[Nhcoll-l] Antw: Re: Test for formalin

Fri May 29 02:16:06 EDT 2020

Hi all,
Dear Irene,

Thanks very much for the interesting information.

I heard about the use of digital density meters and I also know museums
and collections that work with such devices.
But I am still sceptical about this.
What about the organic components, which are dissolved out of the
preparations by the alcohol (fats, dyes, stomach contents of small
animals ...)
In this case it is no longer a pure water-alcohol solution and the
density datas are falsified.

Allthe best
Joachim

--  
Joachim Haendel

Center of Natural SciencesCollections
of the Martin-Luther-University
- Entomological Collection -

Domplatz 4
D-06099 Halle (Saale)
Germany

Phone:  +49 345 - 55 26 447
Fax:  +49 345 - 55 27 248
Email: joachim.haendel at zns.uni-halle.de

>>> Irene Finkelde <irenefinkelde at gmail.com> 29.05.20 3.09 Uhr >>>
Hi All

 The paper test suggested by Dries and the NIWA test with marker, which
bleeds in alcohol, are great because they are quick and simple – but
they do not give quantitative results of how much formalin/formaldehyde
is in the fluid preservative, nor the concentration of the alcohol
solution. For your purposes Mandy, this may not be necessary, but I
thought I would share some methods for quantitatively determining
formalin/formaldehyde concentration in case anyone else on the list-serv
is also looking for methods. 

 For testing alcohol concentration, a digital density meter is really
the most effective method. However, this is a very costly piece of
equipment and many organisations do not have budget to buy one. A
hydrometer can be used if you have sufficient fluid volume. I have
refined a method, initially published by Theresa Mayfield, that uses
salts (potassium carbonate and sodium chloride) to distinguish between
ethanol, isopropanol and aqueous solutions (formalin). It requires a
2-4ml sample of fluid and can give a good indication of alcohol
concentration. As highlighted by Rob, this is not a test for the
presence of formalin, but rather just that the solution is aqueous or an
alcohol with water combination. This method is awaiting peer review, but
if anyone has any queries please get in touch and I would be happy to
share my research.

 To determine the amount of formaldehyde/formalin in solution there are
several methods available. I have tested three commercially available
methods, and a titration method to determine formalin concentration
initially developed by Rob Waller and refined (very slightly) by myself.
In testing these different methods, comparisons and assessments about
the advantages and disadvantages of each method were made. 

 One of the first challenges is getting your head around the terminology
we use when describing formalin, and this seems to vary between
countries and institutions. What we often call “10% formalin” is
actually a dilution factor, from diluting a 1 part 100% formalin stock
solution with 9 parts water. This 100% formalin stock solution is 37% by
weight or 40% by volume formaldehyde gas in water. This means that “10%
formalin” is 3.7% (w/w) or 4% (w/v) formaldehyde gas in water, which is
40,000 mg/L formaldehyde.

The titration method, has the best resolution of the methods tested,
only needs to be conducted once without the need for multiple dilutions,
also gives results for titratable acidity, and has a small sample size
of 0.75ml. Due to the costs of equipment set up and materials for
analysis, this would be a good method for institutions who want to
quantify the amount of formalin/formaldehyde in solution in fluid
preservatives and were aiming to conduct many tests, which would reduce
the overall cost per test.The paper that details the titration method
and comparison to the commercially available methods, is also currently
awaiting peer review, to be published later this year in Collection
Forum.

Two types of commercially available formaldehyde test strips were tested
(MQuant and Quantdiscussed on the listserv previously, these test strips can be very
challenging to use and require significant dilution and calculations to
get accurate results. They measure in the range of 0mg/L to 100mg/L or
200mg/L. “10% formalin” (4% w/v formaldehyde gas in water) is 40,000mg/L
so to get results in the range that the test strips can read dilutions
up to 1:1000 may need to be made. This can be time consuming and costly
as often more that one test strip and dilution are required to get a
result within the test strips range. 

 A commercially available titration test kit, which uses the same
chemical reaction as the titration method above, was also tested (Hach
Formaldehyde Test Kit: Model FM-1). This can test formaldehyde
concentration in solution within the ranges of either 0.05 - 1% or 0.5%
- 10% formaldehyde in solution (here is where terminology is important –
what we often call “10% formalin” is 4% w/v formaldehyde gas in water). 
 The solid reagent supplied with this test kit is insoluble in ethanol,
which is an issue when testing for residual formalin in alcohol
solutions. When I tested ethanol solutions, I first dissolved the
contents of the reagent sachet in 10ml demineralised water and added
that to the sample before titration. Even though the sample was diluted
the drops of titrant were still counted as though each drop represented
0.05% formaldehyde. 
 The resolution of the results with this commercially available method
is not as great as the titration method above, and the sample size for
the tests is significantly larger (1ml or 10ml), however it is a simple
to use method and all the required materials are supplied. I would
recommend for people wanting to use this method to contact the supplier
when ordering and request for a lid for the test vial, to avoid spills
when mixing the solid reagent with the fluid preservative sample using
the manufacturer's published method. 

 Methods to test fluid preservatives need a lot more research, and this
will enable us to have a greater understanding of the fluid chemistry
and the impacts on specimens long-term preservation. 
>From a health and safety perspective it is important for us to quantify
how much formaldehyde is in solution in fluid preservatives, be it from
preservation in formalin or residual in alcohol preservatives from
initial fixation in formalin. 

 If anyone would like more information about any of these methods, they
will hopefully be published later this year, but in the meantime I would
be happy to discuss them with you – please get in touch!

 All the best, 
 Irene Finkelde 

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