Sensors and Actuators B 195 (2014) 44–51 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical jo u r nal homep age: www.elsevier.com/locate/snb UV photo-ionization based asymmetric field differential ion mobility sensor for trace gas detection Suresh M. a,∗ , Nilesh J. Vasa a,1 , Vivek Agarwal b , Jacob Chandapillai c,2 a Department of Engineering Design, Indian Institute of Technology Madras, Chennai 600036, India b Department of Electrical Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India c Fluid Control Research Institute, Kanjikode West, Palghat, Kerala 678623, India a r t i c l e i n f o Article history: Received 25 July 2013 Received in revised form 21 December 2013 Accepted 3 January 2014 Available online 13 January 2014 Keywords: Differential ion mobility Asymmetric wave electric field UV photo-ionization Volatile organic compounds Trace gas sensing FA-IMS a b s t r a c t A high-field Asymmetric Waveform Ion Mobility Spectrometry (FA-IMS) with ultra-violet (UV) photo- ionization source is proposed and demonstrated for measurement of trace amounts of volatile organic compound (VOC) gases. Experimental studies performed with the sensor using a high frequency asym- metrical waveform differential field for detection of acetone, hexane and acetone–hexane mixture in trace concentrations are discussed. The detection limit as estimated for a signal-to-noise ratio of 3 is of the order of 100 ppb for acetone and hexane. Experimental studies clearly show that selective sensing of a gas in a mixture of gases is also possible by appropriate value for the compensation voltage. Numer- ical Simulation is also performed using two-dimensional fluid-flow equations to estimate the motion of ions in an electric field. The study also demonstrated influence of parameters such as flow velocity, duty-ratio, on compensation voltage for detection of trace VOC gases with asymmetrical high-frequency electric field. Results based on theoretical study are in agreement with the experimental studies. © 2014 Elsevier B.V. All rights reserved. 1. Introduction There is an increasing interest in study of patho-physiological and metabolic processes in human body through compositional analysis of human exhaled air [1–8]. Certain clusters of volatile organic compounds (VOCs) in human breath are considered to serve as non-invasive potential biomarkers for various disease states such as hyper-lipidemia, cancer, diabetes, kidney and liver disease, recent smoking behavior, etc. Techniques for trace gas detection, such as Proton-Transfer Reaction Mass Spectrometry (PTR–MS) [6], Gas Chromatography Mass Spectrometry (GC–MS) [5], Selected- Ion Flow-tube Mass Spectrometry (SIFT–MS) [7], Tunable Diode Laser Absorption Spectroscopy (TDLAS) [8], Cavity Ring-Down Spectroscopy (CRDS) [8], have been reported for investigations for human breath. A robust, compact, sensitive and economically viable, with fast analysis and response is needed for widespread and real-time analysis of trace gases. Some of laser based trace gas sensing systems require special installation environments and are not suited to large scale deployments. Recently, super-luminescent diode with a wavelength in an optical communication band has ∗ Corresponding author. Tel.: +91 491 2566120; fax: +91 491 2566326. E-mail address: mshere@gmail.com (S. M.). 1 Tel.: +91 44 22574706; fax: +91 44 22574732. 2 Tel.: +91 491 2566120; fax: +91 491 2566326. been reported for NH 3 and H 2 O vapor measurements [9] based on the absorption spectroscopy technique. The approach allows detection of multiple gas species, but the wide range of VOCs has specific absorption bands in the mid-infrared region (between 2 m and 5 m). On the other hand, Ion Mobility Spectrometry (IMS) have been reported [10–20] for detection of trace VOCs for chemical-biological applications. IMS methods have been based on Time-of-flight (TOF) [11], ion-focusing aspiration based sensing [12] or sensing based on differential mobility of ions in high and low electric fields (FA-IMS) [13–20]. A typical TOF based ion mobility spectrometer (TOF-IMS) is com- prised of an ionization source associated within an ion reaction chamber, an ion drift chamber, an ion/molecule injection shutter placed between the ion reaction chamber and the ion drift cham- ber and an ion collector (Faraday plate). The separation of ions requires an appreciable length of drift-tube to travel before they are separated. The length of the drift tube used in IMS is typically about 13–30 cm and the resolution of these instruments reduce if the tube length is shortened. TOF-IMS chiefly relies on separation of different ion species due to differing ion mobilities in an elec- tric field applied longitudinally in direction of ion motion inside the drift-tube. On the other hand in a FA-IMS sensor, separation of ions is caused due to differential ion mobilities in high (a few kV/cm to 10 kV/cm) and low fields when an asymmetric electric field waveform (E F ) of high frequency, typically 1–2 MHz, is applied in a direction transverse to flow of ions [17–19]. During each cycle 0925-4005/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2014.01.008