[NHCOLL-L:1275] RE: testing fluid solutions

[Robin McPhee]

Hi Amy,
I've not used the leuco-basic fuchsin impregnated papers, but I've used
Merck Formaldehyde (HCHO) test strips (10-100mg/l) and found formaldehyde in
most of the fish specimen spirit solutions (which were either 50%
isopropanol or 70% ethanol). So it is possible to get positive HCHO results
from alcohol solutions.  The HCHO I found is probably residual HCHO from the
initial fixing of the specimens.  

I've spoken with an industrial chemist who mentioned that the presence of
alcohol may affect the reliability of the HCHO results.  But I tested the
strips in a series 50% isopropanol solutions with known concs. of
formaldehyde and the results were reasonable (especially with the
difficulties of matching actual strip colours with the results colour
chart.)  Also, I got a zero HCHO result on a pure 50% isopropanol solution 

As HCHO solutions have a higher density the water, if the solution you wish
to test is relatively clean you may be able to use a density meter to
indicate if the solution is closer to a HCHO solution density or a spirit
solution density (but you will need to be wary of low alcohol solutions). 

In a test I did with a Paar density meter gave the following results
100% water & 0% HCHO solution = 0.999 mg/l  
95% water & 5% HCHO solution (=1.85% HCHO) = 1.004 mg/l
90% water & 10% HCHO solution (=3.7% HCHO) = 1.009 mg/l  

As alcohol is less dense than water any density reading you get should be
less than pure water.  so 70% ethanol solutions should be ca. 0.880 mg/l
and 50% isopropanol should be ca. 0.91 mg/l.  
However, if the solution is old then it may well have lost some of the
alcohol, and the density may well be closer to that of water.

These results are only from my own quick tests and trials, so I'd take them
with a grain of salt. 
Anybody else had any sort of similar results or comments??

Cheers
Robin    
  
> -----Original Message-----
> From:	Amy Estep [SMTP:aestep at ou.edu]
> Sent:	Tuesday, October 16, 2001 5:34 AM
> To:	nhcoll-l at lists.yale.edu
> Subject:	[NHCOLL-L:1273] testing fluid solutions
> 
> What method do my fellow fluid collections managers use to distinguish
> alcohol from formalin when the solution in a jar is unknown? Preferably,
> something less hazardous to my health than nasal analysis *grin*.
> 
> I have heard of leuco-basic fuchsin impregnated papers that turn pink
> only in formalin.  Can anyone comment on this paper or a better method?
> 
> Thanks,
> Amy
> 
> --
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Amy D. Estep
> Curatorial Specialist in Herpetology
> Sam Noble Oklahoma  Museum of Natural History
> University of Oklahoma
> 2401 Chautauqua Avenue
> Norman, OK  73072
> v:  405-325-1516
> f:  405-325-7771
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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