Aplicações

Hydroxyl is an important functional group and knowledge of its content is required in many intermediate and end-use products such as polyols, resins, lacquer raw materials and fats (petroleum industry). The test method to be described determines primary and secondary hydroxyl groups. The hydroxyl number is defined as the mg of KOH equivalent to the hydroxyl content of 1 g of sample.The most frequently described method for determining the hydroxyl number is the conversion with acetic anhydride in pyridine with subsequent titration of the acetic acid released: H3C-CO-O-CO-CH3 + R-OH -> R-O-CO-CH3 + CH3COOH. However, this method suffers from the following drawbacks: - The sample must be boiled under reflux for 1 h (long reaction time and laborious, expensive sample handling) - The method cannot be automated - Small hydroxyl numbers cannot be determined exactly - Pyridine has to be used, which is both toxic and foul-smellingBoth standards, ASTM E1899-08 and DIN 53240-2, offer alternative methods that do not require manual sample preparation and therefore can be fully automated: The method suggested in ASTM E1899-08 is based on the reaction of the hydroxyl groups attached to primary and secondary carbon atoms with excess toluene-4-sulfonyl-isocyanate (TSI) to form an acidic carbamate. The latter can then be titrated in a non-aqueous medium with the strong base tetrabutyl- ammonium hydroxide (TBAOH). The method suggested in DIN 53240-2 is based on the catalyzed acetylation of the hydroxyl group. After hydrolysis of the intermediate, the remaining acetic acid is titrated in a non-aqueous medium with alcoholic KOH solution. The present work demonstrates and discusses an easy way to determine the hydroxyl number according to ASTM E1899-08 or DIN 53240-2 with a fully automated titrimetric system for a great variety of industrial oil samples.

As the determination of the exact content of individual glycerides in fats and oils is difficult and time-consuming, several fat sum parameters or fat indices are used for the characterization and quality control of fats and oils. Fats and oils are not only essential for cooking, they are also an important ingredient in pharmaceuticals and personal care products, such as ointments and creams. Consequently, several norms and standards describe the determination of the most important quality control parameters. This Application Bulletin describes eight important analytical methods for the following fat parameters in edible oils and fats: Determination of water content in accordance with the Karl Fischer method Oxidation stability in accordance with the Rancimat method Iodine value Peroxide value Saponification value Acid value, free fatty acids (FFA) Hydroxyl number Traces of nickel using polarography Special care is taken to avoid chlorinated solvents in these methods. Also, as many of the mentioned methods as possible are automated.

Os poliuretanos são um dos tipos de plástico mais comumente usados. Eles são produzidos pela reação de polióis brutos com isocianatos. Dependendo do material de partida pode ser obtida uma grande variedade de plásticos. A determinação do índice de acidez, do índice de hidroxila e do teor de isocianato desempenha um papel importante na análise de matérias-primas para plásticos. O índice ácido da matéria-prima poliol é geralmente usado no controle de qualidade para garantir a uniformidade entre lotes. Além disso, é usado como fator de correção para calcular o verdadeiro número de hidroxila. Neste Boletim de Aplicação é descrita a determinação do índice de acidez de acordo com ASTM D4662 e ASTM D7253. Uma matéria-prima para poliuretanos são os polióis. Os polióis contêm vários grupos hidroxila. Portanto, o número de hidroxila de uma matéria-prima se correlaciona diretamente com a quantidade de polióis presentes e é, portanto, um importante parâmetro de controle de qualidade. Neste Boletim de Aplicação é descrita a determinação do índice de hidroxila de acordo com ASTM E1899 e DIN 53240-3. Como os polióis reagem estequiometricamente com os isocianatos, o conhecimento do teor de isocianato é um importante parâmetro de qualidade para a produção de poliuretanos. Neste documento é descrita a determinação de acordo com EN ISO 14896 método A, ASTM D5155 método A e ASTM D2572.

O sistema de titulação apresentado pode ser utilizado para a determinação totalmente automatizada do número de hidroxila (HN) de acordo com ASTM E1899 e EN ISO 4629-2. O método permite a determinação de polióis e oxoóleos sem ferver sob refluxo ou outra preparação de amostra e é, portanto, um grande benefício para laboratórios que precisam lidar com um alto rendimento de amostras. As normas EN 15168 e DIN 53240-3 baseiam-se no mesmo método de análise da ASTM E1899.

The hydroxyl number (HN) is an important sum parameter for quantifying the presence of hydroxyl groups in chemicals. As a key quality parameter, it is determined in various substances. For pharmaceutical samples, USP chapter <401> and Ph. Eur. Chapter 2.5.3 describe the determination. However these methods either use toxic pyridine and require refluxing or have long reaction times. In this Application Note, an alternative method according to ASTM E1899 is presented. This method is pyridine-free and does not require refluxing or long reaction times. The determination is performed at room temperature with only a small sample size. The analysis including all preparation steps is performed with a fully automatic OMNIS system. This allows parallel analysis of multiple samples, increasing productivity in the laboratory by 50%.

The hydroxyl number is an important sum parameter for quantifying the presence of hydroxyl groups in a chemical substance. As a key quality parameter, it is regularly determined in various polymers like resins, paints, polyesterols, fats and solvents. Unlinke other standards, ASTM E1899 works pyridine-free and without refluxing at elevated temperatures for a longer time. It is performed at room temperature, requires only a small sample size, is applicable to extremely low hydroxyl numbers (<1 mg KOH/g sample) and can be performed fully automatically. This Application Note describes the potentiometric determination of the hydroxyl number in 1-octanol and polyethylene glycol according to ASTM E1899, EN 15168 and DIN 53240-3. Using the OMNIS DIS-Cover technique all sample preparation steps can be fully automated. Moreover, the use of an OMNIS Sample Robot allows parallel analysis of multiple samples. The average time per analysis for one sample is thus reduced from approximately 24 min to 12 min., increasing productivity in the laboratory considerably.