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Can Acetone/DI Water Cleaning cause weight gain in 304SS 26Ga Needles?

(-----) 2006

Working on a cleaning verification procedure for Hypodermic needles (.018"OD x .005"ID x .30" Long).
A little background first: Prior to mfg. use, we ultrasonically clean the needles in high purity IPA, rinse, and let air dry. Sometimes we see a color change in the IPA indicating we have washed something off. After drying, we bond the needle into a plastic connector, using a UV Cure adhesive. After bonding, we select random samples, and perform destructive pull testing, for QC check. Sometimes we get a low pull-force, the failure is always at the bond line between the needle and adhesive. We suspect that our needle vendors fail to properly clean the needles sometimes.
What I would like to do is implement a simple cleanliness test. A summer intern in our Chem lab developed the following procedure:
1) Weigh and record weights of 3 or 4 sample of needles, 1-5 grams each. Used a precision digital balance (.01 mg Accuracy)with glass enclosure.
2) Place each sample in separate beaker.
3) Add 50% Acetone/DI water mixture to each beaker. HPLC grade Acetone.
4) Ultrasonic for 60 minutes.
5) Pour out mixture, and place needles on clean petri dish.
6) Oven Dry 1 hour at ~100 °C
7) Weigh each sample. Calculate the difference.

Problem is, 2/3 of the samples gain weight instead of loosing?
Is it possible to grow oxide layer, would it be very heavy?

Just in case there might be some fluid left in the bores, I baked samples for 3 days, and did not see any change in weight from the initial bake.
Cleaning and measurements done in a Cleanroom, little dust; being careful not lose or misplace even one needle during transfers.

Typical Weights:
Single needle weight: 8.9 mg
Alum Weighing Dish: 1059.39 mg
Dish and un-clean Needles: 4448.79 mg
Same Dish, and cleaned needles: 4456.79 mg
Alum Weighing dish: 1059.35 mg (Weight after tests to verify no measurement drift)

Mark Curtis
- Northridge, California, USA


I would check the quality of my acetone and cleanliness of soaking beakers. Perhaps try using straight acetone - pesticide grade.

Terry Tomt
- Auburn, Washington


Interesting question. Almost 50 years ago, the elderly lady that ran the organic storeroom final rinsed with methyl or ethyl alcohol rather than acetone because she said that acetone left a trace film on the glassware. As I remember, it seemed to be somewhat true.
Triple rinsing the cleaning container and the rinse container befor use seems needed.
For the sonnication, I would stand the needles on end (big end down) so the gas bubbles formed would have a tendency to percolate the contaminants out. Laying on their side would have less of a flushing mode.
Would like to hear what you finally find as a solution.

James Watts
- Navarre, Florida

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