Several considerations for purchasing instruments for trace gas chromatography-(4)
What is the relationship between sample collection, pre-processing and GC purchase? Through the above several lectures, we have realized at one time that the use of gas chromatography for trace analysis is indeed a comprehensive experimental technique. We can summarize the trace chromatographic analysis process into the following four stages: ①sample collection; ②sample preparation (pre-processing); ③chromatographic analysis; ④data processing and result expression. What is the relationship between sample collection, pre-processing and GC purchase? Through the above several lectures, we have realized at one time that the use of gas chromatography for trace analysis is indeed a comprehensive experimental technique. We can summarize the trace chromatographic analysis process into the following four stages: ①sample collection; ②sample preparation (pre-processing); ③chromatographic analysis; ④data processing and result expression. If sample collection and pre-processing are relatively successful, in chromatographic analysis and data processing, even if the sensitivity of the selected chromatograph is not high, the separation efficiency of the analytical column is low, and the performance and function of the data processing device are average, it can still be obtained. More ideal experimental results. Conversely, if the purchased instrument and data processing device have a higher configuration and a high-efficiency chromatographic column is selected, the sample pre-processing process can be greatly reduced. In the current trace analysis, time-consuming, laborious and inefficient sample collection and processing are still the bottleneck in the entire chromatographic analysis. Sample collection and processing time sometimes accounts for two-thirds of the entire analysis time. It should be pointed out that no matter what the most advanced chromatograph and equipment, true high-performance chromatographic columns, and the most complete data processing device, satisfactory analysis results cannot be obtained from an improper sample collection and processing. Therefore, when choosing the type and performance of the instrument (including the data processing device), it is necessary to consider how to give full play to the comprehensive analysis capabilities of the selected instrument, so as to simplify the sample pre-processing process or not require sample pre-processing at all. In order to purchase gas chromatographs and supporting equipment more effectively when doing trace gas chromatographic analysis, we summarize some principles and methods of sample collection and preparation as well as the relationship with chromatographic analysis methods as follows: (If you understand more detailed content Please refer to relevant professional books) 1. Sample collection: When doing analysis in China, the general sample preparation (pre-processing) is done by the chromatographer, while the sample collection is done by other staff. In order to select a suitable sample preparation method and the accuracy and reliability of the analysis results, we should mention that not only the analysts have an understanding of the source of the prepared samples, the collection method, and the collection process, but the personnel responsible for purchasing the instrument are no exception. Do you know how to collect samples? The material composition of the sample? What is the concentration? What are the main components in the sample? What are the location and site conditions for collecting samples: a) the best time to collect the samples; b) the location where the samples are collected; c) the process of collecting the samples (valid time); d) the time interval for collecting the samples; should it be destructive or non-destructive? Destructive sampling method? Transportation and storage of collected samples; l. What chromatographic analysis results are expected to be obtained after sampling? 2. The principles that should be followed when selecting the method and technique of sample collection and processing? a The sample of the component to be tested must be representative; b The collection method should be consistent with the analysis purpose to ensure that the sample you want can be collected; c How to prevent and avoid the component to be tested from changing and avoiding changes during sample processing Loss; d When carrying out the chemical reaction (derivation, catalytic conversion) of the component to be tested, it must be known and quantitatively completed; e. The sample processing method should be as simple and easy as possible, and the processing device and sample volume should be compatible; 3. Why choose samples for processing? The purpose of sample pretreatment can be summarized as: a) separation of the components to be analyzed; b) enrichment; c) transformation; d) derivatization (converted to the state of chromatographic analysis); * Direct injection analysis is not possible: such as: a) There are many varieties (the adverse effects of water and oxygen on the instrument and the chromatographic column); b) the composition and concentration of the sample are complex and changeable (the matrix interferes with the trace components to be analyzed); c) the physical form of the sample is wide (viscosity, solid Multiphase samples); d) There are too many interference factors in direct analysis; * Consider using sample pretreatment methods to make up for the lack of existing instruments or analysis conditions a) Different quality requirements for analysis and testing; on-site environment does not allow (such as time); b ) The state, instability or chemical activity of the sample; c) The existing analysis conditions are not allowed; d) The purchased instruments and equipment are not available; e) The technical level of the operators is limited; 4. Commonly used sample pre-processing technology and equipment: Although sample pre-processing technology is still the bottleneck of trace chromatographic analysis, with the development of science and technology, many traditional sample pre-processing technologies or equipment have been greatly improved and perfected. The processing methods and technologies have also come out one after another. At present, sample preparation methods are coexisting with multiple processing technologies, and the new and old technologies are constantly being combined. The choice of sample processing technology depends on the analysis purpose, analysis method or existing conditions. In short, specific issues must be analyzed in detail. Commonly used or relatively new sample preparation techniques mainly include: a headspace technology; b membrane extraction technology; c solid phase extraction technology; d solid phase microextraction technology e microcapture technology; f supercritical extraction technology; g microdialysis technology; h Trace derivatization technology; i Combination of several other preparation technologies;
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