Development of a device to measure MCC-IMS peaks of pure analytes (IMS-BOX)

Abstract

Ion mobility spectrometry coupled with multi-capillary columns (MCC-IMS) is a highly sensitive instrument to analyse air samples and gaseous elements therein (ppmv pptv-range). The MCC-IMS is characterized by its ability to pre-separate specimens. It provides an additional dimension (drift-time) to the retention time of the pre-separation column and has the advantage of analysing especially humid air without a filter system or further devices like membranes. Therefore, the MCC-IMS can be used as diagnostic instrument for diseases like asthma [14], sarcoidosis [20], lung cancer [21] or ammonia during haemo-dialysis [13]. Breath analysis can also be used for drug or disease monitoring. For example, Propofol, a hypnotic used for maintaining general anaesthesia, can be measured in exhaled breath [3, 10, 15, 16] or acetone, a VOC from fatty acid metabolisation [9]. The MCC-IMS is a relatively new device and comprehensive databases with clearly identified compounds, like those defined for gas chromatography/mass spectrometry, are lacking so far. Air or breath analysis with MCC-IMS measures many compounds in the chromatogram, which cannot be identified yet in many cases. Especially in case of drug monitoring via exhaled breath it is obligatory to know the exact position of the compound in the chromatogram before breath analysis. Otherwise peak assignment of a breath sample remains uncertain. Actually, in such cases the retention time and the drift time or the 1/K0-value will be added to the Peak name or number. Generally, the role of sample collection is crucial [8]. One way of peak assignment with the MCC-IMS is the analysis of the highly pure substance of interest (e.g. of a certain drug) prior to further experiments, in case they are known or expected. Different sampling introduction systems were compared by L. Arce et al. including permeation tubes, sample containers, headspace sampling with a syringe, ceramic evaporators, membrane inlets, solid-phase microextraction, stir-bar sorptive extraction, thermal desorber units, multi capillary columns, fluid chromatography and electrospray ionization with respect to the analytes, different ionisationosurces like UV, corona discharge, s-radiation and electro-spray. In addition, the limits of detection are considered [1]. Especially permeation tubes goes back to the 1970s [6, 7, 12, 18]. The elimination of room air pollution is sometimes critical, because it contains a large amount of different volatile organic compounds (VOCs) also in trace concentrations to be considered as potential contaminations. If compounds of room air and the pure substance have a similar retention time or inversed reduced ion mobility, a clear assignment of its position in the MCC-IMS chromatogram is difficult. Commercial available systems like HovaCAL® (IAS GmbH, Frankfurt, Germany) [19] developed to realise multi-compound calibration down to the pptV range including relative humidity values up to 100 % for identification of analytes are highly expensive. Therefore, for laboratory use, an exponential dilution unit was developed by Sieleman using a glas flask directly, containing a volume of about This work is dedicated to our friend and colleague Rouven Hellbruck. Rouven deceased on January 4th 2013. S. Kreuer (*) : R. Hellbruck : T. Fink :N. Heim : T. Volk :A. Wolf Department of Anaesthesiology, Intensive Care and Pain Therapy at Saarland University Medical Center, Building 57, 66421 Homburg, Germany e-mail: Sascha.Kreuer@uniklinikum-saarland.de