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Offline phth

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nonane contamination
« on: November 22, 2017, 06:06:10 PM »
I seem to be having a contamination problem with nonane, and I cannot figure out where it is coming from. I was wondering if anyone has observed the same problem.  So far I can't trace it back to solvents or septa... :-[
Thanks

Offline wildfyr

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Re: nonane contamination
« Reply #1 on: November 23, 2017, 10:00:05 AM »
As in, something is in your nonane, or nonane is getting into something else.

Offline OrganicDan96

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Re: nonane contamination
« Reply #2 on: November 23, 2017, 12:47:47 PM »
are you sure its nonane?

Offline pgk

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Re: nonane contamination
« Reply #3 on: November 23, 2017, 01:22:59 PM »
Nonane and similar aliphatic hydrocarbons are usual components of petroleum ethers and hydrocarbons based-glassware grease. As being highly hydrophobic, non-polar and having high boiling point (>130oC), they are not easily removed from glassware by washing with detergents, rinsing with acetone/ethanol or drying in the lab’s oven. So, traces of nonane and similar hydrocarbons might remain in the glassware and significantly contaminate reagents and products, especially when working in mg scale.
« Last Edit: November 23, 2017, 01:52:02 PM by pgk »

Offline phth

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Re: nonane contamination
« Reply #4 on: November 23, 2017, 03:03:25 PM »
As in, something is in your nonane, or nonane is getting into something else.
Nonane is in my something.

Offline wildfyr

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Re: nonane contamination
« Reply #5 on: November 23, 2017, 07:36:29 PM »
Tried rinsing stuff with hexane or toluene or diethyl ether? I'm pretty shocked it won't get evaporated in an oven. Gasoline evaporates off concrete under ambient conditions pretty quickly, and it contains nonane.

Are you dead sure it's nonane?

Offline pgk

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Re: nonane contamination
« Reply #6 on: November 24, 2017, 12:41:56 PM »
Theoretically, yes but in practice, no!
In common lab practice, drying of glassware is effectuated by heating in the oven at 50-60oC for 20-30 min or less, if hurrying up.
On the other hand, n-nonane has MW = 128, bp = 151oC and heat capacity = 0.506 cal/(grxgrad) at 60oC.
According to the Trouton’s rule, n-nonane has evaporation enthalpy ΔH = 21x(273 + 151) = 8,904 cal/mol = 8.9 kcal/mol  that corresponds to latent heat of vaporization = 70 cal/gr.
Thus, when placed in an oven and heated from room temperature (20oC) to 60oC, 1 gr of n-nonane needs the offer of 70 + 0.5x40 = 90 cal (which is not so fast procedure in an oven that is plenty of various glassware), in order to start to evaporate.
Then, the kinetics of evaporation follows the corresponding Langmuir’s equation. However, evaporation stops when the vapor pressure over the n-nonane droplets equalizes with its partial pressure in the oven’s atmosphere. Furthermore, condensation starts when the partial pressure continues to increase. Note that both these procedures are quite fast in an oven that is plenty of vapors from various solvents.
In other words and in order to completely remove heavy solvents (bp > 100oC) from glassware, drying must be effectuated at 70-80oC for a few to several hours, depending on the boiling point of the particular solvent.
The same happens to the heavy fractions of gasoline. Anyway, concrete substrate in open space is different than the oven’s inner environment.
PS: Note that Trouton's rule leads to approximations and thus, estimated thermodynamic values are indicative and may slightly differ from experimental ones.
« Last Edit: November 24, 2017, 01:36:53 PM by pgk »

Offline wildfyr

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Re: nonane contamination
« Reply #7 on: November 25, 2017, 10:14:18 PM »
Well I have a somewhat dickheaded request then: why not either turn the oven up or heat gun the glassware for a minute under vacuum before use?

Doing this might at least hint at your contamination source.

Offline Arkcon

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Re: nonane contamination
« Reply #8 on: November 26, 2017, 08:48:39 AM »
Not really a bad idea, wildfyr:.  When confronted with a trace contamination that a sensitive analytical method keeps turning up, what's needed is vigorous, even extreme cleaning.  If only to track down the source, and then say, "Did my best, and can only get the contamination just so low."  Maybe, for the best results, you'll need to purchase dedicated vials, and use them only once.  But you'll have to justify that.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline phth

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Re: nonane contamination
« Reply #9 on: November 26, 2017, 05:29:41 PM »
Well I have a somewhat dickheaded request then: why not either turn the oven up or heat gun the glassware for a minute under vacuum before use?

Doing this might at least hint at your contamination source.

No you're right I haven't been heating my flasks real hot prior to use.

Offline Flatbutterfly

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Re: nonane contamination
« Reply #10 on: November 28, 2017, 03:47:18 PM »
Further to pgk's comment: do you use Apiezon grease on your glass joints?

Offline phth

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Re: nonane contamination
« Reply #11 on: November 29, 2017, 12:55:12 AM »
Further to pgk's comment: do you use Apiezon grease on your glass joints?

Wow, you're right. I did one time to measure the vacuum difference comparing apeizon to silicon grease because it was discounted.  I switched back and noticed the problem over time.

Offline pgk

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Re: nonane contamination
« Reply #12 on: November 29, 2017, 05:38:55 AM »
Overheating flaks, followed by cooling prior to use risks to attract atmospheric humidity which will start to condensate in the cooled flask. So, the best is to heat the flask with the flame, waiting to cool at 60-70oC and then keeping it in the oven, ready for use.
« Last Edit: November 29, 2017, 08:08:06 AM by pgk »

Offline wildfyr

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Re: nonane contamination
« Reply #13 on: November 29, 2017, 03:10:41 PM »
pgk, isnt it standard to allow glassware to cool down under N2 flow or vacuum? phth is an experienced enough chemist not to make that mistake! (I hope).

Offline Flatbutterfly

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Re: nonane contamination
« Reply #14 on: November 29, 2017, 03:52:42 PM »
Apiezon grease consists of high MW hydrocarbons.  Nonane might be the lowest boiling component of the grease or part of Apiezon in your sample.  Further to wildfyr’s comment, how did you confirm that your contaminant was nonane?  [GC (MS), H-NMR ?]  Most chemists use far too much Apiezon on their ground glass joints: you need the thinnest of films (without streaking).  It is also notoriously soluble in CH2Cl2 and once your solvent is contaminated then all is lost for those experiments.  Run an H-NMR of your NMR solvent with a trace of Apiezon (blobs around 0.9 and 1.3 ppm); silicone grease appears at ~0 ppm.  Use Teflon joints for solvent pots.  And good luck!

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