Journal of Chromatography A, 1062 (2005) 285–289 Short communication Liquid chromatography determination of residue levels on apples treated with cetylpyridinium chloride Sergio Rodr´ ıguez-Morales a,b , Xiang Zhou a , Hamid Salari a , Rafael Castillo b , Philip J. Breen a , Cesar M. Compadre a,∗ a Department of Pharmaceutical Sciences, University of Arkansas for Medical Sciences, 4301 West Markham, Slot 522-3, Little Rock, AR 72205, USA b Pharmacy Department, UNAM, Ciudad Universitaria, Mexico DF 04710, Mexico Received 19 March 2004; received in revised form 2 November 2004; accepted 11 November 2004 Available online 8 December 2004 Abstract Cetylpyridinium chloride (CPC) has been found to be effective in reducing microbial contamination in apples. A sensitive and specific HPLC method was developed to determine CPC residues in apples treated with CPC. This method involves ion exchange solid-phase extraction, and the use of stearylpyridinium chloride (SPC) as internal standard. Limit of quantitation, was 0.5 g/ml of CPC for the apple ethanolic extracts. The observed residues in apple (2.35–4.35 g/g of apple) were lower than those previously reported for chicken and beef. The method is specific, sensitive, reproducible and accurate. © 2004 Elsevier B.V. All rights reserved. Keywords: Cetylpyridinium chloride; Apples; Residue levels 1. Introduction The incidence of food poisoning in humans by Escherichia coli O157:H7 is increasingly of concern. This microorgan- ism was first recognized as a cause of food-borne illness in a 1982 outbreak, which was traced to contaminated hamburg- ers [1]. Since then, many other outbreaks of E. coli O157:H7 infections have been associated with contaminated hamburg- ers [2], dry-cured salami [3], mayonnaise [4], drinking wa- ter [5], and unpasteurized commercial apple juice [6]. Apple juice contamination has been traced to apples that had contact with soil and possibly animal feces [7–10]. Previously we have established that cetylpyridinium chlo- ride (CPC, Fig. 1) is effective in reducing bacteria in poultry [11–13] and beef [14] and apples [15]. The U.S. Food and Drug Administration has recently approved the use of CPC to reduce bacterial contamination on poultry. It is in this con- ∗ Corresponding author. Tel.: +1 501 686 6493; fax: +1 501 686 6057. E-mail address: compadrecesarm@uams.edu (C.M. Compadre). text that we have explored the potential of CPC as a chemical rinse to reduce bacteria from contaminated apples. In order to establish the practicality of the use of chemical rinses for mi- crobial decontamination of a particular food, it is necessary to assess the chemical residues produced by the treatment. Recently we reported an HPLC method for measuring the CPC residues that is applicable to beef and chicken carcasses [14,16], where a description of methods for CPC analysis in different matrix was reviewed. Since then, another assay methodology has been described [17] but its suitability and validation on biosurfaces remains to be determined. Addi- tionally, CPC residue analysis of treated vegetables has been performed, but validation of the method was not reported [18]. From the evaluation of CPC residues in beef and chicken tissues [14,16] it is evident that CPC residues levels are strongly influenced by the nature of the treated food surface or tissue. In particular, it has been demonstrated that CPC binds to proteins [19] and fats [14]. Fruits are very rich in carbohy- drates and very low in proteins and fat [20,21]. Thus, in apples 0021-9673/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2004.11.039