Determination Sodium Sulphate Assay by Ion-Exchange and Gravimetric Methods

The method test methods were carried out in the analysis of Sodium Sulphate. Sodium sulphate assay by Ion Exchange Method and Gravimetric Method.

REFERENCE

EP 97 - European Pharmacopoeia.

Health & Safety Data Sheets for Reagents & Chemicals used in the analysis.

Health & Safety Data Sheets for samples being analyzed.

PRINCIPLES

Sulphate is indicated by forming the insoluble barium salt and this is confirmed by adding dilute iodine which is not decolourised showing the absence of sulphites & dithionates. The mixture is then decolourised by adding Tin (II) chloride solution. On boiling, no coloured precipitate is produced distinct from selenates and tungstates.

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CHEMICALS & REAGENTS

1.0 Water - De-ionised or distilled.

2. 0.25 M Barium Chloride - 6.0 g of BaCl2 2H2O (Analytical reagent) dissolved in 100 ml of Water.

3. 2 M Hydrochloric Acid - HCl 7.3g (Analytical reagent) made up to 100 ml Water.

4. 0.05M Iodine solution (I2) - Dissolve 2 grams of Potassium Iodide (Analytical Reagent) in the minimum amount of water add 1.3 g Iodine (Analytical Reagent) and dilute to 100 ml with water.

5. Tin (II) chloride solution - Dissolve 33 g of Tin (II) Chloride (Analytical Reagent) in 10 ml hydrochloric acid 36% w/w dilute to 100 ml with water. To keep the solution add a piece of granulated tin (Analytical Reagent) and store it in the dark.

6. Hydrochloric acid 36% w/w (Analytical Reagent)

EQUIPMENT

1. Boiling tube 50 ml

2. Bunsen Burner

INTERFERENCE - No interference

SAMPLING - No special requirements

Procedure Sulphates Test

1. To 40 to 50 mg of the substance being examined dissolved in 5 ml of water or to 5 ml of the prescribed solution add 1 ml of 2 M hydrochloric acid and 1 ml of 0.25 M barium chloride. A white precipitate is produced.

2. Add 0.1 ml of iodine solution to the suspension obtained during reaction A; the suspension remains yellow (distinction from sulphites and dithionites) but is de-colourised by adding, dropwise, tin(II) chloride solution (distinction from iodates). Boil the mixture; no coloured precipitate is produced (distinction from selenates and tungstates).

A11 CALCULATION OF RESULTS - n/a

ACCURACY

A qualitative test will show sulphates as a present.

REPORT

1. Report sulphate as positive or negative. Quote the name of the analyst, test method and any recommendations. Ensure the sample is identified.

Sodium Sulphate Assay by Ion Exchange Method

B1 SECTION B. Titration with Sodium hydroxide EP method Scope - suitable for sodium sulphate analysis

REFERENCE

EP 97 - European Pharmacopoeia

Health & Safety Data Sheets for Reagents & Chemicals used in the analysis

Health & Safety Data Sheets for samples being analysed

PRINCIPLE

A solution containing a known amount of the sample is passed through an Ion Exchange column which removes the sodium ion replacing it with a hydrogen ion. The resulting solution is titrated with a volumetric solution of IM Sodium Hydroxide. The hydrogen ion concentration is then calculated as the equivalent Sodium Sulphate content.

REFERENCE STANDARD

1 M Sodium Hydroxide with a certificate guaranteeing the strength.

CHEMICALS & REAGENTS

1. Water - De-ionized or distilled
2. 0.1 M Sodium Hydroxide (Volumetric Solution)
3. 1 M Sodium Hydroxide (Volumetric Solution)
4. Methyl Orange Solution - 0.1% w/v solution in 20% ethanol

Sensitivity: Not more than 0.1 ml is sufficient to change the colour to red

EQUIPMENT

1. 200mm x 20 mm column packed with strongly acidic ion-exchange resin at a flow rate of about 4 ml per minute.
2. 500 ml conical flask.
3. 50 ml Burette - Calibrated.
4. Balance weighing to the nearest 0.1 mg.

INTERFERENCE

If a significant amount of other anions and cations are present the calculation will not give the correct percentage of Sodium Sulphate.

SAMPLING

Precautions: The Health and Safety Datasheets for the samples being collected or analyzed.

B9.1 Powders need to be sampled with care and it is best to take the sample from several points and pass them through a quartering device to ensure the sample is representative of the whole. Ensure that the sample is sealed so it does not pick up moisture.

