Selective phase distortions caused

The effect is thought to have two origins. First, a cooler mobile phase and by implication cooler sample causes an initial sample focusing at the head of the column. Second, the cooler eluent flow reduces the analyte mobility at the center of the column, thus balancing the enhanced temperature and hence mobility in the center of the column caused by friction heating (Figure 18-3) [14]. At its most serious, not only efficiency but also peak distortion has been observed caused apparently by a temperature in-balance. The selection of the optimum column inlet temperature is not totally clear, and this is an area of ongoing research. 

A side effect of a lack of temperature control is that changes can alter the refractive index of the mobile phase, causing basehne disturbances and reducing sensitivity The problem is principally with refractive index detection [39], but it can also influence spectroscopic detectors and their light path can be distorted. Temperature has also been reported to alter the nature of some stationary phases. For example, it caused a change in the chiral selectivity of the resolution of dihydropyrimidone acid and its methyl ester on amylose and cellulose stationary phases [40],... 

For (b), two models are plausible One may assume either an antiferro-electric pattern of tilted columns for which small fields cause a deviation of the tilt directions and for which a larger threshold field changes the pattern of tilt directions into a ferroelectric structure. Alternatively, a helical tilt may be distorted at lower fields and unwound at higher fields. As the helix pitch in columnar phases is usually much shorter than the wavelength of visible light, no selective reflection of light is expected and one may best distinguish between the two cases by X-ray or circular dichroism measurements. Only... 

The volume of the calibration mixture injected must be selected to avoid distortion of any component peak shapes caused by overloading the sample capacity of the column. Distorted peaks will result in dbplacement of peak apexes (that is, erroneous retention times) and hence errors in boiling point determination. The column liquid phase loading has a direct bearing on acceptable sample aze. 

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