Guidelines for the Correct Selection and Use of CTC Headspace Bottles

　　1、 Core standards for selecting CTC headspace bottles

1. Material adaptability

-Glass bottle: Choose high borosilicate glass, high temperature resistance (>400 ℃), strong chemical inertness, suitable for acidic/alkaline and organic solvent systems. PTFE sealing gasket is required to avoid trace analysis errors caused by surface adsorption.

-Plastic bottles: limited to non-polar volatile compound analysis (such as aliphatic compounds), high-density fluoropolymer (PFA) coated plastic bottles should be selected to enhance chemical and temperature resistance (<120 ℃).

-Special material: Quartz glass is used for ultra trace analysis (ppt level VOCs), and dark brown glass prevents degradation of photosensitive substances.

2. Optimization of sealing performance

-Bottle cap type:

-Spiral cap: Easy to operate, torque needs to be controlled within 20-50 N · cm to avoid air leakage or crushing of the sealing gasket.

-Jaw cover: with aluminum foil gasket, the sealing performance is better than that of screw cover, suitable for a small amount of samples.

-Crimp cover: rolled edge sealing, suitable for automated production lines (such as the pharmaceutical industry).

-Gasket material:

-PTFE/silicone gasket: has a wide temperature resistance range (-60 ℃~250 ℃), but needs to be replaced regularly to prevent sealing failure caused by cold flow.

-Pre opening gasket: to avoid manual puncture damage to sealing and reduce the risk of cross contamination.

-Metal seal (such as copper ring): used for ultra-high sensitivity analysis (ppb level), but high cost and not corrosion-resistant.

3. Matching capacity and specifications

-Capacity selection:

-10-20 mL: Conventional liquid samples (such as blood and water samples), balancing headspace gas volume and detection sensitivity.

-50-100 mL: Solid headspace (such as soil samples), ensuring sufficient headspace.

-Micro bottle (<5 mL): For trace samples (such as a single drop of essential oil), a micro injection system is required.

-Bottle design:

-Straight tube type: with a large liquid surface area, it is conducive to the release of volatile substances, but it occupies more positions in the automated sampler.

-Cone shaped bottle: reduces residual condensed water and is suitable for high humidity headspace gas analysis.

-Automation adaptability:

-The diameter and height need to match the CTC automatic sampler tray (common specifications: Φ 20 mm × 80 mm or Φ 30 mm × 100 mm).

-The thread specifications of the bottle mouth (such as 10-425 or 12-400) should be compatible with the size of the injection needle to avoid needle bending or poor sealing.

4. Preprocessing and Special Requirements

-Cleaning requirements: Glass bottles need to be cleaned sequentially with chromic acid solution, ultrapure water, methanol ultrasonic cleaning, and dried at 120 ℃; Soak the plastic bottle in 10% NaOH overnight and blow dry with nitrogen.

-Corrosion resistance: Choose PTFE fully lined bottles or glass bottles coated with polyimide (PI) for strong acid/strong alkali systems.

-Low temperature application: Low temperature resistant glass bottles (such as borosilicate glass) should be used for liquid nitrogen cryogenic headspace to avoid low-temperature brittleness.

-Biosafety: Pathogen samples need to be designed to prevent breakage (such as necked down bottles) and validated by high-pressure sterilization (121 ℃, 15 min).

　　2、 Correct usage steps for CTC headspace bottle

1. Parameter setting and preparation

-Temperature control:

-Sample bottle temperature: usually set to 50 ℃ (or adjusted according to sample properties).

-Valve box temperature: generally set to 130 ℃.

-Pipeline temperature: always set at 140 ℃.

-Transmission line temperature: should be ≥ injection valve temperature (＞ 100 ℃) and ＜ injection port temperature to avoid water vapor condensation.

-Temperature stability: After all set temperatures have stabilized, place the sample and equilibrate for 30 minutes.

2. Blowing and Sample Preparation

-Blow off: Set the blow off pressure to 0.2-0.3 MPa, press the blow off button for 30 seconds, and then turn off to clean any residue in the pipeline.

-Connection of sampling pipe: tie the sampling pipe into the headspace bottle, tie the sampling pipe to the chromatographic injection port, observe that the pressure reading is stable, and adjust the "carrier gas adjustment" knob to increase the pressure by 0.02 MPa.

3. Injection and Sampling

-Injection: Press the "Injection" button and start the chromatograph sampling at the same time. After hearing a "click" followed by a "bang" sound (insert and remove the sample needle), take out the sampling tube 2-3 seconds later.

-Pull out the sample tube: After hearing a "bang" sound, the sample light will turn off. Pull out the sample tube and reset the "carrier gas adjustment" knob to zero.

-Blow again: Blow for 30 seconds to ensure that there is no residual sample gas in the pipeline.

4. Key precautions

-Gas purification: The gas used for headspace needs to be purified to avoid interfering with the analysis results.

-Split ratio calculation: GC gas total flow=headspace gas flow+GC gas flow, which needs to be measured by a flow meter before calculation.

-Time setting: The time for the sample to fill the quantitative tube should be sufficient, the equilibrium time of the quantitative tube should not be too long, and the injection time should be long enough to ensure accuracy.

-Pressure regulation: When manually adjusting, it is necessary to record the sample pressure and carrier gas pressure values to avoid changes in valve status affecting the results.

-Regular cleaning: The headspace bottle and injection tubing need to be cleaned regularly (with pure water, methanol, or anhydrous ethanol) to prevent residue interference.

　　3、 Common Problems and Solutions

1. Insufficient sealing: Check if the torque of the bottle cap meets the standard (20-50 N · cm), replace the aging gasket or sealing gasket.

2. Cross contamination: Use pre opened gaskets to avoid manual puncture; Rinse immediately after each use.

3. Abnormal temperature control: Ensure that the temperature of the transmission line is lower than the temperature of the injection port to avoid condensation of water vapor; Regularly calibrate the headspace analyzer.

4. Injection needle blockage: When inserting or removing the injection needle, loosen the injection port bracket to avoid the sealing gasket blocking the needle.

5. Trace analysis error: Choose quartz glass bottles or PTFE coated bottles to reduce surface adsorption; Perform silanization treatment (such as thiosilanization).