ANALYTICAL POCEDURE FOR THE DETERMINATION OF LINCOMYCIN IN HONEY BY LIQUID CHROMATOGRAPHY-MASS SPECTROMETRY

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1 Bull Vet Inst Pulawy 54, , 2010 ANALYTICAL POCEDURE FOR THE DETERMINATION OF LINCOMYCIN IN HONEY BY LIQUID CHROMATOGRAPHY-MASS SPECTROMETRY TOMASZ BŁĄDEK, ANNA GAJDA, MAŁGORZYTA GBYLIK, ANDRZEJ POSYNIAK, AND JAN ŻMUDZKI Department Pharmacology and Toxicology, National Veterinary Research Institute, Pulawy, Poland Received for publication March 4, 2010 Abstract A reliable and sensitive liquid chromatography-electrospray ionisation tandem mass spectrometry analytical method has been developed for the determination of lincomycin in honey samples. After extraction with phosphate buffer by ultrasound, the extracted solution was subjected to the polymeric solid-phase extraction cartridge to remove endogenous compounds. The analysis was carried out on a triple-quadropule tandem mass spectrometer in the multiple reaction monitoring (MRM) mode via electrospray interface operated in positive ionisation modes. The procedure was validated in accordance with the European Commission Decision 2002/657/EC. The mean recovery of the analyte was 80%, with the corresponding intra- and inter-day variation less than 10% and 15%, respectively. Decision limits (CCα) and detection capability (CCβ) were 5.60 and 6.11 µg kg -1, respectively. Key words: honey, lincomycin, liquid chromatography-mass spectrometry. Bacterial diseases of honey bee Apis mellifera may severely decrease the bee population and honey production. Two of the most important bacterial diseases that affect the larvae of the honey bee are American fouldbrood, and European fouldbrood caused by Paenibacillus larvae and Melissococcus pluton, respectively. As a consequence, various treatments have been considered to prevent such diseases including the use of antibiotics. Unfortunately, home-made uncontrolled treatments with these drugs increase the risk that residues can be present in beehive products (mainly honey) and that undesired effects on consumers such as allergic reactions or bacterial resistance can potentially occur. Regulatory agencies have defined maximum residue levels (MRL) for veterinary medicines in various food products (10), but up-to-now no harmonisation related to honey has been defined worldwide. More recently, residues of lincomycin were detected in honey imported into the European Union from China (7). Within the EU, no lincomycin is authorised to be used in apiculture and therefore the detection of such antibacterial compound in honey is indicative of misuse. Consequently, there is an ongoing requirement for the development of suitable methods for the detection of lincomycin in the honey samples. A variety of chromatographic methods has been developed for the determination of lincomycin in animal products (4-6), and some publications describing its determination in honey (1, 3, 9, 11) are available in literature. Some EU countries enforce a tolerable analytical limit of 10 µg kg -1 in unspecified materials, which would include lincomycin residues in honey (1). This paper presents a new and reliable method, developed in our laboratory, for the determination of lincomycin in honey with the use of the liquid chromatography-electrospray ionisation tandem mass spectrometry (LC-MS/MS). The whole procedure was validated in compliance with the requirements of the European Commission Decision 2002/657/EC (2). Material and Methods Reagents and chemicals. All organic solvents were of HPLC grade and all chemicals were of analytical grade. Lincomycin hydrochloride (95% purity) was purchased from Sigma-Aldrich. Strata X (33 µm, 100 mg, 6 ml) solid phase extraction (SPE) columns were obtained from Phenomenex and Oasis HLB (60 mg, 3 ml) were obtained from Waters. Phosphate buffer (0.1 M, ph 9) was prepared by dissolving 17.4 g of dipotassium hydrogen phosphate in 1,000 ml of water, without ph adjustment. Water was deionised (>14 MΩ x cm) in-house by Millipore system.

