Automatic titrator

cyrilp

cyrilp

Premium Member
I'm planning to build a prototype of a fully automated titration chem analyzer for my tank. By fully automated I mean that it will take a sample, conduct all tests and then flush itself completely on its own. Yes it's not an easy DIY project but I really determined to do it :)

Initially I'm shooting for Alk measurement but later on it should be possible to add several other tests and I'm looking for your help to determine which titration tests will be important and feasible to implement. Mg? Ca? Some others? Each reagent will come at the price of adding a dedicated analytical grade solenoid valve and they cost alot. So each test should be important enough to justify the cost. For example, adding Ca test will cost ~$250 (off the shelf parts) if I need to keep titrant and indicator solutions in separate conteiners.

And just to clarify, I'm thinking to use colorimetric titration procedures with color sensor to avoid the hassle with pH probes in the chamber. This will allow me to reduce the sample volume down to 1-2ml I hope. And with 1ml sample you can really let it run a test every day or even twice a day without worrying about changing your salinity dramatically.

Thanks,
Kyryl
 
Alkalinity would be my first priority, too. Given that level of cost, I'd personally choose to measure only that, most likely. I only test calcium every few months, and don't see much point in measuring in more frequently for my systems. Same for magnesium.
 
Yes, MT device is looking good and all but it doesn't do what I want and the price is well beyond 10K if equipped properly. I want the machine to be completely automated and maintenance-free for many months or even a year. Also, any automatic titration systems that I see around uses pH electrodes to control titration process. While it's more flexible and precise, it requires electrode to be calibrated from time to time and it doesn't work with micro samples. You need ~20-50-100ml of sample to be able to stir it properly and have the pH electrode submerged in the solution. As the result, you have to spend much more titrant and care about your tank salinity variations as you take 100ml out of the system every day or so.

I'm shooting for 1-2ml sample volumes, autosampling and mainenance free operations in continuous mode.

The question for you guys: Would it be possible to mix bromcresol green+methyl red indicator with the titrant (I'm thinking HCl) and store it for a year in one bottle? Why cheaper test kits do that and more respectable brands dont?

Thanks,
Kyryl
 
No, you should not be mixing pH indicators. I don't know of anyone that does. The best pH indicator for seawater is Metacresol-Purple. There are other issues with many indicators. They often need a correction error for seawater, as the chloride ion skews the value. For example, Cresol Red has a + 0.5 offest, which means that in seawater you must subtract .5 from the reading. pH 8.3 - 0.5 = 7.8 seawater pH.

I like your project :D
 
Boomer, I mean mixing indicator with titrant (HCl) just to reduce the total number of liquids I'm going to handle.

Cheap test kits provide premixed bromcresol with titrant in one dropper bottle and you just count drops to come up with alk. Obviously the color intensity will change while titrating but I can handle that.
 
Ok cyrip but when I say this to mix bromcresol green+methyl red indicator I read it as you want to mix indicators for testing pH not Alk :lol: On that note, I think you may be fine. Habib may be a good guy to ask. I'll ask him to come here for a look :D
 
I thought they mix bromcresol with methyl red for sharper color responce in Alk titration. At least that's what I got from lab supply company where I bought indicator. The result is very similar to Habib's popular product :)
 
OK. It took me a week to build the device for alkalinity titration and then another week to rebuild it to achieve much better repeatability of measurements at the cost of some added complexity.

The machine works pretty stable and beats Habib's test kit by the factor of 10 in precision (0.01meq/L) and repeatability (1%). The sample volume is only 0.5mL, so it's possible to test alkalinity every couple hours not worrying about the salinity in the system. Also, it's fully automatic and can draw samples from two different points in the system (I'm going to measure tank alk and calcium reactor effluent alk). It uses DI water supply for rinse and dumps the waste directly into the sewer drain.

I want you guys to take a look and tell me what you think. Is it feasible to push the plans to the crowd in DIY forum? It's definitely not for everyone as you have to mess with stepper motors, microcontrollers and tiny electronic devices.

Will post pictures shortly...
 
Way to go cyrilp :thumbsup:

What was the total cost of the unit ?

