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Calibrating PH Meters !

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Calibrating PH Meters !

Post by Admin on Fri Oct 28, 2011 6:51 pm

Nancy mentioned the variation in `Rainwater` PH on KP the other day so I thought I`d run some tests to confirm !

Tetra liquid test kit reagents are fairly reliable in my experience when compared with digital meters /photometers etc ... SO ?

PH of rain here in the Welsh Tundra @ 13.2C was Arrow



The Mettler Toledo PH Meter did not concur Suspect and was almost one whole PH point higher Question

Calibration was called phor Rolling Eyes

Generally I run a 2 point calibration simultaneously on all the PH Meters using PH 4.01 plus 7.00 solutions but did not have time yesterday.

I Calibrated 3 times using the PH 4.01 solution just to be absolutely sure Very Happy



I then `RE-TESTED` the Rainwater which by this time had risen in Temp to 19C and acidified further down to PH 5 Shocked confirmed by both Tests ? this phenomenon continued down to PH 4.7 as the Temp increased due to gasses being trapped in the `Breathed On` standing non agitated Rainwater:?:








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Re: Calibrating PH Meters !

Post by DaveB on Fri Oct 28, 2011 7:23 pm

Mio When calibrating p.H. meters I use the Pinpoint calibration solutions, usually 7.0 and 10.0. Do your calibration solutions have differnt reading for different temps? When calibrating I usually calibrate to the nearest the temp of the pond is. At the moment I calibrated at 15 degs C. Which is 7.036 and 10.107. During the calinbration period I maintain the calibration solutions at the same temp as the pond. This seems to work for me and I have found that when the probe is new it reads the same as the test kit (API low range p.H test kit)However after a period the p.h meter usually reads lower than the test kit so based on this I change the probe on a yearly basis. By which time the probes have a discrepency of 0.3. I also usually change them prior to winter when I believe accuracy to be more important ( certainly more so when I was running RO). I understand that the Pinpoint meters are probably not the best But have found them better than most of what I have tried before.

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Re: Calibrating PH Meters !

Post by Admin on Fri Oct 28, 2011 8:27 pm

DaveB wrote:Mio When calibrating p.H. meters I use the Pinpoint calibration solutions, usually 7.0 and 10.0. Do your calibration solutions have differnt reading for different temps? When calibrating I usually calibrate to the nearest the temp of the pond is. At the moment I calibrated at 15 degs C. Which is 7.036 and 10.107. During the calinbration period I maintain the calibration solutions at the same temp as the pond. This seems to work for me and I have found that when the probe is new it reads the same as the test kit (API low range p.H test kit)However after a period the p.h meter usually reads lower than the test kit so based on this I change the probe on a yearly basis. By which time the probes have a discrepency of 0.3. I also usually change them prior to winter when I believe accuracy to be more important ( certainly more so when I was running RO). I understand that the Pinpoint meters are probably not the best But have found them better than most of what I have tried before.

3 point calibration is the most efficient Dave in my experience with 7 being the `reference` point solution.

http://liainternational.co.uk/aboutphmeasurement.aspx

I didn`t have time to properly calibrate it yesterday so just grabbed what I had in a draw quickly which was PH 4.01and tested it to gauge how far off it was @ .59 PH too high.

The two calibration options on my `Hand Held` Meters are PH 4.01 and 7...

I don`t yet have a Pinpoint PH Meter but do have their ORP and Hardness meters.... Smile

The Calibration solution in the pic is a Laboratory grade sachet but normally I use either Hanna or Pinpoint which as you know are sold in packs of 3 for calibrating correctly.... here Very Happy

http://www.ebay.co.uk/itm/pH-4-7-10-Calibration-3-x-Fluid-Solution-Sachets-/280732639739?pt=UK_Pet_Supplies_Fish&hash=item415cf821fb#ht_3746wt_1185

I always calibrate Meters at original solution Temp/Values Dave ... but temp compensation is fairly accurate if not ...

