Way to calibrate PH meter without solution

aisach

aisach

Active Member
the church man

the church man

Well-Known Member
wheely said:
I stuck my cheap yellow one in coke, and set it to 2.7 i think. works great!
Click to expand...
How do you know its working? Other than your plants aren't dying?

I'm jw, I actually bought more calibration solution today

Sent from my EVO using Rollitup mobile app
 
datboytrue

datboytrue

Active Member
I usually just get a bottle of 7.0 water and callibrate it to 7.1


Sent from my RM-915_nam_usa_228 using Tapatalk
 
the church man

the church man

Well-Known Member
datboytrue said:
I usually just get a bottle of 7.0 water and callibrate it to 7.1


Sent from my RM-915_nam_usa_228 using Tapatalk
Click to expand...
That may not be as accurate as you think. Thinks like temperature and gas concentrations will affect the pH of the water...

churchhaze said:
I know this thead is old, but just wow. "You can calibrate to distilled water"....... And all this time I thought we needed to use buffer solutions, but it turns out you can just use distilled water, something with 0 buffering capacity, and the ability to swing wildly just from the CO2 in the air! Speaking of experts..... A pH reading of distilled water is likely to not even be accurate, let alone 7.0pH

I think you're better off searching science blogs for making a buffer solution than here prodigalSun. The only guy who knew what he was talking about here ended up suggesting that nothing DIY would be precise enough. The question I'd ask him if i could go back to 2009 is... precise enough for what? lol I do have a milligram scale, and if you dilute something by half, you essentially make the calculation twice as precise.
Click to expand...
Lol the only buffered, pH predictable testing liquid that we all have fairly easy accessible is blood; which should have a pH of 7.4. But please don't try that at home
 
F

Fabulos

New Member
PH calibration solutions are buffers meaning they are buffered against changes in pH by other substances. Do not use RO, distilled, or DI water to calibrate. They have no buffering capacity meaning that CO2 in air will form carbonic acid which will add hydrogen ions. The pH will decrease and not be pH 7 (theoretical for pure water). Next problem a pH meter needs conductivity of at least 100 uS/cm or 50-65 ppm (depending on conversion factor) to work. Adding KCl will increase EC but does not add any buffering capacity so pH changes very easily.

pH of coke = 2 to 2.5 phosphoric acid
pH of OJ = 3.9 citric acid
pH of baking soda = 7.8 sodium bicarbonate (great buffer)
 
C

churchhaze

Well-Known Member
Phosphoric acid + potassium or sodium hydroxide
citric acid + potassium hydroxide
sodium bicarbonate + hydrochloric acid

A pH buffer is either:
strong acid + weak base
or:
weak acid + strong base

tl;dr: just go buy a buffer solution.

Fabulos said:
PH calibration solutions are buffers meaning they are buffered against changes in pH by other substances. Do not use RO, distilled, or DI water to calibrate. They have no buffering capacity meaning that CO2 in air will form carbonic acid which will add hydrogen ions. The pH will decrease and not be pH 7 (theoretical for pure water). Next problem a pH meter needs conductivity of at least 100 uS/cm or 50-65 ppm (depending on conversion factor) to work. Adding KCl will increase EC but does not add any buffering capacity so pH changes very easily.

pH of coke = 2 to 2.5 phosphoric acid
pH of OJ = 3.9 citric acid
pH of baking soda = 7.8 sodium bicarbonate (great buffer)
Click to expand...
 
F

Fabulos

New Member
I was just pointing out the pH of common household items is not intended to replace pH calibration solution produced by reputable manufacturers. The only way to know the true pH value is to have a known reference standard. I agree that buffer is cheap enough to buy as a prepared standard. If using pH buffer from a bottle, once it is opened it is good for about 6 months. Unopened depends on the manufacturer. Some have a shelf life of 5 years. Manufactures do make sachets of solution that are single use packets. Use one to calibrate and store meter upright in sachet until next use. Rinse with purified water before storing.

Unless you know about offset and slope, you most likely are not getting an accurate reading any ways. A pH electrode should have an offset of +- 30 mV (pH 7 buffer value) and a slope better than 90% ( manufacturers state 85% but that is pretty low. I believe the EPA/FDA have slope at 92%) or 162 mV. A pH meter with mV option has to be used to read the voltage. For example a pH probe in pH 7 has a mv of -15 and in pH 4 193 mv the slope would be 193-15 = 178 mV (Theoretical is 59.16 mV/pH @ 25 oC). 59 x 3 = 178. The probe has 100% slope.

A tester will give you decent accuracy as long as it is taken care of. The pH electrode last about 1-2 years. A tester gets you in the ball bark. The only way to hit the bulls eye is to have a meter with a mV option or GLP to know if the offset and slope are acceptable. Within the specs above you will get an accuracy of +/- 0.1 pH. This is different that the meter accuracy stated by the manufacturers. The meter accuracy is how ell the meter reads mV and not the system with the pH electrode. The accuracy with the pH electrode will depend on cleaning, storage, reference, age, etc.

