Development history and trend of the hottest gas c

Development history and trend of gas chromatograph

since the world first established practical gas-liquid chromatography in 1952, in just a few decades, gas chromatograph, as a representative of analytical and testing instruments, has developed into an industry with considerable production scale, and formed a discipline with considerable detection technology knowledge. By studying the development of gas chromatograph, it can give useful enlightenment to users and bring some help to the work of relevant professionals

now take the gas chromatograph series of Japan Shimadzu company, which is widely used in China, as an example, such as gc-7a in 1983, gc-9a in 1985, GC-14A in 1990, GC-17A in 1995, and so on. In terms of several main aspects of these instruments, namely, adding experimental theory, they will also continue to improve and guide technological innovation, such as thermal unit control, furnace temperature control, flow control, data processing system, detector system, system control, etc, To describe the development track of gas chromatograph technology progress, and predict the development trend of gas chromatograph in the future

development track of gas chromatograph technology progress

1 injection and de heater temperature control of the detector in the next 10 years

gc-7a and gc-9a both use a complete total heating block unit, the injection port of 3c-14a and the detector share a total heating block unit, and 3c-17a is changed to have an independent heating unit system for each injection port and detector

the total heating block unit refers to that the injection port and detector are all or part concentrated on a large heating block, with a heating rod, a temperature controller and a constant temperature block to control the temperature. It has the advantages of simple structure, few components and low cost. Due to the large heat storage value, it is easy to maintain stability after reaching the temperature. Its disadvantages are: the temperature of all parts on the heating block can only be set to be the same, but not different, which limits the use of detection means; Due to the large volume of the heating block, the heating and cooling speed is slow, and it is difficult to change the conditions; When heating up, all parts are heated, and unused parts are also subject to thermal fatigue loss during the heating and cooling process

independent heating unit means that any injection port and detector have independent heating, temperature control and constant temperature devices. Its advantage is that any component can be set to different temperatures, and because the heating block is small in size and low in heat storage value, the heating and cooling speed has been greatly improved. It can provide functions such as programmed temperature rise at the injection port, which enriches the means of chromatographic technology. Its disadvantage is that each system is an independent system, with high technical requirements for temperature control, more components and relatively high cost

the gas chromatograph using the total heating block unit generally adopts U-shaped columns (such as gc-7a, gc-9a, GC-14A), because the position of each component is limited in a heating block and must be arranged compactly. The gas chromatograph with independent heating unit generally adopts a circular column, because its sample inlet and detector need to be separated by a certain distance. The reason is that the cooling of each independent heating unit is achieved by cooling the surrounding air. If the sample inlet and detector are too close, it will affect the heat dissipation effect of each other. From total heating block unit to independent unit heating is a general trend

2 oven temperature control

the performance level of gas chromatograph furnace temperature control can often reflect the level and level of this instrument. The evolution of furnace temperature control technology can be seen from the change of column temperature box heat outlet. Gc-7a has no heat outlet of column temperature box, and its temperature rise and drop speed is frighteningly slow, which makes the operator dare not change the conditions easily; Gc-9a and GC-14A have slit type heat exhaust ports, which improves the effect to a certain extent; GC-17A is further changed into two square heat outlets, and the cooling effect is satisfactory

in terms of the operating system of furnace temperature control, gc-7a adopts the mechanical dial mode, which is very inconvenient. Starting from gc-9a, electronic control is used to input parameters with keyboard. It can be said that Shimadzu's gas chromatograph has been modernized since gc-9a. GC-17A is controlled by the workstation, so it is very convenient to program temperature control

3 gas flow control gc-7a and gc-9a.gc-14a all adopt classic mechanical meter valve control, such as pressure gauge and rotameter

generally, rotameters are used for components that need to accurately control the flow of carrier gas, and pressure gauges are used only for parts that need to be roughly controlled. For example, pressure gauges are basically used for hydrogen and air flow control as auxiliary combustion gases

the advantages of mechanical meter valve control are: reliable, durable and. Its disadvantage is that it should be slowly raised from the zero point every time it is turned on, and then turned back to the zero position when it is turned off. Because there are inevitable artificial differences in each adjustment, it is difficult to maintain the same flow every time, so the flow cannot be changed during the detection process. Electronic pressure control uses solenoid valve instead of mechanical meter valve. It only needs to input a value to find the predetermined flow or pressure, which is convenient, accurate and rapid. It can also provide programmed pressure rise means, which can be described as a revolution in flow control

electronic flow control overcomes the defects of mechanical flow control, but it also brings new problems:

(1) if the air source pressure changes too much, it is easy to be damaged due to strong impact, and the mechanical meter valve does not have this problem