Interestingly `Room Temp` is recommended for all testing of liquids ?

Corning instructions here >

https://docs.google.com/viewer?a=v&q=cache:CUye0JhI6zEJ:www.epa.gov/pesticides/methods/atmpmethods/EQ-01-04.pdf+laboratory+standards+calibrating+ph+meters&hl=en&gl=uk&pid=bl&srcid=ADGEESiyzlTUp4iiZIwh59XpPbglnb5178QS6gRsQlIThafOjLcAgK4WEAM2T9GgF68nKz-7tUDxW3Tasx0ucWnMVO9v8PLanM1886HoM_jjAB2WjKEEqkGmDL4pl2Eg5IAiXtiMg-cw&sig=AHIEtbTPieA7IG1vTjOtL64468IdYkOvlA





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Re: Calibrating PH Meters !

Post by Admin on Fri Oct 28, 2011 9:07 pm

Certipur by `Merck`was the Name of the Calibration Solution in the pic Dave

These are Laboratory Standard Solutions and good quality Very Happy

https://uk.vwr.com/app/catalog/Product?article_number=1.99001.0001

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Re: Calibrating PH Meters !

Post by Admin on Tue Nov 01, 2011 3:49 am

Whilst baling pooled rain water off the WLP cover Rolling Eyes I decided to collect some for sampling like-I-Do Laughing and Lo&Behold the same results and patterns repeated themselves Shocked

PH 6.09

Temp 15.4C

EC/TDS 17uS/cm and 8 ppm respectively.

Zero measurable GH/KH



ORPmv at it`s peak 265 ( must be polluted Shocked )



As the Temp increased the EC/TDS followed suit and the PH continued to decline.




Until I commenced aeration which halted the decline in it`s tracks Arrow



PH now up to 5.70 @ 19.3C EC/TDS 23/11.

I will continue aerating in a bid to determine C02 content at the highest PH achievable.



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Re: Calibrating PH Meters !

Post by DaveB on Tue Nov 01, 2011 6:34 am

Mio Good work. A TDS of 8ppm is almost RO water. perhaps you could explain why its not wanted apart from any sulphur content acid rain ????

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Re: Calibrating PH Meters !

Post by Admin on Tue Nov 01, 2011 6:43 am

PH is still climbing Dave ... report back later Cool I`m inundated atm Rolling Eyes


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Re: Calibrating PH Meters !

Post by Admin on Tue Nov 01, 2011 9:22 am

PH now @ 5.72 and climbing albeit at a snails pace !

EC/TDS = 28/14ppm

Temp 20.3C

CO2 is by far the more abundant of the gaseous species commonly found in rainwater ...

Nitric Acid (NO) Sulphur Dioxide (SO2) are present in lower values but are much stronger acids than CO2/Carbonic Acid etc.

http://www.gewater.com/handbook/ext_treatment/ch_4_aeration.jsp

http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/acidcom.html

All gases become less soluble as the Temp increases.

I didn`t collect sufficient rain to test D.O/Nitrate etc which might account for the increase in TDS ?






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Re: Calibrating PH Meters !

Post by Admin on Wed Nov 02, 2011 1:58 am

Final PH was 6.5 with an EC/TDS of 34/17ppm.

No Nitrate or measurable alkalinity which leads me to conclude the TDS content is D.O.C ie pollution.

Interesting that aeration alone is buffering the PH by de-gassing CO2/SO2/NO etc .. and almost certainly why my PH remained just above the neutral 7 when there was no measurable KH.


Last edited by Admin on Wed Nov 02, 2011 3:26 am; edited 1 time in total

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Re: Calibrating PH Meters !

Post by Admin on Wed Nov 02, 2011 2:31 am

Applying George Miller`s CO2 calculation equation we arrive at ?

CO2=PH (a) 5.47-PH (t) 6.05-0.3 = 0.88 CO2 in the rain water. Very Happy

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