Benzene Detector Tube No. 121SP
This document outlines the specifications and performance of the Gastec Benzene Detector Tube No. 121SP, designed for measuring benzene (C6H6) in the air.
Performance
These tubes are designed to be connected when in use.
| Measuring range | 0.2 to 20 ppm | 20 to 66 ppm |
| Number of pump strokes | 3 (300 ml) | 1 (100 ml) |
| Correction factor | 1 | 3.3 |
| Sampling time | 6 min | 2 min |
| Detecting limit | 0.1 ppm (3 pump strokes) | |
| Colour change | White → Brown | |
| Corrections for temperature & humidity | Unnecessary | |
| Relative standard deviation | 10% (for 0.2 to 5 ppm), 5% (for 5 to 20 ppm) | |
| Shelf life | 2 years |
Reaction Principle
The detector tube system consists of a pretreatment tube and a detector tube.
- Pretreatment tube: Removes interference gases.
- Detector tube: Reacts with benzene. The chemical reaction is as follows:
2C6H6 + HCHO → C6H5CH2C6H5 + H2O
C6H5CH2C6H5 + H2S2O7 → Condensation polymer
Possible Coexisting Substances and Their Interferences
The following substances may coexist with benzene and their potential interference is noted:
| Substance | Concentration | Interference | Changes colour by itself to |
| Hexane | ≤ 500 ppm | No | No |
| Toluene | ≤ 300 ppm | No | |
| Xylene | ≤ 350 ppm | No |
Aromatic hydrocarbons other than benzene are trapped in the white layer of the pretreatment tube. If the pretreatment reagent is entirely consumed (the whole white layer turns brown), a higher reading will be obtained.
Calibration Gas Generation
Calibration gas is generated using the diffusion tube method.
Diagram Description: The diagram shows two detector tubes. The top tube illustrates the 'pretreatment layer (white)' and a connection for a pump. The bottom tube displays the 'detecting layer (white)' with a scale indicating concentrations from 0.2 to 20 ppm, along with pump stroke information (n=3) and the model number (121SP).
