Accuracy of pH meters
 

Had a lengthy discussion with one of the reps at Labcor
http://www.labcor.com/index.asp here in Canada (Cole-Parmer in the
U.S.).

He "educated" me to understand that a low priced unit like
http://www.labcor.com/catalog/produc...&sel=356240 2
has a much wider margin for error than the +/- 0.2 published. Namely
it's true accuracy is +/- 0.5 to 0.7. Hence a reading of 3.5 could
literally range from 2.8 to 4.2. He said this is true for any
pen-style meter regardless of make.

Even a more expensive unit like this one
http://www.labcor.com/catalog/produc...&sel=356130 1
with an published accuracy of +/- 0.01 pH has a true margin of error
of +/- 0.5. Just as useless as the first one.

I was "sold" (almost) this unit
http://www.labcor.com/catalog/produc...&sel=356142 0
which apparently has a true margin of error of +/- 0.05. It's price
is $360 Can. and replacement probes are $100 Can.

Have I been "sold" (almost)?

I think I remember reading some threads in this NG where winemakers
were experiencing frustration with adjusting acidity. I.E. the taste
outcomes from acidity adjustments where worse than the original
unadjusted wine. Speculation: could this be because inexpensive (and
grossly untrustworthy) meters are misleading us?

Or ...

Am I remember wrong to begin with?

And ...

Can a fairly inexpensive meter with a "published" accuracy of +/- 0.05
for example be trusted? It never occurred to me that a listed
accuracy range may be suffering from a huge dose of optimism and
literary licence.

Now I'm really confused!

Funny taste in my mouth, in Calgary,

Jim

Accuracy of pH meters
 

"glad heart" > wrote in message
om...
> Had a lengthy discussion with one of the reps at Labcor
> http://www.labcor.com/index.asp here in Canada (Cole-Parmer in the
> U.S.).
>
> He "educated" me to understand that a low priced unit like
>
http://www.labcor.com/catalog/produc...&sel=356240 2
> has a much wider margin for error than the +/- 0.2 published. Namely
> it's true accuracy is +/- 0.5 to 0.7. Hence a reading of 3.5 could
> literally range from 2.8 to 4.2. He said this is true for any
> pen-style meter regardless of make.
>
> Even a more expensive unit like this one
>
http://www.labcor.com/catalog/produc...&sel=356130 1
> with an published accuracy of +/- 0.01 pH has a true margin of error
> of +/- 0.5. Just as useless as the first one.
>
> I was "sold" (almost) this unit
>
http://www.labcor.com/catalog/produc...&sel=356142 0
> which apparently has a true margin of error of +/- 0.05. It's price
> is $360 Can. and replacement probes are $100 Can.
>
> Have I been "sold" (almost)?
>
> I think I remember reading some threads in this NG where winemakers
> were experiencing frustration with adjusting acidity. I.E. the taste
> outcomes from acidity adjustments where worse than the original
> unadjusted wine. Speculation: could this be because inexpensive (and
> grossly untrustworthy) meters are misleading us?
>
> Or ...
>
> Am I remember wrong to begin with?
>
> And ...
>
> Can a fairly inexpensive meter with a "published" accuracy of +/- 0.05
> for example be trusted? It never occurred to me that a listed
> accuracy range may be suffering from a huge dose of optimism and
> literary licence.
>
> Now I'm really confused!
>
> Funny taste in my mouth, in Calgary,
>
> Jim

Jim, many home winemakers believe the tart taste of juice or wine is
directly related to pH. However, research suggests this is not the case.
The tart taste of wine is more related to titratable acid (TA) and only
indirectly related to pH. Perhaps this is why tasting the juice or wine
seems more important than measuring either TA or pH.

Margalit states in his book "Concepts in Wine Chemistry," page 299 "
.............the major factor in acidity taste is the TA, and the pH is just
a minor correction."

Here are some other references:
Amerine, M.A. et al. - Acids and acid taste; The effect of pH and titratable
acid" - Am. J. Enol. Vit. 16 (1965) 29.
Nagel, C.W. & McElvain, J.R. - "An analysis of the influence of pH and
titratable acid in the scoring of wine" - Am. J. Enol. Vit. 28 (1977) 69.
Noble, A.C. et al. - Comparison of sourness of organic anions at equal pH
and equal titratable acids" - J. Sensory Studies 1 (1986) 1.

