Packed columns sample suitability

Also, subcritical (hot/liquid) water can be used as a mobile phase for packed-column RPLC with solute detection by means of FID [942]. In the multidimensional on-line PHWE-LC-GC-FTD/MS scheme, the solid sample is extracted with hot pressurised water (without the need for sample pretreatment), and the analytes are trapped in a solid-phase trap [943]. The trap is eluted with a nitrogen flow, and the analytes are carried on to a LC column for cleanup, and separated on a GC column using the on-column interface. The closed PHWE-LC-GC system is suitable for many kinds of sample matrices and analytes. The main benefit of the system is that the concentration step is highly efficient, so that the sensitivity is about 800 times better than that obtained with traditional methods [944]. Because small sample amounts are required (10 mg), special attention has to be paid to the homogeneity of the sample. The system is... 

Chiral SFC can be performed in open tubular [41,42], and packed column [43,44] modes. Packed column SFC can be further categorized into analytical, semipreparative, and preparative SFC [7, 8], Packed column SFC is more suitable for fast separations than open tubular column SFC, since a packed column generally provides low mass transfer resistance and high selectivity [45, 46], Packed column SFC also provides high sample loading capacity [27,47], which can increase sensitivity. Only packed column SFC is suitable for preparative-scale enantioseparation. This chapter will focus on chiral separation using packed column SFC in the analytical scale. 

The current BP methods for determination of solvent residues in pharmaceuticals remaining from the manufacturing process rely on direct injection of the sample dissolved in a suitable solvent (often water) and are based on packed column GC. Some examples are given in Table 11.4. 

Packed-column SFC also is suitable for preparative-scale enatioseparations. Compared with preparative LC, sub- or supercritical fluid chromatography results in easier product and solvent recovery, reduced solvent waste and cost, and higher output per unit time. Because of its reduced sample capacity, SFC usually allows the separation of 10-100 mg samples per run. Chromatographers can compensate for these sample amounts by using shorter analysis times and repetitive injections (Wolf and Pirkle, 1997). 

The separation of a mixture by GC also depends on the flow rate of the carrier gas. A low rate allows extensive equilibration of the sample between the stationary phase and the gaseous phase and leads to better separation however, the recorder peaks become very broad. A high flow rate greatly decreases column efficiency by decreasing equilibration time. A suitable flow rate for a 0.5-cm packed column is between 50 and 120 mL/min. 

Organic substances can be extracted from aqueous samples by solid-liquid (known as solid phase) extraction. The process is simple, fast, and cost effective in comparison to LLE. In addition, the analysis can be carried out using a smaller volume of sample. By using a suitable capillary column, a detection level comparable to LLE-packed column could be readily attained. The method requires a... 

Size-exclusion chromatography is a liquid chromatography technique in which a polymer sample, dissolved in a solvent, is injected into a packed column (or a series of packed columns) and flows through the col-umn(s) and its concentration as a function of time is determined by a suitable detector. The column packing material differentiates SEC from other liquid chro-... 

In column chromatography, the stationary phase exists in a closed column that is adequately packed with a suitable sorbent. The stationary phase is preequilibrated with the mobile phase before the first sample is introduced. In this case, the stationary phase cannot be in contact with vapors of the mobile phase during the chromatographic process. 

To omit unconventional instrumentation that was not suitable for routine analysis, as proposed by De Graeve et al.88, Bellia et al.81 developed a quite simple method to determine papaverine in blood samples, using conventional flame ionization or a nitrogen-phosphorus detector. The internal standard, strychnine, was added to the sample prior to extraction, which was carried out with toluene after basification, back extraction with acetic acid and extraction of the liberated base with diethyl ether. The gas chromatography was done on a packed column with 2 % 0V-101 at 275°C. To minimize the adsorption effects, the column was silanized by in situ injection and by injection of a concentrated solution of papaverine and the internal standard prior to routine analysis. Precision and accuracy of the method is shown in Table 14.13. 

The story of the discovery of chromatography is classical [16,17]. A most lucid analysis of Tswett s work from the point of view of the preparative applications of chromatography, has been written by Verzele and Dewaele [18]. The Russian botanist Tswett discovered arormd 1902 that plant pigments could be separated by eluting a sample of plant extract with a proper solvent on a column packed with a suitable adsorbent [1]. Did he name the technique chromatography because it separates pigment mixtures into a rainbow of colored bands, or because "tswett" means color in Russian, or both Nobody knows. What is remarkable, however, is the extreme care with which Tswett selected the adsorbents he used [19-21]. For the famous separation of a- and j3-carotenes, he tried 110 different adsorbents and selected inulin (a water-soluble polyfructose plant reserve material) as the... 

Capillary columns are used to separate 1,1,1-trichloroethane from the other components in a mixture. Capillary columns provide wider versatility offering superior resolution of components. A comparison of capillary and packed column for analysis of volatile organics by GC is available (Clark and Zalikowski 1990). Narrow-bore capillary columns have high resolving power but may not be suitable for headspace analysis because of easy column saturation (Ohno and Aoyama 1991). Wide-bore capillary columns are suitable in such cases (Ohno and Aoyama 1991). Different detectors can be used ECD, HECD, and MS have been described. The MS is the most selective detector, but the HECD is the most sensitive. Both closed path and open path Fourier transform infrared spectrometry (FTIR) have recently been used for the determination of 1,1,1 -trichloroethane in air (Carter et al. 1992 Trocha and Samimi 1993 Xiao and Levine 1993). Although the FTIR methods have higher detection limits than some of the other conventional methods, they afford the opportunity of remote monitoring of real-time samples (Xiao and Levine 1993). 

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