Evaluation of a differential mobility spectrometer/miniature mass spectrometer system.
ABSTRACT A planar differential mobility spectrometer (DMS) was coupled to a Mini 10 handheld rectilinear ion trap (RIT) mass spectrometer (MS) (total weight 10 kg), and the performance of the instrument was evaluated using illicit drug analysis. Coupling of DMS (which requires a continuous flow of drift gas) with a miniature MS (which operates best using sample introduction via a discontinuous atmospheric pressure interface, DAPI), was achieved with auxiliary pumping using a 5 L/min miniature diaphragm sample pump placed between the two devices. On-line ion mobility filtering showed to be advantageous in reducing the background chemical noise in the analysis of the psychotropic drug diazepam in urine using nanoelectrospray ionization. The combination of a miniature mass spectrometer with simple and rapid gas-phase ion separation by DMS allowed the characteristic fragmentation pattern of diazepam to be distinguished in a simple urine extract at lower limits of detection (50 ng/mL) than that achieved without DMS (200 ng/mL). The additional separation power of DMS facilitated the identification of two drugs of similar molecular weight, morphine (average MW = 285.34) and diazepam (average MW = 284.70), using a miniature mass spectrometer capable of unit resolution. The similarity in the proton affinities of these two compounds resulted in some cross-interference in the MS data due to facile ionization of the neutral form of the compound even when the ionic form had been separated by DMS.
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ABSTRACT: Mixtures of ions produced in sources at atmospheric pressure, including chemical ionization (APCI) and electrospray ionization (ESI) can be simplified at or near ambient pressure using ion mobility based filters. A low-mobility-pass filter (LMPF) based on a simple mechanical design and simple electronic control was designed, modeled and tested with vapors of 2-hexadecanone in an APCI source and with spray of peptide solutions in an ESI source. The LMPF geometry was planar and small (4 mm wide × 13 mm long) and electric control was through a symmetric waveform in low kHz with amplitude between 0 and 10 V. Computational models established idealized performance for transmission efficiency of ions of several reduced mobility coefficients over the range of amplitudes and were matched by computed values from ion abundances in mass spectra. The filter exhibited a broad response function, equivalent to a Bode Plot in electronic filters, suggesting that ion filtering could be done in blocks ~50 m/z units wide. The benefit of this concept is that discrimination against ions of high mobility is controlled by only a single parameter: waveform amplitude at fixed frequency. The effective removal of high mobility ions, those of low mass-to-charge, can be beneficial for applications with ion-trap-based mass spectrometers to remove excessive levels of solvent or matrix ions. Copyright © 2013 John Wiley & Sons, Ltd.Rapid Communications in Mass Spectrometry 01/2014; 28(1):135-142. DOI:10.1002/rcm.6762 · 2.64 Impact Factor
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ABSTRACT: Development of miniaturized ion trap (IT) mass analyzers for portable mass spectrometry has taken advantage of the latest technology in conventional machining and microfabrication. Researchers are now turning to new materials, such as polymers and ceramics, as well as alternative electrode shapes and arrangements to create the precisely-shaped electric fields needed for good performance on small-scale devices. Polymer-based construction allows lightweight structures, complex shapes and inexpensive production of small ITs. Simplified electrode arrangements, such as ITs made from two patterned ceramic plates, allow precise electric fields and simplified electrode alignment.TrAC Trends in Analytical Chemistry 11/2011; 30(10):1560–1567. DOI:10.1016/j.trac.2011.07.003 · 6.61 Impact Factor
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ABSTRACT: The direct separation of five acidic phytohormones including auxin (indole-3-acetic acid, indole-3-propionic acid, indole-3-butyric acid), jasmonic acid, and abscisic acid by differential mobility spectrometry-mass spectrometry (DMS-MS) with the use of the polar gas-phase chemical modifier 2-propanol was demonstrated. The method was rapid and simple to operate with selectivity and repeatability. The influence of experimental conditions on the separation, such as modifier types and concentration, separation voltage, temperature and so on, was systematically investigated. The field mobilities dependence was measured as the normalized α function using the developed DMS-MS method. All the analytes behaved as type A ions and the clustering separation mechanism dominated. These results not only gave insights of ion properties but also contributed to the prediction of DMS separation by choosing targeted and appropriate conditions for the study of acidic phytohormones.International Journal of Mass Spectrometry 04/2014; 362. DOI:10.1016/j.ijms.2013.12.025 · 2.23 Impact Factor