[tkdk83]

Hello everyone,

Long time reader and first time poster. I have learned some very interesting things reading through these forums and kind of came up with a question of my own.

Can Titration be used to analyze mercury in drinking water? What indicators or dilution/conversion would be used?

I am trying to come up with a new method.

Thank you so much in advance everyone!

[Stepan]

Concentration of mercury in drinking water it regulated. You need to achieve very low sensitivity of approximately 1 ppb or less (<1 ug/L) this is hard to achieve.  Mercury in water can be present as Elemental, Salt or in form of Organometallic compound. Simple titration will not be able to cover all 3 forms.

You method can probably be used for different applications (technical or QC control), where only one form of Hg is present, and concentrations are in ppm of % range

[tkdk83]

thank you for the reply Stepan.

I am actually trying to analyze methyl mercury at this point so that is my primary focus.

Any ideas?

[rackye]

there is an instrumental method to analyze mercury called cold vapor generation, tittration is not possible because amounts of mercury in water is too small

[Stepan]

thank you for the reply Stepan.

I am actually trying to analyze methyl mercury at this point so that is my primary focus.

Any ideas?

You can use titration or any other method - it does not matter. At ppb level - the biggest issue how to detect residual mercury. You cannot use colorimetric indicators - they are not sensitive enough. Your best bet is to use instrumental method: Cold Vapour AA, ICP MS, electrochemical, mercury sensors to detect the end point.

Now we have different problem: If you use instrumentation to detect the end point on titration curve, why do you need titration? You can use the same instrument to detect the mercury itself.

Titration is labour intensive method. Most laboratories are trying to avoid it where it is possible. In case of mercury (and most metals) AA and ICP are absolute leaders. They are fast, inexpensive, and approximately 1,000-100,000 times more sensitive than the traditional methods. Pure chemical methods are irreplaceable in macro- analysis (1-100% range), where instrumental methods are too sensitive.     

[tkdk83]

Hey Stefan thank you for your great responses! much appreciated!

I thinking that I am going to analyze Lead then if Hg has such low concentration where titration is difficult to use.

How would you do titration method in Pb analysis? Which indicators etc?

Thank you

[Borek]

Similar problem, in water amount of lead won't be high and titration methods are much better for larger amounts, not for traces.

[rackye]

i was thinking what about if you contaminate your sample with a known amount of lead, mercury or whatever you want to determine? then you titrate.it should exist a relation between the end potin of titration, the unknown amount of the analyte and the amount you added... i really don't know if that's true

[tkdk83]

Thank you for the responses once again.

well what i am trying to do is basically find out is what would be the best method to analyze Lead water whether it is drinking or water found in the environment.

I am really interesting in developing a new method rather than rahashing ones that already exist.  It doesn't have to be 100% precise just somewhat logical.

[Borek]

Titration doesn't work for too diluted substances, try to calculate titration curve for 10^-7M acid titrated with whatever base concentration you want. It simply doesn't make sense. Heavy metals in drinking water are usually in trace amounts, so standard methods won't work. Spectroscopy or some electrochemical method is a way to go.

[Stepan]

Thank you for the responses once again.

well what i am trying to do is basically find out is what would be the best method to analyze Lead water whether it is drinking or water found in the environment.

I am really interesting in developing a new method rather than rahashing ones that already exist.  It doesn't have to be 100% precise just somewhat logical.

Dear tkdk83,

There are hundreds of reagents suitable for lead titration. Most of them where developed in 1910's - 1930's. Selection of the right heavily depends on particular application.  You can use Sulfates, Chromates, Iodides, Sulfides and countless number of organic indicators. Some, most common, you can find in Analytical Chemistry handbooks. Generally speaking, selection of the reagent is part of development process. Nobody can tell you what to use without scientific review of what you are trying to analyse. And there is no such thing as "universal" reagent.

The second problem you will meet is selectivity. It is almost impossible to test lead with wet methods (classical methods) in presence of other heavy metals. You need to develop a method specific for your tested material: whatever is good for lead paint analysis, will not work for lead ore, or lead in blood.

The third problem: like I mentioned, chemistry lost interest in development of new titration methods and instruments, about 50-60 years ago. Titrators of all kind of designs, including automated, manual, computerized and other are available since 1930 (mechanical since 1950's). I am afraid, your instrument may not find it customer.

In few words, I would discourage you from investing your talents into invention of titration methods. This is in the past.

If you have interest in chemistry and are handy person, there is enough interest in truly valuable instruments and methods. I would order custom-made instruments from you myself (as long as they can deliver a result). Just let me know that this is something you want to try.

Good Luck