Temperature, column effect

The robustness of an analytical procedure is a measure of its capacity to remain unaffected by small but deliberate variations in the analytical procedure parameters. The robustness of the analytical procedure provides an indication of its reliability during normal use. The evaluation of robustness should be considered during development of the analytical procedure. If measurements are susceptible to variations in analytical conditions, the analytical conditions should be suitably controlled or a precautionary statement should be included in the procedure. For example, if the resolution of a critical pair of peaks was very sensitive to the percentage of organic composition in the mobile phase, that observation would have been observed during method development and should be stressed in the procedure. Common variations that are investigated for robustness include filter effect, stability of analytical solutions, extraction time during sample preparation, pH variations in the mobile-phase composition, variations in mobile-phase composition, columns, temperature effect, and flow rate. 

For reproducible separations by IPC, it is important to thermostat the column. Temperature effects in IPC are more important than in some other liquid chromatography methods. 

A barometer located at an elevation above sea level will show a reading lower than a barometer at sea level by an amount approximately 2.5 mm (0.1 in) for each 30.5 m (100 ft) of elevation. A closer approximation can be made by reference to the following tables, which take into account (1) the effect of altitude of the station at which the barometer is read, (2) the mean temperature of the air column extending from the station down to sea level, (3) the latitude of the station at which the barometer is read, and (4) the reading of the barometer corrected for its temperature, a correction which is applied only to mercurial barometers since the aneroid barometers are compensated for temperature effects. 

So far the plate theory has been used to examine first-order effects in chromatography. However, it can also be used in a number of other interesting ways to investigate second-order effects in both the chromatographic system itself and in ancillary apparatus such as the detector. The plate theory will now be used to examine the temperature effects that result from solute distribution between two phases. This theoretical treatment not only provides information on the thermal effects that occur in a column per se, but also gives further examples of the use of the plate theory to examine dynamic distribution systems and the different ways that it can be employed. 

It is seen that a very significant temperature increase occurs particularly at high pressures. It would appear that, due to the poor radial thermal transfer in the column, the thermostat had little effect on the temperature change. Katz et al. [15] concluded that increases in column temperature resulting from high inlet pressures could seriously affect the accuracy of retention measurements. The heat evolved on changing the flow rate from 4 to 18 ml/min., accompanied by a corresponding... 

Column temperature alarm Not a complete indication at this stage. It may be a spurious alarm Cross-examine related indicators Data collection Can operator acquire irrelevant or insufficient data Can operator fail to crosscheck for spurious indications Identification/lnterpretation Can operator fail to consider all possible system states and causes of problem Can operator fail to perform a correct evaluation Can operator fixate on the wrong cause Goal Selection Can operator fail to consider possible side-effects Can operator fail to consider alternative goals Can operator fixate on the wrong goal ... 

The Effect of Column Temperature on the Separation of a Carbohydrate Mixture... 

This impressive effect of temperature on efficiency and resolution is not common and improvements of this order of magnitude are not always realized by raising the column temperature. Nevertheless, temperature is a variable that needs to be considered depending on the type of mixture being separated. 

Important because of the recondensation effect. Particularly important when the column temperature is near the boiling point of the principal sample component or solvent. 

Temperature variation may also be a relevant factor in flowrate stability. Since the viscosity of the solvent is temperature dependent, wide swings in the ambient temperature can directly affect pump performance. The direct effects of temperature on pump performance usually are far smaller, however, than the effects on retention and selectivity therefore, control of column temperature is generally sufficient to obtain high reproducibility. 

Parameters that should be tested in HPLC method development are flow rate, column temperature, batch and supplier of the column, injection volume, mobile phase composition and buffer pH, and detection wavelength [2], For GC/GLC methods, one should investigate the effects of column temperature, mobile phase flow rate, and column lots or suppliers [38], For capillary electrophoresis, changes in temperature, buffer pH, ionic strength, buffer concentrations, detector wavelength, rinse times, and capillaries lots and supplier should be studied [35, 36], Typical variation such as extraction time, and stability of the analytical solution should be also evaluated [37],... 

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