Technical mixtures are manufactured by industry in many individual batches using set production conditions. The composition of the mixtures, as is evident from the chromatograms (fingerprints), will be similar but never exactly the same (see below). Sometimes there is a variation in the manufacturing process thereby producing a more radical change in the composition of the product mixture.

This is the case for Aroclors®, technical mixtures of PCBs made by Monsanto during the period of the 1930s through 1977. A certain batch of Aroclor 1254 (54% chlorine by weight) that was being made by chlorinating biphenyls was chlorinated in two stages. Normally this was a single stage process. The resulting product of the two stage manufacturing process was a material containing significantly higher concentrations of the non-ortho substituted congeners, which also happen to be more toxic.

Identifying and quantifying Aroclor 1254 in the environment is confusing to the analyst when they encounter what on the surface appears to be 1254 but on closer examination is quite different.

To prepare you for this AccuStandard (as an exclusive) makes available both types of Aroclor 1254 (Type 1 and Type 2, both with 54% chlorine by weight). The commonly occurring Aroclor 1254 is available as C-254N and C-254S-TYPE1 (C-254S), and is the same as the C-254N and C-254S that you have been obtaining from AccuStandard for the past 16 years. The second type of Aroclor 1254, that was made by a different manufacturing process is available as C-254S-TYPE2.

The same is the case with Aroclor 1221 (21% chlorine by weight) where there are two different types. Type 1 is the one commonly available and contains measurable quantities of certain dichloro- and trichloro- congeners. The peaks found in gas chromatograms attributable to those congeners are absent in Type 2 of Aroclor 1221.