Standard Magnesium Solution

Any color does not exceed that produced by 1.0 mL of Magnesium Standard Solution (see Solutions and Indicators) in the same volume as that of a control containing 2.5 mL of the sample solution (corresponding to 10 mg of sample) and the quantities of the reagents used in the test. 

Magnesium Standard Solution (50 pig Mg in 1 mL) Dissolve 50.0 mg of magnesium metal (Mg) in 1 mL of hydrochloric acid in a 1000-mL volumetric flask, dilute to volume with water, and mix. 

Sensitiveness To 10 mL of a 1 200,000 solution in a mixture of equal parts (v/v) of methanol and water add a 1 100 solution of sodium hydroxide until the pH is 10. The solution is pure blue and free from cloudiness. Add 0.2 mL of Magnesium Standard Solution (10 jxg Mg ion). The color of the solution changes to red-violet, and with the continued addition of magnesium ion, it becomes wine red. 

EDTA solution CioHi4N2Na208 2H2O, 0.025 mol/L for samples with S<20. Dissolve 18.61 g of ethylenediaminetetraacetate (disodium salt, dihydrated, analytical-reagent grade, a.g.) dried at 50 °C for 1 h) in distilled water and dilute to 2000 mL. Determine the exact titre by standardization with the magnesium standard solution. 

The amount of magnesium ion set free is equivalent to the cation present and can be titrated with a standard solution of EDTA and a suitable metal indicator. 

Phosphate may be determined by precipitating as Mg(NH4)P04,6H20, dissolving the precipitate in dilute hydrochloric acid, adding an excess of standard EDTA solution, buffering at pH = 10, and back-titrating with standard magnesium ion solution in the presence of solochrome black. 

This colour change can be observed with the ions of Mg, Mn, Zn, Cd, Hg, Pb, Cu, Al, Fe, Ti, Co, Ni, and the Pt metals. To maintain the pH constant (ca 10) a buffer mixture is added, and most of the above metals must be kept in solution with the aid of a weak complexing reagent such as ammonia or tartrate. The cations of Cu, Co, Ni, Al, Fe(III), Ti(IV), and certain of the Pt metals form such stable indicator complexes that the dyestuff can no longer be liberated by adding EDTA direct titration of these ions using solochrome black as indicator is therefore impracticable, and the metallic ions are said to block the indicator. However, with Cu, Co, Ni, and Al a back-titration can be carried out, for the rate of reaction of their EDTA complexes with the indicator is extremely slow and it is possible to titrate the excess of EDTA with standard zinc or magnesium ion solution. 

Buffer solution. Add 55 mL of concentrated hydrochloric acid to 400 mL de-ionised water and mix thoroughly. Slowly pour 310 mL of redistilled monoethanolamine with stirring into the mixture and cool to room temperature (Note 2). Titrate 50.0 mL of the standard magnesium chloride solution with standard (0.01M) EDTA solution using 1 mL of the monoethanolamine-hydrochloric acid solution as the buffer and solochrome black as the indicator. Add 50.0 mL of the magnesium chloride solution to the volume of EDTA solution required to complex the magnesium exactly (as determined in the last titration), pour the mixture into the monoethanolamine-hydrochloric acid solution, and mix well. Dilute to 1 litre (Note 3). 

Procedure. To a 50 mL sample of the water to be tested add 1 mL buffer solution (ammonium hydroxide/ammonium chloride, pH 10, Section 10.54) and 30-40 mg solochrome black indicator mixture. Titrate with standard EDTA solution (0.01 M) until the colour changes from red to pure blue. Should there be no magnesium present in the sample of water it is necessary to add 0.1 mL magnesium-EDTA solution (0.1 M) before adding the indicator (see Section 10.54). The total hardness is expressed in parts of CaC03 per million of water. 

Discussion. In mixtures of magnesium and manganese the sum of both ion concentrations may be determined by direct EDTA titration. Fluoride ion will demask magnesium selectively from its EDTA complex, and if excess of a standard solution of manganese ion is also added, the following reaction occurs at room temperature ... 

