Fast capillary columns

Fast capillary columns (0.10 mm i.d.) are used for rapid analyses because the same resolution can be generated in a shorter time. 

Figure 4.6 The LMCS system incorporates a moveable cryogenic ti ap T through which the capillary column is passed. The modulator (M) can be a pneumatic or motor driven device that moves T up and down as required, according to either preselected times (for a selective mode) or at a fast constant period for GC X GC.

Fast chromatography involves the use of narrow-bore columns (typically 0.1-mm i.d.) that will require higher inlet pressures compared with the conventional wide-bore capillary columns. These columns require detectors and computing systems capable of fast data acquisition. The main disadvantage is a much-reduced sample loading capacity. Advances in GC column technology, along with many of the GC-related techniques discussed below, were recently reviewed by Eiceman et... 

GC-MS analysis is schematically indicated in Figure 7.13. In GC-MS data collection, account should be taken of the fact that GC peaks eluting from a capillary column are only a few seconds wide, which imposes fast scan times. As most compounds analysed by GC-MS are low-MW (<800 Da), a relatively short... 

FIGURE 14.3 Fast analysis of control drugs and metabolites using a 15 cm x 300 fim inner diameter capillary column packed with 3 /tin C18 particles (Micro-Tech Scientific MC-15-C18SS-320-EU) operated at 10 /tL/min gradient flow rate. UV at 278 nm. (Source Drug Enforcement Administration, Southwest Laboratory, Vista, California and S. DiPari.)... 

In order to perform qualitative and quantitative analysis of the column effluent, a detector is required. Since the column effluent is often very low mass (ng) and is moving at high velocity (50-100 cm/s for capillary columns), the detector must be highly sensitive and have a fast response time. In the development of GC, these requirements meant that detectors were custom-built they are not generally used in other analytical instruments, except for spectroscopic detectors such as mass and infrared spectrometry. The most common detectors are flame ionization, which is sensitive to carbon-containing compounds and thermal conductivity which is universal. Among spectroscopic detectors, mass spectrometry is by far the most common. 

This instrument features five detectors (Table 1.7). In the flame ionization detector, the high-speed electrometer, which ensures a very low noise level, is best suited to trace analysis and fast analysis using a capillary column. 

HPLC on a Cosmosil 5 Cis column, using a perchloric acid-acetonitrile eluent (pH 7.6), followed by CLD in the presence of hydrogen peroxide and bis(2,4,6-trichlorophenyl) oxalate (42), was applied to the determination of 1-aminopyrene (43a) and various diaminopyrenes (43b-d). Ascorbic acid was added to avoid oxidative degradation of the aminopyrenes in the presence of metals LOD in the sub-fmol range (SNR 3)147. A fast (less than 10 min) HPLC-ELCD method was proposed for determination of dopamine (19b) and its metabolites in microdialysates, using packed fused silica capillary columns LOD 0.05 Xg/L of dopamine in a 2 XL sample, RSD 3% (n = 10)148. 

Ultra-high flow on capillary columns (0.180 mm i.d.) versus narrow bore (1 mm i.d.) permits to reduce the sample-handling time and to improve column capacity and robustness [14], Moreover, these columns are able to work with sub-2 pm particles, which offer very fast methods to determine the chemical-physical properties of NCE. 

Figure 13 Topographic plot of results from GC-DMS characterization of a mixture of explosives using a 2 m long capillary column with a fast temperature ramp. Source (A. Cagan, H. Schmidt, and G.A. Eiceman, NMSU, August 2005 unpublished results.)...

Chankvetadze et al. prepared a 20-cm-long silica capillary column modified by in situ coating with amylase tris(3,5-dimethylphenylcarbamate) [199] for the fast separation of enantiomers. They showed the separation of 10 pairs of enantiomers. The monolith columns exhibit a slightly lower resolution but significant faster separation compared with a conventional 25 cm packed HPLC column. 

---