BASF SM02001EE Analytical Method - Inorganic Chemicals - Volumetric Determination of Ammonium Chloride Concentration

BASF, the world's largest chemical company, has a broad portfolio including chemicals, plastics, pigments, master mixes, additives, dispersions, polyurethanes, and more. These types of product codes typically indicate internal or customer-specific qualities, such as:

• Masterbatches (color or additive concentrate for plastics)
• Pigment preparation or dispersion
• A specialized additive or formulation in fields such as coatings, plastics, or electronics.

Master mixtures typically contain colorants, UV stabilizers, antistatic agents, flame retardants, or processing aids (e.g., elastostats for antistatic thermoplastic polyurethanes or other functional lines) under brands derived from legacy pigment or plastics divisions.

The BASF SM02001EE standard is for the volumetric determination of ammonium chloride concentration. According to this standard,

• The component to be identified: Ammonium chloride.
• Matrix: Ammonium chloride.
• Safety requirements: General laboratory safety procedures must be followed.
• Analytical method:
• Principle: Volumetric determination of ammonium.
• Effective range: The method is designed for use with concentrations between 0,1 and 100 g/100g.
• Accuracy: For typical values, the maximum error is plus/minus 0,05 g/100g.
• Devices:
• Precision balance (plus/minus 0,0001 g)
• 250 ml volumetric bottle
• 250 ml conical bottle
• 25 ml volumetric pipette
• 50 ml burette
• Reagents:
• Hydrochloric acid
• Sodium hydroxide solution
• Methyl red
• A 20% formaldehyde solution is ready for use. A 30% formaldehyde solution is diluted with distilled water in a 2:1 ratio, phenolphthalein is added, and neutralized with sodium hydroxide solution (color change from colorless to light pink).
• Process:
• Titration determination: Only standard solutions produced by known and reliable manufacturers and precisely adjusted to a titer of 1.000 (at 20 degrees Celsius) should be used. The maximum deviation due to temperature change should be 0,02 percent per degree Celsius. The solution used for titration is stable for a limited time and must be recalibrated after prolonged storage. The resulting value should be taken into account in the calculation.
• Procedure: 10 g of ammonium chloride, along with rinsing, is transferred to a 250 ml volumetric flask, dissolved, and filled to the flask mark. 25 ml of this solution is pipetted into a 250 ml conical flask and neutralized with hydrochloric acid against methyl red. 20 ml of formaldehyde solution is added, and titration is performed with sodium hydroxide until the solution turns from yellow to orange.

Ammonium chloride is a white crystalline salt widely used in fertilizers, pharmaceuticals, and analytical chemistry. In aqueous solution, it behaves as a weakly acidic salt due to the partial hydrolysis of the ammonium ion. Because the ammonium ion is a very weak acid, direct acid-base titration of ammonium chloride with a strong base such as sodium hydroxide is not possible, resulting in an indeterminate endpoint.

The standard volumetric method for determining the concentration (or purity percentage) of ammonium chloride uses an indirect acid-base titration employing the formaldehyde reaction. This approach converts the weak ammonium system into a stronger acid that can be accurately titrated.

In principle, ammonium chloride reacts with neutralized formaldehyde to form hexamethylenetetramine, releasing a quantitatively equivalent amount of hydrochloric acid to the available ammonium chloride. The resulting acid (a strong acid) is then titrated with a standard sodium hydroxide solution using phenolphthalein as an indicator. The endpoint is the appearance of a persistent pale pink color.

This method is widely used in pharmaceutical analysis (e.g., determination of ammonium chloride samples) and quality control.

The required reagents are as follows:

• Ammonium chloride sample
• Neutralized formaldehyde solution
• Standard 0,1 M sodium hydroxide solution
• Phenolphthalein indicator
• Distilled water

During the process, standardization is typically performed with oxalic acid or potassium hydrogen phthalate. For example, approximately 0,63 g of oxalic acid dihydrate is precisely weighed, dissolved in distilled water, and brought to a volumetric flask of 100 mL. 20 mL is pipetted and titrated with sodium hydroxide to the pink endpoint using phenolphthalein.

During sample preparation and titration, approximately 0,1–0,2 g of ammonium chloride sample is precisely weighed and transferred to a 250 mL conical flask. It is dissolved in 20–30 mL of distilled water. 5–10 mL of neutralized formaldehyde solution is added. If necessary, another 20 mL of distilled water is added. 2–3 drops of phenolphthalein indicator are added. It is immediately titrated with standardized 0,1 M sodium hydroxide from the burette until a persistent pale pink color appears (endpoint). The volume of sodium hydroxide used is recorded. Repeat for accuracy (usually 2–3 titrations).

This volumetric method provides accurate and reliable results for determining the concentration of ammonium chloride in samples and is a standard technique in many laboratory guidelines and pharmacopoeias.

The formaldehyde method (hexamine or indirect alkalimetric method) is necessary for the accurate volumetric determination of ammonium chloride concentration because direct acid-base titration of ammonium chloride with sodium hydroxide is neither practical nor accurate. This is because...

• Ammonium ion is a very weak acid.
• Direct titration with sodium hydroxide gives an indeterminate endpoint.
• The formaldehyde reaction solves this problem.

For many years, our organization, with its competent and experienced team, has been understanding the needs of its customers, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services compliant with the BASF SM02001EE standard.