For ensuring the quality and safety of cigarette packaging, it's essential not only to monitor the production process in real-time but also to conduct thorough testing of raw materials and finished products. Common parameters tested include VOCs (volatile organic compounds), formaldehyde, and ortho-benzene. In this article, I'll share some common issues encountered during VOC testing and practical solutions to address them.
Common Issues with VOC Detection
Our company uses an Agilent 7890A+7694E headspace gas chromatograph for VOC analysis. One frequent problem is contamination of the headspace pipeline, which can lead to residual substances like ethanol, propanol, ethyl acetate, and n-propyl ester remaining inside. These residues can affect the accuracy of the calibration curve, resulting in unreliable test results.
Problem Analysis
To determine if the headspace pipeline is contaminated, first check if the gas phase is clean. If the baseline is stable and no material peaks are present, the gas phase is likely uncontaminated. However, since the headspace operates at lower temperatures (typically 80–120°C), some organic compounds may remain there. To confirm contamination, place empty bottles in the sample tray and run a blank test using the normal VOC detection procedure. If material peaks appear, the headspace pipeline is likely polluted.
Solutions for Headspace Contamination
Here’s how we clean the headspace pipeline:
- Prepare 12 sample vials (reusable), 10 bottles filled with about 1/6 of distilled or ultra-pure water, and 2 empty bottles.
- Disconnect the transfer line from the GC inlet and set a carrier gas flow of less than 100 ml/min.
- If the transfer line isn’t disconnected, set the GC oven temperature to 200°C for 5 minutes and use a split ratio of 40:1 or 50:1.
- Set the headspace parameters: sample balance at 125°C, sample ring at 140°C, and transfer line at 150°C. Set the time events as follows: equilibration time 2.5 min, press time 1 min, inflation time 1 min, loop equilibration 1 min, and injection time 1 min.
- Load the 10 water bottles and 2 empty bottles into the sample tray and run the headspace analysis.
- Check the residual condition after the run. If the cleaning isn’t sufficient, repeat the process.
This method may not completely eliminate all residues, but it significantly reduces contamination, improving the accuracy of VOC measurements. Regular maintenance and proper cleaning procedures are crucial for maintaining reliable and consistent results in VOC testing.
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