The range extension of the test tube: Â Â Â The amount of the active ingredient of the detector in the detection tube is proportional to the concentration of the gas to be detected. The amount of reagent adsorbed on the carrier determines the range of the detection tube.
However, the amount of reagent adsorbed on the carrier has a certain limit.
In order to reduce the amount of detection and reduce the reagent to a smaller amount, the color change of the color gradation will be light and unsuitable for observation.
In order to pursue a larger amount of detection, the amount of reagent added is more, which may cause the reaction time to be delayed or even not fully reacted. The method used at this time is to solve the problem by reducing or increasing the sampling amount within the limits of the reagent dosage. This is the same as the method used in chemical capacity analysis and colorimetric analysis.
The use of range extension in the detection tube method is divided into two cases:
First, it is applied in the manufacture of test tubes. For example, the hydrogen sulfide gas detection tube produced by our company has a cargo range of (2~50)ppm. At this time, the sampling amount is 100ml, the measuring range is (0.5~10)ppm, and the sampling amount is 300ml; the detection range is ( 0.5~1.0%) At this time, the sampling amount is 100ml, and the detection range is (1~20)%. At this time, the sampling amount is 20ml, diluted with air to 100ml and then passed into the detection tube. The result of this method is Direct reading on the test tube does not require calculation.
The second is: the range expansion is used, and the hydrogen sulfide gas detection tube is still taken as an example. Various types of hydrogen sulfide detection tubes can be extended according to their range during use. The method is as follows: If you are using a detection range of 5 to 100ppm hydrogen sulfide detection tube, the sampling with a syringe should be 100 ml when injecting When the volume of 50 ml is found to be more than 1/2 of the tube range (ie, greater than 50 ppm), the injection can be stopped. At this time, the result of the scale indication multiplied by 2 is the measurement result. The same test tube is 100 ml sample gas. After injection, when the discoloration height is less than the minimum range of the detection tube (ie less than 5ppm), in order to obtain accurate results, the sampling volume can be increased at this time, and the operation is repeated. The enlarged volume should be an integral multiple of 100 ml until the scale can be read. At this time, the result of the scale indication divided by 100 ml is the measurement result. For example, when the detection range is 0.5-10 ppm, the normal injection volume is 300 ml, but if the first 100 ml is finished, Read the scale, the next 200 ml can be removed from the operation, then the scale indication result multiplied by 3 is the measurement result, should pay attention to:
1 When using a syringe to inject 50 ml, the gas in the cylinder is compressed by the advancement of the piston. When the piston is pushed to 50 ml, it should be static for a period of time, and the data should be read after the pressure inside and outside the cylinder is balanced.
2. The injection volume should not be less than 50 ml, nor more than 500 ml, otherwise a large error will occur.
Since the detection tubes for measuring various gases have different reaction properties, not all types of detection tubes can perform this range expansion. In the specification, the detection tube adopting this method is not given, and the method will make the measurement accuracy. Greatly reduced.