Accuracy of pH meters
 

Thanks Lum. I always appreciate your perspective. Am I hearing a
recommendation to temper the analytical method and lean more on
sensory perceptions? I'd like nothing more than to keep several
hundred dollars in my pocket an not buy a pH meter. Yet, I struggle
to get a meaningful fix on TA based on color change, especially for
reds. I'm left guessing. At my current level my SQ (Sensory
Quotient) is not well enough developed to serve me very well. So, I
need some aids to give me a sense of what I have. I think a pH meter
would help me but I need to be able to trust it's accuracy. Is there
a trustworthy meter out there for less than $360 Can.?

Cheers

Accuracy of pH meters
 

Hi Jim;
I picked up a pH pen from Hoskins Scientific in Vancouver that I am very
happy with.
It is a model 98128 by Hanna, waterproof, reads to two places of the decimal
and cost just over C$100.
Stated accuracy is +/- 0.01 with an EMC (?) deviation of +/- 0.02
I don't know if it stays within the stated accuracy of +/- 0.02 or not but
isn't that why we calibrate the instrument (?).
A pH meter is basically a micro-ammeter. It can be checked/calibrated
against a standard.
I calibrate my pen at pH 4 and 7. If it then reads the pH 4 buffer
accurately (+/- 0.02) I am satisfied that it will be accurate enough to read
pH 3.4 which I try to keep my red musts at or below. If it reads the pH 7
buffer accurately (+/- 0.02) I am satisfied that a test for TA at pH 8.2
will be close enough - certainly more accurate than trying to eye-ball a
colour change.
The Hanna calibration is automatic - just dip it into the buffer and it
adjusts itself. There is nothing that I have to physically adjust.
I used to have a C$149. Corning pH pen. It was terrible...
Did the Labcor rep work on commission ??? LOL !!!

Hope this helps.

Roger



"glad heart" > wrote in message
m...
> Thanks Lum. I always appreciate your perspective. Am I hearing a
> recommendation to temper the analytical method and lean more on
> sensory perceptions? I'd like nothing more than to keep several
> hundred dollars in my pocket an not buy a pH meter. Yet, I struggle
> to get a meaningful fix on TA based on color change, especially for
> reds. I'm left guessing. At my current level my SQ (Sensory
> Quotient) is not well enough developed to serve me very well. So, I
> need some aids to give me a sense of what I have. I think a pH meter
> would help me but I need to be able to trust it's accuracy. Is there
> a trustworthy meter out there for less than $360 Can.?
>
> Cheers

Accuracy of pH meters
 

"glad heart" > wrote in message
m...
> Thanks Lum. I always appreciate your perspective. Am I hearing a
> recommendation to temper the analytical method and lean more on
> sensory perceptions?

Jim, my approach to winemaking is measure, then taste, then measure, than
taste. Of course, the other method of taste, then measure, then taste, then
measure works pretty well too. Seriously, I think a reliable hydrometer and
pH meter are indispensable for serious winemaking.

I keep a saturated solution of distilled water and potassium bitartrate (buy
cream of tarter at grocery store) next to my pH meter. A saturated solution
has a pH of 3.56 at room temperature and I use it as a sanity check after I
calibrate the meter.

> I'd like nothing more than to keep several
> hundred dollars in my pocket an not buy a pH meter. Yet, I struggle
> to get a meaningful fix on TA based on color change, especially for
> reds. I'm left guessing. At my current level my SQ (Sensory
> Quotient) is not well enough developed to serve me very well. So, I
> need some aids to give me a sense of what I have. I think a pH meter
> would help me but I need to be able to trust it's accuracy. Is there
> a trustworthy meter out there for less than $360 Can.?

I really can't help you with selecting a pH meter. I am using an old (1973)
Orion meter I purchased at a surplus store many years ago. I replace the
probe about every two years.

Regards,
lum

Accuracy of pH meters
 

> Can a fairly inexpensive meter with a "published" accuracy of +/- 0.05
> for example be trusted? It never occurred to me that a listed
> accuracy range may be suffering from a huge dose of optimism and
> literary licence.

Rather than rely on the manufactures marketing collateral, why not
test the meter against a solution of known strength?

I have Hanna's digital PHEP 5 (80USD). It uses a two point
calibration. I first calibrate with their 4.01 / 7.01 solutions, cycle
power on the meter, then measure the *known strengths* of the
calibration solutions. It consistently reads the calibration
solutions +/- 0.05 after calibrating the meter.

I'm not sure if you can then infer that the meter is accurate outside
the 4-7 range (e.g. 3-4 for wine, 8.2 for titration), but I don't see
why you couldn't. I'm sure someone will jump in if there is a problem
with my logic ;-)
Regards,
Jody

Accuracy of pH meters
 

Accuracy of pH meters
 

Thanks for the comments everyone. The Labcor rep does NOT work for
commission and seemed very knowledgable on the subject which is why I
let myself get quite confused.

