Saturday, October 1, 2016

How does a GC work?

We all talk about GC/MS analysis. But few of us outside of the archane world of a chemist's lab truly know what they are.

Was looking for something else in my archives and came across this, from a chemist in Connecticut whose real name always remained a mystery.  He was an online friend who knew a LOT about Essential Oil chemistry, and delighted in teaching it.

The topic of the message was "pretty smelling mystery oil" so it would appear I had been talking about something that I couldn't identify...  and the subject of analysis came up.  this was his explanation of "how it works":

From: DrPriszm@aol.comDate: Sun, 13 Oct 1996 01:29:59 -0400
Well, not really, but you're close!  Get ready for the $1.39 course on gas
chromatography! (But only if you promise to attend my real class in person!)
A gas chromatograph is really like an oven.  Inside the oven is a hollow tube which is coiled round and round like a garden hose so it will fit in the oven, because it may be 25 meters long.  Inside the tube is something similar to sand, very fine sand. There is some type of gas always flowing through the tube, from one end to the other.  
On the front end of the tube, where the gas is coming from, is an injection port.  It is through this port that the sample is injected onto the column, or tube.  The flowing gas carries the sample through the column.  As the sample travels through the column, the
various components of the sample separate, and form bands in the column.
Picture a marching band shoulder to shoulder marching down a street, and then gradually they start separating until they are 10 feet apart of each other.  Now they're marching single file, but they're separated by that 10 feet?  O.K. so far?  Good. 
Now at the end of the column, there is a detector. There are many types of detectors, but it really doesn't matter.  As each component marches past the detector on its way out of the column, the detector produces an electrical signal.  If the component is present in a high concentration, the detector produces a big signal.  If the component is only present in a small concentration, the detector produces a small signal. 

The signal then goes to a strip chart recorder.  You know what that is? Picture the device that the old fashioned lie detectors used to use.  You know, the pen would move on the paper and produce a wiggly line?  Same thing. The strip chart recorder draws peaks when the detector "sees" a component. Big peak for high concentrations, small peaks for small concentrations. 
This is the printout of a very simple oil with one major component

Here comes the math, be brave.  Simultaneously when the detector sends its signal to the strip chart recorder, it sends an identical signal to a computer processor.  The computer automatically computes the area under the peak of each component, and compares it to the area of the peak of a standard.  Then, by a simple proportion, it calculates the concentration of the unknown peak to the concentration of a standard compound whose
concentration we do know.  
Let me give you an example.  I take a known amount, say one gram of eucalyptol, the major component of eucalyptus oil, and inject it into my G.C. (gas chromatograph).  I get a peak, and that peak is always the same height as long as I inject one gram of eucalyptol into the G.C.  If I inject 1/2 gram of eucalytol, I get a peak 1/2 the height, and so on.  So I tell the computer that when you see a peak that is exactly the same height as my one gram standard, report that one gram of eucalyptol is in my sample.  Now the peaks are not all on top of each other, because you couldn't tell them apart.  They are separated on the paper just as the components are separated on the column.  The first peak to appear corresponds to the first peak that comes through the column.  
Your chromatogram of essential oils may contain hundreds, or even thousands of peaks!  How then, do we identify which peaks correspond to which components?  Well, we have to inject hundreds or thousands of standards of known components into the G.C. We then note the time it takes, from injection, until the compound hits the detector in
We call this the elution time, or the time it takes for a compound to elute from the column.  Each compound has a unique elution time, and can be identified this way.  Now, let me tell you that it is WAY more complicated than that, and I could go into the various types of columns, injectors,detectors, gases, etc., but that is the gist of it.      
GC of one of the most complicated oils - Rose Otto. See the multitude of peaks?

I had one supplier who would send a gc upon request...  with the major peaks marked by hand.  Their equipment was not hooked up to a machine... he identified the peaks by hand.   Also, the detail (and accuracy) an analyst can give is determined to a great part by the depth/breadth of the "Library" of analyses they have access to.  

I'm hoping this description makes a little bit of sense!  (Yes, it's simplistic. There may be those who will scoff at the analogy of the marching band.  Feel free to scoff.)

Sunday, September 18, 2016

To fridge or not to fridge? That is the question.

I was asked twice this week about refrigeration of essential oils, specifically if there are any that should not be refrigerated.

My answer (compiled from different places that I responded:)
That depends on who you ask. Robert Tisserand suggests refrigerating all of them. We do not refrigerate the Roses because it causes them to crystalize. (ditto aniseed.) this can happen at cool room temperature, as well.  If it does, just sit the bottle in a cup of WARM water (think baby bath) for a few minutes to re-liquify. We don't like the idea of repeatedly heating an oil if we can avoid it, so we do not refrigerate those two. 

The "base note" oils, the long lasting woods, roots, and Patchouli all improve with age, so why would you want to prevent that? I would never refrigerate those. Again, cool room temperature and shielded from light and direct heat. 
A friend shared her EO storage refrigerator. Now, THIS is a serious user.  Most folks use an under counter/dorm sized box.

What SHOULD be refrigerated are the citrus rind oils, orange, mandarine, etc., and the conifers... the "needle oils"... pines, firs, spruces, etc. They are the two shortest lived categories so definitely benefit from refrigeration. As for all the oil in between... that is preference. If you are going to be using your oils within a reasonable time, then, you could refrigerate, but it's not necessary. If you know you have enough.. let's say Lavender, to last you for 10 years, yes, refrigerate it, and store it under nitrogen. But if you buy what you need and replace it with the next harvest, then it is truly personal choice. 

Something else, Lynette asked if any oils could be harmed by refrigeration. Thinking of how thick and "sticky" myrhh and vetiver can be... and if they were refrigerated...they would be.. think 'cold molasses." The shorter lived ones, and the Blue oils benefit by it though.  

OH.. another thought. the distiller of our beautiful Frankincense sacra suggested that I NOT refrigerate her. She says that WINTER for those trees is, perhaps 68 degrees Farenheit and the cold would shock the oil. the resins do not have a terribly long shelf life, so, again, perhaps best to buy what you will use in a year or two, and then repurchase. 

Regarding the Frankincense comment above.  Robert Tisserand was kind enough to join the discussion, and said that while Patchouli, for example, does  not need refrigeration, "I find the idea that Frankincense oil would be "shocked" by refrigeration a delightful one, but oils are not people. Any frankincense oil high in a-pinene or a-thujene needs cool temps to reduce oxidation."   (We are storing our bulk Sacra (and other Frankincense oils) under a layer of nitrogen to protect from oxidation.  You might want to consider both sides of this discussion in deciding how to store yours.)

Another thought. You can further protect the oils by NOT storing them in half full/half empty bottles. Decant those 15 ml bottles down to 5 or 2 mls as you use them up. that helps protect them against oxidation, which is their worst enemy. 

Another participant in the discussion reminded us to keep child safety in mind.  If you are storing your oils in your kitchen refrigerator, *please* store them in a locked safety box.  Children are used to food and beverages being in the refrigerator.   If you are able to get an under-counter or dorm sized fridge for your fragile oils, please consider padlocking it shut.  Your child or a visiting child's safety is worth the inconvenience.   

I love the questions we are asked!