39=
The results obtained at 198" with the OV-17 stationary phase are comparable with those obtained at lower temperatures with the mixed phase QF-I + DC-zoo; however OV-17 often permits one to obtain better separations. For example, it is superior for the four BHC isomers, for the methyl ester of some herbicides, and for compounds of the DDT series; however, the dieldrin/+,$'-DDE separation is not satisfactory at rgS" whereas it is at 175" (Table ).
The use of OV-,17 as a stationary phase has contributed to the solution of some of the problems in pesticide residue analysis, for example, the systematic analysis of pesticides in water (to be published). The pesticides are first separated into four groups, and the components of the first two groups are separated very well on the column with OV-17 (Figs. and).
In addition, excepting for dimethoate, paraoxon and methylparaoxon, all the compounds listed in Table are regularly eluted and give symmetrical peaks. There is, however, some disadvantage to this column since larger amounts of substances are necessary to obtain detector responses equivalent to those obtained when using other stationary phases such as the mixed QF-I + DC-200 phase.
This work was carried out with aid from the C.N.R.