Surely a less expensive pH meter that's calibrated to control
solutions should measure pH within an acceptable margin of error (near
the listed margin of error). At least that's what reason and
[hopefully] sound judgement tell me tonight. I'd much rather spend
$80 US than 3 or 4 times that if I can count on accuracy.

Jim

Accuracy of pH meters
 

Lum,

I'd love to do a sanity check periodically too. How do you make up a
saturated solution of potassium bitartrate (clearly I'm a non-chemist).
Does it just mean adding cream of tarter until the solution will hold no
more and it just falls to the bottom? Will this solution be good for a pH
of 3.56 for some period of time?

Thanks,

Ed


> I keep a saturated solution of distilled water and potassium bitartrate
(buy
> cream of tarter at grocery store) next to my pH meter. A saturated
solution
> has a pH of 3.56 at room temperature and I use it as a sanity check after
I
> calibrate the meter.
>

Accuracy of pH meters
 

Sounds to me like he was doing a dirty and referring to the drift of an
uncelebrated pH meter.

If you do not calibrate it, it can easily be off that much. If you
calibrate it, it should be very close to the accuracy they advertise,
assuming the electrode is good. I think he was playing loose with his
comments.

Ray

"glad heart" > wrote in message
om...
> Thanks for the comments everyone. The Labcor rep does NOT work for
> commission and seemed very knowledgable on the subject which is why I
> let myself get quite confused.
>
> Surely a less expensive pH meter that's calibrated to control
> solutions should measure pH within an acceptable margin of error (near
> the listed margin of error). At least that's what reason and
> [hopefully] sound judgement tell me tonight. I'd much rather spend
> $80 US than 3 or 4 times that if I can count on accuracy.
>
> Jim

Accuracy of pH meters
 

"Ed Marks" > wrote in message
...
> Lum,
>
> I'd love to do a sanity check periodically too. How do you make up a
> saturated solution of potassium bitartrate (clearly I'm a non-chemist).
> Does it just mean adding cream of tarter until the solution will hold no
> more and it just falls to the bottom? Will this solution be good for a pH
> of 3.56 for some period of time?
>
> Thanks,
>
> Ed

Ed, making a saturated solution of potassium bitartrate is easy. Just add
enough powder until some is left on the bottom of the container.
You know the solution is saturated as long as you can see crystals. My
solutions seem to keep for several weeks. However, they do become moldy
after a while and the pH is no longer 3.56.
lum

Accuracy of pH meters
 

Thanks for your help Lum.

Ed

"Lum" > wrote in message
...
>
> "Ed Marks" > wrote in message
> ...
> > Lum,
> >
> > I'd love to do a sanity check periodically too. How do you make up a
> > saturated solution of potassium bitartrate (clearly I'm a non-chemist).
> > Does it just mean adding cream of tarter until the solution will hold no
> > more and it just falls to the bottom? Will this solution be good for a
pH
> > of 3.56 for some period of time?
> >
> > Thanks,
> >
> > Ed
>
> Ed, making a saturated solution of potassium bitartrate is easy. Just add
> enough powder until some is left on the bottom of the container.
> You know the solution is saturated as long as you can see crystals. My
> solutions seem to keep for several weeks. However, they do become moldy
> after a while and the pH is no longer 3.56.
> lum
>
>
>

Accuracy of pH meters
 

I think Ray hit the nail on the head, my background is calibration and
the original premise seems odd. He may have also been talking about
non temperature compensated probes but I don't know. I'm not saying
he was making it up, I had a Checker and hated it, mine was gawd
awful. Some have had good success with them though.

I have the PHEP5 also and love it, but I do calibrate it each use.
That is standard practice even with an expensive meter.

I can check 5 points and the accuracy has never been worse than 0.05
from 3.00 to 10.00.

I posted a pH meter FAQ a while back, you can find it with a Google
search or I can repost.
Regards,
Joe
>
> If you do not calibrate it, it can easily be off that much. If you
> calibrate it, it should be very close to the accuracy they advertise,
> assuming the electrode is good. I think he was playing loose with his
> comments.
>

Accuracy of pH meters
 

what are the proportions of the measurements that you use to arrive at the
3.56?
I bought a used ph meter from ebay, a red hanna handheld for about 16.
Would like to calibrate its accuracy, but don't have any 7.0 solution
around...

