Standardisation of a Vapour Generator for Calibration of Environmental Monitoring Instruments

Abstract

Very low vapour pressure of 2,4,6 trinitrotoulene (TNT) yields extremely low vapour concentrations at different flow rates in the air, yet considerable quantity of vapours and TNT dust during handling may be present at the workplace environment which is harmful to the health of the personnel working there. The explosive vapours, such as TNT, 2,6-dinitrotoluene (DNT), etc., though harmful to the health of the personnel, are not covered either in the emission standards or in the ambient air quality standards. Presently, no instrument is available for air monitoring of TNT vapours. These vapours need to be collected on-site to estimate TNT concentration. Realising the need for real-time air monitoring of TNT, efforts have been made to understand and device an instrument for on-site determination of TNT vapours parts per billiion (ppb) range. Low-level TNT vapours and TNT buried in the soil in military operations are required to be detected. The instruments for this require careful calibration to yield accurate and reliable results. Hence, an effort has been made to develop a trace-level ppb vapour generator. The vapour generator of a spiral glass column of length 170 cm and inner diameter 4 mm 2 0.5 mm has been used. An activated charcoal glass tube has been used for sampling TNT vapours. The adsorbed TNT vapours were desorbed and analysed using high performance liquid chromatography. The solid support used has been studied. These vapours generated at different flow rates have been evaluated. The calibrated instrument can be used for in situ and on-site analysis of samples of TNT and also for samples collected.

Landmine Detection Technologies to Trace Explosive Vapour Detection Techniques

“…Pulsed vapour generator have also been designed and used in various studies [34][35][36] . Activated carbon or XAD have been used to standardise these explosive vapour generators using liquid chromatography or gas chromatography 30,37 . In one of the research, in place of glass column, a copper column was used and the TNT and DNT were coated on sand granule before filling the column.…”

Comment on “Tunable Generation and Adsorption of Energetic Compounds in the Vapor Phase at Trace Levels: A Tool for Testing and Developing Sensitive and Selective Substrates for Explosive Detection”

“…The generation of explosive vapors from solid samples at controlled temperatures goes back over 3 decades. − Thus, there is a substantial history in the development of explosives vapor generators, although some of this literature is in government or institutional reports rather than the peer-reviewed literature . Vapor generators have also been described based on known masses or mass flows derived from the vaporization of solution standards of known concentration or the thermal desorption of known masses originally deposited from solution. − Some references for explosives vapor generators have been summarized in Moore’s review of explosives detection instrumentation and Yinon’s book on explosives detection .…”

“…Historically, several methods have been used to analyze output vapor streams. Adsorbent collection tubes or cold traps have been used to accumulate the output for analysis using GC. ,, Similarly, collection tubes or cold traps have been used with subsequent high performance liquid chromatography (HPLC) analysis. , The use of collection tubes provides an average output over time and may provide material for compositional analysis, but it may not reveal real time-dependent dynamics in the generator output. The weight losses of permeation bags or diffusion tubes also provide average mass flow rates over time and only provide data on the source, not the diluted output flow. , IMS for output analysis has been used in a number of formats.…”

“…17,18,20 Similarly, collection tubes or cold traps have been used with subsequent high performance liquid chromatography (HPLC) analysis. 27,28 The use of collection tubes provides an average output over time and may provide material for compositional analysis, but it may not reveal real timedependent dynamics in the generator output. The weight losses of permeation bags or diffusion tubes also provide average mass flow rates over time and only provide data on the source, not the diluted output flow.…”

Evaluation of Non-Contact Sampling and Detection of Explosives using Receiver Operating Characteristic Curves

“…Great efforts have been made to generate consistent vapors of various compounds for landmine determination [215], environmental chemical monitoring [216], explosives detection [217][218][219][220] and sensor calibration [221] throughout the past decades. One technique such as Controlled Odor Mimic Permeation Systems (COMPS) uses a thin plastic film to release vapors generated from the solid compounds into the headspace at a fixed rate [11,222].…”