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Topic: FTIR  (Read 15096 times)

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Offline Golden_4_Life

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Re: FTIR
« Reply #15 on: May 19, 2010, 11:29:42 AM »
Well this certainly does help out, and I sincerely appreciated the timely and well-considered replies.
For my part, at the 1 p.m. meeting I will tell them:
1) IT is possible to use the DCM/acid extraction method to recover the PDMS analyte.  Also, that toluene is another solvent that has been shown to be effective.

2) Use of the FTIR to quantify PDMS presents a whole 'nother realm of issues, namely,
a) the sod.chlor. plates: it is difficult to sometimes get the drop to be right in the center of the plate and the variance in the "volume" of a "drop" is another counfounder.
b) suggest we order/purch. a "flow cell" (not sure from whom or price$?) but this has been shown by other investigators (quoting this online source ;) of forum writers Train, Marquis) to be effective.
c) will try to use a pipetteman to repeatably deliver 10uL of sample instead of relying on drops.

3) Problems to resolve: a) signature peaks to use for quantifying is a dilemma---when I tried using the 1014/1091 doublet it was effective; however, when I used the 1260 singlet it also appeared in my negative controls. So, some "method devel" is indicated here.
I think they will be pleased to at least see effort/progress notwithstanding the problems encountered.
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Offline Golden_4_Life

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Re: FTIR
« Reply #16 on: May 19, 2010, 12:44:24 PM »
 Offering a 'mole snack" to whomever can convincingly explain to me why I see the 1259 cm-1
peak in my "reagent blank" and "sodium chlor plates only" blank.  The solvents I used were opened the day of the test and I do not believe them to be contaminated with PDMS.
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Offline marquis

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Re: FTIR
« Reply #17 on: May 19, 2010, 08:13:34 PM »
This is kind of an off chance, but still..

Are you using gloves when running this test?  You might check and see if any ingredient in the glove could generate a false peak in this range.

We were using the white/ opaque gloves for this test. It turned out that there was a vinyl plasticizer in the gloves that threw a peak at 1259.  When we switched to the purple gloves, the problem went away. 

It seems simple, but the glove problem took a lot of time and effort to solve.  It also took GC/MS, GPC, and AA.

Good luck.


Offline Train

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Re: FTIR
« Reply #18 on: May 19, 2010, 09:02:53 PM »
Did you try brand new salt plates?  They shouldn't be absorbing at 1259 unless there's some contamination.  According to my textbook, "Reasonable care must be taken in handling salt cells and plates. . . . Care should be taken to prevent contamination with silicones, which are hard to remove and have strong absorption patterns." (emphasis added)

I always flushed with copious amounts of solvent and took the background with the flow cell in the instrument filled with diluent.


Offline Golden_4_Life

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Re: FTIR
« Reply #19 on: May 20, 2010, 01:12:15 PM »
First off a summary of the meeting: 1) I explained to the group (upper mgm't and sales director) that "yes, we can assay for dimethicone using the FTIR that we already have; however, we are at best semi-quantitative for now".  I showed three slides of FTIR scans taken at three different concentrations and using DCM as the extraction solvent--and that the Negative Controls showed a small peak also.  I told them that I may have not removed the residual PDMS from the plate or that there was inherent co-signaling or (as you'all cited yesterday that either trace levels of PDMS were in the gloves--as the 1014/1091 spectra did not show contamination in the NegCtl.  THey seemed pleased with this explanation.  I told them that I will also use toluene as xtrc'n solv in a future run as other Investigators have used it with success and it may offer us another ''angle" on the problem.  2) One of the senior managers asked me "would you say that you finish this testing and give us a final assessment in 3 months time?"  I replied "yes, but I will need to purchase resources--namely the flow cell and some toluene".  He said "sounds good. We have had to send-out our lotions for dimethicone so it seems like we might be able to get it done in-house".  So overall, it was good.  Also, interesting how managment seemed to be less "interested" in the science and more concerned about the bottom line of "when" I could get finished.  But there is some very interesting science in play here.  Marquis and Train--ENJOY your Mole Snaks--I have clicked "give" on your profiles.  Thansk again I will be positng more updates.
G-4-L
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Offline marquis

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Re: FTIR
« Reply #20 on: May 22, 2010, 01:48:59 PM »
You asked where to get the specialty equipment (in this case a fluid cell) for your IR.

I would recommend asking the instrument manufacturer, for a start.  It doesn't happen often, but every once in a while a manufacturer will make an accessory that only one instrument can use.  Got caught in that with an ATR, once.

As for the fluid cell.  Try to get one where the spacers can be changed.  It may turn out that one thickness of liquid will work out best. In which case you change the spacer.

Also, some of the fluid cells come molded together.  You couldn't change the thickness without destroying the cell.

The fluid cells that allow you to change spacers usually allow you to clean all parts of the fluid cell.  That can be very helpful.  Especially when tracing down a "ghost" peak.

Offline Golden_4_Life

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Re: FTIR
« Reply #21 on: May 26, 2010, 01:08:50 PM »
Thanks for that tip Marq!
I have recv'd the 'go ahead' from upper management to purch a flow cell--your advice is appreciated.
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Offline Golden_4_Life

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Re: FTIR
« Reply #22 on: May 28, 2010, 03:51:27 PM »
I will be posting up some images of new data via FTIR on simethicone, may need help from the forum ''brain-trust" with some of the interpretation/analysis--is it legit to post raw data images and tables on this website?
Golden4Life

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