Newsgroup: it.discussioni.ingegneria
Titolo: gypsum supersatured concentration: problem

Hi to everyone..
I' m  a student in chemical engineering  in Italy.
I' ve a problem.
Does anybody know how can i mesaure concentration of a calcium dihydrate
supersatured solution (gypsum) ?
I tried with a spectrophotograph..but i haven' t had any results..
Someone suggested to me to use conductivemeter technical?
Thanks by now.
Armando.

 wrote in message
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...
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Thanks for your suggestion..
but i must measure the concentration of too many solutions..
I ' m studing the supersaturation vs time from  a given initial
supersaturation..
At any time i must measure supersaturation and how it changes in the time...

 wrote in message
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Titration with standard EDTA solution is easy, accurate, and cheap.
There are a number of indicator dyes which can be used for this.
Armando Santucci wrote in message ...
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wrote:
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early part of the 20th century.
Must have been alchemy, it's pre-WWW, and thus not able to be 
conveniently discovered by today's students using search engines, 
so the data obviously doesn't exist - it's a figment of old
chemists and librarians imaginations :-).
Note that Ion Chromatography ( eg Dionex systems ) is very fast, 
and can perform quantitative multi-ion analyses in a few minutes.
       Bruce Hamilton   

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to avoid such disasters?
You just dilute the sample, most Ion Chromatographs use
~0.1M aqueous sodium hydroxide/sodium acetate mobile phases,
sensitive conductive or pulsed electrochemical detectors, 
and ion exchange columns with suppressor systems ( which are
often self-regenerating ). Such systems can detect down to 
ppb concentrations but cope with % concentrations of other
species, so it's easy to dilute samples into the linear range.
           Bruce Hamilton  

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wrote:
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precise?
Obviously it depend on the circumstances and the setup, but our
Dionex has a sample injection valve and we used it to monitor
the changes in chloride, nitrate, phosphate and sulphate in a 
processing solution during process development.
 
The chloride was present at % levels, the others at ppm levels.
We made up standard mixtures representing the extremes, and
analysed samples diluted 10,000x and 10x with water, with about
a 9 min run time. We used 10ul injections - which means small 
scale experiments don't encounter major sample abstraction 
problems - experiments are samples by syringe or pipettor and
dispensed straight into the diluent. We could process 3 
samples/hr for all analytes, although it was more common to 
process 4-6 samples/hr for the ppm analytes.
IIRC, recoveries for spikes were between 90 - 105 % for the 
ppm samples. The repeatability was so good that no internal 
standards were used, with many samples only analysed once, 
but still accurately monitoring very small changes in the analytes.   
Note that Ion Chromatographic methods have displaced some
of the traditional wet chemical methods in standard methods 
( such as ASTM ), and the main stumbling block has not been
lack of precision, but the initial capital cost of the
Ion Chromatograph ( around $25,000 when we purchased our
DX300 system, admittedly with a wide range of columns for 
anion, cation, and carbohydrate analysis ). 
The ongoing chemical consumption costs are very low ( 50% 
NaOH low in carbonate ), and columns will last for years 
( ours is about 8 years old ), which is fortunate, as the 
column and guard can cost about $2000.
          Bruce Hamilton   

Obviously it depend on the circumstances and the setup, but our
sisi, anche per me dipende dalle circostanze, ma se smetteste di
crosspostare in inglese tutta 'sta roba da alchimisti praticoni? ;)
hola,
_kloro_

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 wrote in message
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If you've got the kit, use potentiometric titration with a calcium-selective
electrode (or amalgamated gold and a smidgeon of Hg(II):EDTA) - unless you
enjoy looking for iffy colour endpoints.