I see no reason not to post it ;)
 
Here's the device. It's not a cranberry juice in 1L bottle but a mix of HCl with Bromocresol Green/Methyl Red :)
LCD screen, two FMI metering piston pumps, four 3-way miniature solenoidvalves, reaction vessel made of a 5cc syringe, two membrane air pumps (one for air, the other for drainage)...
IMG_6595.jpg


This is electronics and motors: two OEM FMI pumps, Cubloc Basic stamp microcontroller, two stepper motor drivers (IM483) and +5/+12VDC power supply...
Electronics.jpg


A closer view...
Electronics2.jpg


Reaction chamber in the middle of titration process. Note the air bubbles for mixing:
Titration_start.jpg


Titration endpoint. Color sensor on the left (TCS230) and white LED on the right side of the chamber.
Endpoint.jpg
 
Boomer, the total cost will depend on where are you going to source the parts from. If it's eBay for pumps and stepper drivers, surplus sites for valves and pumps then one can build it for under $300. If I would buy parts retail then it goes all the way up to $2,000 and if you want it to be real fancy, you can spend $3-4K on it by going with HPLC parts - microbore tubing, precision valves and gear pumps etc :)
 
OK. It took me a week to build the device for alkalinity titration and then another week to rebuild it to achieve much better repeatability of measurements at the cost of some added complexity.

The machine works pretty stable and beats Habib's test kit by the factor of 10 in precision (0.01meq/L) and repeatability (1%). The sample volume is only 0.5mL, so it's possible to test alkalinity every couple hours not worrying about the salinity in the system. Also, it's fully automatic and can draw samples from two different points in the system (I'm going to measure tank alk and calcium reactor effluent alk). It uses DI water supply for rinse and dumps the waste directly into the sewer drain.

I want you guys to take a look and tell me what you think. Is it feasible to push the plans to the crowd in DIY forum? It's definitely not for everyone as you have to mess with stepper motors, microcontrollers and tiny electronic devices.

Will post pictures shortly...
 
Is it feasible to push the plans to the crowd in DIY forum?

I would cyrilp, this is a first :D

My IE7 is behaving lately...

Lets not get into that right now I'm about ready to throw this 2 wk old Dell out the window :lol: It is so bad they are sending me a new one. And No Vista, back to XP
 
Any updates on this titrator? Is it still working as planned or have you discovered any problems? Posted a parts list anywhere?
Allen
 
Well, the work is in progress. As I tried to learn more about mab automation, I discovered that I was messing with some 60-year old technology. Obviously automatic titration was around since 50's and there are better ways to do it other than deal with vessels, stirrers, pumps and silly solenoid valves.

Apparently a lot more advanced way to conduct analytical tests exists since late 70s - Flow Injection Analysis (FIA). And in 90s they came up with improved technique called Sequential Injection Analysis (SIA):
http://www.flowinjection.com/
http://www.globalfia.com/

The principle is very simple. Instead of mixing sample with reagents in a titration vessel, they put everything in a microbore teflon tubing and they propell the sandwich of a sample, reagent and, for example, indicator at a constant and repeatable speed to the detector. In our case we think about spectrophotometric detector which can measure absorbance at a given vawelength.

This approach reduces the complexity of the instrument, allows for much higher precision, detection levels and repeatability and finally, requires a lot smaller amounts of sample and reagents. We are talking microliters here. No wonder if the tubing has only 0.5mm Internal Diameter.

So, what I'm doing now is I'm trying to build a device (actually, trying to find spare time to build a device) that will be based on SIA principle and will measure Alk, Ca and Mg. There is a good paper available that describes the method:
http://www.jstage.jst.go.jp/article/analsci/20/8/1205/_pdf

All the necessary components for alkalinity measurements are already in place and the device is working to some extent but it's far from being perfect, let alone photogenic :)

This approach requires some more sophisticated components - syringe pumps, selector valves and costs more than you can imagine. But we have eBAy, right? :)

Stay tuned!
-Kyryl
 
You must log in or register to reply here.

Similar threads

R
How is my chemistry looking?
Replies
1
Views
196
Uncle99
Uncle99
Broken reefer
Alk and cal
Replies
10
Views
2K
Broken reefer
Broken reefer
M
Back to this wonderfull hobbie after 10 years
Replies
4
Views
277
griss
griss
H
Alkalinity/Calcium Balance
Replies
1
Views
2K
griss
griss
C
High Zinc in ICP Test & Switching to ATI Essentials – Need Advice
Replies
17
Views
3K
Reefing102
Reefing102
Back
Top