19
Time Controlled Cryogenic
Zone Compression (T-CZC): A Novel Gas Chromatographic Tool for Increasing Sensitivity
by D. Krumwiede, H. Mehlmann, Kyle D’Silva POPs Center of Excellence, Thermo Fisher Scientific (Bremen) GmbH, Hanna-Kunath-Strasse 11, 28355 Bremen, Germany
The analysis of semi-volatile trace contaminants represent a unique challenge to the analytical chemist. Modern techniques of gas chromatography and mass spectrometry have reduced instrumental limits of detection from the nanogram range in the 1970s, using packed chromatography columns and quadrupole mass spectrometry; to the low femtogram range during the twenty-first century, using capillary columns coupled to high resolution or tandem quadrupole mass spectrometers [1].
Some compounds which require such low levels of detection are chlorinated dioxins and furans; a group of structurally similar halo-organic compounds, which are of great interest because some of these congeners are extremely toxic, persistent and bio- accumulative [2].
For such compounds low limits of detection can now be achieved in many sample types with the combination of sensitive mass spectral detection and careful chromatography. Generally, when even lower limits of detection are required, the analytical chemist has the possibility of combining increasingly selective sample preparation together with significantly increased sample size.
However, when sample sizes are small, and residue levels are low, a unique analytical
challenge is presented, such as with dried blood spot (DBS) analysis. Typical DBS sample sizes can be small, only 50-150 µL [3]. Residue levels are very low, especially for lipophillic compounds like dioxins, and there is no opportunity to scale up sample size to achieve low limits of detection. Usually this challenge would preclude the analysis of dioxins and furans in such samples. However, large archives of dried blood spot samples exist in hospitals globally. These are routinely sampled from children at birth in many countries [3]. These samples present an unprecedented sample resource for epidemiological and toxicological studies of population background exposure to dioxins and furans, providing these significant analytical challenges can be overcome.
Cryogenic peak modulation is a well
established technique used for comprehensive GCxGC applications since 1991 [4]. In GCxGC a cryogenic modulator continuously and rapidly traps and releases the eluent from a first dimension column onto another short second dimension column in a very narrow band. The combination of two different column phases for the first and second dimension results in a substantial increase of chromatographic separation power. This is due to combined chromatographic selectivity, cryogenic peak focusing and fast second dimension chromatography. Each first dimension chromatographic peak is modulated and several second dimension chromatograms are obtained (Figure 1); dedicated software tools allow to construct two-dimensional chromatograms for data evaluation. This
Figure 1: Cryogenic signal enhancement in CZC (left figure) versus GCxGC (right figure)
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60
