Factors affecting the top air phase chromatograph - Database & Sql Blog Articles

Heng Jiaxing AO3401

Photocoupler

(1) Effect of heating temperature: It is necessary to ensure that volatile substances are volatilized from the sample and achieve a stable dynamic balance. The higher the heating temperature, the more volatile substances are measured by the interference, and the appropriate temperature is selected to reduce the interference. Alternatively, if the sample is in a high temperature thermostat, injection at room temperature will condense the higher boiling component.

(2) Effect of activity coefficient: Adding electrolyte or non-electrolyte to the sample can increase the activity coefficient and determine the activity.

(3) Influence of pressure: The sample gas sealed in the container rises at a rising temperature, the pressure is greater than the atmospheric pressure of the outside, and the sample is taken from the container with a syringe, which causes an error.

(4) Influence of space: The volume of the upper space should be moderate, and the smaller one can increase the sensitivity, but if it is too small, the phase balance is not easy to be achieved, and the sampling is not easy to be uniform.

(5) Effect of the injector: The sampling should not be as fast as taking the liquid sample. The core welding should be lifted slowly, and the inner wall of the injector should be wetted with a little distilled water before sampling to make the wall and core weld more tight.

In addition, the size of the vaporized bottle and the amount of sample should be considered.

Application Analysis

Gas chromatography is one of the most widely used analytical techniques due to its high sensitivity, good resolution, fast analysis speed and low sample consumption. It has become an important monitoring tool in the fields of food, food, medicine, and the environment. In the grain and oil testing, the determination of solvent residue in soybean oil is convenient by static headspace gas chromatography. The solvent used in China's leaching method is a mixture of various alkanes with hexacarbon alkane as the main component. The solvent residue was determined by direct injection method, pre-vaporizer method and headspace gas chromatography. The direct injection method was contaminated by the instrument; the pre-evaporator method was not suitable because the pre-vaporizer was difficult to standardize; Chromatography is more suitable.

The analysis conditions are as follows:

Gas chromatograph: FID; stationary phase: 5% DEGS white support; vaporization chamber temperature: 140 ° C; column: stainless steel column; column temperature: 60 ° C; N2: 30 mL / min.

a: retention time 0.690, peak height 29102.889, peak area 149969.000;

b: retention time 0.823, peak height 30855.480, peak area 253712547.

The retention time is affected by factors such as column length, column temperature, carrier gas flow rate, hydrogen and air flow rate. The same compound has the same retention time under the same chromatograph and identical chromatographic conditions. In actual work, due to the influence of injection speed, injection position, etc., the exact same chromatographic conditions are not easy to grasp. If the instrument is operating normally, the retention time measured multiple times is better repeatable under the same chromatographic conditions. In the actual work, we have summarized the following experiences.

(1) Residue of solvent residue The oil sample is required to be heated in a 50 ° C incubator for 30 min. In the test, we found that the heating was at least 1 h, so the stability measured was good. The constant temperature of the headspace sample continues to lengthen, and the peak area measured by the chromatogram is basically unchanged after the constant temperature time.

(2) The national standard requires the absorption of 0.10~0.15mL liquid gas injection chromatography. In fact, we draw 60μL. On the one hand, the airtightness of the full scale is poor. On the other hand, the injection volume is small and the separation effect is good and the column efficiency is high.

(3) The flow rate of the gas should be well mastered. The flow rate of hydrogen is not required to extinguish the fire. It should be as slow as possible. The flow rate of the carrier gas is one of the important reasons for determining the chromatographic separation. Generally, the carrier gas flow rate is high and the peak is narrow, otherwise it is wider, but the flow rate is too high or too low. There are adverse effects, and the appropriate flow rate should be selected according to the instrument conditions.

Headspace gas chromatography is generally classified into static and dynamic headspace gas chromatography. Static headspace gas chromatography can be analyzed with a simple glass bottle. Generally, each headspace bottle can only be taken once in a quantitative analysis, and it takes a certain time to reach equilibrium. Dynamic headspace gas chromatography requires more instruments and takes more time, so the cost is higher. Also. When an inert gas is introduced into the liquid or solid surface, impurities in the purge gas are carried into the sample, the adsorbent is also selected, and there is a problem of incomplete adsorption and desorption.