{"id":120,"date":"2011-01-15T20:11:07","date_gmt":"2011-01-16T00:11:07","guid":{"rendered":"http:\/\/web.colby.edu\/colbyatsea\/?p=120"},"modified":"2011-01-16T06:54:41","modified_gmt":"2011-01-16T10:54:41","slug":"making-the-invisible-visible-analysis-of-hydrogen-peroxide-concentrations-in-seawater","status":"publish","type":"post","link":"https:\/\/web.colby.edu\/colbyatsea\/2011\/01\/15\/making-the-invisible-visible-analysis-of-hydrogen-peroxide-concentrations-in-seawater\/","title":{"rendered":"Making the Invisible Visible – Analysis of Hydrogen Peroxide Concentrations in Seawater"},"content":{"rendered":"
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Chemiluminescence of HOOH and AE<\/p><\/div>\n

During the cruise I will be measuring the concentrations of hydrogen peroxide (H2<\/sub>O2<\/sub>), superoxide (O2<\/sub>–<\/sup>), and antioxidants. \u00a0 All of these species are colorless, odorless, and found at extremely low concentrations. \u00a0The challenge for analytical chemists is to make these invisible species visible. \u00a0 A good example of a qualitative analytical measurement is the use of litmus paper<\/a> to detect the acid\/base properties of solutions (litmus paper is red in acid and blue in base). \u00a0 In my measurements I need a more sensitive technique that can be automated to perform hundreds of measurements per day with as little human intervention as possible. \u00a0 The technique that I have selected is chemilumniescence – a chemical reaction that produces light. \u00a0 Recent advances in light detector technology makes it possible to measure individual photons produced by a chemical reaction. \u00a0By adding an acridinum ester reagent to seawater I can produce the blue chemiluminescence shown above. \u00a0 The method is very sensitive because of sensitive light measurements and because Avogadro’s number<\/a> is big, very big!<\/p>\n

Consider adding ten drops of 3% (1 molar)\u00a0hydrogen peroxide to a 6 lane swimming pool. This is a 2.5 billion fold dilution of H2<\/sub>O2<\/sub> resulting in a concentration of 0.4 nM (4×10-10<\/sup> M). \u00a0 This concentration is close to the lower limit of H2O2 I can detect in seawater – an extremely low concentration. \u00a0 However, in only 1 drop of the pool water we will still have 40 billion of molecules of hydrogen peroxide because Avogadros number (6.02×1023<\/sup> molecules\/mole) is so huge. \u00a0It is relatively easy to measure billions, millions, and even thousands of photons. \u00a0I “simply” need to convert the H2O2 into light to make the measurement.<\/p>\n

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Structure of AE. Click on image to see reaction with HOOH.<\/p><\/div>\n

The chemiluminescent reagent used in this method is 10-methyl-9-(p-formylphenyl)-acridinium carboxylate trifluoromethanesulfonate, abbreviated AE. \u00a0AE reacts selectively with H2O2 in seawater to produce blue light. \u00a0 \u00a0The reaction only occurs under basic conditions, so I add base to a mixture of seawater and AE to trigger the reaction. \u00a0The mixing is performed in a glass flow cell<\/a> that helps automate the reaction and maximize photon collection by the detector. \u00a0 The schematic below shows the tubing system that I use \u00a0to deliver the sample and reagents to the flow cell. A peristaltic pump pushes the solutions through the green valve on the way to the flow cell. \u00a0The valve can select for solutions in loop 3 or 5 automatically every few minutes. \u00a0 When the valve is set to inject (loop 5) I measure the light coming from the AE-H2O2 reaction in the flow cell. \u00a0 On the ship I replace the syringe shown in the diagram with a direct connection to the flowing seawater line coming from the sea chest on the ship. \u00a0 This way I can get real-time measurements of H2O2 in the surface ocean.<\/p>\n

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Instrument for measuring hydrogen peroxide (tubes at the top are connected to the ships seawater system)<\/p><\/div>\n

The photograph to the left shows the analytical system running on the Melville.\u00a0Typical data from the instrument shows an increase in hydrogen peroxide near the surface and decreasing concentrations with depth. \u00a0 This is what I would expect for a photochemical species, a compound formed by the interaction of sunlight with seawater. Interestingly, the maximum concentration of hydrogen peroxide is not at the surface, suggesting that another source of hydrogen peroxide may be present. \u00a0 We know that some phytoplankton produce hydrogen peroxide. \u00a0 \u00a0Do my profiles support a biological source of HOOH? \u00a0 If yes, why would phytoplankton produce HOOH at concentrations high enough to be detected in the surface ocean. \u00a0These are a few of the questions I hope to answer on the cruise.<\/span><\/p>\n

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Profile of HOOH in the surface ocean. Notice that oceanographers plot things backwards.<\/p><\/div>\n

Check back for future blogs describing the other instruments on the ship and more oceanographic data.<\/p>\n

-Whitney<\/p>\n


\n<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

During the cruise I will be measuring the concentrations of hydrogen peroxide (H2O2), superoxide (O2–), and antioxidants. \u00a0 All of these species are colorless, odorless, and found at extremely low concentrations. \u00a0The challenge for analytical chemists is to make these … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":184,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"ngg_post_thumbnail":0,"footnotes":""},"categories":[17554,1178,1],"tags":[],"_links":{"self":[{"href":"https:\/\/web.colby.edu\/colbyatsea\/wp-json\/wp\/v2\/posts\/120"}],"collection":[{"href":"https:\/\/web.colby.edu\/colbyatsea\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/web.colby.edu\/colbyatsea\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/web.colby.edu\/colbyatsea\/wp-json\/wp\/v2\/users\/184"}],"replies":[{"embeddable":true,"href":"https:\/\/web.colby.edu\/colbyatsea\/wp-json\/wp\/v2\/comments?post=120"}],"version-history":[{"count":14,"href":"https:\/\/web.colby.edu\/colbyatsea\/wp-json\/wp\/v2\/posts\/120\/revisions"}],"predecessor-version":[{"id":222,"href":"https:\/\/web.colby.edu\/colbyatsea\/wp-json\/wp\/v2\/posts\/120\/revisions\/222"}],"wp:attachment":[{"href":"https:\/\/web.colby.edu\/colbyatsea\/wp-json\/wp\/v2\/media?parent=120"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/web.colby.edu\/colbyatsea\/wp-json\/wp\/v2\/categories?post=120"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/web.colby.edu\/colbyatsea\/wp-json\/wp\/v2\/tags?post=120"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}