Quantitative measurements in continuos-flow HPLC/NMR

Two methods for the quantitative determination of compounds in continuous-flow HPLC/NMR are described. The first method uses an internal standard (caffeine) of known concentration directly mixed into the mobile phase, while with the second method, a known amount of internal standard is injected onto the column during the chromatographic run. The latter method was validated using several nitroaromatic compounds and explosives. Deviations between the injected and calculated amounts of analytes are usually below 10 per cent while the relative standard deviation ranges from 2 per cent in the upper microgram range to 40 per cent at the limit of detection.