Determination and identification of pesticides from liquid matrices using ion mobility spectrometry
Introduction
Unlike in mass spectrometry, ions can be measured by an aspiration type ion mobility spectrometry (IMS) at normal atmospheric temperature and pressure. This technique is based on ion mobility which is dependent to the molecular weight, charge and shape [1]. Naturally, the mobility of ions increases with decreasing molecular weight and increasing charge. Using the IMS model MGD-1 vapor analyzer, it is possible to analyze volatile or semi-volatile organic compounds that have a high proton affinity or electronegativity in the gas phase [2], [3]. Such compounds are e.g. aldehydes, ketones, halogens, halogenated hydrocarbons, cyanides, nitrogen compounds, ammonia, and some polyaromatic compounds [1], [4], [5]. In addition, organophosphorus (OP) compounds generally form protonated molecules, and the compounds that contain electronegative functional groups, such as halogen atoms or nitrogen groups produce more negative ions than normally in traditional IMS [5], [6].
The first multichannel IMS was developed for on-line gas detection of chemical warfare agents in 1992 [7], [9]. With this technique, it is possible to detect chemical warfare nerve agents such as sarin, soman, tabun and VX [1], [7], [9], [10], but also OP and carbamate pesticides [8]. This technique has also been used as a civil application for on-line monitoring of ethanol concentration from beer and yeast fermentation processes [11]. However, the IMS cannot be used for detecting those compounds that are difficult to ionize and produce product ions (e.g. hydrocarbons, heavy metals).
Pesticide intoxications are very widely occurred in agriculture, especially in the developing countries. Acute pesticide poisonings are known to be a major public health problem, for example, in Sri Lanka [12]. On a world-wide scale, there are approximately 3,000,000 and 100,000 cases of acute pesticide and OP intoxications, respectively, and approximately 220,000 deaths per year [13], [14]. For this reason, rapid, simple and sensitive field methods are required to check the presence of these compounds. Traditional methods such as gas chromatography (GC), high-performance liquid chromatography (HPLC) and GC coupled with mass spectrometry (GC-MS) are the best available methods. However, these methods are known to be expensive and quite laborious. In this paper, we describe the use of an aspiration type IMS for the detection of pesticides such as sulfotep, propoxur and nicotine from a liquid matrix.
Section snippets
Instrumentation
A ceramic evaporator was used to vaporize pesticide solutions. IMS model MGD-1 (Environics Oy, Kuopio, Finland) contains two different sensors: an open type ionization cell (ImCell™) and a commercial semiconductor cell (SCCell). The ImCell™ which has no membranes was used in this study. The detection system was composed of a commercially available MGD-1 and a personal computer. More information about the IMS model MGD-1 can be found from http://www.environics.fi. The MGD-1 was equipped with a
Results and discussion
In this study, the responses from 2-propanol background differed clearly from the responses of pesticides. Table 1 shows the detection limits of the IMS for used pesticide compounds. On the basis of projections, the sensitivities of detection for different insecticide compounds decreased in the order: sulfotep (6.4 μg/ml), propoxur (20.9 μg/ml) and nicotine (32.4 μg/ml).
Typical responses of different detector channels of MGD-1 for 2-propanol and two concentrations of sulfotep are presented in Fig.
Conclusions
Based on these results, it was concluded that the IMS model MGD-1 with ASPRM and neural network methods can be used to detect and identify some of the semi-volatile insecticide compounds even if they are present in liquid samples. The instrumentation required is simple and inexpensive and the analysis time is rapid compared to other traditional detection techniques, and due to that this technique would seem to make it potentially valuable for the analysis of pesticides even at residue levels.
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2019, International Journal of Mass SpectrometryCitation Excerpt :Also, pesticides have been detected and analyzed using stir bar sorptive extraction and thermal desorb ion mobility spectrometry (SBSE-TD IMS) [20]. Tuovien and coworkers described the use of an advanced signal pattern recognition method (ASPRM) linked to the IMS for determination of three semi volatile pesticides sulfotep, propoxur and nicotine in liquid samples with detection limits of 6.4, 20.9, 32.4 mg/L, respectively [21]. Zou et al. [22] developed a method for analysis of 30 pesticides in drinking water with dispersive solid phase extraction (DSPE) based on multiwalled carbon nanotubes (MWCNTs) and pulse glow discharge ion mobility spectrometry.
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2017, TrAC - Trends in Analytical ChemistryCitation Excerpt :On the other hand, and despite the IMS method performed, analytes must be ionized prior entering into the mobility cell, so an ionization source must be inevitably coupled to the ion mobility spectrometer. In the case of the determination of residues and contaminants in food products, radioactive ionization sources mainly based on 63Ni were initially used [29,30], although other radioactive ionization sources such as 241Am-based [27,28] and 3H-based [31] have also been investigated. However, due to safety reasons, these ionization sources have been gradually replaced by photoionization [32], corona discharge (CD) [33,34] and pulse glow discharge (PGD) sources [35–37].
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