I have two points about SPME use, pls input your experience.
1.When runing a SPME injection, splitless mode is recommended in some materials. There is still an attachment, "close for 3 min". I don't understand if "close for 3 min" means that during the first 3 minuts the injection is splitless and then change to split? Or the gas flow should be stop for 3 min to allow complete desorption?
2.I am prepared to analyze bad odour of our perfum. SPME is my first choice to extract head smell. But which solvent is best? Acetone, Ethanol, DFM or tolune?
Thank you in advance.
By Anonymous on Friday, November 7, 2003 - 03:56 am:
Do you need to dissolve the perfume in a solvent? Why not neat? You may need a diluent that is relatively invisible to your MS detector if you are using one.
Also you may need a narrower liner for SPME injection to improve the more volatile peaks - see your GC manufacturer (a splitless liner may do).
I would think the "close for 3min" refers to closing the spilt vent for injection and opening at 3mins.
There are several SPME phases to choose from - see Sigma-Aldrich (Supelco) web pages.
By Anonymous on Friday, November 7, 2003 - 01:13 pm:
You should not put your perfume in a solvent, it will overwhelm the headspace and saturate your fiber. Analyze your sample neat, as suggested by David, or dilute it in water.
Most people us a splitless injection for spme samples. I doubt if it is necessary to purge the inlet after 3 minutes, but it wouldn't hurt.
By Anonymous on Friday, November 7, 2003 - 02:03 pm:
David and anon,
So does "closed for 3 min" mean "Pulse splitless" in Agilent Chemstation? What goal will be reached at by this motion?
I really found that using solvent made big trouble for me. Peak of acetone is of a
large tail while peak of DMF is broaden unbelievable. Now I also feel strange why I choosed to use diluent before this analysis.
Thank you for you shared experience.
By Consumer Products Guy on Monday, November 10, 2003 - 06:43 am:
Michelle, since you've identified the perfume itself as the source of the problem, why not just dissolve it in alcohol and do GCMS comparison vs. control sample of perfume? If you are the perfume supplier, then it makes sense to pursue this; if you're not, let the perfume house worry about this, because you're not going to be to do anything about the off-odor anyway, even if you identify it. We normally make up about 10% solution of the perfume in alcohol, and do GCMS on either HP-1 or HP-5 type columns, and look for differences. SPME is a viable technique, but may not be needed here.
By Anonymous on Monday, November 10, 2003 - 10:44 am:
In my version of Chemstation you would do this by choosing splitless operation for your inlet, then specify a time and a flow in the "purge flow to split vent" box.
Alternatively, since you probably have tons of sample on your fiber, you could choose to run a split injection at something like 5:1.
I also think the consumer products guy has a good point about running a standard liquid injection. Good luck.
By Anonymous on Tuesday, November 11, 2003 - 06:33 am:
In the splitless mode closed for 3 minutes means the split vent will be closed for the first 3 minutes after the injection and then open to provide a split flow (helps flush the injection port). This is NOT the same as pulse splitless. In pulse splitless, if I understand this right, there will be a momentary increase in the inlet pressure in the injector, I believe this it to help counter the solvent expansion during vaporization and try to eliminate any blow back, where the solvent expands too fast and is blow backwards into the rest of the injector pneumatics causing carryover and ghost peaks to appear.
By Anonymous on Wednesday, November 12, 2003 - 12:41 am:
I am not the perfume supplier. Consumer complained our wash product having bad odor so we want to assure there is a variant in our product. Considering the matrix, I choosed SPME to analyse the headspace smell. But the result is not clear since the matrix itself has many voc's.
However it is enough to compare the perfume std and perfume added. In our lab, pulsed splitless and pulsed split inlet mode are countered scarsely. I will appreciate if anyone can introduce some application cases.
Thank you of all.
By Consumer Products Guy on Wednesday, November 12, 2003 - 06:43 am:
Michelle, do your or your sensory people also detect an off odor? How does a retain from the same lot smell? Have there been other complaints about this lot or just this one? We find occasionally that consumers will intentionally or unintentionally adulterate a product, these are not usually worth our time to pursue.
By Anonymous on Wednesday, November 12, 2003 - 02:06 pm:
Dear Consumer Products Guy,
I finished this task already. Surely there is difference between Std and Sample. The off odor is obvious and characteristic. Now perfume supplier and formulator team are searching for the cause together.
And last month I began to take a part of work from centre QA so your advice is really helpful for me to avoid not worth job. Many thanks.