Expert: George Maxwell - 8/5/2007

Question
Dear Mr.Maxwell
I have a question about Canada Balsam.As you know, it has always been used as a cytological  cement in mounting biological samples in microscopic slides and coverglasses.

We are going  to buy 25 ml of this material for each of our educational kits .In Iran , we buy chemicals from retailers which sell CB and  pour cements from a main container into little bottles .They say these main containers are from Merck.They claim that they are using Merck materials but I want to be sure that some other material isn't offered in Merck bottles with Canada Balsam/Merck labels.Imo labels can be eaisly copied.Canada Balsam is rare and costly.I should  be sure that we pay for right chemical  and not for another  cytological cement.

I apprecite if you let me know whether there is any simple chemical method ,excluding analytical experiemtns and physical appreances which can help identifying of CB.

With thanks for your time ,I appreciate a prompt reply.

Best Regards
A.Kaveh

Answer
Thank you for your question. (this is a second copy).

Although we currently use a different brand of cement, I have used Canada Balsam in the past.

One of the problems that you may have in this case is that CB is very similar chemically to its inferior competitiors.
There are a couple of methods used to assess purity of CB, but I'm not sure how applicable they will be to you.
If neither of the below methods are possible, I would suggest that you request that your supplier forwards the Merck purity / data sheet that accompanies each batch of chemicals that Merck sends out: by comparing batch numbers on the purity sheet and the chemicals supplied to you, you have at least a basic check.

Methods used:

1) Refractive Index: if you have a refractometer or similar, CB should give a result in the range of
n = 1.54 - 1.55. Merck provide comprehensive data on the refractive index etc of each batch of their products.
This method is particularly useful as contaminated or imitation CB often gives a noticeably different RI result.

2) Spectroscopy: particularly IR and UV: again, the Merck product will conform closely to standards set out in the data sheet. This is the only way that I know of by which the absolute puity of CB can reliably be assessed.

Other methods (e.g. a simple test for the prescence of a functional group) are unlikely to be of value to you: most competitiors use a lower-quality turpentine that nonetheless contains many similar groups. Smell, appearance and flash-point will likewise not vary greatly.

We have found refractometry to be the quickest and cheapest way of assessing the purity of mounting fluids. Analytical bench top methods are (as you stated) of little use because of the complexity that would be required to achieve useful results.

I hope this is of use to you, but please don't hesitate to contact me if I can be of further assistance.
Many thanks.