Separation of aryl nitro-compounds by HPLC on monolithic columns
thesisposted on 01.08.2011, 11:30 by Farida Al-Harthy
The project has demonstrated the use of both poly(styrene-divinylbenzene) PS-DVB and silica monolithic columns for the separation of nitro-compounds. Methods were developed with PS-DVB and ODS silica packed columns for the separation of these compounds. The first part of the project was the preparation of the monolithic stationary phases prepared from PS-DVB of (250 μm I.D. × 70 mm) functionalized with methacrylate by in-situ polymerisation. The alkylated PS-DVB then was used successfully for the first time in the separation of three aryl nitro-compounds (2-NA, 1,4-DNB and 4-NT) on micro-HPLC. However, the efficiency of this column was poor N = 318 (4675/m).The second part of the thesis used a commercial column (Chromolith Performance from Merck), with different diameters for the separation of nitro-compounds. Nitrocompounds were analysed on both Chromolith Performance 3 mm I.D. column and Chromolith Performance 4 mm I.D. column by HPLC/UV. Van Deemter plots showed that the 3 mm I.D. column gave higher efficiencies at higher flow rates than the 4.6 mm I.D. column. The plate number was 8216 (H = 0.0121 mm) at a flow rate of 0.4 ml/min (1.0206 mm/sec) and for Chromolith 4.6 mm I.D. it was 9436 (H = 0.0105 mm) at a flow rate of 0.8 ml/min (0.8577 mm/sec). The nitro-compounds analysed in this study were nitroaromatic, nitramines and nitrate esters which are used in the manufacture of explosives. These compounds were analysed for the first time using a Chromolith Performance 3 mm I.D. column on LCMS using both ESI and APCI in negative ionization modes. The sensitivity was higher in the APCI than the ESI mode in terms of higher intensity and lower background noise especially for nitroaromatic compounds. The LC-ESI-MS method was evaluated by injection of samples of pentaerythritol tetranitrate (PETN) in different concentrations. Calibration curves were constructed over the range of 1-1000 pg/μl with a correlation coefficient of (R2 = 0.9986) and with a concentration range between 1-200 ng/μl with a correlation coefficient of (R2 = 0.9971) and were found to be linear. The limit of detection (LOT) for pentaerythritol tetranitrate (PETN) was 5 pg/μl at a signal-to-noise ratio (S/N) of 3:1 and the limit of quantification (LOQ) was 10 pg/μl at a signal-to-noise ratio of 10:1. The applicability of the monolithic column for the LC-ESI-MS method was evaluated by injection of samples of the commercial explosives, P9 and Semtex 1H. The results showed that Semtex 1H contains 35% PETN using calibration curve 1-200 ng/μl and was much higher than in P9 0.0082% using calibration curve 1-1000 pg/μl.