Are you living with your head in the clouds? Not to worry, so do I!
It is nice up there, completely filled with the aromas of tasty foods and the smells of perfume, scattered with alcoholic notes and fragrances from wine and beer, and just the occasional bad smells of rancid butter or sulfuric compounds, or even the typical smell of chloroform.
This time I want to share with you one of the most basic senses, directly linked to our memories. It is being said that certain smells trigger ones memory to days gone by. In my case it is coconut suntan lotion as I grew up in the seventies near the seaside and nobody seemed worried about getting too much sun and wanted to get a deep tan. The smell of coconut pushes me back to my childhood, making sandcastles and watching my mother knitting socks on a beach chair, getting the family ready for winter already.
But let us move away from fond memories of endless summers and start talking analysis here. Analyzing a headspace in a vial with a GC or GC-MS is extremely common and has many different applications, ranging from environmental analysis of volatile components, over flavor analysis in foods and fragrance analysis, and residual solvent analysis in pharmaceuticals.
Before I dive into the touch points where we encounter a product where headspace analysis is involved, I want to share some basics.
Principles of static headspace analysis
The samples are being heated and shaken, so the volatile compounds are driven into the headspace above the sample: this is called incubation. Equilibrium is being created between the sample and the space above. When this is reached a gas tight syringe or a sampling loop takes the sample and injects it into the GC. During injection the split flow is typically set to “on” as the injection volumes are 1ml and over and we need to take care to not overload the injection port. It is also typical to use a column with a thick film to capture the compounds on the phase, or perhaps even cryogenically cool the column or the oven. Typically the thicker the film, the lower split flows can be set and the higher the volume of sample can be injected.
Method development involves determining the time and temperature of incubation and the ratio between sample and headspace. A good balance is needed so sampling is not performed when the steady state is not yet reached. There are excellent papers describing the principles of headspace.
Syringe type headspace technique
In the case of a syringe type headspace technique sampling is performed with a gas tight syringe. Typically this syringe is heated and the plunger has a Teflon end, preventing the volatiles from escaping the sampling. This technique works really well and is often used for analyzing blood alcohols or environmental samples. The biggest benefit of this technique is the variability of the injection volume; it is simply a parameter in the methodology. Also in the modern samplers, it is fairly easy to switch between liquid, headspace and SPME injection techniques so the purchase of such a sampler allows the lab more flexibility.
Like what you are learning?
Valve and Loop type headspace technique
Sampling is now completely different, the vial is pressurized and the sample loop is filled with the headspace of the vial. This technique is used a lot where the methodology is fixed and the lab needs to focus on a dedicated system for headspace analysis. A typical example of this is residual solvent analysis in the pharmaceutical industry.
Headspace analysis is everywhere
Headspace analysis touches many aspects of our lives, many products we all know are being controlled, developed and researched using this technique.
Let us start with an application close to my heart as a Belgian and beer lover. There are compounds that give a buttery type flavor and are regarded as “off flavors.” Typically a cryogenic step is needed to determine this diketones, but latest technologies allow for skipping the hassle of using carbondioxin or liquid nitrogen.
Many of you are aware that we can measure alcohol in the blood, again headspace is the technique of choice in many hospitals all over the globe. Easy, fast and rugged methodology is key here so patients are assisted in a timely way.
But in case you need medicine, rest assured that the pharmaceutical industry has excellent and stringent quality controls. A typical application is the analysis of residual solvents, and here again headspace analysis is used.
Moving away from beer and the possible bad consequences of consuming too much, there are more fields where headspace is used. We monitor also our food packaging and our environment on the presence of volatile organic compounds such as aromatics and chlorinated compounds.
So, if you are reading this whilst having some beverage and a packet of crisps, overlooking a river, be aware that what you see and what you taste has been developed, researched and analyzed using headspace analysis.