Simultaneous determination of seven pesticides in waters using multi-walled carbon nanotube SPE and NACE.

In this work, NACE with UV detection is combined with SPE using multi-walled carbon nanotubes (MWCNT) as stationary phase to determine a group of seven pesticides (pirimicarb, pyrifenox, penconazol, carbendazim, cyromazine, pyrimethanil and cyprodinil) in mineral water samples using ametryn as internal standard. The optimized BGE, consisting of a mixture of MeOH and ACN (1:2 v/v) with 90 mM SDS and 20.5 mM HClO(4), was satisfactory to get a good resolution of the seven compounds in less than 13 min. On-line preconcentration was carried out by electrokinetic injection of the sample dissolved in 78:22 v/v MeOH/ACN, 1.11 mM HClO(4). Repeatability was studied for the same day (n=4), for nine different days (n=36) and for four different capillaries. RSD values were appropriate in all cases, i.e. in the range 4.3-9.4% between different capillaries. MWCNT of 10-15 nm od, 2-6 nm id and 0.1-10 mum length were used as SPE materials for the preconcentration of these pesticides from water samples. SPE parameters influencing the enrichment were optimized and the most favorable conditions were as follows: the amount of stationary phase, eluent, sample pH and sample volume were 40 mg MWCNT, 10 mL ACN and 10 mL dichloromethane containing 5% v/v formic acid, pH 8.0, and 750 mL, respectively. Mean recovery values ranged between 53 and 94% for Milli-Q water and between 47 and 93% for mineral waters (RSD values were in the range 2-16%). The method allowed the determination of these pesticides at concentrations below the maximum residue limits established by the European Union legislation (LOD in the range 27-58 ng/L). When the cost, amount and type of the carbon nanotubes used in this work are compared with those carbon nanotubes previously used in the literature it is clear that the proposed materials can be used as economical stationary phases, even cheaper than conventional SPE cartridges.