Abstract A comparative study of two mathematical ap- proaches was performed in order to correct systematic er- rors due to the presence of the unexpected interferences which appear when the quantitation of the analyte in real samples is carried out with calibration curves built using standards in pure solvent. These methods consisted in the establishment of different mathematical expressions which transform the concentration (Cs) obtained using calibra- tion graphs built using pure solvent into the corrected con- centration (C M ) that should be obtained if the quantitation is carried out with calibration curves built using standards dissolved in blank matrix extracts. In the two approaches the correction is performed from the results of an interme- diate precision study which was carried out using both calibration graphs (prepared using pure solvent and blank matrix extract). By using ANCOVA to compare the slope of both solvent-based and matrix-matched calibration graphs, matrix effect was found in the determination of deltamethrin in tomato and acrinathrin in tomato and pep- per. In these cases, both approaches led to good results. Keywords Pyrethroids · Photochemically induced fluorescence · Vegetables · Matrix effect · ANCOVA · HPLC Introduction Although pyrethroid residues in vegetables cause risks to human health and other animal species, they constitute the main alternative to the acutely-toxic organophosphates and carbamates [1]. Actually, pyrethroids are increasingly be- ing used for insect control on greenhouses because of their advantageous environmental properties such as short life and relatively low mammalian toxicity [2] and the compar- atively low application rates required for insect control. In the province of Almería (Spain), one of the main ar- eas of cultivation under plastic of Europe, pyrethroids have been used more and more in recent years. So, of the total number of analyses carried out in the last two years (16,000) in the laboratory CUAM (Almería, Spain), cred- ited by the norms ISO 17025, 22.5% of the pesticides de- tected were pyrethroids. This fact shows the necessity of developing methods for the determination of pyrethroid residues, which can be applied to different commodities. In order to control these pesticides in food, many ana- lytical procedures have been developed. Generally, pyre- throid insecticides are analysed by gas chromatography (GC) [3, 4, 5, 6] and liquid chromatography (LC) [7, 8, 9, 10, 11]. However, in several cases, another substance or substances present in the different matrices analysed af- fect the signal of analytes and, if this effect is not kept in mind, systematic errors (constant and/or proportional er- rors) will affect the results and cause bias [12]. Constant errors are caused by the blank matrix and are independent of the true concentration of the analyte while proportional errors are caused by errors in the calibration. In both cases, errors can be detected using statistical procedures [13, 14] and their importance can be calculated and used in the correction of analytical results. There are several options to correct these systematic errors [15]. The use of standards in blank extracts (matrix- standard calibrations) is the option followed by many in- vestigators and routine laboratories due to the ease of use and effectiveness of the approach to avoid false quantita- tion [16, 17, 18, 19, 20, 21, 22]. However, due to the exis- M. Martínez-Galera · T. López-López · M. D. Gil-García · J. L. Martínez-Vidal · D. Picón-Zamora · L. Cuadros-Rodríguez A comparative study of the correction of systematic errors in the quantitation of pyrethroids in vegetables using calibration curves prepared using standards in pure solvent Anal Bioanal Chem (2003) 375 : 653–660 DOI 10.1007/s00216-003-1752-1 Received: 1 October 2002 / Revised: 10 December 2002 / Accepted: 10 December 2002 / Published online: 13 February 2003 ORIGINAL PAPER M. Martínez-Galera · M. D. Gil-García (✉) · J. L. Martínez-Vidal · D. Picón-Zamora Department of Analytical Chemistry, University of Almería, 04071 Almería, Spain e-mail: mdgil@ual.es T. López-López Laboratory of Pesticide Residues CUAM, 04700 El Ejido, Almería, Spain L. Cuadros-Rodríguez School of Qualimetrics, Department of Analytical Chemistry, University of Granada, Granada, Spain © Springer-Verlag 2003