibromomethane and the detection limits were 2, 0.02, 1 and 0.1 ng, respectively. And the linear ranges of two orders of magnitude were achieved. As the detector of gas chromatography, IMS can provide more information for compound identification because of its second dimensional separation and can realize selective detection of different compounds.

[Automatic continuous monitoring of volatile organic compounds using ion mobility spectrometer array].

An ion mobility spectrometer array was designed, in order to broaden the detection range of ion mobility spectrometer and improve the accuracy of compound identification. This instrument was based on the combination of ionization sources of 63Ni positive ion mode, 63Ni negative ion mode and photoionization mode with vacuum UV lamp, and it can continuously monitor the volatile organic compounds in air. With the automatic system of sampling and injection of this instrument, the positive ion of dimethyl sulfoxide and negative ion of dichloromethane were detected simultaneously. By comprehensive analysis of spectra with ion mobility spectrometer array, acrylonitrile, m-xylene and acetone were identified, which were difficult to be distinguished under the 63Ni positive ion mode. Acetone samples were determined quantitatively within four days continuously, and the results indicated that the linear range of acetone in this instrument was 2 orders of magnitude. The linear correlation coefficient R was higher than 0.995, and the relative standard deviations were controlled in the range of 4.0%-18.3%. Methacrylate leaked in simulation was monitored on-line for 24 h continuously, using the method of dynamic tracking, and the result showed the leaking time and the concentration of methacrylate directly.