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FLEXO Magazine : June 2009
TECHNOLOGIES & TECHNIQUES Residual Solvents in Printed Film A Review/Analysis of Manual Headspace Injection vs. Automatic Headspace Sampling Systems By Burton S. Todd I n this series on the fundamentals of gas chromatography, we are looking at the use of the GC in quality control of printed fl exible packaging by printers and converters. Its primary use is to test for residual solvents in printed fl exible packaging materials. Headspace gas chromatography (HS-GC) is used to test for low levels of residual solvents in printed fl exible packaging materials. This injection technique is simple to use, does not contaminate the gas chromatograph and can provide very accurate quantitative results. HEADSPACE INJECTION TECHNIQUE The headspace injection technique can be performed manually with a gas-tight syringe or automatically with a headspace autosampler. For the purpose of analyzing residual solvents in fl exible packaging, the headspace injection is performed in three steps: 1. A fi xed size sample of printed fi lm is heated in a sealed headspace vial. 2. A known portion of the headspace vapor is removed from the heated vial. 3. The headspace gas sample is injected into the GC injection port. MANUAL HEADSPACE TECHNIQUE Gas chromatographic hardware has developed considerably over the past 40 years and so has the headspace injection technique. When originally developed, the headspace GC was performed using pint canning jars as the headspace sample container. The canning jar lid had a hole drilled into the center of the lid into which a plug septum was inserted. A large section of printed fi lm was cut out and sealed in the jar and closed with a normal canning lid ring. The pint jar was then placed into a laboratory oven for 20 to 30 minutes to drive the volatile solvents out of the printed sample. Once the headspace sample had been heated for a suf- fi cient length of time the operator donned a pair of heavy gloves, removed the heated jar from the lab oven and using a FIGURE 1. Manual headspace sampling. FIGURE 2. Manual headspace steps. 26 FLEXO JUNE 2009 www. f le xography. org FLEXIBLE PACKAGING
Sustainable Spring 2009