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Hi Silvio, I am guessing that the granitic glasses you were referring to may not have been hydrous or perhaps they had much lower H2O contents than your andesitic sample. Na counting losses correlate positively with Na abundance and with H2O content of the glass. I assume you are using EDS. You can virtually eliminate the problem if you: lower the beam voltage (10 kV?) move the nose piece of the detector closer to the sample to get more counts and shorten the time for analysis most critically, use a cooling stage to lower the sample temperature to that of liquid N2. I have tested an albite-composition glass with 9 wt% H2O in it under these conditions and easily got stoichiometrically perfect Ab analyses out of it. So, you may have to invest in the freezing stage if you want to continue using a finely focused beam. There really is very little choice about that. I don’t know who might make these things, but people do have them. Manchester and Stellenbosch both have (or had) such facilities, for example. Prof. John D. Clemens Dept of Earth Sciences University of Stellenbosch +27 (0)21 808 3159 On 30 Jan 2019, at 13:44, Silvio Ferrero <[log in to unmask]<mailto:[log in to unmask]>> wrote: Dear All, We are experiencing almost complete alkali loss during microprobe analyses of andesitic glasses with narrow beam (diameter around 1 micron), at 9 nA and 15 kV. The glass under investigation is hydrous (around 5 wt% H2O), and based on other data we were expecting 1-2 wt% Na2O. Our analyses show instead a remarkably constant amount of 0.05-0.1 wt% Na2O over 20 analyses. Analyses on granitic standards during exactly the same session show a very limited loss for Na (around 20% relative), and in both cases the Na is only measured for 6 seconds. Few analyses were conducted with diameter of 3-4 microns, and still the Na was in the same range of values. Larger beams cannot be used because we are analyzing small melt inclusions in garnet. I´m fully aware of the alkali loss problem in alkali-rich glasses, but I never experienced a almost complete (around 90% relative I would say) loss of Na in any previous case study. Anyone has experienced such a problem analyzing hydrous andesitic glasses with very narrow beams? Any insights, suggestion or comment is welcome! Silvio -- Silvio Ferrero tel. 0049(0)3319775705 Universität Potsdam Institut für Erd- und Umweltwissenschaften - Dept. of Earth and Environmental Sciences - Haus 27, Karl-Liebknecht-Straße 24-25 14476 Potsdam "In those early days people laughed at me. They quoted Saussure who had said that it was not a proper thing to examine mountains with microscopes, and ridiculed my action in every way. Most luckily I took no notice of them" (Henry Clifton Sorby) To many petrologists a volatile component is exactly like a Maxwell daemon; it does just what one may wish it to do. (The evolution of the igneous rocks, N.L. Bowen, 1928) ######################################################################## To unsubscribe from the GEO-METAMORPHISM list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=GEO-METAMORPHISM&A=1 [http://cdn.sun.ac.za/100/ProductionFooter.jpg]<http://www.sun.ac.za/english/about-us/strategic-documents> The integrity and confidentiality of this email are governed by these terms. Disclaimer<http://www.sun.ac.za/emaildisclaimer> Die integriteit en vertroulikheid van hierdie e-pos word deur die volgende bepalings bereël. Vrywaringsklousule<http://www.sun.ac.za/emaildisclaimer> ######################################################################## To unsubscribe from the GEO-METAMORPHISM list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=GEO-METAMORPHISM&A=1