0 1 2 3 4 5 Time (minutes) 0 1 2 3 4 5 Time (minutes) Diamond Analytics Application Note: DA1000-B Bhupinder Singh 1 ; David S. Jensen 2 ; Andrew J. Miles 2 ; Andrew E. Dadson 2 ; Matthew R. Linford 1 1 Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT-84602, USA 2 Diamond Analytics, 1260 S 1600 W, Orem, UT-84058, USA Introduction Two significant critical pairs 1-3 of acidic herbicides: 2,4-D and MCPA, dichlorprop and mecoprop were separated along with dicamba, which is another important herbicide, on the nanodiamond-based, core-shell, mixed- mode/C 18 4 µm Flare column. The structures of these chemicals are given in Figure 1, where 2,4-D and MCPA, dichlorprop and mecoprop differ by a CH 3 group at the ‘Y’ position of the general structure of the molecules. Figure 1. Structures of 2,4-D (X = Cl, Y = H), MCPA (X = CH 3 , Y = H), dichlorprop (X = Cl, Y = CH 3 ), mecoprop 2,4-D (X = CH 3 , Y = CH 3 ), and dicamba (on right). The performance of the Flare column was compared to commercial C 18 and PFP columns, which showed co-elution of 2,4-D and MCPA, and of dichlorprop and mecoprop. Dicamba, another important acidic herbicide, was present in some of the test mixtures. Results and Discussion EPA-Method 555 was employed with a commercial C 18 column in an attempt to separate mixtures of (a) 2,4-D, MCPA and dicamba, and (b) dichlorprop and mecoprop. Figure 2. Attempted separations on a commercial C 18 column of (a) MCPA, 2,4-D, and dicamba, and (b) dichlorprop and mecoprop. See Separation Conditions 1 below. As shown in Figure 2, the commercial C 18 column was unable to resolve 2,4-D from MCPA and dichlorprop from mecoprop, and dicamba eluted before 2,4-D and MCPA. Because of a previous report that showed the separation of various chlorinated analogues of 2,4-D on a PFP column, but not of 2,4-D Comparison of the Flare Mixed-Mode Column Against Commercial C 18 and PFP Columns for the Separation of Critical Pairs of Acidic Herbicides (a) (b) Dicamba 2,4‐D & MCPA Dichlorprop & Mecoprop