Sodium hydroxide, 1 kg

Desiccants can absorb water and bind it chemically (reversibly or irreversibly) or physically. The main desiccants can be subdivided into four categories:

• non-renewable chemical desiccants
• renewable chemical desiccants
• silica gels
• molecular sieves

The most common technique for measuring the amount of nitrogen in organic matter is the Kjeldahl method, which is used in a wide range of sectors such as environmental analysis, food analysis, water analysis and agricultural analysis, as well as in the pharmaceutical and chemical industries. In this traditional method, a precisely weighed sample is broken down using concentrated sulphuric acid, a process which digests its organic contents and reacts nitrogen to form ammonium sulphate.(CHNO)(s) → CO₂ (g) + SO₂ (g) + H₂O (g) + NH₄SO₄ (solv, H₂SO₄)A catalyst or catalyst mixture consisting of copper, selenium, mercury and/or titanium is added to speed up the reaction. Sodium or potassium sulphate is used to give the sulphuric acid a higher boiling point. If the nitrogen is contained in a nitro, nitroso or azo compound, however, the mixture must be reduced with zinc before digestion takes place.
The nitrogen is now present in the sulphuric acid as ammonium sulphate. Adding a strong base (such as NaOH) neutralises the sulphuric acid and liberates ammonia from the solution.NH₄SO₄ (solv) + 2 NaOH (aq) → Na₂SO₄ (aq) + 2 NH₃ (g) + 2 H₂O (l) The ammonia is led into an acid (such as boric acid) by means of steam distillation.B(OH)₃ (aq) + 2 H₂O (l) + NH₃ (g) → B(OH)₄^- (aq) + NH₄⁺ (aq) The resulting strong base (borate ion) is back-titrated with a strong acid (hydrochloric acid or sulphuric acid). The excess weak boric acid is not captured in the process. A Tashiro's indicator that changes colour in the acid is used for titration. The amount of acid that has been used up can then be converted into the amount of nitrogen in the sample. NH₄⁺ (aq) + B(OH)₄^- (aq) + HCl (l) → NH₄Cl (aq) + B(OH)₃ (aq) + H₂O (l)To calculate the protein content of the sample, the varying nitrogen content of the amino acids must be checked and the relevant conversion factors applied. The nitrogen contained in food derives mainly from proteins, but different samples may also contain other sources of nitrogen.

Determination of biological oxygen demand (BOD)

BOD (biochemical oxygen demand) is a measure of the amount of oxygen that microorganisms need to break down the organic material in a water sample over a specific period of time. It is important to calculate the oxygen concentration at the start and end of the measuring time, which is usually five days and is expressed as an index (BOD₅). Chemical, electrochemical or physical methods are used for this calculation.

Acids and bases of p.a. quality are highly pure substances specifically produced for analytical purposes. Carl Roth provides the appropriate acid or base for various applications, such as titrations, spectroscopy, or chromatography.

• High purity
• High batch consistency
• Detailed specifications
• Good price-performance ratio

Acids in p.a. quality enable reproducible and reliable results, which are essential in chemical analysis. They form the foundation for work in research, development and quality assurance.

• High purity
• High batch consistency
• Detailed specifications
• Good price-performance ratio

The Wöhlk reaction is a classic amino test for aldoses (glucose, galactose, lactose, maltose) – it is used to distinguish between aldoses and ketoses and is particularly useful for determining glucose in urine samples. With a few drops of potassium hydroxide solution, known as Wöhlk-Malfatti test; with methylamine instead of ammonia, also known as Fearon’s test.

Reagents required: 10% ammonia solution, sodium hydroxide, hydrochloric acid, diluted, optional

Application: The aldose (such as glucose) reacts with ammonia in an alkaline solution. This results in the formation of an aldimine (reaction of the aldehyde group with ammonia). Subsequent rearrangement produces a coloured amine derivative, often with a red-violet colour.