Quantitative Analysis of Explosives by Thermal Desorption–GC–MS Method

With the growing public interest to military and homeland security, a reliable analytical technique for identification and quantitation of explosives is in high demand. Many methods have been proposed including colorimetric assays¹ and tandem mass spectrometry² . EPA has also published a standard method using GC-ECD and GC-MS³ to detect trace explosives. These methods either require a high resolution detector that is not ready for large-scale deployments, or focus on samples in solution. Recently, there are reports⁴ that established sampling protocols to collect analytes in vapor phase by using sorbent based thermal desorption tubes, followed by a quantitative GC-MS analysis. In this application note, a thermal desorption system from CDS Analytical coupled to mainstream GC-MS was tested on explosive standards spiked in thermal desorption tubes.

Camsco Tenax 1/4” x 3.5” thermal desorption tubes were the sampling device. The thermal desorber was a CDS 7550S 72-position autosampler equipped with Camsco 1/8” x 115 mm focusing trap, which was packed with 80/100 Supelcoport (3% SP-2100) and Tenax sorbent. A Shimadzu QP-2010 GC/MS system with Thermo Scientific TG-SQC capillary column was used as the separation and detection instrument. The optional Peltier cooling module was not equipped for this application. Experimental parameters are listed below:

7550S Thermal Desorber:                                   GC:

Valve oven:                     250 °C                              GC conditions

GC transfer line:             0.01” ID                            Oven temp.:                         40.0 °C

                                         200 °C                              Injection temp.:

Tube purge flow:            120 mL/min                     0 min                                    160 °C

Pre-heat time:                 10 s                                  2 min                                    175 °C

Tube desorber:                                                         4 min                                    270 °C

Rest temp.:                      35 °C                               10 min                                  160 °C

Dry purge temp.:             35 °C                               Injection mode:                    Split

Dry purge time:               0.5 min                            Pressure:                              30 psi

Desorb temp.:                  280 °C                            Split Ratio:                            10.0

Desorb time:                    10 min                            Temp. program:

Trap:                                                                          40.0 °C hold 6 min

Rest temp.:                       40 °C                              120.0 °C ramp to 100.0 °C

Desorb temp.:                  250 °C                            40.0 °C ramp to 260.0 °C

Desorb time:                    4 min                               hold 10.5 min

>> Download the Full Application Note as a PDF

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