DART-MS

For elucidation of biosynthesis and TA identification in plants mass spectromet-ric procedures including LC-MS [16, 17], LC-MS/MS [18] and DART MS (direct analysis in real time MS) [19] were successfully applied. 

Many publications exist in the field of food analyses. Gerda Morlock described in 2004 the determination of heterocyclic aromatic amines after a 6-step AMD-separation. She used an HPTLC-MS online extractor, developed by Luftmarm [93a]. In 2004 a patent application was made for the mode of operation of this so-called ChromeXtrakt device [93b]. In her latest paper (2006), the quantification of isopropylthioxanthon (ITX) in food using HPTLC/FLD coupled with ESI-MS and DART-MS was reported. The prepared samples were separated on a HPTLC-plate and determined by a fluorescence detector (FLD). Positive results have been verified by ESI-MS (Electrospray-Ionisation-Mass-Spectrometry) and DART-MS (Direct Analysis in Real Trme-Mass-Spectrometry) [93c]. 

FIGURE 13.2 Reproducibility test of repeated injections of a rat plasma sample containing 1 (J.M of benzoylecgonine on the DART/MS/MS system. The %CV of the peak height is 3.1%. (Reprinted from Yu, S. et al., Anal. Chem., 81, 193, 2009. With permission.)... 

A major limitation of the DART/MS/MS method in bioanalysis is the potential metabolic interference resulting from ion source fragmentation. The helium atom at the excited state carries an internal energy of 19.8 eV, which is higher than the bond energy in many labile metabolites. Since no chromatographic separation is used in the DART/MS/MS method, metabolites with labile chemical bond, such as a glucuronides or A-oxides, may break down in the ion source and interfere with the assay of the parent compound [27], This limitation is believed to be more of a... 

Another new technology that has the potential to be useful for various EDM assays is direct analysis in real time (DART) MS (Cody et al., 2005 Cody, 2009). DART is an open-air ionization teehnique that can be adapted to standard atmospherie pressure ionization (API) sources as part of a triple quadrupole MS system. The main advantages of DART are no sample preparation and fast assays. Yu et al. (2009) have recently published a report showing that DART MS/MS eould be applied to metabolic stability assay samples. The main limitation of DART is that because there is no ehromatographic step, there is the potential for interferences from metabolites that are labile in this source (e.g., glueuronide metabolites of the test compound) this issue could lead to a false-positive result in some cases. In spite of this issue, DART may become a useful teehnique for some special EDM assays. 

VOC emissions from tobacco plants exposed to ozone were investigated with PTR-MS in conjunction with GC-MS, and the formation of volatile Ce emissions was found to be inversely proportional to the O3 flux density into the plants [57]. Jasmonic acid, a signaling compound with a key role in both stress and development in plants who elicits the emission of VOCs, was sprayed on the leaves of the Mediterranean tree species Q. ilex, and the emissions and uptake of VOCs were detected with PTR-MS and GC-MS after a dark-light transition [58]. Monoterpene and methyl salicylate emissions were enhanced and formaldehyde foliar uptake decreased significantly 24 h after the jasmonic add treatment. The release of VOCs from eucalypt as a function of temperatures from ambient to combustion were analyzed by PTR-MS, GC-MS, and direct analysis in real time (DART) MS [59]. The biogenic VOCs seem to provide a protection against high temperatures [60] and oxidation stress [61]. 

FIGURE 49.4 (A) HPTLC-DART-MS with the desorption at an angle option and the motorized rail equipped with the x-y-z table (B) HPTLC-DART-TOF-MS of an isopropylthioxanthone zone recorded within seconds directly from the plate. 

In the following section, three approaches are focused on and exemplarily described, for which instrumentation and support are commercially available and for which own research experience are given. One HPTLC-MS application is based on an interface using an elution head (high-performance thin-layer chromatography-electrospray ionization mass spectrometry, HPTLC-ESI-MS) the other two applications are using either laser light (HPTLC-MALDI-MS) or a gas beam for desorption (HPTLC-DART-MS). They all are soft ionization techniques however, when combined with analyzers suited for structure elucidation, like ion trap or tandem mass spectrometry (MS/MS), structural information is also available. 

