Sunday, April 1, 2012

Field Asymmetric Ion Mobility Spectrometry (FAIMS): Quick screening detection and quantification of volatile organic compounds

 This article originally appeared in the January 2012 issue of inform magazine.

Field Asymmetric Ion Mobility Spectrometry (FAIMS): Quick screening detection and quantification of volatile organic compounds by Russell Parris and Steve Freshman

FAIMS portable instrumentation brings the “lab to the plant floor” providing a highly sensitive and selective approach to analyzing chemicals of interest right at the point of need.

Field asymmetric ion mobility spectrometry (FAIMS), also known as differential mobility spectrometry (DMS), is a gas detection technology that separates and identifies chemical ions based on their mobility under a varying electric field at atmospheric pressure. Samples in the vapor phase are introduced via a carrier gas to the ionization region, where the components are ionized via a charge transfer process or by direct ionization, depending on the ionization source used. It is important to note that both positive and negative ions are formed. The ion cloud enters an electrode channel, where an RF (radio frequency) waveform is applied to create a varying electric field under which the ions follow different trajectories dependent on the ions’ intrinsic mobility parameters. A DC voltage (compensation voltage) is swept across the electrode channel shifting the trajectories so different ions reach the detector, which simultaneously detects both positive and negative ions. The number of ions detected is proportional to the concentration of the chemical in the sample.

A detailed FAIMS overview is available at (Lonestar is a FAIMS portable sensor manufactured by Owlstone.)

FAIMS produces a unique, data-rich, two-dimensional fingerprint of the chemicals present within a sample matrix of interest. Chemicals are identified by their respective peak locations within the chemical fingerprint, and their concentrations are determined by the peak heights. FAIMS analyses of solid and liquid matrices are accomplished by analyzing the headspace created above the samples. Gas mixtures can also be analyzed. A static or dynamic technique can be employed depending on what needs to be determined. To solve the detection problem and provide a finished solution, the application must undergo a method development process. The target analyte response is identified in the sample matrix and then the instrument is calibrated for this response.

FAIMS rapid detection can be used within the edible oils industry for such applications as at-line screening of raw material contaminants, flavor thresholds, preservative levels, and the age of oils.

Figure 1 is a schematic of a typical instrumental setup that could be used for the determination of such things as tert-butylhydroquinone (TBHQ) concentration, oil cooking time, and the differentiation of various edible oils.

Figure 1. Edible oil analysis instrumental schematic. Abbreviations: LPM, liters per minute; barg, bar gauge; Mpa, megapascals. (Comment: Clean air flowing through the headspace at 2.3 LPM.)
For the TBHQ detection application, a 20 mL oil sample is placed into a glass bottle within the sample holder and heated to 30°C. Equilibrium is reached in approximately 3–5 minutes, at which time the headspace is continually flushed with clean, dry air. A FAIMS dispersion field (DF) matrix is created over a range of electric fields characterizing the headspace response. A precalibrated instrument then gives the user a concentration measurement with predetermined alarm levels reflected in a red light/green light response.

Fig. 2 highlights the ability of the FAIMS platform to differentiate and screen for various edible oils. Both the positive and negative mode compensation voltage (CV) plots of various palm oils can be analyzed simultaneously to further enhance detection efforts.

Figure 2. Field asymmetric ion mobility spectrometry (FAIMS) positive and negative mode compensation voltage plots of various vegetable oils illustrating the ability to rapidly differentiate edible oils. Abbreviations: RIC, reactive ion current; A.U., arbitrary unit; DF, dispersion field

As the cooking time increases, various volatile organic compounds emerge. A clear linear response curve (Fig. 3) enables the method developer to quantify the age of the oil used in a particular process.

Figure 3. Calibration of cooking oil time derived from the FAIMS response (insert), enabling the user to accurately determine the aging of the oil during its useful lifetime. PPIP: positive product ion peak; CV, compensation voltage. For other abbreviations, see Fig. 2

Based on the requirements and specifications of a particular application, additional parameters such as the temperature of the sample matrix can be optimized before conducting the analysis to achieve the desired result. The impact of temperature on sensitivity is illustrated in Fig. 4.

Figure 4. Characterization of TBHQ (tert-butyl hydroxyquinone) in oil at different concentration levels and different sample holder temperature regimes. Abbreviation: DF, dispersion field.

In this comparative analysis, the incubation temperature of TBHQ oil samples was changed. Increasing the incubation temperature of the TBHQ samples from ambient to 40°C lowered the sensitivity of the FAIMS spectrometer from 50 ppm to 10 ppm. By using this 40°C method, it is now possible to build a detection algorithm for TBHQ from 10 ppm to 200 ppm with 10% precision and accuracy. Once the algorithm is created, the TBHQ concentration of outgoing products can be reported in real time. (Note: A video demonstration showing a FAIMS-based instrument in action is available at

Portable Rapid Detection

Using its proprietary FAIMS-based platform, Owlstone Inc. (Cambridge, UK) has created a portable rapid detection instrument, Lonestar, that can rapidly identify and quantify chemicals of interest at ppm/ppb levels. The heart of its detection technology is a one centimeter square-sized silicon chip (3 millimeters in thickness) spectrometer (Fig. 1).

Figure 1.This dime-size silicon chip is a complete chemical detection system with the ability to rapidly monitor a broad range of chemicals at very low quantities with high confidence.

Ions with the correct differential mobility pass through the device and hit the detector electrode. The ion current is an indicator of concentration.

Working with solid, liquid, and gaseous samples, nontechnical operators are able to use the instrument right at the point of need within a plant. The operator presents a small sample to the instrument and simply pushes a button to start the analysis. The concentration levels for the chemicals of interest within the specific matrix are reported based on the preprogramming of the instrument.

Within the edible oils industry, rapid, at-line screening applications of this instrument include the monitoring of raw material contaminants, flavor thresholds, preservative levels, fatty acid methyl esters, and residues from cleaning-in-place, to name just a few.
Russell Parris graduated from the University of Manchester with a Ph.D. in analytical chemistry. He worked within the UK Ministry of Defence before moving to Owlstone Inc. (Cambridge, UK), where he now leads the chemistry group in developing and supporting new and existing FAIMS applications. He can be reached at

Steve Freshman holds an M.B.A degree in marketing. He is responsible for FAIMS partnering efforts globally at Owlstone. He can be reached at
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