Are there conversion factors to convert other disinfection biproducts (DBP) into equivalent chloroform values?
Conversion factors for DBPs.
To convert DBP species into equivalent chloroform concentrations, use the multipliers given in the table below. The multipliers are molar mass ratios (the molar mass of chloroform divided by the molar mass of the corresponding DBP).
||Analyte Chemical Form
||Molar Mass (g/mol)
||CCl 2 HCOOH
The predominant DBPs formed by chlorination of drinking water are trihalomethanes (THMs). The four trihalogenated compounds that form are: chloroform, bromoform, dibromochloromethane, and dichlorobromomethane. These four compounds are known as the Total Trihalomethanes (TTHMs) group that is regulated under the Safe Drinking Water Act.
Laboratories using Gas Chromatography (GC) or Gas Chromatography Mass Spectrometry (GC/MS) report the individual values for the four THM species. The values are added together to give the total TTHM value that is reportable for compliance monitoring. The three non-chloroform species are converted to equivalent chloroform values and added together. The Hach THM method 10132 does not distinguish between species, but reads out as chloroform.