With the DART ion source with the desorption at an angle option, the scanning of surfaces by DART-MS was possible, and a simple gas beam focus visualization technique was suggested for any surface analysis using DART-MS [74], This visualization is based upon the use of different chemical reactions which lead to color formation upon local heating of the surface (e.g.,derivatiza-tion on a TLC/HPTLC plate). Such a visualization is important for selecting the optimal coordinates of the DART ion source with regard to the sample for an optimal detectability. 

Compounds Matrices m/z HPTLC-DART-MS Signal Assignment Reference... 

Morlock, G, Schwack, W. (2006) Quantification of ITX in food by HPTLC/FLD coupled with ESI-MS and DART-MS. CAMAG Bibliography Service CBS, 96, 11-13. 

Morlock, G., Schwack, W. (2006) Determination of iso-propylthioxanthone (ITX) in milk, yoghurt and fat by HPTLC-FLD, HPTLC-ESI/MS and HPTLC-DART/MS. Analytical and Bioanalytical Chemistry, 385, 586-595. 

The first commercial coupling of HPTLC with DART was reported by Morlock and Ueda in 2007 using a silica gel 6OF254 HPTLC plate and an lonSense excited gas stream DART installed on a JMS-TIOOLC (AccuTOF-LC, JEOL) for qualitative analysis of isopropylthioxanthone and caffeine [18]. Later, Dytkiewitz and Morlock [19] used the lonSense TLC-DART MS interface for the identification of lubricant additives in mineral oil. Developed RP chemically bonded diol (C2) F254 and silica... 

Silicon nitride coated CNT-templated UTLC plates were employed for analyte detection via DESI-MSI and direct analysis in real-time mass spectrometry (DART-MS) after chromatography. Rhodamine B (m/z 443.2 M+) and Basic Blue 7 (m/z 478.3 M ) were desorbed with methanol as spray solvent at 0.003 mL min within 45 min for scanning an 85-mm plate section (Figure 9.9). Dimethyl Yellow (m/z 226 [M-i-H]+), Oracet Red G (m/z 238 [M-i-H]+), Solvent Blue 35 (m/z 351 [M-t-H]+), Sudan Red G (m/z 279 [M-i-H]+), and Solvent Blue 22 (m/z 305 [M-i-H]+) were detected within 3.5 min with a snbstantially optimized interface for HPTLC-DART-MS applying a helium flow of 3 L min at 500°C (Figure 9.10) [2]. 

The lack of quantitation limits the use of DART in many fields. A new system was proposed, which possesses an option for quantitative analyses [3]. This group demonstrated the analysis of a total extract of Schisandra chinensis fruit on a TLC plate. Three major lignin compounds were identified and quantitated. UV densitometry, TLC-DART-MS, and HPLC-UV were compared as detection methods. For DART analysis, the width of a TLC plate was cut to a narrow slice of 3 mm. The developed... 

Kim, H.J., Oh, M.S., Hong, J., and Jang Y.P. 2011. Quantitative analysis of major diben-zocyclooctane lignans in Schisandraefructus by online TLC-DART-MS, Phytochem. Anal, 22 258-262. 

Another ionization technique that can be carried out under atmospheric conditions and is utilized for direct analysis in real time is DART-MS. Similar to DESI-MS, samples do not require pretreatment, and thus, the time required for DART-MS analysis decreases. The DART ion source has been used to analyze a number of substances such as drugs in seized materials and biological fluids, dyes and inks, food, and environmental compounds. All of these analytes can be ionized directly on surfaces such as glass, TEC plates, concrete, and paper [11]. 

Several applications of forensic science were reported. Methilenedioxymetham-phetamine (MDMA) was detected by placing ecstasy pills in front of the DART ion source. Ropero Miller et al. characterized 25 cocaine samples acquired by local police. The use of DART-MS allowed for the detection of adulterants and other components, thus generating a complete profile of the samples [12,13]. 

The first use of TEC-DART-MS was described in the analysis of milk products [14]. Since then, innovations in ionization techniques under atmospheric conditions were made, which led to increased precision in the quantitative assessment of substances present on TEC plates. Currently, a new version of DART-MS is available in which the angle of the carrier gas flow can be adjusted and a motorized rail can be used to adjust the position of the ion source toward spots on the TEC plates [15], TEC-DART-MS also has been used for the detection of organophosphorus in fatty foods [16]. 

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