What parameters should be paid attention to when operating a second-hand gas chromatograph

Gas chromatographs are commonly used analytical instruments in laboratorie.
It is widely used in many field.
So, how do you determine the stability and accuracy of a sample when performing gas chromatographic analysis? What parameters should be paid attention to when operating a second-hand gas chromatograph? In addition to the performance of the gas chromatograph, the operating procedure is correct and the sample is well prepared, the following issues also need to be considered: (1) Injection port temperature The setting of the injection temperature of the chromatograph is slightly reduced during injection, because when the sample is not separated When the sample stays in the vaporization chamber for a long time, the vaporization rate is slightly slower, which will not affect the separation effec.
Solvent focusing and/or stationary phase focusing can also compensate for slow vaporizatio.
However, the low temperature upper limit of the fuel injection port ensures that the components to be tested are fully vaporized without instantaneous separatio.
Otherwise, too low injection temperature will lead to the loss of high boiling point components, thus affecting the sensitivity and reproducibility of the analysi.
Of course, too high a temperature can cause the sample to decompos.
Therefore, the inlet temperature of the sample should be optimized according to the specific conditions of the sampl.
When changing the inlet temperature of the used gas chromatograph, the setting of the instantaneous no-flow time should be re-optimize.
(2) The temperature of the detector is 20℃~30℃ higher than that of the sample.
(3) The choice of column temperature is beneficial to the separation of components, but when the temperature is too low, the components may coagulate or increase the mass transfer resistance in the column, resulting in the expansion of chromatographic peaks, and even the trailing of chromatographic peak.
High column temperature is favorable for mass transfe.
However, when the column temperature is too high, the distribution coefficient becomes smaller, which is not conducive to the analysi.
The results show that the optimum column temperature is equal to the average boiling point of the sample, or 10°C higher than the average boiling point
(4) In order to reduce the initial spectral bandwidth, the carrier gas velocity for splitless injection should be higher, and the upper limit should be based on the degree of resolutio.
The diversion outlet flow (after opening the diversion valve) is generally 30 to 60 mL/mi.
As long as the opening time of the diversion valve is set correctly, the change of the diversion outlet flow within this range has little effect on the analysis result.
(5) Sampling speed and quantity of samples The sample quantity generally does not exceed 2 μ.
A large number of samples should be selected with a large number of linings, otherwise the sample will flow behin.
The injection speed should be faster, try to choose an autosample.
If manual sampling is used, sampling speed reproducibility can affect gas chromatograph analysis result.
(6) Determination method of instantaneous splitless time The determination of instantaneous splitless time (also known as separation delay time, solvent blowing time) depends on the properties of the sample and solvent, the volume of the liner, the injection volume, the injection speed and the loa.
air spee.
Therefore, time should be determined after all remaining conditions have been determine.
Here's a simple way to measure used gas chromatograph experiment.
First, set a longer time (90~120 s) to ensure that all sample components enter the colum.
After analyzing the sample, take the peak area (k value should be greater than 5) as the measurement index, and the peak area value is 100% of the sample entering the chromatographic colum.
Then gradually shorten the injection time (70, 50, 30), and calculate the ratio of the peak area of ​​the same component to the peak area of ​​di one analysis under different solvent blowing times until the peak area is less than 95.At this time, time is shorte.

The peak area of ​​the same component can reach 95~99% of the peak area of ​​di one analysis, and the blowing time is the better conditio.
For the analysis of high boiling point samples, extending the non-transfer time can help to improve the sensitivity of the gas chromatograph.
For the analysis of low-boiling point samples, the non-split time should be shortened as much as possible to eliminate solvent trails to ensure the accuracy of the analysi.
For thermally labile compounds, use the cold column injection technique whenever possibl.