The purpose of concentration with a nitrogen blower is to reduce the sample volume and increase the concentration of the analyte

Concentration principle: After the sample is extracted and purified, the volume becomes larger, the concentration of the analyte decreases, which is not conducive to detection, so the purpose of concentration is to reduce the sample volume and increase the concentration of the analyte. The common methods are as follows: Atmospheric concentration-suitable for volatilization For components with relatively low boiling point and boiling point, by increasing the temperature, the solvent is removed from the liquid state to the gaseous state, or it is pumped away or collected again through the condenser, so as to achieve the purpose of concentration. Decompression and concentration-by vacuuming, a negative pressure is generated in the container, the boiling point of the substance is reduced without changing the chemical properties of the substance, and some solvents with unstable chemical properties or high boiling point at high temperature are converted from liquid to liquid The gaseous state is pumped away or collected again through the condenser. Freeze-drying-while vacuuming and depressurizing, the solvent is sublimated, suitable for biologically active samples. Nitrogen blown concentration-suitable for small, volatile extracts. Inert gas is used to purge the heated sample liquid, so that the sample to be processed is quickly concentrated to achieve the effect of rapid separation and purification. This method is easy to operate, especially can process multiple samples at the same time, greatly reducing the detection time. It is widely used in pesticide residue testing, batch processing of samples in the pharmaceutical industry and general research.

The influencing factors of nitrogen blowing concentration can increase the recovery rate of the target substance by appropriately increasing the temperature. For different substances, the temperature and pressure during concentration can be appropriately controlled by setting the parameters of the concentrator to shorten the concentration time to achieve a better recovery rate.

1. The effect of the water bath temperature on the nitrogen flow. The concentration tube is immersed in the water bath, and the temperature of the solution in the concentration tube is controlled by heat transfer. Usually the temperature control range of water bath is from 30 ℃ to 60 ℃. The temperature setting depends on the boiling point of the solvent in the concentration tube and the nature of the substance being analyzed. The temperature of the water bath is generally lower than the boiling point of the solvent, otherwise the evaporation rate may be too fast and the recovery rate may be reduced. However, if the temperature is set too low, the concentration time will be too long, and a long nitrogen purge will also cause the substance to be tested to evaporate. When setting the temperature of the water bath, the boiling point and volatility of the solvent should be fully considered. High temperature can shorten the concentration time, avoid long-term contact between the target substance and air, reduce the volatilization of the target substance, but excessively high temperature will cause the solvent to boil, thereby reducing the recovery rate

2. The effect of nitrogen flow pressure on the recovery rate The nitrogen flow rate of the vortex nitrogen blowing concentrator is changed by adjusting the nitrogen inlet pressure, the pipe diameter is unchanged, and the flow rate is proportional to the pressure. The greater the pressure of the nitrogen flow, the greater the nitrogen flow rate. The nitrogen flow hits the test tube wall to form a vortex. The greater the solvent contact surface area and the vortex shear force, the faster the solvent evaporates. At the same time, purging the nitrogen continuously can avoid the chemical reaction between the solvent and the air.

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