Thanks.
Rick

"Lum" > wrote in message
...
> "glad heart" > wrote in message
> m...
> > Thanks Lum. I always appreciate your perspective. Am I hearing a
> > recommendation to temper the analytical method and lean more on
> > sensory perceptions?
>
> Jim, my approach to winemaking is measure, then taste, then measure, than
> taste. Of course, the other method of taste, then measure, then taste,
then
> measure works pretty well too. Seriously, I think a reliable hydrometer
and
> pH meter are indispensable for serious winemaking.
>
> I keep a saturated solution of distilled water and potassium bitartrate
(buy
> cream of tarter at grocery store) next to my pH meter. A saturated
solution
> has a pH of 3.56 at room temperature and I use it as a sanity check after
I
> calibrate the meter.
>
> > I'd like nothing more than to keep several
> > hundred dollars in my pocket an not buy a pH meter. Yet, I struggle
> > to get a meaningful fix on TA based on color change, especially for
> > reds. I'm left guessing. At my current level my SQ (Sensory
> > Quotient) is not well enough developed to serve me very well. So, I
> > need some aids to give me a sense of what I have. I think a pH meter
> > would help me but I need to be able to trust it's accuracy. Is there
> > a trustworthy meter out there for less than $360 Can.?
>
> I really can't help you with selecting a pH meter. I am using an old
(1973)
> Orion meter I purchased at a surplus store many years ago. I replace the
> probe about every two years.
>
> Regards,
> lum
>
>
>

Accuracy of pH meters
 

"Rick Vanderwal" > wrote in message
...
> what are the proportions of the measurements that you use to arrive at the
> 3.56?
> I bought a used ph meter from ebay, a red hanna handheld for about 16.
> Would like to calibrate its accuracy, but don't have any 7.0 solution
> around...
>
> Thanks.
> Rick

Rick,

Add potassium bitartrate crystals to distilled water until no more crystals
will dissolve. The solution is saturated if you can see crystals on the
bottom of the container after mixing well.

lum
Del Mar, CA

Accuracy of pH meters
 

Thanks fellas for the great comments.

I really appreciate the "pH meter FAQ" you posted Joe. That's great.
I was looking at the pHep 5 awhile back and thought it would be a good
fit for the money. Can you test a large number of samples after
careful calibration (as long as the meter is turned on), or do you
have to keep returning to the calibration procedure?

Thanks, and cheers,

Jim

Accuracy of pH meters
 

Jim,
Yes and no. I have one of the first ones and it has an annoying power
off feature I can't seem to disable. You get about 5 minutes of use
then it powers down.

I recalibrate each time I power it up since mine does not keep it's
settings. (I would recalibrate anyway, it's my nature...) I talked to
someone at tech support at Hanna about that and he said mine had bad
firmware. He told be it's not supposed to do that and I should return
it. At that point the meter was over a year old and decided I would
just live with it rather than return it. Mine is 2 or 3 years old and
still going. The one good thing about the power down setup is it
saves on batteries, these are original. I'm sure I use it hundreds of
time a year, I have around 15 or 20 lots going plus I do testing for
others since I have the equipment.

It's a good meter for the money even with the quirks. It has ATC, the
probe is stable and it also indicates sample temp on a small display.
It's a toss up as to whether or not its a throw away meter since you
can replace the probe too. I'm probably going to replace my meter
sooner or later, but it's already paid for itself in peace of mind. I
have had a few Pinot Noirs that had really high pH that I never would
have caught, they did not taste low in acid to me.

By the way, I would never say spending more on a meter is a bad idea;
if I had a commercial operation I would use this meter for spot checks
and an expensive one for measurements I documented and made business
decisions on. (Measure twice, cut once.. ) :o) I just think paying
over $100 for a meter used in a hobby is a bit steep, since the probe
will eventually need replaced and that will cost at least $100. This
meter is a pretty good bet.

Regards,
Joe


> I was looking at the pHep 5 awhile back and thought it would be a good
> fit for the money. Can you test a large number of samples after
> careful calibration (as long as the meter is turned on), or do you
> have to keep returning to the calibration procedure?
>
> Thanks, and cheers,
>
> Jim

Accuracy of pH meters
 

Thanks a million Joe for the fullness and helpfulness of your
response. The experienced winemakers on this forum, like yourself,
generous with help and mentorship, make this NG one of my favourite
daily links.

In a year or two (hopefully) I too will become a net contributer
rather than mostly a consumer of help and good information.

From the newbies to the more experienced winemakers he

THREE CHEERS!!

Jim