The sulphate is precipitated as barium sulphate from acid solution, the precipitate is filtered off and dissolved in a measured excess of standard EDTA solution in the presence of aqueous ammonia. The excess of EDTA is then titrated with standard magnesium chloride solution using solochrome black as indicator. 

Procedure. Prepare a standard magnesium chloride solution (0.05M) and a buffer solution (pH 10) see Section 10.72. Standard EDTA (0.05M) will also be required. 

The following substance, namely magnesium acetate potassium citrate potassium hydroxide potassium nitrate and sodium chloride can also be assayed for their respective elements as shown in Table 25.1 below. However, all the respective solutions of the said pharmaceutical substance and their standard solutions must be prepared as prescribed in BP (1993) strictly to obtain the best results. 

Procedure. Steam is passed through the steam distillation apparatus for 20-30 min. Check the performance by pipetting 5 ml ammonium-N standard solution into the distillation unit, add 1 drop octan-2-ol, 6 ml magnesium hydroxide suspension and steam distil the released ammonia into 5 ml boric acid solution in a 100-ml conical flask. After approximately 40 ml distillate has been collected over a 5-min period, wash the tip of the condenser into the distillate, add 2-3 drops mixed indicator solution and titrate with 0.005 M H SO until the colour changes from green to purple. A blank distillation/titra-tion is carried out using 5 ml ammonia-free water and subtracted from the standard titre to give a result which should be 5.00 ml. 

Magnesium stock standard solution, 1000 pg Mg + mh - dissolve 1.5581 g magnesium oxide (previously dried at 105°C overnight and cooled in a desiccator) in the minimum of hydrochloric acid (approximately 5 M). Dilute with water to 1 I in a volumetric flask to obtain a solution of 1000 pg Mg + ml-k... 

Procedure. Carry out the extraction and then determine phosphorus as in Method 5.9a, except that working standard solutions should be made up in the Mehlich 1 extractant. Determine potassium and magnesium as in Method 5.10, except that standards are made up in Mehlich 1 extractant. Determine calcium as in Method 5.2, except that standards are made up in Mehlich 1 extractant. The composition of composts is so variable that appropriate dilutions of extracts may be required, and calculations adjusted accordingly. 

Elemental composition (anhydrous MgCE) Mg 25.54%, Cl 74.46%. Aqueous solution of the salt may he analyzed for Mg hy AA or ICP method (See Magnesium). The chloride ion can he identified hy ion chromatography or measured by titration with a standard solution of silver nitrate using potassium chromate as indicator. 

Magnesium stock solution—using distilled or deionized water prepare six magnesium standards in 100 ml volumetric flasks of 0.1, 0.3, 0.4, 0.5, 0.6, and 0.8 pg mk concentration from the stock solution. Also prepare 250 ml of a 0.2 pg mpi magnesium standard. 

To prepare a 0.02 N standard solution of calcium and magnesium salts, pour 75 ml of a 0.1 N calcium chloride solution and 25 ml of a 0.1 TV magnesium sulphate solution into a 500-ml measuring flask, and then add distilled water up to the mark on the flask. 

Five standard solutions were prepared for measuring the lead concentration in two solutions. A and B. The two solutions A and B contain the same concentration of magnesium used as an internal standard. The following data were obtained ... 

In the back-titration method, a measured amount of an excess standard EDTA solution is added to the sample. The analyte ion combines with EDTA. After the reaction is complete, the excess EDTA is back-titrated against a standard solution of magnesium or zinc ion. Eriochrome Black T or Calmagite is commonly used as an indicator. After all the remaining EDTA chelates with Mg2+ or Zn2+, ary extra drop of the titrant solution imparts color to the indicator signifying the end point. The cations that form stable complexes or react slowly with EDTA can also be measured by the back-titration method. 

Final Preparation Pipet 50.0 mL of Magnesium Sulfate Solution into the flask, add exactly the volume, / , in milliliters, of Standard EDTA Solution, determined as directed under Titer Determination (below), then dilute to volume with water, and mix. 

There is no "standard consensus concentration of magnesium bicarbonate solution for deacidification of paper. Some conservators prefer a high concentration to assure an adequate alkaline reserve. Others object to the "chalky feel of papers so treated. A concentration of 0.05M was used in this study unless otherwise indicated. 

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