Minimizing thermal degradation in gas chromatographic quantitation of pentaerythritol tetranitrate

Trace Explosives Vapor Generation and Quantitation at Parts per Quadrillion Concentrations

“…In addition, PETN is exceedingly thermally labile when compared to TNT and RDX, making generation and quantitation difficult. Previous efforts have focused on developing analytical methodologies that preserve intact molecular PETN, with little or no thermal degradation, by deposition of PETN solution on TDS tubes and subsequent desorption and analysis by GC . In the current work it was necessary to operate the nebulizer heat tube at 100 °C when generating PETN vapor, as the normal operating temperature of 130 °C caused excessive thermal degradation of PETN.…”

“…Previous efforts have focused on developing analytical methodologies that preserve intact molecular PETN, with little or no thermal degradation, by deposition of PETN solution on TDS tubes and subsequent desorption and analysis by GC. 14 In the current work it was necessary to operate the nebulizer heat tube at 100 °C when generating PETN vapor, as the normal operating temperature of 130 °C caused excessive thermal degradation of PETN. As was the case with RDX, due to the elevated temperature of the air in the vapor handling system, a vapor concentration well in excess of the saturated vapor concentration is possible based on the Clausius−Clapeyron equation; a saturated vapor concentration of 13.7 ppb is possible for PETN at 66 °C.…”

“…Sample time changed as a function of vapor concentration using previously established calibration methods for thermal desorption tubes, as demonstrated elsewhere. ,− Briefly, each sample tube was spiked with 3,4-DNT to serve as an internal standard, and the sample was desorbed from the tube and trapped on a cryo-cooled PTV inlet and subsequently desorbed for GC/μElectron Capture Detector (ECD) analysis (7890A GC, Agilent). Analyte response was normalized to the 3,4-DNT signal and quantified using a calibration curve prepared per previous references. ,− …”

“…Research at the United States Naval Research Laboratory has recently focused on the generation and validation of a variety of trace-explosive vapors. ,− An alternative vapor-generation technique has been developed to overcome the weaknesses of the aforementioned techniques, notably a lack of vaporization efficiency, narrow operating conditions for avoiding vapor pulsations, limited dynamic range, and the potential for thermal degradation of analytes. This alternative method for trace-explosive vapor generation uses a pneumatically modulated liquid delivery system (PMLDS) coupled to a nebulizer .…”

“…Typical vapor validation methods rely on the use of thermal desorption tubes for the collection of sample with subsequent analysis via hyphenated gas chromatography techniques. In such an approach, vapor is first adsorbed by sampling onto a large volume of sorbent material (e.g., Tenax-TA) in a sorbent tube; the sorbent tube is then manually inserted into a thermal desorption system (TDS); the vapor is desorbed from the sorbent and trapped on a low-volume programmable temperature vaporization (PTV) inlet (located where a GC inlet liner would typically be found), followed by a second desorption step for delivery into the GC column. ,− For very low vapor concentrations, this approach can be a time-consuming process limited by sample flow rate and the presence of chemical noise associated with the sampling media. An alternative to the TDS-PTV-GC method is online PTV-GC instrumentation, where analyte is sampled directly to a PTV inlet held at a low temperature (with or without a stationary phase for analyte capture) and subsequently desorbed for GC analysis …”