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Measuring pH - standard tools/methods?

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merkin

merkin

Rising Star
Yeah, not so advanced at all! Didn't really know where to post this and have been searching for ages now without a win...so:

What do you recommend as a (non-expensive) way to measure pH in all these teks? I have one of those yellow/red ATC plastic 'pen' units (0.01) and it is extremely temperamental and sometimes takes forever to settle and often doesn't seem to read accurately. I have tried calibration but it often seems to defy settling. This is my second one (just couldn't calibrate the last one and it never agreed with the pH strips) and I just don't trust the thing but pH strips just don't get accurate enough to distinguish a reading of 8.75.

Also, do you dip it in and leave it in while you add base or acid? or do you remove and clean and then add and then dip the reader in after every change? I have been trying to separate some rue harmalas per phlux's telepathine method but finding it impossible to be so subtle as to hit the desired pH.

As someone with zero chemistry background after high school (oh so very long ago), I am pretty ignorant of basic methods and common tools. Googling and eBay just seem to bring up these same devices. Any pointers would be appreciated. Thanks
 
The context matters a lot, as does the definition of 'non-expensive'.
A quick and dirty way I use all the time is laughably cheap. I got 160 1-14 pH papers for 0.65 euros on a popular auction site, removed the staple from the stacks, and cut each strip into like 20 miniature strips. Thats 3600 pH papers for the price of three gum balls, I use tweezers to handle them and if I'm careful I can get two readings from each one. But these ultra-cheap papers only read to 1 pH increment and they have a buffer capacity, meaning they will read very dilute acids or bases as pH 6 no matter the actual pH. But its the easiest way to go when salting out mescaline or DMT with a separatory funnel.
For more accurate and sensitive papers pHydrion is a famous brand.
I've heard of people using pen type pH meters successfully for titrations and harmine/harmaline separation but they are crude, cumbersome, and generally only use one-point calibration.
When I unpacked my home lab and needed to replace my broken old lab pH meter I resisted the urge to get a cheap pen type and got a good 40 euro probe-on-a-rope unit with two point calibration. For me this bordered on expensive but being just short of a lab meter made it worthwhile.

In your specific example of working with harmalas you might want to switch from phlux to the VDS protocol, as the VDS protocol relies on swings in the pH curve rather than exact pH values. You say your pen doesnt settle on a value, if that just means it varies back and forth by 0.2 you'll still be able to clearly see the pH depression that signals harmine/harmaline separation in the VDS tek.
pH probes can be left in while adding acid or base but they shouldnt be left in for hours, shouldnt be in strong acid or base, and should always be cleaned with distilled water and stored in the specified KCl solution [usually 3M] after your work is done.
 
There are also "narrow range" pH papers. I bought some from China and as Elrik said, you can cut them to smaller pieces. I usually take a pair of tweezers and dip a tiny square of the strip into the solution in question.

pH papers are indispensible especially when the solution is very hot or thick or highly acidic/basic - the conditions that would damage the pH probe.

For backsalting (to indicate neutralization point), I use solution of nitrazine (a.k.a. Nitrazine Yellow). It is not super cheap, but a gram of it will last you for many years.

I also use pH pen for the pH separation of harmalas. I also like to use it for continuous measurements - its major advantage is that you can observe the pH changes over time.
 
As a side thought, its a good idea to find a way to hold the probe or pen if leaving in while stirring in acid/base. Particularly if using a magnetic stir plate!
A surprisingly simple method is to just tie two clothes pins together with a twist tie.
For something more adjustable a different method can be devised. I like to use a dial indicator mount from my machine shop. I've seen skinny clip-on snake lights that could serve a similar function.
 

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Xcellent! Thanks for the suggestions guys. Checking out aliexpress to do some shopping!

I notice there's a lot of different papers in the 4-9 range with varying degrees of scope but almost nothing in the higher range except the 1-14 full spectrum options. Is there a reason? I presume I am looking for accuracy in the 6-9 range for harmaine/harmaline? Will have to read up on the VDS method. I've been kinda enjoying extracting harmalas and happy to drag the process out. Maybe this will all improve my spice extractions which are not optimal due to trying many different solvents in search of the best one. No 'naphtha' round here.

Aliexpress sell the same Smart Sensor probe model in your pic Elrik so I'm gonna go for that. Love the ghetto clamps! Very inspiring...
 
merkin said:
I notice there's a lot of different papers in the 4-9 range with varying degrees of scope but almost nothing in the higher range except the 1-14 full spectrum options. Is there a reason? I presume I am looking for accuracy in the 6-9 range for harmaine/harmaline? Will have to read up on the VDS method.
Click to expand...

The pH separation works for me under constant stirring with pH pen inside on continous measurement. Note the pH jumps up as you add base but then falls down as the base reacts. It is hard to observe pH changes with just pH papers but may be doable.

I use ammonia solution as the base since there are have been some issues noted with carbonates.
 
Hi blue.magic - What issues with carbonates are you referring to? I am having lots of issues with caapi extraction following gibran's tek. I am getting too much yield and I think its due to NaOH and Na2CO3 contamination.I wash like crazy but pH stays almost unchanged it doesn't seem to help.

Would ammonia be better (I can get lab version) and how do you use it? Sorry, I don't mean to hijack my own post here! Maybe you wouldnt mind responding here: Too Much Yield from Caapi
 
I'm drooling over the technical specifications on benzymes new meter and if my nearly new one does break I would be tempted...
But it should be pointed out that a unit like that is far beyond what the 90% majority of people here would actually need.
 
I hear ya. Not many people, including myself, are going to use the ISE functionality. The A211 is the basic pH meter, with similar specs.

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I had a meter once with button cell batteries that had an unstable readout and I think that was because of the button cells. Their voltage is less stable than for example a 9 volt block.
 
Jees I think you just described my meter! Its just too unstable, even on my pool water it takes about 10+ minutes to reach a reading which then doesnt match what the usual phenol red type testing kit says! Anyway, I have ordered one of the smart sensor devices from aliexpress (amazon for the rest of us) along with some basic paper strips. Unfortunately shipping will take a while but I look forward to something a bit more reliable. Harmalas will just have to stay harmalas in the meantime :)
 
merkin said:
Hi blue.magic - What issues with carbonates are you referring to?
Click to expand...

This has been discussed in the thread on verifying VDS protocols (the Van Der Sypt article on low tech harmala extraction, separation and THH synthesis).

Since the thread is uber massive, here is a short answer from Jees in my thread about harmine-DHH separation.

Basically carbonates give off CO2 that skews the measurement and are "messy" (whatever that means :) ) - it seems harder to get realiable results with carbonates. Maybe also due to poor solubility?
 
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