Determination of trace impurities in industrial dicyclohexylamine by programmed elevated temperature method

Summary

This experiment is from the official website of College of Chemistry, Qingdao University of Science and Technology.

Operation method

Determination of trace impurities in industrial dicyclohexylamine by programmed elevated temperature method

Principle

For wide-boiling multicomponent compounds using programmed ramping chromatography, the column temperature is increased linearly or non-linearly with time at a predetermined heating rate, so that all components of the mixture will exit the column at their optimal column temperatures. When a low enough initial temperature is used, the lower boiling components can be better separated, and as the column temperature increases, each higher boiling component is "pushed out of the column" by the increased column temperature, and the higher component boiling points can be accelerated out of the column, resulting in good sharp peaks. Therefore, the program temperature chromatography is mainly through the selection of the appropriate temperature, and obtain a good separation and ideal peak shape, while shortening the separation time. Generally speaking, samples with boiling points in the range of 80-100°C or higher require the use of programmed temperature increase chromatography. Program heating mode - the so-called "program" that is, the way the column temperature increase, mostly according to the change in column temperature over time to classify. 1, linear heating: column temperature (T) with the time (t) proportional to the increase in temperature. T = T0 + r tTo: the starting temperature, r: heating rate (℃ / min) 2, non-linear heating (1) linear -Constant heating: firstly linear heating up to the highest use temperature of the fixing solution, then constant temperature until the last few high-boiling components are rinsed out. Suitable for the separation of high boiling point. (2) Constant temperature - linear heating: first, separate the low-boiling components at constant temperature, then increase the temperature linearly until the separation is completed. (3) Constant temperature-linear-constant temperature heating: Separate the low-boiling-point components at a constant temperature first, then increase the temperature linearly to a high temperature in the middle, and then rinse out the high-boiling-point components at a constant temperature. Suitable for samples with a wide range of boiling points. (4) Multiple speeds of heating: start with r1 speed and then r2 and r3 speeds. In this experiment, the industrial dicyclohexylamine samples were separated and analyzed by the method of thermostatic-linear-constant temperature heating. At present, the programmed heating chromatographic system, most of the dual-column dual gas path, in order to compensate for the baseline drift caused by the loss of the stationary solution in the process of heating, and to increase the stability of the column. In the dual-column system, generally the analytical column and the reference column have the same stationary phase, or two stationary phases with different properties can be loaded to analyze different types of samples and expand the application surface. However, it should be noted that the thermal stability of the two stationary phases should be the same, i.e., the maximum use temperature should be the same or close to the same temperature, otherwise the loss of stationary phases cannot be compensated for and the stability becomes worse.

Move

I. Chromatographic conditions

Instrument: Shimadzu GC-9A gas chromatograph.

Column: 2%PEG20M+2%KOH

Stretcher: Chromosorb (acid washed, silane, 60-80 mesh)

Temperature: Tc: 130℃ for 3 min, heating rate is 3℃/min, final temperature 180℃ for 20 min; Ti: 200℃; TD: 200℃.

Detector: Hydrogen flame ionization (FID)

Carrier gas: N2 flow rate: 30 mL/min; gas: H2 flow rate 40 mL/min; combustion gas: air flow rate 500 mL/min Output attenuation: optional; paper speed: 5 cm/min; sample: 0.1-0.2 μL

Experimental steps

1, according to the above chromatographic conditions to start the instrument, a rise in temperature so that the temperature of the detector and gasification chamber to meet the requirements, according to the above conditions set the program temperature.

2、After the program setting is completed and the baseline is stable, inject 0.2 μL of dicyclohexylamine with a micro syringe. At the same time, press the start button, the program heating will be carried out automatically and the chromatogram will be recorded. If it is necessary to repeat the previous program rise process, you can reset the set value and repeat the process.

Characterization: Under the same conditions, inject the standard sample to identify the outflow peaks.

4、Quantification: Normalization method or external standard method can be used for quantification.

Caveat

1、 Rising temperature method is different according to different instrument models, operate strictly according to the instructions.

2， in the warming process, the column pressure increases with the increase in temperature, the flowmeter rotor down, this is a normal phenomenon, but must ensure that the program changes to maintain consistency.

3， in the program temperature, try to use a lower vaporization temperature, so as to avoid the loss of low boiling point components of the feeder silica gel pad caused by the baseline instability, the appearance of strange peaks, the silica gel pad is best to aging treatment. Immerse it in ethanol for one day, wash it with water, and then age it at 200 ℃ for two hours.

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