Indoor EnvironmentPrinciple of TVOC analyzer

　　The main sources of TVOC are building materials, decorative materials, office and daily necessities, and outdoor sources. Building materials include wood-based panels, foam thermal insulation materials and plastic plates; Decorative materials include paint, coatings, adhesives, wallpapers, carpets, etc; Office and daily necessities include cosmetics, detergents, printers, inks, and household fuels; Outdoor sources include fuel combustion and transportation.
At present, the detection methods for TVOC are adsorption tube sampling and thermal desorption gas chromatography analysis. Thermal desorption can be divided into two types: primary thermal desorption and secondary thermal desorption.
The principle of thermal desorption method uses a TVOC adsorption tube with Tenax TA as the adsorbent to collect a certain volume of air sample, and volatile organic compounds in the air flow are retained in the adsorption tube. Thermal desorption is carried out at high temperatures to desorb volatile organic compounds. The sample to be tested in the collection tube enters the gas chromatography with the carrier gas, and after separation, it enters the hydrogen flame ionization detector (FID) for detection. Qualitative retention time and quantitative peak area. The secondary thermal desorption instrument will enrich the target substance desorbed from the collection tube through a cold trap, and then enter the gas chromatograph for analysis along with the carrier gas through secondary thermal desorption.
Compared with direct gas injection and solvent desorption injection, thermal desorption technology can achieve analysis of target substances in samples at lower concentration levels, with lower detection limits and lower determination limits. Due to the fact that thermal desorption does not use solvents for sample desorption, there are no solvent peaks in chromatographic analysis, which reduces the influence of solvents on the analysis of target substances and is more environmentally friendly.
ATDS-20A Fully Automatic Thermal Analyzer
1、 Instrument Introduction

The ATDS-20A fully automatic thermal desorption instrument is a replacement product independently developed and launched by our company, which is directly aimed at domestic and foreign users. This instrument is suitable for qualitative and quantitative detection of various gases with boiling points below 350 ℃ in chemical building materials, food, atmosphere, and indoor environments. It can be connected to any domestic or foreign gas chromatograph or gas chromatography-mass spectrometry instrument. Its automation level, repeatability, sensitivity, and other indicators can fully meet the newly issued national standards for environmental detection, and it has its own unique functional advantages and satisfactory performance and price ratio in structure. The new generation fully automated thermal desorption instrument features fully automated design, touch screen display, and more convenient operation, capable of continuously running 20 samples.
IIInstrument features and main functions
1. Can automatically run 20 samples without the need for personnel on duty;
2. Power on self-test, fault alarm and prompt, using independent patented technology to automatically locate and calibrate the sample disk;
3. Microcomputer program control, main functions include:
⑴ Method parameter setting, real-time animation display of working status, and running time;
⑵ The desorption zone, injection valve, sample transfer tube, and secondary desorption zone are all separately heated and temperature controlled;
⑶ Set up the analysis program and press the run button to automatically complete the analysis of all samples;
⑷ Normal temperature secondary desorption components or low-temperature secondary desorption components can be added according to user needs;
⑸ The GC and chromatographic data processing workstations can be started synchronously, and the device can also be started using external programs;
4. The machine comes with the function of simulating and sampling standard samples, which makes it more convenient to create working curves through a thermal desorption instrument;
5. Can load the built-in sampling tube activation program to automatically activate the desorbed sampling tube;
6. Through time programming, automatic functions such as desorption, blow adsorption, re desorption, injection, and backwash cleaning can be achieved;
7. Adopting electronic refrigeration and second-order thermal desorption process to ensure narrow chromatographic peak shapes;
8. The sample transfer tube and injection valve have automatic blowback function, which avoids cross contamination of different samples;
9. In order to make it more convenient and accurate to use with imported gas chromatographs, this instrument is also equipped with dedicated interfaces for various imported instruments, which are easy to connect;
10. For active substance analysis, an elastic quartz tube can be selected as the sample transfer tube;
11. The injection needle is easy to replace and can be connected to all models of GC injection ports at home and abroad.

3、 Main technical parameters of the instrument
1. Desorption 1 temperature control range: room temperature -450 ℃, set in increments of 1 ℃;
2. Temperature control range of valve injection system: room temperature -300 ℃, set in increments of 1 ℃;
3. Temperature control range of sample transfer pipeline: room temperature -300 ℃, set in increments of 1 ℃, using 24V low-voltage power supply;
4. Desorption 2 temperature control range: room temperature -450 ℃, set in increments of 1 ℃; Heating rate>3000 ℃/min;
5. Cold trap temperature control range: -35 ℃ - room temperature, set in increments of 1 ℃, using advanced electronic refrigeration equipment;
6. Temperature control accuracy:<± 0.5 ℃;
7. Desorption recovery rate:>99% (depending on the composition);
8. Backblowing cleaning flow rate: 0-100ml/min (continuously adjustable);
9. Simulated sampling flow rate: 0-160ml/min (continuously adjustable);
10. RSD: ≤ 2.5% (benzene in 0.05 μ g methanol);
11. Enrichment time: 0-60 minutes;
12. Injection time: 0-60 minutes;
13. Sample grade: 20 digits;
14. Sampling tube specification: 1/4 inch x 3.5 inches (American standard);
15. Injection method: Six way valve motor drive;
16. Instrument dimensions: length x width x height=350mm, 450mm x 510mm^3；
17. Instrument weight: approximately 40kg.

4instrumentApplication scope:
1. HJ/644-2013 Determination of volatile organic compounds in ambient air - Adsorption tube sampling - Thermal desorption gas chromatography-mass spectrometry method;
2. HJ/T400-2007 Sampling and Determination Methods for Volatile Organic Compounds and Aldehydes and Ketones in Vehicles;
3. GB/T18883-2002 Indoor Air Quality Standards;
4. HJ/583-2010 Determination of Benzene Compounds in Environmental Air Solid Adsorption/Thermal Desorption Gas Chromatography;
5. GB/50325-2020 Code for Indoor Environmental Pollution Control of Civil Building Engineering, etc.
6. HJ734-2014 Determination of Volatile Organic Compounds in Waste from Fixed Pollution Sources by Solid Phase Adsorption/Thermal Desorption Gas Chromatography, etc.