Hi Georges and Pier, My previous email was to mainly answer the question: "WHY do we need to add P2O5 to the 85 % orthophosphoric acid??" by millionh@yahoo,com . The words, "100%" H3PO4 or water-free I used, is kind of oral language. Of course, theoretically all the water can become phosphoric acid by the reaction of P2O5 + 3H2O = 2H3PO4 under the correct reactive conditions, but practically it's not the case as Pier pointed out. But whether the acid is completely water-free or not, it doesn't matter regarding the carbonate isotope analyses as long as the portion of the remaining water in the acid is relatively insignificant and you have the carbonate standards (I would say at least two), such as NBS19, run along with your carbonate samples in the same batch analysis by using the same batch of the acid because the systematic errors during the sample preparation processes can be subtracted out (or significantly eliminated) via the solid carbonate standard calibration. Wenbo -----Original Message----- From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Georges L. Paradis Sent: Monday, September 18, 2006 9:37 AM To: [log in to unmask] Subject: Re: [ISOGEOCHEM] preparing 100% phosphoric acid Dear Pier and Wembo, Thanks for the clear demystification of the "Phosphoric acid folklore". I refer to it as folklore because I found that if you ask 7 labs how they prepare their acid, you'll get 7 different answers. Some of those will inevitably describe the acid as anhydrous or water-free, which as Pier plainly pointed out, there is no such state of phosphoric acid. Since there seems to be much variation in acid prep technique (even though we'll all continue to cite Coplen, 1983, Thanks Ty!), we are probably all using slightly different reaction conditions. If that is true, then our isotopic fractionation factors must be inaccurate. If that is true, then isn't our (the isotope community) data comparable by using a good calibration traceable to NBS19? Much thanks, Georges ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Georges L. Paradis ICPMS Lab Manager Department of Earth Science, Marine Science Institute University of California Santa Barbara Santa Barbara, CA 93106 805-893-7182 [log in to unmask] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ----- Original Message ----- From: Pier de Groot <mailto:[log in to unmask]> To: [log in to unmask] Sent: Monday, September 18, 2006 1:32 AM Subject: Re: [ISOGEOCHEM] preparing 100% phosphoric acid Wembo and others, Just a note on the phosphoric acid discussion. What Wembo states, to have 100 percent-water free acid is not completely true. By extracting water (either by heating or by adding P2O5) the acid polymerizes and liberates water - and with polymerization viscosity increases. Even if getting more than 100 percent acid (some name the acid with 1.93 density 103 percent acid) by continued polymerization water is formed. By adding water in priciple the acid de-polymerize. Probably a reason why the concentrated acid is highly hygroscopic. In fact phosphoric acid has different 'forms', such as orthophosphoric acid (H3PO4), pyrophosphoric acid (H4P2O7), and polyphopsphoric acid (chain and ring shaped polymerized acid; highly concentrated acid may crystallize). One also can gently heat the acid while connected to a low-vacuum line. No back-hydration of the acid by air-humidity can occur then (if simply heated in open-air) and also eventual dissolved gases are better removed. But the original procedure (McCrea, 1950), as part of the calibration of the carbonate acid digestion method and of the isotopic fractionation(s) related to this method, was by adding P2O5, a spatula-tip of CrO3 (acid turns yellow and after heating into green) and about 3 ml of H2O2 is added after a 7 hours heating. The CrO3-H2O2 procedure was included because the phosphoric acid in older days probably contained some traces of organic matter (was less pure as it is nowadays). Using lower density acid in automates (for viscosity reasons) has a risk to deviate from the original McCrea (1950) calibration and related isotopic fractionations, and thus from the proper scale. In any case, the less dense acid contains more water, increasing possibilities of isotopic exchange with the oxygen in the produced CO2. Wasn't it Harmon Craig in the early days of existence of the isogeochem list who warned against deviating from the original calibrated procedure...(must still be in the archives...)? Some thoughts. Best wishes, Pier. **************************************************************** Delta Isotopes Consultancy Dr. Pier A. de Groot Pastoor Moorkensstraat 16 2400 Mol - Achterbos Belgium Tel. +32 (0)14 326 205 e-mail: [log in to unmask] or [log in to unmask] Associate editor for stable isotopes of eEarth on-line magazine http://www.electronic-earth.net Visit my WEB-site about my "Handbook of Stable Isotope Analytical Techniques", with a link to the Elsevier web site on the handbook (marked: 'Order Now'): http://users.pandora.be/handbook/index.html last update: August 15, 2005 Volume I is now available. Volume II is expected to be available second half of 2006. **************************************************************** Why we are searching for extraterrestrial intelligence While we lack it so much on Earth? **************************************************************** _____ From: Wenbo Yang <[log in to unmask]> Reply-To: Stable Isotope Geochemistry <[log in to unmask]> Date: Sun, 17 Sep 2006 17:29:38 -0700 To: <[log in to unmask]> Subject: Re: [ISOGEOCHEM] preparing 100% phosphoric acid Yes, the easiest way to make "100%" H3PO4 is to just simply heat the 85% H3PO4 on a hot plate to remove (or evaporate) the 15% H2O in fume hood. But the alternative way is by chemical reaction: P2O5 + 3H2O = 2H3PO4, so that you can get the "100%" H3PO4 or the water-free H3PO4 acid, too. -----Original Message----- From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of millionh@yahoo,com Sent: Sunday, September 17, 2006 9:56 AM To: [log in to unmask] Subject: [ISOGEOCHEM] preparing 100% phosphoric acid I know this topic have been on this site few months ago. I have some questions and suggestion on the topic, how to make 100 % phosphoric acid. I have been following the same procedure Pier described on this site, that is following Bowen's (1966) and Coplen et al. (1983). (i.e., adding P2O5 to 85% orthophosphoric acid and heating at 200 oC) But, the On-line lab manual for Stanford by Mucciarone uses very simple method for his Kiel device. Just heat the ACS grade 85% commercial Phosphoric acid to get ride of the 15% water out of it. Does anyone see any problem with this method? The specific gravity he is using is 1.89 to 1.90 which is similar to the method most are using. WHY do we need to add P2O5 to the 85 % orthophosphoric acid?? Thanks _____ Get your own web address for just $1.99/1st yr < ">http://us.rd.yahoo.com/evt=43290/*http://smallbusiness.yahoo.com/domains <http://us.rd.yahoo.com/evt=43290/*http://smallbusiness.yahoo.com/domains> > . We'll help. Yahoo! Small Business <http://us.rd.yahoo.com/evt=41244/*http://smallbusiness.yahoo.com/> <http://us.rd.yahoo.com/evt=41244/*http://smallbusiness.yahoo.com/> .