PROCEDURE

Precautions: Read Health & Safety Data Sheets for all Chemicals & Reagents before commencing the analysis.

Weigh accurately 1.2 - 1.4 g in 50 ml of water and pass through a column (200 mm x 20 mm) packed with strongly acidic ion-exchange resin at a flow rate of about 4 ml per minute. Elute with water (about 300 ml) until 50 ml requires not more than 0.05 ml of 0.1 M sodium hydroxide VS for neutralisation. Titrate the elute with 1M sodium hydroxide VS using methyl orange solution as an indicator. Each ml of 1 M sodium hydroxide S is equivalent to 0.0710 g of Na2SO4.

CALCULATION OF RESULTS

% Na2SO4 = 0.0710 x V x100 % (Where W = Weight taken & V = Volume of 1 N Sodium Hydroxide)/W

ACCURACY

A uniform sample, result should give a precision of ±0.5%.

REPORTS

The results shall be reported to the nearest 0.1% as a percentage of Sodium Sulphate (Anhydrous) Identify the

sample and state whether the result meets the specification. The report shall quote the test method the analyst, any recommended action and date of analysis.

Sodium sulphate Assay by Gravimetric Method

An assay using the Gravimetric Method used in Weinheim for denture products.

SCOPE

Generally applicable for sulphates - takes longer than the volumetric method but is more accurate

REFERENCE

The method used for denture cleanser raw materials in Weinheim

DEFINITIONS AND  PRINCIPLE

After the reaction with barium chloride, the barium sulfate obtained is determined by gravimetric analysis.

REFERENCE STANDARD

A Sodium Sulphate (Anhydrous dried) with an assay certificate may be used to check this method if required.

CHEMICALS & REAGENTS

Concentrated hydrochloric acid 36%w/w (Analytical reagent)

20% barium chloride solution (Use barium chloride analytical reagent)

De-ionised water or distilled water

EQUIPMENT

1. A3 filter crucible.
2. Suction bottle.
3. Water-jet vacuum pump.
4. Drying oven 105 ± 2°C.
5. Muffle furnace 500 ± 10°C.
6. Folded filter.
7. Balance reading to 0.01 g.
8. 300-ml beakers.
9. 100-ml graduated cylinder.

INTERFERENCE

The method is reasonably robust for pure chemicals but the mixture continuing Ethylene Diamine Tetra Acetic acid will interfere and dissolve the barium sulphate. Salts other than Sodium as the cation will not give an accurate result as the calculation cannot take this into account. Tung states that Selenate’s impurities also interfere.

Procedure

Precautions: Read the Health & Safety Data Sheets for Chemicals & Reagents used in this analysis and also read the Instruction Manuals for all equipment used in the analysis.

Weigh 3±0.3 g of a representative sample of the test substance, accurate to 0.01 g, into a 300-ml beaker and dissolve in 100 ml of water. After the evolution of gas has stopped, carefully (evolution of gas) add 10 ml of concentrated hydrochloric acid. Filter the solution through a folded filter until clear and flush the filter with 10 ml of water. Heat the collected filtrate to boiling with stirring, and slowly add 50 ml of 20% barium chloride solution. Heat for an additional 5 min and cool the sample overnight.

Filter the resulting precipitate by suction through a pre-tempered (2 h, 500 °C) and weighed filter crucible (m1) and wash the precipitate with 50 ml of hot water. Then dry the crucible to constant weight, first in the drying oven (30 min, 105 °C) and then in the muffle furnace (500 °C), and re-weigh (m2).

CALCULATION OF RESULTS

Let:

SO4 = sulfate content as %

m2 = weight of the full crucible in g

m1 = weight of the empty crucible in g

F = analytic factor, 0.4116

E = weighed-in quantity in g

Then:

          (m2 - m1) x 100 x F (m2 - m1) x 100 x 0.6075

SO4 = ------------------ % ; % Na2SO4 = -------------- %

                          E                                     E

ACCURACY

The method gives good precision and on the final weight of 1.000 g of Barium Sulphate, a precision of 0.005 g shall be achievable. The true result will be lower than this due to the solubility of Sodium Sulphate. The calculation will not be correct if there is contamination from metal ions such Ca or K, Dithionates and Sulphites will give inaccuracy.

REPORTS

Report the Sodium Sulphate as Anhydrous Sodium Sulphate to the nearest 0.1% and quote the method as 24176C and the name of the analyst. Ensure the sample is correctly identified and state whether it is within specification. Also, give any recommended action

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