羟基在吡啶溶液中被邻苯二甲酸酐酯化。多余的邻苯二甲酸酐用中和用氢氧化钠溶液中的水水解。酯化过程中出现的酸度和水解过程中形成的邻苯二甲酸的酸度，在酚酞作为指示剂的情况下，用氢氧化钠溶液中和。羟基值是由用于滴定空白和测试溶液的氢氧化钠溶液体积之间的差值来计算的。

The hydroxyl groups are esterified by phthalic anhydride in pyridine solution. The excess of phthalic anhydride is hydrolyzed with water containing in the sodium hydroxide solution used for the neutralization. The acidity which appears during the esterification and of the phthalic acid formed during the hydrolysis is neutralized by sodium hydroxide solution in the presence of phenolphthalein as indicator. The hydroxyl value is calculated from the difference between the volumes of sodium hydroxide solution used for the titration of the blank and of the test solution.