Optimization of Solid-Phase Microextraction Procedure Coupled to GC-ECD for Triazole Fungicides Determination in Juice Samples

A solid-phase microextraction (SPME) procedure followed by gas chromatography electron capture detection (GC/ECD) for the determination of triazole residues was developed. An experimental design with two steps was done. Firstly, a 2(6-2) fractional factorial design for screening several experimental variables (fiber-coating type, extraction temperature, extraction time, stirring rate, desorption temperature, and desorption time) was done. After, a two-factor central composite design for optimizing, the experimental conditions were carried out. The chosen experimental conditions were: fiber, PDMS/DVB; extraction time, 45 min; extraction temperature, 60 A degrees C; desorption time, 3 min; desorption temperature, 260 A degrees C, and stirring speed, 500 rpm. Using those conditions the limits of detection obtained for tetraconazole, myclobutanil, and diniconazole were in the order of few mu g L(-1) in grape and apple liquid extracts. Recoveries were from 93.6% to 112.1%. Relative standard deviation ranged from 1.2% to 11.6% (apple) and 6.7 to 18.0% (grape). The method was applied to five grape samples and 13 apple samples collected in Navarra, Rioja, and Basque Country. Quantification was performed by the standard addition method. Three standard additions by duplicate covering adequate range concentration were used. Myclobutanil was found in three apple samples (110-122 mu g L(-1)) and diniconazole in one grape sample (9.4 mu g L(-1)).