Is it true that one of the first commercial uses of plasma ashing was to ablate fish to expose mercury contamination?
Sitting around the lunch table the other day, our chemist and founder, Stephen Kaplan, expanded on an early use of plasma for one of the first commercial applications: ashing fish to expose mercury (or other metals) to evaluate the impact of contamination from industry. While it seemed like a logical use of the technology, I couldn’t get my head around this as one of the first commercial applications….so did a bit of research and finally reached out to one of the experts in the field of vacuum technology: Donald Mattox. He confirmed that low pressure plasma ashing has been used for over 50 years for trace element analysis – an early use of replacing wet chemistry!
Don sent the following citations confirming the use:
1962: C. E. Gleit and W.D. Holland, “Use of electrically excited Oxygen for the low temperature decomposition of organic substrate” Anal Chem. Vol. 34 (11) pp 1454-1457
1977: M. Velodina, “Quantitative determination of Mercury in Organic materials by means of a low temperature, high frequency discharge plasma in oxygen” Analytical Letters 10(14) 1189-1194
And Don added one of his favorite Oxygen plasma cleaning stories (from his book “Foundations of Vacuum Coating Technology”)
When preparing to aluminize the Palomar mirror, John Strong notified the mirror polishers that he would be using a new cleaning technique using ‘a special fatty acid compound with precipitated chalk.’ When he arrived the ‘special fatty acid compound’ was Wild Root Cream Oil hair tonic (ad jingle: ‘You better get Wild Root Cream Oil, Charlie; It keeps your hair in trim; Because it’s non-alcoholic, Charlie; It’s made with soothing lanolin’). He stated, ‘In order to get glass clean you first have to get it properly dirty.’ The oil residue was ‘burned-off’ using an oxygen plasma in the vacuum deposition chamber. (From The Perfect Machine: The Building of the Palomar Telescope, Ronald Florence, pp 382-386, HarperCollins, 1994).
I’m assuming that the following US Patent from 1978 helps corroborate his story: 4088926: Plasma Cleaning Device (for cleaning organic contamination on optical surface)
I found this quite interesting and did some additional research that I would like to share with my readers:
Plasma, atmospherically, has been used professionally by museums and NASA to remove carbon contamination or char, selectively, as a restoration technique for fine art.
Before and after image of artwork cleaned by atomic oxygen.
Some later work of interest was published by Texas A&M: Used RF plasma to selective remove inorganic mater from paint and prevent damage to the substrate (rock). Organic components can then be analyzed and dated.
1992: Direct Radiocarbon Dating of rock Art. Radiocarbon, V 34, No. 3, 1992, P 867-872. J. Russ, M. Hyman and M. Rowe, TAMU.
I could go on and on and on… Plasma truly offers us a tremendous tool box for modification of myriad materials!