Improvement of EPA method 8330: complete separation using a two-phase approach.

Complete separation of the 14 nitroaromatic and nitramine analytes targeted in EPA Method 8330 was achieved using a 30 x 4.6 mm Bondesil CN guard column in series with a 250 x 4.6 mm Bondesil C18 column (5 microns particles). Consistent with Method 8330 specifications, the mobile phase in the separation was 1:1 methanol:water and the flow-rate was 1.5 ml min-1. The success of this two-phase system proved to be largely a consequence of the unique resolution afforded by the Bondesil C18 column: complete separation of the 14 explosives could not be achieved using other CN/C18 column combinations. Additionally, while Method 8330 calls for a 100-microliter injection loop, separation on the Bondesil CN/C18 system was possible only using a 20-microliter injection loop. The loss of resolution with larger injection volume appears to be a result of the injection solvent, methanol, modifying the composition of the mobile phase both in the CN guard column and in the initial portion of the C18 column. The current method nevertheless represents an improvement over Method 8330, which calls for both a screening and confirming analysis. By separating the 14 Method 8330 analytes in a single run, the two-phase approach can increase sample throughput by decreasing analysis times.