Before using the capillary column of gas chromatograph, the performance evaluation should be carried out. The main evaluation indexes include column efficiency, surface inertness, thermal stability and so on. Next, the chromatographic engineer of Luchuang analytical instrument will introduce you one by one.

 

Column effect - ensure the best separation effect

 

Column efficiency n / M (number of theoretical plates per meter length) is a measure of separation capacity. If the column has a high number of theoretical plates, its separation ability is very strong, which means that the resolution of the two peaks is good.

 

Retention factor (RI) - ensure repeatability between columns

 

Retention factor RI is used to measure column selectivity and elution sequence of components. If the difference of retention factors between columns is small, the elution sequence is the same.

 

Comparison rate (β) - a measure of retention time repeatability

 

The ratio β is a measure of the retention time of components, and its size depends on the thickness of the fixed phase liquid film. The smaller the difference of β ratio, the better the reproducibility of retention time between columns.

 

Column loss (PA) - low column loss to ensure high sensitivity

 

Column loss is caused by the volatile components produced by the degradation of stationary phase, expressed as PA. Column loss will cause baseline fluctuation and noise increase, and reduce the accuracy and accuracy of peak measurement. Low column loss reduces background noise and increases detection sensitivity. In addition, if the loss of column is low, the service life of chromatographic column is long, the pollution of detector is reduced, and the maintenance times of detector is greatly reduced.

 

Inert (as) - peak recognition of chromatographic column is more accurate

 

The inertness of chromatographic column is measured by the symmetry of peak, expressed as, which directly affects the elution and recovery of polar (active) components. The closer the as value is to 1.0, the better the symmetry of the peak shape is (small tailing), so the more accurate the quantitative analysis of the peak is, and the more accurate the quantitative analysis of the acid and alkaline compounds is. Good inertia of chromatographic column can ensure the reliability of the results.

 

Maximum operating temperature maot

 

The maximum operating temperature (maot) of the stationary phase is the highest recommended temperature, at which the chromatographic performance remains unchanged. For specific specifications of stationary phase and chromatographic column, this index is listed on the ordering information, and it is also indicated on the test report attached to each chromatographic column. For temperature programmed operation, maot is generally 20 ℃ - 25 ℃ higher than constant temperature operation.

 

Constant temperature maximum operating temperature

 

The constant temperature maximum operating temperature means that the column loss does not exceed a certain value at this temperature. In order to obtain good analytical results near the specified upper temperature limit of the column, Varian established a specific level of column loss. Exceeding the upper temperature limit specified by the column does not mean that the liquid stationary phase is destroyed, but the column loss is higher than the column loss value given by Varian. Generally speaking, the column loss will double for every 12 ℃ rise in temperature. Once the temperature decreases, the column loss returns to the low temperature value.

 

Constant temperature and maximum operating temperature of other Varian stationary phases

 

The maximum operating temperature of constant temperature refers to the reduction of the amount of stationary phase to 50% after 6 months of continuous use at this temperature. When the operating temperature is higher than the maximum temperature given by Varian, the column life will be reduced, and the elution sequence may be changed due to the thermal degradation of some fixed phase components.

 

Maximum operating temperature of programmed temperature rise

 

The other maximum operating temperature is the maximum operating temperature under the programmed temperature rise condition. The difference only lies in the time range, which is defined as the reduction of fixed phase by 50% in 200 hours. Generally speaking, the maximum operating temperature of programmed temperature rise is 20 ℃ - 25 ℃ higher than the maximum operating temperature of constant temperature.

 

Minimum operating temperature Tmin

 

The lowest operating temperature refers to the lowest temperature that can be used. At this time, the stationary phase is liquid. Under the lowest operating temperature, the stationary phase is not destroyed, but the peak shape and resolution are very poor.

 

Learn more about capillary columns, or purchase columns. Welcome to call 028-85115092 or search Chengdu Moore Scientific Instrument Co., Ltd