Atmospheric pre concentratorIt is an analytical instrument used to concentrate volatile organic compounds (VOCs) in atmospheric samples and is a key pre-treatment equipment in the field of environmental monitoring. This instrument achieves sample concentration and impurity separation through multi-stage cold trap technology, commonly using a three-stage or four stage cold trap structure, supporting a sample injection volume range of 4-2000ml, with a concentration ratio of over 1000:1 and a detection limit as low as 0.1ppbv, which can meet the detection needs of trace VOCs. The core principle is based on the adsorption desorption cycle, which achieves the enrichment of target compounds through temperature difference control: the first stage cold trap removes interfering substances such as water vapor and CO ₂ within the range of -30 ℃ to -190 ℃, while the third or fourth stage focused cold trap rapidly heats up and introduces the concentrated sample into a gas chromatography-mass spectrometry (GC-MS) for analysis.

　　Atmospheric pre concentratorDetailed operation guide:

1、 Preparation before use

1. Check the equipment status

Confirm that the power and gas sources (high-purity nitrogen or zero air, purity ≥ 99.999%) are connected properly.

Check if the refrigeration system (liquid nitrogen or mechanical refrigeration) is ready and if the cold trap temperature can reach the set value (such as -150 ℃).

Ensure that there are no leaks in the injection pipeline and valve circuit, and that the adsorption tube is installed in place.

2. Select and install adsorption tubes

Select suitable adsorption tubes with fillers (such as Tenax TA, Carbopack B/X, graphitized carbon black, etc.) based on the target VOCs types (such as C2-C12 hydrocarbons, halogenated hydrocarbons, oxygen-containing compounds, etc.).

The adsorption tube needs to be pre aged (heated to 250-350 ℃ with high-purity carrier gas for 30-60 minutes) to remove background interference.

3. Set method parameters (through control software)

Sampling volume: usually 100 mL-1 L (adjusted according to concentration);

Sampling flow rate: 50-200 mL/min;

Cold trap temperature: Level 1 (water vapor capture, about -30 ℃), Level 2 (medium boiling point substances, -50 ℃), Level 3 (low boiling point substances, -150 ℃);

Desorption temperature and time: such as 350 ℃, 2-5 minutes;

Transmission line temperature: ≥ 120 ℃, to prevent condensation.

2、 Sample collection (pre concentration process)

1. Start the system self-test

Run 'Leave Check' or 'System Purge' to ensure that the pipeline is clean and free of residue.

2. Start sampling

Place the sampling probe in the air source to be tested (such as atmosphere, flue, indoor air);

Start the 'Sample' program, and the instrument will automatically:

Control the flowmeter for stable sampling;

The air sequentially passes through a dehydration trap (Nafion membrane or low-temperature cold trap) → a multi-stage adsorption cold trap;

VOCs are gradually enriched, and water vapor and inert gases are discharged.

3、 Thermal desorption and injection

1. Rapid heating and desorption

After the sampling is completed, the system automatically heats the cold trap/adsorption tube instantaneously (such as 350 ℃) to release VOCs instantly.

2. Focus and Injection

The desorbed gas is carried into the focused cold trap by the carrier gas (captured again at low temperature, forming a narrow peak);

After focusing, the focusing trap rapidly heats up and injects the concentrated VOCs into GC or GC-MS in the form of narrow pulses.

4、 System cleaning and standby

Baking pipeline

After detachment, the system automatically performs high-temperature blowing (such as 300 ℃, 5 min) on the adsorption tube and transmission line to remove residues.

Restore initial state

Re cool the cold trap to the set temperature;

Reset the valve position and prepare for the next injection.

5、 Data recording and maintenance

Record information: sampling time, location, volume, temperature and humidity, target compound, instrument status.

Regular maintenance:

Replace the injection spacer and O-ring;

Clean or replace the water removal film;

Calibrate Mass Flow Controller (MFC);

Check the liquid nitrogen level (if using liquid nitrogen refrigeration).