The headspace sampler is a key equipment for achieving efficient sample pretreatment in gas chromatography analysis, and its operational standardization directly affects the accuracy of analysis results. The following are the core usage details based on technical standards and practical experience summary:

1、 Principles and core advantages

-Principle: Headspace injection technology extracts the top gas directly for chromatographic analysis through gas-liquid (or gas-solid) two-phase equilibrium of volatile components in a closed container.

-Advantages: Eliminate tedious preprocessing steps, avoid organic solvent contamination of chromatographic columns and injection ports, significantly improve analysis efficiency.

2、 Sample bottle pretreatment and selection

-Cleaning process

-New bottle treatment: Soak overnight in chromic acid solution → Ultrasonic cleaning with ultrapure water 3 times → Burn in a muffle furnace at 400 ℃ for 2 hours to remove organic residues.

-Reuse bottle treatment: acetone ultrasonic degreasing → deionized water rinsing → nitrogen blow drying, detergent is prohibited to prevent residual interference.

-Bottle inspection

-Integrity testing: visually inspect the integrity of the bottle mouth thread, and repair minor scratches with fine sandpaper; Magnetic bottle caps need to be tested for adhesion to prevent air leakage.

-Specification matching: Select a pressure resistant bottle based on the nature of the sample (if the pressure system needs to withstand 0.2-0.3MPa), and control the volume within 10-20mL.

3、 Sample loading specifications

-Liquid sample

-Anti bubble operation: Insert the tip of the pipette into the liquid surface and slowly release the sample. The volume is strictly limited to 1/3~1/2 of the bottle volume, with sufficient headspace reserved.

-Volatile samples: pre cooled to 4 ℃ and covered with ice bath to reduce volatilization losses.

-Solid/semi-solid samples

-Uniform spreading: Powder thickness ≤ 5mm to ensure sufficient volatilization; Place the paste above the magnetic stirrer to avoid contact with the bottle wall.

-Reagent addition sequence: Inject diluent (such as acetone) first, then add internal standard, and finally add saturated saline solution to reduce the activity of the solution. Acid base adjustment should be completed before sample loading to prevent gas from breaking the seal during the reaction.

4、 Optimization of sealing system

-Selection of spacer and puncture

-Material: PTFE/silicone composite gasket is preferred, which is corrosion-resistant and has strong sealing performance.

-Puncture depth: rapid vertical penetration during manual injection; Adjust the automatic sampler to 2/3 of the thickness of the spacer to avoid puncturing the bottom rubber layer.

-Aluminum cover crimping process

-Manual pressing: Apply pressure evenly until there is a "click" sound to confirm bite; The electric capping machine is set with a pressure of 8-12N · m, and the sealing of each batch is randomly inspected (underwater bubbling method).

5、 Balance conditions and injection control

-Balance parameter setting

-Temperature fluctuation: The temperature control accuracy of the constant temperature oscillator is ≤± 0.5 ℃, and the equilibrium of lightweight components takes 30 minutes, while complex substrates require 60 minutes.

-Pressurization method: high-purity nitrogen is blown back, with a pressure maintained at 0.2-0.3MPa to prevent deformation of the bottle body.

-Accurate management of injection volume

-Quantitative ring cleaning: Clean and dry with acetone before each replacement, and the injection volume should not exceed 80% of the quantitative ring volume

-Cross contamination prevention: When injecting multiple samples, a new quantitative ring must be replaced.

6、 Maintenance and troubleshooting

-Daily maintenance

-Instant cleaning: Disassemble the bottle cap assembly after each use and clean the spacer groove with methanol ultrasonic cleaning; Check the thread wear of the bottle mouth every week and use specialized tools to trim burrs.

-Common problem handling

-Leakage: Check if the gasket puncture hole is closed and if the aluminum cover is tightly engaged.

-Poor reproducibility of peak area: Verify sample equilibrium time, temperature stability, and quantitative ring cleanliness.