BTW The bicarbonate buffer system keeps us alive. If our blood pH varies by a few tenths we do not live. Respiratory acidosis will result in increased breathing to move CO2 out while alkalosis results in labored breathing causing CO2 to increase in the body. H2O + CO2 = H2CO3 = H+ + HCO3-. Increase CO2 reaction moves right. Decrease [CO2] the reaction moves left.
 
fandango

fandango

Well-Known Member
Illegal Smile said:
You can calibrate just fine to distilled water which by definition is 7.0. But it does not make a good storage solution which is why you need 7.01 solution for both.
Click to expand...
Guess it depends on who makes the distilled water....just opened a new bottle and it is coming out @ 7.7
 
F

Fabulos

New Member
Do not calibrate in distilled, deionized or reverse osmosis water! The pH measurement is an electrical measurement. Typically a pH electrode needs a minimum of 100 uS/cm of conductivity to work. RO water is between 20-30 uS/cm. High purity KCl would have to be added to measure and even then the measurement would have to be in a closed system such as with a flow cell to prevent CO2 from entering and forming carbonic acid.

Purified water also leaches ions from the hydrated layer of the pH indicating probe. We store in storage solution to maintain the hydrated layer. It takes 3-4 hours to form this layer. This is why pH in calibration buffer changes over time when calibrating a dry electrode versus a hydrated electrode.

There are pH electrodes with higher flow rates of reference electrolyte. Most probes will have a single ceramic junction which allows 15 uL/hour of flow. A triple ceramic junction will allow 45-60 uL/ hour. An open junction has around 200 uL/hour flow rate. Higher flow rates for lower EC solutions.
 
tracis420farmin

tracis420farmin

New Member
hI guys, noob farmer checkin in and thought Ide reply to this , it really helped me get out of a tight spot. I found this really kool site that lists Ph levels of common household drinks, I used one of the suggestions. calibrated my pen and wallah..presto!! I even think I ended up using a glass of vitaminD milk which falls in the range of 6.5. May not be ideal but it sure got me close enough ti get me out of a jam..hope this helps somebody..http://www.gourmetomatic.com/ph_guide_ph _of_common_beverages.html
 
FriendlyPharmacist

FriendlyPharmacist

Active Member
Fabulos said:
I was just pointing out the pH of common household items is not intended to replace pH calibration solution produced by reputable manufacturers. The only way to know the true pH value is to have a known reference standard. I agree that buffer is cheap enough to buy as a prepared standard. If using pH buffer from a bottle, once it is opened it is good for about 6 months. Unopened depends on the manufacturer. Some have a shelf life of 5 years. Manufactures do make sachets of solution that are single use packets. Use one to calibrate and store meter upright in sachet until next use. Rinse with purified water before storing.

Unless you know about offset and slope, you most likely are not getting an accurate reading any ways. A pH electrode should have an offset of +- 30 mV (pH 7 buffer value) and a slope better than 90% ( manufacturers state 85% but that is pretty low. I believe the EPA/FDA have slope at 92%) or 162 mV. A pH meter with mV option has to be used to read the voltage. For example a pH probe in pH 7 has a mv of -15 and in pH 4 193 mv the slope would be 193-15 = 178 mV (Theoretical is 59.16 mV/pH @ 25 oC). 59 x 3 = 178. The probe has 100% slope.

A tester will give you decent accuracy as long as it is taken care of. The pH electrode last about 1-2 years. A tester gets you in the ball bark. The only way to hit the bulls eye is to have a meter with a mV option or GLP to know if the offset and slope are acceptable. Within the specs above you will get an accuracy of +/- 0.1 pH. This is different that the meter accuracy stated by the manufacturers. The meter accuracy is how ell the meter reads mV and not the system with the pH electrode. The accuracy with the pH electrode will depend on cleaning, storage, reference, age, etc.

BTW The bicarbonate buffer system keeps us alive. If our blood pH varies by a few tenths we do not live. Respiratory acidosis will result in increased breathing to move CO2 out while alkalosis results in labored breathing causing CO2 to increase in the body. H2O + CO2 = H2CO3 = H+ + HCO3-. Increase CO2 reaction moves right. Decrease [CO2] the reaction moves left.
Click to expand...


Ugh.... Did someone mention anion gap?
 
PDU

PDU

Member
If I get the PH right in lets say a 5 gal bottle and use what I need and then cap off the rest, will the PH stay the same PH level in the stored?
 
P

Pyromallat

New Member
so i saw this on a page about regulating water ph using vinegar and the guy said that after adding 8 to 9 tablespoons of vinegar the ph stopped getting lower so i thought that a buffer solution could be made with this method
 

Attachments

You must log in or register to reply here.
Top