| Explosive DART Data and Method Optimization
Explosives were among the first chemicals sampled using DART back in 2005. We revisited the topic recently using our iPod automation method with the DART-SVP and X-Z Scanner to determine the optimum gas temperature for desorption. Since we do not typically know the ideal temperature for generating high quality mass spectra of these compounds, we spotted small aliquots of some dangerous materials on the X-Z sampling screen. We then analyzed them while varying the DART gas temperature, without operator intervention. Accurate mass data were collected providing very high specificity and improving confidence in the results.
For these experiments a DART-SVP was interfaced to the Thermo Exactive Orbitrap for High Mass Resolution screening of PETN and RDX. The analytes were prepared at a final concentration of 1 µg/mL (1 ppm) from reference standards. The samples were spotted (5 µL per sample spot) directly onto a stainless steel mesh support for direct transmission mode analysis with DART.
The X-Z scanner Experiment Module is controlled by the DART Automated Software Method operated via the iPod Touch. The X-Z scanner was used to run an automated temperature ramping method that analyzed the samples at 175, 200 and 225°C DART heater temperatures. This provides a thermal profile and enables the optimum temperatures to be selected.
The Thermo Exactive was operated with external mass calibration performed before analyses, and all analytes had ~1 ppm mass accuracy. The instrument was run in negative mode with resolution of 50,000. Dichloromethane (CH2Cl2) was used as a dopant during the DART analysis to promote ionization and the formation of the [M+Cl]- ion. The vapor from small vial of CH2Cl2 was enough to promote Cl-adduct formation.
In the Figure below you can see how the higher temperature provided superior signal intensity for the PETN. These samples were analyzed for 5 seconds at a time, and the exact positioning and timing provides good reproducibility as well.
Of course, with the accurate mass analysis of the Orbitrap, high specificity is obtained. Below you can see the RDX mass accuracy obtained in this screening method with the experimental data in the bottom and the calculated in the top.
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|About IonSense |
IonSense, Inc. provides open-air mass spectrometry solutions to the fields of food safety, forensics, drug development, and chemical analysis. They manufacture and develop direct analysis in real time (DART®) technology licensed from JEOL USA, Inc. and atmospheric solids analysis probe (ASAP™) licensed from M&M Consulting.
DART and ASAP Sources are available for most commercial LC/MS systems. Look here to see if your system is DART-ready. And check here to see if your system is ASAP-ready.