The calibration of headspace gas analyzer is the core link to ensure its measurement accuracy, which requires systematic management based on hardware performance, environmental conditions, and operating standards. The following provides a detailed explanation from three aspects: pre calibration preparation, core steps, and verification and maintenance:
1、 Preparation stage before calibration
-Equipment and standard gas selection
-Standard gas requirements: Select nationally certified standard gases (such as 1% O ₂+10% CO ₂ mixture) with concentrations covering three intervals of 20%, 50%, and 80% of the instrument range to ensure the linearity of the calibration curve.
-Equipment inspection: Confirm that the sensor is unobstructed, the pipeline is well sealed, and the battery or power supply is stable; Perform cleanliness checks on auxiliary tools such as puncture needles and sampling bottles.
-Environmental control
-The laboratory temperature is maintained at 20-25 ℃ with fluctuations of ≤± 2 ℃, and the humidity is controlled at 45%~60% RH to avoid gas volume expansion/contraction caused by temperature and humidity changes.
-Ventilation facilities should ensure the timely discharge of harmful gases to prevent safety hazards caused by standard gas leaks.
-Personnel protection and training
-Operators need to wear chemical resistant gloves and goggles, familiarize themselves with the instrument manual and emergency response procedures.
2、 Core calibration steps
-Zero point calibration
-Introduce high-purity nitrogen gas (O ₂<0.1ppm) as the "zero gas" and continuously blow the gas path for more than 5 minutes. After the reading stabilizes, perform the zeroing operation.
-Range calibration
-Introduce standard gases close to full range (such as O ₂=5%, CO ₂=30%), adjust the instrument gain parameters to make the displayed value consistent with the standard value.
-Multi concentration point verification
-Select standard gases with low, medium, and high concentration gradients for sequential injection, establish calibration curves, and calculate linear errors.
3、 Verification and maintenance after calibration
-Data recording and analysis
-Record the calibration date, standard gas batch number, environmental parameters, and deviation values of each concentration point in detail, and generate a PDF report for archiving.
-If the relative error of a single calibration is greater than 5%, the cause needs to be investigated and recalibrated.
-Functional testing
-Conduct blind testing using actual samples with known concentrations and compare historical data to determine stability.
-Periodic maintenance
-Sensor lifespan management: O ₂ sensors are replaced every 6 months, and CO ₂ sensors are replaced every 15 months.
-Hardware maintenance: After each calibration, wipe the sampling port with a dust-free cloth dipped in ethanol, and check the sealing of the solenoid valve monthly.
Through the above systematic calibration process, the headspace gas analyzer can maintain a measurement accuracy of ± 0.1% (O ₂)/± 2% (CO ₂) for a long time, providing reliable data support for fields such as food preservation and industrial process control. It is recommended to refer to the specific equipment manual to refine the operation details and optimize the calibration plan based on actual needs.