In the present research, the separation of a series of organophosphorus pesticides (fensulfothion, fenamiphos, profenofos, fonofos, isofenphos, dialifos, sulprofos and prothiofos), by using nano-liquid chromatography (nano-LC) with UV detection is described. Three 100 microm ID capillary columns, packed with different silica-based stationary phases (CN, C(18), and phenyl), were investigated. Among these, the phenyl column offered the best results in terms of chromatographic performance, and was selected for pesticide analyses. Parameters, such as sample dilution solvent, injection volume, mobile phase composition and flow rate, were optimized in order to define the ideal experimental conditions. With the aim of improving sensitivity, on-column focusing of large injection volumes was applied: a sensitivity increase of circa 100-fold was attained, with limits of detection (LODs) and quantification (LOQs) within the 4.4-37.5 and 14.5-125.0 ng/mL ranges, respectively. The method was validated, with satisfactory results, through the measurement of the following parameters: limits of detection and quantification, precision, linearity and recovery. Finally, five different baby foods, previously fortified with a solution of the eight aforementioned pesticides, and then subjected to liquid-liquid extraction and solid-phase extraction clean-up, were analyzed.