View source for Micro-chemical test for magnesium

Author: [[user:CBlaeuer| Christine Bläuer]]<br>

back to [[Micro-chemical testing]]

For more information on the required equipment and materials see the Micro-chemistry article. 

== Procedure ==
 
=== Mg<sup>2+</sup> test using ammonium hydrogen phosphate and ammonia  ===
 
Acidify the sample drop with a small drop of dilute (2M) hydrochloric acid. Add a drop of di-ammonia hydrogen phosphate solution (10% aqueous solution). Invert the slide and hold the drop over an open bottle of concentrated ammonium hydroxide so that the ammonia vapor reaches it. Alternatively a drop of 2M ammonium hydroxide solution can be added to the test drop, but the first procedure usually gives better results.

If  Mg<sup>2+</sup> is present typical crystals of magnesium ammonium phosphate (MgNH<sub>4</sub>PO<sub>4</sub>.6H<sub>2</sub>O) can be observed in the center of the test drop. Detection limit for Mg<sup>2+</sup> = 0.05 µg.

'''''Ions that may inhibit the test or affect its sensitivity:'''''
If calcium ions are present, these form a white, flocculent precipitate of calcium phosphate which can interfere or even inhibit the formation of magnesium ammonium phosphate

===Mg<sup>2+</sup> test using cesium chloride and sodium hydrogen phosphate === 
Acidify the sample drop with a small drop of dilute (2M) hydrochloric acid. Add to it a drop of di-sodium hydrogen phosphate solution (10% aqueous solution). Add one crystal of cesium chloride to the solution.

If  Mg<sup>2+</sup> is present, very small octahedral crystals of cesium magnesium phosphate (CsMgPO<sub>4</sub>.6H<sub>2</sub>O) will quickly form near the dissolving grain of CsCl. Detection limit for Mg<sup>2+</sup> = 1 µg.

'''''Ions that may inhibit the test or affect its sentivity:'''''
Ions of the elements Sr, Ba, Zn, Cd, Sn, Pb, Ag and Cu interfere with or mask the reaction.
Calcium ions form a white, flocculent precipitate of calcium phosphate that interferes or even inhibits the formation of the cesium magnesium phosphate formed.

===Mg<sup>2+</sup> test using Titan yellow, a triazin dye, after [1] ===
Put 1 drop of the test solution on a spot plate, acidify with diluted (2M) hydrochloric acid and 1 drop of the titan  yellow solution. Add 1 or 2 drops of sodium hydroxide solution and stir with a glass rod.
If Mg<sup>2+</sup> is present a red, flocculent precipitate will form. Detection limit for Mg<sup>2+</sup> ca. 1.5 µg

'''''Ions that may inhibit the test or affect its sentivity:'''''
The presence of calcium leads to a slightly orange to reddish staining of the solution which cannot be confused with the red, flocculent precipitation. Control tests with known substances will help to recognize a positive reaction for Mg<sup>2+</sup> unambiguously.

Nickel, zinc, manganese and cobalt ions interfere with the reaction [2] 

== Literature ==
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[[category:Bläuer,Christine]][[category:complete]][[category: microchemistry]]