This application note demonstrates quantitative sample preparation of calibration standards using the CDS 7550S automated thermal desorber. The internal standard loop of the 7550S is utilized here to automate the process of preparing calibration standards onto pre-conditioned thermal desorption tubes.
Gas chromatography (GC) is an analytical technique by separating a mixture of compounds for a downstream detector to identify the chemical composition of each component. Direct liquid injection intot the GC inlet is the most common method of introducing sample onto the GC column. However, in many situations, the analyte identity, analyte concentration, or the matrix are not compatible for GC analysis. To tackle this challenge, various sample introduction techniques, including Purge and Trap, Thermal Desorption, Pyrolysis, and Solid Phase Micro Extraction were developed to introduce analyte onto the GC column to achieve the best separation result.
Here the CDS 7550S automated Thermal Desorber incorporates a sample concentration feature, which is designed to assist in sample preparation of calibration standards. Sample concentration works successively adding one more aliquots of standard gas directly from a sample loop of a known volume.
A CDS 7550S automated thermal desorber with the internal standard and Peltier options. In concentration mode, calibration standard is added directly to the sample tube.The calibration standard that was used was a pre-mixed 1 ppmv gas used for EPA TO-15 containing 65 analytes (Restek PN 34436). This was done for four total samples in which one, two, three, and four aliquouts of standard gas were added to each tube. The volume of the sample loop is 5 mL. After the standard was added into each tube, the sample tube was returned the autosampler rack where the tube was stored until all calibration standards were prepared. Once all samples were prepared, the VOCs were desorbed from the thermal desorption sample tube to the analytical focus trapped electronically cooled by a Peltier unit. The sample tube was manufactured by Camsco and packed with Carbograph 1/Carbograph 2/Carboxen 1000 (P/N SU644-4).
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