Sodium Sulphate Analysis 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

Identify of Sodium Sulphate


A1 EP 97 - European Pharmacopoeia

A2 Health & Safety Data Sheets for Reagents & Chemicals used in the analysis

A3 Health & Safety Data Sheets for samples being analyzed


A4.1 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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A6.1 Water - De-ionised or distilled

A6.2 0.25 M Barium Chloride - 6.0 g of BaCl2 2H2O (Analytical reagent) dissolved in 100 ml of Water

A6.3 2 M Hydrochloric Acid - HCl 7.3g (Analytical reagent) made up to 100 ml Water.

A6.4 0.05M Iodine solution (I2) - Dissolve 2 grams Potassium Iodide (Analytical Reagent) in the minimum amount of water and add 1.3 g Iodine (Analytical Reagent) and dilute to 100 ml with water.

A6.5 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.

A6.6 Hydrochloric acid 36% w/w (Analytical Reagent)


A7.1 Boiling tube 50 ml

A7.2 Bunsen Burner

A8 INTERFERENCE - No interference

A9 SAMPLING - No special requirements

Procedure Sulphates test

A10.1 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.

A10.2. 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).



A qualitative test will show sulphates as a present.


A13.1 Report as sulphate as positive or negative. Quote name of analyst, test method 24176A and any

recommendations. Ensure 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


B1 EP 97 - European Pharmacopoeia

B2 Health & Safety Data Sheets for Reagents & Chemicals used in the analysis

B3 Health & Safety Data Sheets for samples being analysed


B4.1 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.

Sodium Sulphate analysis methods by Ion-exchange and gravimetric


B5.1 1 M Sodium Hydroxide with a certificate guaranteeing the strength.


B6.1 Water - De-ionized or distilled

B6.2 0.1 M Sodium Hydroxide (Volumetric Solution)

B6.3 1 M Sodium Hydroxide (Volumetric Solution)

B6.6 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


B7.1 200mm x 20 mm column packed with strongly acidic ion-exchange resin at a flow rate of about 4 ml per minute.

B7.2 500 ml conical flask.

B7.3 50 ml Burette - Calibrated

B7.4 Balance weighing to nearest 0.1 mg


B8.1 If a significant amount of other anions and cations are present the calculation will not give the correct percentage of Sodium Sulphate.


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.


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.


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


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


B13.1 The results shall be reported to the nearest 0.1% as percentage Sodium Sulphate (Anhydrous) Identify the

sample and state whether the result meets the specification. The report shall quote the test method 24176B, the analyst, any recommended action and date of analysis.

sodium Sulphate Assay by Gravimetric Method

Assay using the Gravimetric Method used in Weinheim for denture products.


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


The method used for denture cleanser raw materials in Weinheim


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


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


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

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

De-ionised water or distilled water


A3 filter crucible

Suction bottle

Water-jet vacuum pump

Drying oven 105 ± 2°C

Muffle furnace 500 ± 10°C

Folded filter

Balance reading to 0.01 g

300-ml beakers

100-ml graduated cylinder


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.


Precautions: Read 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 cools 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).



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


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

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

                          E                                     E


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.


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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