(2) in case of accidental power failure, the solenoid valve will stop working and the gas supply will be stopped. The chromatographic column will be easily damaged when there is no carrier gas passing through at high temperature

(3) theoretically, the rotameter is the most stable and accurate element for measuring the carrier gas flow, and it is difficult to produce deviation; Electronic pressure control must be an electronic analog mechanical process, which may have subtle deviations after long-term use

4 data analysis unit

gc-7a is configured with a plotter, gc-9a is configured with an integrator or a data processor that cannot store data, GC-14A is configured with a data processor that can store data, and GC-17A is configured with a chemical workstation for data processing. Data system data processing system is the part of the gas chromatograph that has made the fastest progress and benefited the users the most. It makes the operation of the instrument more convenient. Before the invention of integrator, measuring the peak area of chromatographic peak can only be measured manually with integrator or weighed by paper cutting, which often takes half a day for a chromatographic peak. Now, all spectral data can be obtained soon after the detection is completed

from plotter to integrator, and then from data processor to chemical workstation, the progress of which is mainly due to the rapid development of electronic technology

5 detector system

among the various components of the gas chromatograph, the detector is relatively stable, the internal structure and composition have not made revolutionary progress, and the improvement of detection performance is also limited, but the stability speed has made great progress, such as the electronic capture detector of GC-17A, whose stability speed is 10 times faster than that of GC-14A, and the cooling efficiency has reached the amazing speed of reducing 100 degrees Celsius every 10 minutes

6 before the workstation appeared, the total system control part of the host can only manually set various operating parameters of the host. Therefore, to start an instrument, it needs to carry out many trivial setting and adjustment steps, open and close many switches, and adjust many knobs. People who are not familiar with the equipment often make mistakes

after using the workstation, the user can input various instrument parameters and operating procedures of different experiments into the machine, and then work directly next time, completing all steps from startup, detection, processing results and so on. It is no longer necessary to input and determine the parameters of various parts of the instrument one by one, making the operation more convenient. Shimadzu's gas chromatograph series generally uses workstations to directly control the instruments after GC-17A

3 the trend of gas chromatograph in the future

the development process from gc-7a to GC-17A can see a development process from mechanical instruments to instruments. Due to the limitations of electronic technology and materials, the early gas chromatograph also limited the thinking and play of designers, making the chromatographic technology at that time also subject to great limitations, such as programmed temperature rise, programmed pressure rise and other now easy technical means were very boring and impractical at that time

with the development of electronic technology and material science, it not only strengthens the function of gas chromatograph, but also greatly enriches the methods and means of applying gas chromatograph technology. At the same time, it also brings profound influence and promotion to the designer's design idea, so as to promote the progress of gas chromatograph faster

extending from this trend, the author predicts the technical development route of gas chromatograph in the future and sees what it will look like in the future

3.1 computer has become the standard configuration. Due to the wide application of computer technology and the continuous decline of computer price, computer will become the standard configuration of gas chromatograph. At present, the common control panel on the gas chromatograph will be cancelled, and only a few gas flow switches will be left on the side. The operating parameters of each component of the instrument are completely controlled by the computer, which makes the gas chromatograph smaller, simpler in structure and lower in cost

3.2 functional modules that can be flexibly replaced at present, once the gas chromatograph injection port and detector are installed, it is difficult to disassemble or replace them, because their interface parts and gas path connection parts have no unified specifications, and the necessity of frequent disassembly is not considered in the design

in the future, the injection port and each module of the detector will adopt the square interface of unified specification, which is convenient for users to plug and unplug at will and choose different conditions. The socket type air connection port is located at the bottom of the module and is fixed with a hand screw nut at the top of the module

3.3 card of data acquisition at present, various and expensive data acquisition cards of various companies will gradually disappear, and computer cards will replace them. The test data is transmitted to the computer through the line, which further reduces the cost of the instrument

3.4 there are control software that can be shared. At present, the workstations of various gas chromatographs are dedicated, that is, they can only control a certain type of gas chromatograph produced by a certain company

with the high application of electronic components, it means that as long as the electrical signal is controlled, the instrument can be controlled. Therefore, although the signal mode and range of each gas chromatograph are different, if the design and consideration of the compact part of a set of software at the same time do not fully store the signal parameters of several instruments, it can control the instruments produced by different companies by selecting different models

3 . 5. The sharp drop in price and the reduction and intensification of components mean the reduction of costs. In addition to the limited space for the price reduction of detectors, considering the cancellation of control panels, data acquisition cards, and the intensive design of other components, the price of the whole set of instruments (including computers) is estimated to be reduced by at least half