Simultaneous Separation and Determination of Thirteen Antibiotics in Soil and Water by High Performance Capillary Electrophoresis with Pretreatment by Solid Phase Extraction

13 antibiotics in soil or water samples were enriched and purified on SPE column and then separated and determined simultaneously by HPCE with UV-spectrometric detector. Soil sample collected should be pretreated according to a definite process to give analytical sample in solid state, from which 4.000 g were taken and extracted thrice with Na₂EDTA 0.8 g and a mixture of mcllvacine buffer and acetonitrile (1+1), using 20.0 mL in each extraction. The extracts (i.e., the supernatants) were combined and filtered through 0.22 μm filtering membrane. The filtrate was diluted with water according to the ratio of volume of the filtrate to water of 1 to 2.5. This solution was ready to be used for SPE treatment. Water sample collected was first filtered through 0.22 μm filtering membrane, and the filtrate was acidified to pH 5.0 with 0.1 mol·L^-1 HCl solution. This water sample solution was ready for SPE treatment. A portion of 150 mL of the soil sample solution or the water sample solution (as obtained above) was passed through HLB SPE column, and the column was rinsed with CH₃OH-H₂O (1+9) to eliminate impurities, and then eluted with 2 mL of a mixture of CH₃OH and CH₃CN (1+1) to elute the antibiotics from the column. The eluate was collected and evaporated to near dryness by N₂-blowing. 300 μL of water were added to dissolve the residue, and the solution was introduced into the HPCE system for electrophoresis. A mixture of (A) pH 9.0 buffer solution composed of 65.0 mmol·L^-1 of borax and 50.0 mmol·L^-1 of boric acid, (B) methyl alcohol and (C) iso-propyl alcohol mixed in the ratio of A:B:C=88:10:2, was used as electrophoretic medium. The 13 antibiotics could be well separated within 25 min under the following conditions, (a) separation voltage:19 kV; (b) column temperature:23℃; (c) pressure of sample introduction:3.45 kPa; (d) time of sample injection:7 s. UV-detection was performed at 210 nm. Linearity ranges for the 13 analytes were obtained all within 150 μg·L^-1. Detection limits (3S/N) found were in the range of 0.40-1.0 μg·L^-1. Tests for recovery were carried out by addition of standard solution to matrixes of blank solutions, values of recovery found were ranged from 78.5% to 107%.