Ts.21 Doping the EESI solvent with 0.01 M sodium acetate exclusively yielded the [M +Na]+ ion for MTS (m/z 209.0258; 4.8 ppm mass error; Figure 2b). The absence in the [M+H]+and its associated fragments inside the mass spectrum improves analyte sensitivity increasing the mass spectral response by a factor of 2 for the [M+Na]+ ion using 0.01 M sodium acetate in comparison with the formic acid doped EESI plume and no fragmentation with the sodiated ion was observed. A sodium-doped EESI plume was used in all subsequent experiments. The TD probe can attain a temperature of 200 in two min, which was found to be adequate for the desorption of MTS vapor. Following reaching the maximum desorption temperature, the probe was cooled by a flow of chilled air. The flow of cooled gas passed via the probe and exited at the probedx.doi.org/10.1021/ac401054n | Anal. Chem. 2013, 85, 6224-Analytical ChemistryTechnical NoteFigure two. Mass spectra obtained applying thermal desorption of MTS vapor in to the modified EESI ion source (50:50 (v/v) MeOH:H2O) with (a) 0.1 formic acid (v/v) solvent modifier and (b) 0.01 M sodium acetate modifier.tip, which rapidly cooled the sample holder to ambient temperatures having a total run time of 5 min. The AP/TD-EESI-MS evaluation of MTS was carried out using the GTI spiked into 50 mg of starch to simulate the atmosphere of an API. The samples have been preprepared making use of sealed aluminum foil wraps that have been pierced prior to evaluation. The usage of the disposable aluminum wraps prevented sample cross contamination and offered a fast method of exchanging samples, minimizing sample to sample cycle time to six min, which is significantly shorter than previously reported GC-MS and LC-MS run-times of 24 and 11 min, respectively.12,17 An example of the thermal desorption profile and mass spectrometric response obtained for the AP/TDEESI-MS analysis of MTS in starch is shown in Figure 3. The total ion response to get a 50 mg starch sample (Figure 3a), utilized as a surrogate API, spiked with MTS at a degree of 2 ppm initially increases together with the probe temperature and then decreases when the heat is removed plus the cooling gas flow initiated.Formula of 1783624-20-3 The ion response returns to baseline levels within 4 min, however the temperature in the sample holder at this point continues to be too high to be handled (70 ) and requires an additional 1 min of cooling.204715-91-3 structure The selected ion response for the sodiated MTS ion ([M+Na]+, 209.PMID:24179643 02 ?0.02) is shown in Figure 3b. The volatility in the MTS offers a sharp desorption peak, using a peak width at half height of 15 s. The maximum response for MTS is observed at 0.9 min when the TD probe temperature was one hundred . The MTS response returns to baseline levels within 3 min. The mass spectrum obtained in the MTS desorption peak is shown in Figure 3c. The background-subtracted spectrum, averaged across the peak at half height, shows a base-peak response for the sodiated MTS ion (7.7 ppm mass error). The application of AP/TDEESI-MS removes the requirement for lengthy sampleFigure three. AP/TD-EESI-MS analysis of MTS (2 ppm (w/w); one hundred ng MTS in 50 mg starch) (a) total ion response; (b) selected-ion response for the sodiated MTS adduct ion (m/z 209.02 ?0.02); and (c) summed, background subtracted mass spectrum for MTS.preparation and derivatization methods linked with other MTS detection procedures;15,16 mainly because low-volatility APIs will not be desorbed by TD, and sample throughput is maximized by reducing total analysis time and using disposable sample holders. The.