known. The Somogyi-Nelson method uses an arsenomolybdate complex formed by the reaction of ammonium molybdate, (NH4)6 Mo7O24, with sodium arsenate, Na2HAsO7. Colorimetric determination of some drugs containing catechol Some drugs that contain a catechol group react with phosphomolybdic acid (H3PMo12O40) to give the heteropoly-molybdenum blue colour. Micro quantities of the drugs can be determined. Uses in qualitative analysis Examples of simple tests are shown below that rely on the production of the molybdenum blue colour either due to reduction: tests for Sn(II) and Sb(III) tests for organic reducing agents or by detection of the heteroatom silicate phosphate Dittmer's spray reagent for phospholipids is used in thin layer chromatography to detect phospholipids. The spray reagent is prepared as follows: Molybdenum(VI) oxide, MoO3, is dissolved in sulfuric acid A second solution is made up from molybdenum metal dissolved in some of the first solution. The spray is made up of a diluted mixture of the first and second solutions. When applied to the TLC plate, compounds containing phosphate ester show up immediately as blue spots. Isopoly molybdenum blues The isopoly-molybdenum blues have been known for many years. They are the cause of the "blue waters" found near Idaho Springs, known to Native Americans. They were first documented by Scheele and Berzelius. The compounds responsible for the blue colour were not known until 1995. Before then it was well known that there were polymolybdates of Mo(VI). Molybdenum(VI)oxide, MoO3, when dissolved in aqueous alkali forms the tetrahedral molybdate anion, . Dissolving molybdate salts in strong acid produces "molybdic acid", MoO3·2H2O. In between these extremes of pH, polymeric ions are produced which are mostly built from MoO6 octahedral units sharing corners and edges. Examples include , and , which contain the {(Mo)Mo5}-type unit comprising a central MoO7 pentagonal bipyramid sharing edges with five MoO6 octahedra. The later unit occurs also in the giant mixed-valence molybdenum blue species [HxMo368O1032(H2O)240(SO4)48]48− (x ≈ 16) as well as in the cluster described in the next section. The molybdenum blue species are obtained by reduction of acidified molybdate(VI) solutions. The big wheel The first publication of the structure of wheel shaped cluster anion, first determined for the nitrosyl derivative by Achim Müller et al. was announced in New Scientist as "Big Wheel rolls back the molecular frontier". Further work by the same group then refined the initial findings and determined the structure of the wheel produced in molybdate solutions as