What Is GC Headspace...
Due to its ease of use, reliability and robustness, GC headspace is the second most used injection technique after liquid injection of GC applications. Used to analyze volatile organic compounds (VOCs) in a wide variety of matrices, GC headspace is used in almost every industry. VOCs in complex matrices such as blood, polymer, food and pharmaceuticals can be analyzed while leaving non-volatile components behind which may cause maintenance issues and ultimately yield poor performance.
GC Headspace Applications include:
Food – Aroma profiling, packaging, shelf life studies
Polymer – Residual Monomer analysis
Forensic – Blood alcohol
Cannabis – Residual solvents
Environmental – US EPA 5021 or 8260
The key to performing reliable and accurate analysis is reaching equilibrium. A sample is placed into a sealed headspace vial, most commonly a 20ml vial, but 10 ml vials are also used. The sample is heated to a predetermined temperature for an incubation time. During this time, VOC compounds travel out of the matrix and into the headspace of the vial. Compounds that have entered the headspace also travel back into the matrix. The point at which the rate of migration from the matrix into the headspace equals the rate from the headspace back to the matrix is called equilibrium. It does not mean that the concentration of the analyte is equal between the headspace and the matrix. The concentration is determined by what is called the Partitioning Coefficient (K).
Each compound has a specific partitioning coefficient out of a given matrix at a specific temperature and pressure. The higher the partitioning coefficient, the harder it is for that compound to be released by the matrix. For instance in water, at 40 degrees C, Hexane has a partitioning coefficient of 0.14 while ethanol has a partitioning coefficient of 1355. This dramatic difference has to do with the polar nature of water and ethanol making it difficult for ethanol to be released. Different techniques can be used to change K and increase the concentration in the headspace. Increasing temperature is generally the easiest, but there may be limitations such as boiling point of the matrix. Commonly, 1g of salt is added to aqueous matrices to reduce the polarity effect of the water.
There are many automated systems on the market and they each have their advantages and disadvantages, but the most common is a simple syringe headspace analysis. The use of a syringe eliminates valves, heated lines, solenoids and other mechanical devices that can break or be a cause of carryover from sample to sample. Automated systems such as the Flex Autosampler offer precise reliable static headspace analysis and a variety of other features to optimize your application.
The fully programmable Flex 2 autosampler can perform GC headspace analysis for your lab. Due to its robustness, the Flex 2 GC autosampler is fast becoming the instrument of choice for GC headspace analysis.
