Pyrolysis Gas Chromatographic Analysis of Macromolecule Polymer Trace Compounds

In criminal cases, a large number of chemical evidences can be encountered. There are various types of chemical evidence, including explosives, pyrophoric materials, dirt, glass evidence, metals, welding slag evidence, poisons, narcotics, oil and gas certificates, etc. Usually, gas chromatography can be used. Liquid chromatography, atomic emission spectroscopy, atomic absorption spectrometry, ultraviolet-visible spectroscopy, infrared spectroscopy and other conventional instrumental analysis methods were used for qualitative and quantitative analysis. In addition to the above-mentioned material evidence, a large number of other types of chemical evidence that appear in criminal cases are polymer polymer materials, mainly including paint, rubber, plastics, and fibers. Traces of macromolecule polymers cannot be directly analyzed by gas chromatography, and they need to be analyzed and identified by pyrolysis gas chromatography.

Pyrolysis Gas Chromatography, that is, the use of hot wire, Curie point, tube furnace, laser and other crackers, through the instantaneous heating at a constant temperature, the thermal decomposition of macromolecular polymers and macromolecular compounds into a series of volatile small A gas chromatographic analysis method for molecular compounds fundamentally overcomes the limitations of conventional gas chromatography analysis and solves the problem of how to efficiently analyze compounds with higher melting points, less volatile, and thermally unstable compounds. The author uses a pyrolysis gas chromatograph to analyze and identify a large number of macromolecule polymer materials involved in criminal cases in the past few years, covering paints, rubber, plastics, fibers, etc., of which paint is the most. This article will use the vertical tube furnace pyrolysis chromatograph to conduct a summary of the experience of macromolecule polymer physical evidence inspection for the same type of equipment.

1 experimental conditions and methods 1.1 instruments and reagents chromatography workstation.

1.2 Analysis conditions 1.2.1 Paint, fiber analysis conditions: (FFAP) quartz capillary column (Supelco). Column temperature program: After holding at 60C for 1 minute, it was raised to 120C with 8Q for 10 minutes.

Cracker temperature: 650C; furnace pressure: 18psi. 1.2.2 Rubber, plastic analysis conditions: capillary column. After the column temperature program X0C was maintained for 1 minute, it was raised from 10C/minute to 200C for 5 minutes.

1.3 Processing of Samples and Samples For inspection of paints, rubbers, and plastics, the control sample can be scraped into fine powder or cut into thin strips. For fiber samples, the control sample can be cut into 2 to 3 mm long segments with a surgical blade. The appropriate sample plunger is used to carefully pour the appropriate amount of sample into the needle hub and plug it with the header until the instrument is stable. Rapidly inject the syringe into the cracker inlet for analysis. After the completion of a run, use the same method to take the same amount of material for analysis.

1.4 Optimization of experimental conditions The experimental results show that: FFAP column has good separation effect on fiber and paint samples; for rubber and plastic samples, the separation effect of OV-1 column is better. Paint sample 650C is the best cracking temperature; fiber, rubber and plastic samples should use the 750C cracking temperature. 1.5 Experimental Considerations 1 The order of analysis of the samples should follow the principle of testing samples after checking the control samples first. Because the control sample is generally large, once the analysis is unsuccessful, it can be analyzed again. However, if the sample is sampled, the sample size is usually only enough for one analysis. If it is unsuccessful, it will result in irreparable loss.

2 The injection volume of the control sample and the sample should be as consistent as possible. The amount of sample is not the same, there will be some subtle differences in the cracked gas chromatogram, which will bring certain difficulties to the qualitative work.

3 Some of the above-mentioned physical evidence left on the scene of a criminal case is light in size. Before the analysis of the control sample, the color and shape of the sample should be carefully observed, and the part left over from the sample must be ascertained, and then the control sample taken should be determined. Colors and parts, as much as possible to ensure the consistency of the control sample and the sample in the color and location.

2 Analysis of evaluation results and typical analysis of map promotion 2.1 Analysis of the results of the evaluation The author used the above method to analyze and identify a variety of high polymer polymer trace evidence in the hundreds of criminal cases, the results show that the optimization method has a strong ability to identify, The distinction between different physical evidences and similar physical evidences can be distinguished; at the same time, the method has the characteristics of simple operation and no sample preparation. Therefore, it has a wide range of application prospects in the field of trace material identification.