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nbsp; Detector noise is any perturbation on the detector output that is not related to an eluted solute. It is a fundamental property of the detecting system and determines the ultimate sensitivity or minimum detectable concentration. Detector noise has been divided into three types, 'short term noise', 'long term noise' and 'drift' all three of which are depicted in figure 4.   Short term noiseresults from baseline perturbations that have frequencies significantly higher than those of an eluted peak. Short term noise is not a serious problem as it is easily removed by appropriate noise filters without significantly affecting the profiles of the peaks. Its source usually originates from either the detector sensor system or the amplifier.   Long term noiseresults from baseline perturbations that have frequencies similar to those of an eluted peak. This type of noise is the most damaging as

Figure 26 Different Types of Noise Short term noise consists of baseline perturbations that have a frequency that is significantly higher than the eluted peak. Short term detector noise can be easily removed by appropriate noise filters without significantly affecting the profiles of the peaks. Its source is usually electronic, originating from either the detector sensor system or the amplifier. Long term noise consists of baseline perturbations that have a frequency that is similar to that of the eluted peak. This noise is the most significant as it

Separation of a High Molecular Weight Hydrocarbon Wax on a High Temperature Stationary Phase As would be expected the more polar the stationary phase the lower the temperature stability. An example of the use of Dexsil 400 to separate some very high boiling waxes is shown in figure 36. The column was programmed from 50˚C to 380˚C at 4˚C /min. and held at 380˚C for 6.5 min. The carrier gas flow rate was 30 ml/min. The wax components are well resolved and the baseline appears very stable even a 380˚C. The stable base line, with no drift, indicates there is little or no decomposition of the solutes or the stationary phase, even at 380˚C. Stationary phases based on the carborane structure, can extend the temperature range of gas chromatography very significantly, However, having thermally stable stationary phases solves only half the problem, the solutes themselves must be equally stable

In figure 23 the values of (Hmin.) are plotted against solute diffusivity and it is seen that the independence of (Hmin.) on diffusivity is largely confirmed. Close examination, however, shows that neither of the lines for the two solutes are completely horizontal with the baseline, but the dependence of (Hmin) on diffusivity is extremely small for the solute benzyl acetate. The slight slope of the line for the solute hexamethylbenzene might well result from the fact that either the (A) term is not completely independent of the diffusivity (Dm) as shown by the results in figure  21, or the resistance to mass transfer in the stationary phase does make a small but significant contribution to the value of (H). The curves relating the optimum velocity with

Resolving Power of a Column For two solutes to be resolved their peaks must be moved apart and maintained sufficiently narrow to be eluted as discrete peaks. The criterion for the separation of two peaks (usually termed the resolution)  is defined as the ratio of the distance between the peak maxima to half the peak width (s) at the points of inflection. The separation of a pair of solutes  2s, 3s, 4s, 5s and 6s apart are shown in Figure 16. For baseline resolution, the peak maxima should be separated by 6s but for most analyses (especially where peak height measurements are employed) a separation of 4s is usually quite satisfactory. Even employing peak area measurements, a separation of 4s will usually provide adequate accuracy particularly if computer data acquisition and processing is employed. Figure 16. The Separation of Solutes Pairs by 2s, 3s, 4s, 5s and 6s A resolution of 4s will be assumed when dealing with resolution

nbsp; Courtesy of Supelco Inc.   Figure 46 The Separation of Some Aromatic Hydrocarbons The separation of some aromatics contained in a mixture of hydrocarbons is shown in figure 46. A column 30 m long, 0.25 mm I.D., carrying a film of permethylated b-cyclodextrin 0.25 mm thick, was used by Supelco for the separation. The column was operated isothermally at 50˚C and helium was use as the carrier gas at a flow velocity of 20 cm/s. It is seen that baseline separation is achieved for the m- and p-xylenes and that the separation ratio for the two isomers was about 1.03. Chiral analysis in the drug industry is now extremely crucial. There are two factors that have contributed to the importance of chiral GC in drug analysis. Firstly, the critical nature of the enantiomeric character of a drug has now been well established (largely arising from the thalamide disaster). The Food and Drug Administration, as a consequence, has