Test tube cleaning

[ZippyBoy]

Randy,

With all the testing of test kits, I have a few simply questions.

What is the best way to clean the test tubes that come with the kits?

How long are they useable? (ie can I buy chemical refills or do I need to buy new kits)

Could test give false results with old (read worn) plastic test tubes vs glassware?

I have a feeling you are going to say it depends on the test kit, so please refer comments to the Salifert kits.

Thanks,

Keith

[Randy Holmes-Farley]

A fewof general comments, and I hope Habib will address the Salifert kits specifically.

1. Don't mix test tubes from different test kits.

2. Multiple rinsing with RO/DI water (or tap water followed by 1-2 RO/DI rinses) is what I usually do. The things in most test kits are very water soluble and this should clean them OK for most purposes. Especially if it is the same tube used for the same test.

3. I'd use them until there was some obvious problem (like they were so visibly dirty that they didn't come clean). I don't think old glass or plastic is a problem, as long as it isn't too dirty.

4. Some kits/tests are more prone to issues than others. An alkalinity test, for example, should not be very susceptible to problems, whereas things that detect minute quantities of compounds with multiple chemical reactions (like iodine) may be more subject to contamination issues.

5. For some brands of kits you can buy refill chemicals (Hach and LaMotte come to mind) but for others, you may not be able to.

[Habib]

Keith,

I think Randy covered most important points.

I would keep all the parts for a certain kit in it's box. Interchanging syriges, scoops, test tubes etc could give false measurements but also ruin the reagent(s).

Cleaning of syringes is not recommended. I would just empty them.

Test tubes can be cleaned with tapwater say 3 times. Tapwater might be better than RO or DI water because it can remove some acids or bases better.

After cleaning with water shaking out most of the drops is ok. I would not use a tissue.

There are no refills for the Salifert available.
It is very difficult to let you know on the refills label that something might have changed after the refill was packed. E.g. changes in other reagents for that kit. But there are also other reasons for not having refills and none has to do with profits:)

[WaterKeeper]

Skip the usual sulfuric acid/dichromate soaking on those plastic test tubes.:D

[Randy Holmes-Farley]

Hey, one of my favorite reactions. In fact, my thesis was on the surface chemistry of polyethylene film that was initially etched with chromic acid:)

[Habib]

Randy,

In fact, my thesis was on the surface chemistry of polyethylene film that was initially etched with chromic acid

Out of curiosity and interest since I have worked for more than 10 years on polymers; the etching was of the amporphous regions I assume and did you do research on orientation, crystallization, etc vs the surface properties?

[Randy Holmes-Farley]

Yes, it probably etched the amorphous regions mostly. I mostly went on to study surface modifications, rather than crystallinity issues. I took the carboxylic acids and ketones/aldehydes that resulted fromt he chromic acid and converted them into tons of different organic functional groups to look at the effect of specific chemistry on wetting, adhesion, surface reconstruction when heating, etc.