? about calibration fluids

[Mike 1911A1]

I'm using a PH 7.0 and PH 10.0 calibration fluid to calibrate my pin point PH monitor. Can I store the calibration fluids in plastic test tubes and if so, do they have a shelf life? The test tubes would be capped.

Thanks,

Mike

[boxfishpooalot]

Good question, I would like to know also. Only things I could think of would be Co2 changing the ph, although they should be made with normal Co2 concentrations. And also if your dipping the probe in it, any left over tank water would contaminate the mixture changing its ph I think.

Otherwise I dont see it a problem, but we better wait for Randy.

[Randy Holmes-Farley]

Each time they are exposed to air, especially the pH 10, they will change, The pH 10 will drop. It is better to either use the one time use packets, or to use a large bottle that you take small amounts from for use. Also, any traces of tank water on the p[robe getting into the fluids will change the pH a lot.

These articles have more:

Measuring pH with a Meter
http://www.advancedaquarist.com/issues/feb2004/chem.htm

A Comparison of pH Calibration Buffers
http://reefkeeping.com/issues/2005-02/rhf/index.htm

[Mike 1911A1]

I thought that maybe by capping the test tube, this would preserve them. But every time I test, they are exposed to air. I do rinse with tap before testing and in between the 7.0 and 10.0. Probably the best thing is to continue using the single packs one time. Thanks,

Mike

[Randy Holmes-Farley]

Probably the best thing is to continue using the single packs one time.

:thumbsup:


Happy Reefing. :)

[boxfishpooalot]

When using the one time packets. Should you dry off the probe first then dip it in to take a ph reading? If the glass gets dry would that damage it?

Also, If I clean my ph probe with hydrocloric acid will I have to re-calibrate it again?

[Randy Holmes-Farley]

I'd give it a swirl in RO/DI water, and shake it dry.

Yes, recalibrate after an acid blast. :)

[AcroSteve]

I built this calibration station for my fluids. And I had this same question about the shelf life, though I used 35mm film canisters and the surface area may be a little greater than a test tube, but I store in the same container that I test with

http://i11.photobucket.com/albums/a159/sbowman01d/CalibrationStation.jpg

I definitely rinse and dry the probe before switching between the different solutions so there is no cross contamination or dilution.

I know you suggest using new packets every time, but what life should I expect?

Would it be accurate for a month, week, or just a few hours? I always start with the packets.

[Randy Holmes-Farley]

An open pH 10 packet will drop in pH in an hour, but if tightly closed to keep CO2 out, it will last a substantial period. The number of openings and closing, and air volume inside the container probably determines the life, but I'd usually use packets only once. If you next use a new packet, you cna check the old containers to see if they are good. I do that with big bottles of buffer. :)

[AcroSteve]

Thanks Randy. An hour is pretty fast.

I have been dioing some multiple calibrations over the course of a few days, and I figured I would be ok. Now I know better.

What about the 7.0 or the 4.0? Should it last a week?

[Randy Holmes-Farley]

Those last longer, as CO2 entry is not as big of a concern.
pH 4 may last as long as evaporation is not happening.