Can pH buffer solution used for calibrating pH Probes be stored and reused without negatively affecting accuracy?

[Indoor Reef]

After mixing pH buffer solution from the little sachets (6.86, 9.81) what would be the impact on accuracy if these buffer solutions were stored in sealed glass jars and re-used used for calibration at a later date?

 

[fishguy242]

hi, i do not, but curious,following, @vetteguy53081 @Randy Holmes-Farley ?

 

[Randy Holmes-Farley Verified Community Expert]

The pH 9.81 will drift down as it absorbs CO2. I've used buffer solutions for years, just keeping them in the plastic containers they came in, but i did remeasure the pH of them occasionally. The pH 10 solutions drift into the 9.7-9.9 range.

If your meter allows you to input the pH of the buffers, that works fine. if it assumes a certain value, that's not fine.

 

[fishguy242]

The pH 9.81 will drift down as it absorbs CO2. I've used buffer solutions for years, just keeping them in the plastic containers they came in, but i did remeasure the pH of them occasionally. The pH 10 solutions drift into the 9.7-9.9 range.

If your meter allows you to input the pH of the buffers, that works fine. if it assumes a certain value, that's not fine.

sorry, i think i misunderstood question.

i never have, but thought question was ,use solution, then store and reuse.
figured it would dilute solution.
correct?? Thanks

 

[Randy Holmes-Farley Verified Community Expert]

sorry, i think i misunderstood question.

i never have, but thought question was ,use solution, then store and reuse.
figured it would dilute solution.
correct?? Thanks

If the probe has just a bit of RO/DI left on it from rinsing before you put it in (which is appropriate), then the dilution is minor and in general, the pH of buffers is resistant to the impact of dilution.

The pH of a buffer solution is determined by the ratio of concentration of the two ions creating the buffer (HA and A-, as an example). The governing equation is shown below.

pH= pKa+ log( [A−]/ [HA] )


where "pKa" is the pKa of the acid HA.

Thus, since pH is determined by the ratio of HA and A-, diluting them both equally has no substantial impact on pH.

 

[Malcontent]

I used to try and reuse pH buffer or use expired buffer but never had any confidence in my measurements.

Now I just use these. They create 20 mL of buffer solution each, are cheaper than any other lab grade pH buffer, and have the longest shelf life (4+ years):

LOV-515620BT

Buffer Tablets pH 4 (pack of 100)Lovibond's color-coded pH buffer tablets are ideal for the fresh preparation of calibration solutions without producing large quantities of packaging material. Simply dissolve one pH buffer tablet in 20 ml of deionized water. After 90 seconds of dissolution time...

www.novatech-usa.com

LOV-515610BT

Buffer Tablets pH 7 (pack of 100)Lovibond's color-coded pH buffer tablets are ideal for the fresh preparation of calibration solutions without producing large quantities of packaging material. Simply dissolve one pH buffer tablet in 20 ml of deionized water. After 90 seconds of dissolution time...

www.novatech-usa.com

LOV-515600BT

Buffer Tablets pH 10 (pack of 100)Lovibond's color-coded pH buffer tablets are ideal for the fresh preparation of calibration solutions without producing large quantities of packaging material. Simply dissolve one pH buffer tablet in 20 ml of deionized water. After 90 seconds of dissolution...

www.novatech-usa.com

LOV-515621BT

Buffer Tablets pH 4 (pack of 250)Lovibond's color-coded pH buffer tablets are ideal for the fresh preparation of calibration solutions without producing large quantities of packaging material. Simply dissolve one pH buffer tablet in 20 ml of deionized water. After 90 seconds of dissolution time...

www.novatech-usa.com

LOV-515611BT

Buffer Tablets pH 7 (pack of 250)Lovibond's color-coded pH buffer tablets are ideal for the fresh preparation of calibration solutions without producing large quantities of packaging material. Simply dissolve one pH buffer tablet in 20 ml of deionized water. After 90 seconds of dissolution time...

www.novatech-usa.com

LOV-515601BT

Buffer Tablets pH 10 (pack of 250)Lovibond's color-coded pH buffer tablets are ideal for the fresh preparation of calibration solutions without producing large quantities of packaging material. Simply dissolve one pH buffer tablet in 20 ml of deionized water. After 90 seconds of dissolution...

www.novatech-usa.com

 

[vetteguy53081]

After mixing pH buffer solution from the little sachets (6.86, 9.81) what would be the impact on accuracy if these buffer solutions were stored in sealed glass jars and re-used used for calibration at a later date?

I do this now and BBC am able to successfully calibrate. I have now gone to the packet solutions

 

[Indoor Reef]

Thanks everyone! I don't have any plastic containers so I'll make up the buffers and store them in glass jam jars. When I come to the next calibration with fresh buffer sachets then I'll test the old solution and see how much its changed. This will maybe help me understand the resuability over time.