Hi AMMRL Colleagues.
I'd like your insights into extending the life of spinners – specifically
the blue Bruker POM spinners that use O-rings to tighten their grip (but
which do not directly contact tubes).
We've been encountering some problems with samples occasionally being loose
in the spinners in our automated spectrometers (SampleCase-equipped). In one
case, we luckily avoided disaster when a loose sample got jammed in the
hardware, almost breaking inside the magnet.* The source of the problem seems
to be a combination of potential factors, including
* Mechanical wear-induced increase in the diameter of the inner surface of the spinners
* Use of tubes that are too narrow (some are OK in another spinner, some are loose in all spinners)
* Possible loss of tension provided by the O-rings?
* Possible enhancement of mechanical wear via substandard pre-insertion cleaning of the tubes?
* Possible enhancement of mechanical wear via cleaning/detergent?
* Something else?
Our facility's two automated 400 MHz spectrometers handle thousands of samples every
month. Most of the tubes that come through are economy/high throughput grade (e.g.,
WG-1000, Aldrich Blue 200, some unidentifiable, etc.). While most samples fit snugly
in all tested spinners, some tubes are loose in some spinners, and occasionally we
get a tube that is loose in all spinners. Increasing expectations for tube quality
is not realistic - the culture of spending the least possible money on tubes is too
strongly ingrained in some of our PIs.
I'd like to increase the tension in the spinners so every spinner can at least grip
the narrowest expected tubes (maybe 4.92mm) safely. I'm focusing on the O-rings
because they're the only thing I have direct control over that doesn't involve
purchasing a hundred new $$$pinners. The O-ring size is apparently 3mm "thick" with
an inner diameter of 8.5mm, and the material I'm guessing is Buna-N rubber (based
on availability at a couple of vendors). But simply replacing them didn't seem to
improve performance significantly. Moving to an alternative size or material isn't
necessarily straightforward, as there isn't full easy commercial availability of
all materials at all sizes. But I can say I haven't found any magic solution:
2.4x8.3mm and 1.3x8.1mm Buna-N, 2.5x8.5mm silicone (red), and 1.5x8.5mm PTFE O-rings
didn't confer the ability to adequately grip my narrowest tubes on my more problematic
spinners. (The Buna-A and silicone were durometer 70 shore-A, and the PTFE were "rigid").
The gains provided by reduced inner diameter seem to be offset by the thinner material.
Doubling up O-rings on the bottom of the spinner did fulfill the need. Yet I wonder
whether this increases wear on the spinner and/or disturbs airflow.
What is the expected lifetime of a spinner, anyway? Perhaps we're just exceeding the
expected lifetime for some of them. The bores of most look a bit worn, but otherwise
all look OK. We only started using automation routinely in 2017 (though it accelerated
last year), so the spinners in the carousels aren't older than that. I'd love to hear
the experiences of others in high-throughput labs where the open-access environment
makes it difficult to police NMR tube quality.
NOTE: Could cleaning the spinners increase wear? I'd been doing do irregularly for a year,
then stepped it up when COVID hit. My regimen involves soaking them in a solution of
Sparkleen lab glassware detergent, giving them a light scrubbing with a not-so-stiff
brush to remove the gross finger grease buildup, cleaning the bore with a doubled-over
pipe cleaner soaked in Sparkleen solution, rinsing them with tap water, then DI water,
then 70% isopropanol, and left to dry in a hood. For the last several months I've tested
every clean spinner for grip tightness using a trusty Wilmad 528-PP, but it looks like
I need to use something narrower to make the test more stringent. Does anyone have a
quantitative test for spinner grip strength?
Do you have a favorite solution? If you replace your spinners on a regular basis, how
often do you do so? Any insights or tips would be welcome.
Thanks. - Josh
Josh Kurutz, PhD
NMR Facility Manager, Chemistry Dept.
https://voices.uchicago.edu/chemnmr/
jkurutz_at_uchicago.edu
Received on Mon May 24 2021 - 09:52:40 MST