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1 Increasing the column temperature can boost the mass transfer rate and improve column efficiency, but too high a column temperature will reduce the separation between components. By using a lower column temperature, reducing the amount of stationary phase, and appropriately increasing the flow rate of the carrier gas, good separation results can be achieved in a short time ； 2 The vaporization temperature should be set such that the sample vaporizes rapidly without undergoing decomposition; it is usually 20–70°C higher than the column temperature. The column temperature, in turn, should be 20–30°C lower than the average boiling point of the components in the sample. For samples with a wide range of boiling points, a programmed temperature rise is advisable ； Increasing the column length improves separation, but it also prolongs the analysis time; therefore, under conditions where a certain level of separation is sufficient, shorter columns should generally be used ； Injection should be completed within 1 second to reduce peak broadening ； 3 Ignition: Hydrogen flame gas chromatograph – ignition is required when turning it on, and it is also necessary to ignite it again after it goes out for various reasons. However, we often encounter situations where the ignition does not work. The following introduces two ignition techniques: 3.1 The method of increasing the hydrogen flow rate – first increase the hydrogen flow rate, and once ignition occurs, gradually reduce it back to the normal operating level. This method is universal. 3.2 Method of reducing the tail gas flow rate: First reduce the tail gas flow rate, and after ignition, restore it to the normal operating condition. This method is applicable to cases where hydrogen is still used as the carrier gas, and air is used as the assist gas and backflow gas. 4 Adjustment of the gas ratio: For hydrogen-flame gas chromatographs, the recommended flow ratio for the three gases is nitrogen:Hydrogen:Air = 1:1:10. 4.1 Adjustment of nitrogen flow rate Once the conditions of the chromatography column are determined, the flow rate of nitrogen is a key factor in determining the effectiveness of separating the sample components. When adjusting the nitrogen flow rate, it is necessary to inject the sample and observe the separation of the components until the nitrogen flow rate is as high as possible and the sample components are well separated. 4.2 Regulation of hydrogen and air flow rates The effectiveness of regulating the hydrogen and air flow rates can be assessed by the magnitude of the base flow. First, adjust the hydrogen flow rate to be approximately equal to that of nitrogen, and then adjust the air flow rate. When adjusting the air flow rate, it is necessary to observe the changes in the base flow. As long as the base flow is increasing, adjustments should still be made in opposite directions until the base flow stops increasing further. Finally, increase the hydrogen flow rate slightly. 5 Sample injection techniques In gas chromatography analysis, sample injection is generally carried out using a syringe or a six-way valve. When considering injection techniques, syringe injection is the main focus. 5.1 Injection volume The injection volume is related to factors such as vaporization temperature, column capacity, and the linear response range of the instrument; in other words, it should be kept within a range that allows for instant vaporization, while meeting the specified separation requirements and ensuring linear response. Instant injection volume for the packed column flushing method: For liquid samples or solutions of solid samples, it is generally 0.01–10 μl; for gas samples, it is generally 0.11–10 ml. In quantitative analysis, care must be taken to ensure accurate readings of the injection volume. (1) Remove all air from the syringe. This can be achieved by using a micropipette to draw in the liquid sample; simply repeat the process of drawing the liquid into the syringe and then quickly returning it to the sample bottle. There is another better way to remove all the air from the syringe. That involves replacing the syringe 3 to 5 times with a sample amount of about 2 times the planned injection dose; after obtaining the sample each time, pick up the syringe vertically with the needle tip facing upward. Any air still remaining in the syringe should move to the top of the needle barrel. Pushing the syringe plunger will expel the air. (2) Ensure the accuracy of the sample volume: Use a replaced syringe to draw approximately twice the planned sample volume. Hold the syringe vertically with the needle tip facing upward, and pass the needle through a layer of gauze so that the gauze can absorb the liquid discharged from the needle tip. Push the syringe plunger until the desired value is read. Wipe the tip of the needle dry with gauze. At this point, the accurate volume of liquid has been measured; it is now necessary to draw more air into the syringe. If the plunger is accidentally pushed, air can protect the liquid from being discharged. 5.2 Sampling method: Hold the syringe with both hands. When using one hand (usually the left hand) to insert the plunger in reverse direction to add a large volume of sample (i.e., a gas sample), or when very high pressures are applied, it is necessary to prevent the pressure from the gas chromatograph from pushing the plunger out (using the thumb of the right hand). Push the needle tip as deep as possible into the injection port through the gasket, press down on the plunger for 1–2 seconds, and then pull the needle tip out as quickly and steadily as possible (while continuing to press down on the plunger). 5.3 Injection time: The length of the injection time has a significant impact on column efficiency. If the injection time is too long, it will cause the chromatographic zone to widen, thereby reducing column efficiency. Therefore, for flush chromatography, the injection time should be as short as possible, generally must be less than 1 second. This post was last edited by brucehan on 2009-2-4 08:16]