Due to its ease of use, reliability and robustness, static 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, static 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.
Food – Aroma profiling, packaging, shelf life studies
Polymer – Residual Monomer analysis
Forensic – Blood alcohol
Pharmaceutical – Residual solvent for USP 467
Environmental – USEPA 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 coeffient, 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.
If you are just getting started with Headspace analysis, contact us to reach one of our application specialists who would be glad to offer some tips and tricks. Feel free to look at some of our application notes which will help you on your way.
As grain products begin to age, they oxidize. One of the products of this oxidation is Hexanal. Hexanal contributes to the green, grassy odor in food and can ruin a good morning when breakfast takes on an unpleasant taste. The amount of Hexanal in foods in one indicator of the expiration date. This study will examine the formation of Hexanal over time as cereal ages.
Trained analysts can often detect the flavors in liquors by smelling and tasting a sample. However, in order to establish the quality and essence of a liquor sample, further testing is required. Gas Chromatography coupled with Mass Spectrometry (GC/MS) is an effective tool for the determination of the flavor compounds in an alcohol. Utilizing different sampling techniques, the respective efficiency in the determination of flavor compounds in whiskey samples will be investigated using headspace and SPME.
During the synthesis of some pharmaceuticals it is sometimes necessary to use solvents in order to increase the yield or purity of the product. After the pharmaceutical is produced, the solvent(s) are removed to the greatest extent possible. The products are then tested for any residual solvents in order to limit patient exposure United States Pharmacopeia (USP) general chapter 467 describes a static headspace gas chromatography procedure for the determination of residual solvents.
There are several ways to determine the amount of alcohol that is in a person’s system. Blood alcohol determination in the laboratory is used predominantly when a person refuses a breath test. In order to determine blood alcohol content, a person’s blood has to be withdrawn as soon as possible after the occurrence. This application note will examine static headspace sampling of alcohol standards using Gas Chromatography (GC) for separation and Flame Ionization Detection (FID) for analysis.