Thymol, urine preservative

For occupational exposure, it is recommended that urine samples be collected at the end of an 8-hour work shift (ACGIH 1991). Small amounts of thymol can be used as a preservative, and the urine can be stored for 4 days if refrigerated, or at least 3 months if frozen. 

Note Serum samples should be stored in a closed container since otherwise loss of carbon dioxide will occur and will change the pH values, which in turn will affect the calcium assay. Urine samples can be analysed with this slide (ElOl). For this purpose, diluted hydrochloric acid must be added to the urine. It is recommended to collect the urine over 24 hours and to analyse only the total collected sample. Do not use preservative agents such as thymol, citrate, concentrated hydrochloric acid or glacial acetic acid, since these will produce interference. Detailed instructions on the collection procedure are ven in the instrument handbook. 

Note Urine samples must be adjusted before the analysis to pH 3-4 with 6 molar hydrochloric acid. Subsequently the urine sample is diluted 6 fold with deionised water. Glacial acetic acid, concentrated hydrochloric acid, citrate, thymol, toluene, EDTA and fluoride are unsuitable as preservative agents. 

Glacial acetic acid, concentrated hydrochloric acid, toluene, hexameth-ylene-tetramine and boric acid must not be used as preservative agents for urine, since they can lead to increased potassium values, whereas thymol, on the other hand, results in lowered potassium values. 

Thymol was isolated in 1719. In addition to a flavoring agent, it is used to prevent mold and preserve documents, art objects, and urine. It is also a stabilizer for trichloroethylene and halothane. 

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