Micro-chemical test for magnesium: Difference between revisions
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=== Mg<sup>2+</sup> test using ammonium hydrogen phosphate and ammonia === | === 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 | Acidify the sample drop with a small drop of dilute (2M) hydrochloric acid. Add a drop of di-ammonia hydrogen phosphate solution (NH<sub>4</sub>NH<sub>2</sub>NO<sub>3</sub> 10% aqueous solution). Invert the slide and hold the drop over an open bottle of concentrated ammonium hydroxide to expose it to ammonia vapor. 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. | 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. | ||
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===Mg<sup>2+</sup> test using cesium chloride and sodium hydrogen phosphate === | ===Mg<sup>2+</sup> test using cesium chloride and sodium hydrogen phosphate === | ||
Acidify the sample drop with a small drop of dilute (2M) | Acidify the sample drop with a small drop of dilute hydrochloric acid (HCl 2M). Add to it a drop of di-sodium hydrogen phosphate solution (10% aqueous solution). Add one crystal of cesium chloride to the solution. | ||
If | If the amount of Mg<sup>2+</sup> present is very small, octahedral crystals of cesium magnesium phosphate (CsMgPO<sub>4</sub>.6H<sub>2</sub>O) will very 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 that may inhibit the test or affect its sentivity:''''' | ||
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===Mg<sup>2+</sup> test using Titan yellow, a triazin dye, after [1] === | ===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) | Put 1 drop of the test solution on a spot plate, acidify with diluted hydrochloric acid (HCl 2M) and 1 drop of the titan yellow dye 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 | If Mg<sup>2+</sup> is present a red, flocculent precipitate will form. Detection limit for Mg<sup>2+</sup> ca. 1.5 µg | ||
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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. | 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] | Nickel, zinc, manganese and cobalt ions interfere with the reaction [2] | ||
== Literature == | == Literature == | ||
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[[category:Bläuer,Christine]][[category: | [[category:Bläuer,Christine]][[category:approved]][[category: microchemistry]] | ||
Latest revision as of 20:51, 24 November 2017
Author: Christine Bläuer
back to Micro-chemical testing
For more information on the required equipment and materials see the Micro-chemistry article.
Procedure
Mg2+ 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 (NH4NH2NO3 10% aqueous solution). Invert the slide and hold the drop over an open bottle of concentrated ammonium hydroxide to expose it to ammonia vapor. Alternatively a drop of 2M ammonium hydroxide solution can be added to the test drop, but the first procedure usually gives better results.
If Mg2+ is present typical crystals of magnesium ammonium phosphate (MgNH4PO4.6H2O) can be observed in the center of the test drop. Detection limit for Mg2+ = 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
Mg2+ test using cesium chloride and sodium hydrogen phosphate
Acidify the sample drop with a small drop of dilute hydrochloric acid (HCl 2M). Add to it a drop of di-sodium hydrogen phosphate solution (10% aqueous solution). Add one crystal of cesium chloride to the solution.
If the amount of Mg2+ present is very small, octahedral crystals of cesium magnesium phosphate (CsMgPO4.6H2O) will very quickly form near the dissolving grain of CsCl. Detection limit for Mg2+ = 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.
Mg2+ test using Titan yellow, a triazin dye, after [1]
Put 1 drop of the test solution on a spot plate, acidify with diluted hydrochloric acid (HCl 2M) and 1 drop of the titan yellow dye solution. Add 1 or 2 drops of sodium hydroxide solution and stir with a glass rod. If Mg2+ is present a red, flocculent precipitate will form. Detection limit for Mg2+ 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 Mg2+ unambiguously.
Nickel, zinc, manganese and cobalt ions interfere with the reaction [2]