2 206 Standard solutions. A stock standard of lincomycin (1 mg ml -1 ) in methanol was prepared with a shelf life of 1 month and stored at -20 ºC. The concentration was corrected for purity and salt form. Intermediate solutions of the stock standard were prepared in the same solvent that was used to prepare the stock standard. The appropriate working standard solutions for the fortification were prepared daily by diluting the intermediate standards solutions with methanol, and standard solutions for calibration curve were prepared by dilution with 0.1% formic acid in water. Samples. Honey samples were obtained from different apiaries and were of different types ( black and light ). Before the use, the samples were checked to be free of any residues of antibacterial medicines. These samples were used as negative controls (blanks), and for the preparation of lincomycin-fortified controls. Extraction. A test portion of honey sample (1.0 ±0.01 g) was weighed into a 35 ml polypropylene centrifuge tube, and 10 ml of the dipotassium hydrogen phosphate buffer solution was added. Then, the tube was caped, vortex-mixed for 2 min (Reax top, Heidolph), sonicated to dissolve the honey for 15 min (Sonarex, Bandelin), and centrifuged for 15 min at 4 ºC and at 4,200 x g (Sigma laboratory centrifuge). Clean-up. SPE cartridge was placed on vacuum manifold and conditioned with sequential washing with 5 ml of methanol followed by 5 ml of water and 5 ml of the dipotassium hydrogen phosphate buffer solution. Then, supernatant was loaded into SPE cartridge at a flow rate of approximately 2 ml min -1 with the application of mild vacuum. The bed of cartridge was washed sequentially with 5 ml of the dipotassium hydrogen phosphate buffer solution, 5 ml of water, 5 ml of 5% methanol in water and 5 ml of 30% methanol in water. The rinses were discarded and the analyte was eluted with 6 ml of methanol. The collection tube was placed in water bath maintained at 40ºC and the extract was evaporated to dryness under a gentle stream of nitrogen gas. The residue was finally reconstituted with 0.5 ml of 0.1% of formic acid in water (v/v). LC-MS/MS. An Agilent Series 1100 HPLC system (Agilent Technologies, Germany) was connected to a PE Sciex API 3000 quadrupole mass spectrometer (PE Sciex, Canada). The mass spectrometer was operated in electrospray positive ionisation mode (ESI+), and two multiple reaction monitoring (MRM) transitions were monitored in order to give four identification points in compliance with Decision 200/657/EC (2). The mass spectrometer settings were optimised with direct infusion of working standard solution from a syringe pomp, and with LC-injection. The following mass spectrometer parameters were used: dwell-time ms; resolution Q1 and Q3 - unit; nebuliser gas - 11 psi; curtain gas - 6 psi; collision gas - 10 psi; ion spray voltage - 4,800 V; and temperature - 400ºC. The fragmentation reactions used for monitoring were selected on the basis of their significance in products ion spectra. The Analyst software controlled the LC-MS/MS system and processed the data. The chromatographic separation was performed on a Luna octadecyl (150 x 2.0 mm, 3 µm) (Phenomenex) coupled with octadecyl guard column (2 x 4 mm) (Phenomenex). The mobile phase consisted of solvent A - 0.1% of formic acid in water (v/v) and solvent B - acetonitryle. The elution was performed in an isocratic mode, with 90% of solution A and 10% of solution B. The column was operated at 30 C with a flow rate of 0.2 ml min -1, and the injection volume was 30 µl. Validation protocol. The whole procedure was validated in-house according to the European Decision 657/2002/EC (2). The validation study was performed in terms of specificity, recovery, precision, decision limit (CCα), and detection capability (CCβ). The experiments were carried out on three consecutive days and main parameters were determined for honey samples spiked with lincomycin at concentration levels of 5, 10, and 20 µg kg -1. To evaluate possible interferences encountered in the method, the specificity of methods was verified by analysing 20 different blank samples of each tested honey. For the calibration curves, working standard solutions of the analyte at six concentration levels (0, 5, 10, 20, 30, and 50 µg kg -1 ) were analysed on three different days. The repeatability was determined by fortifying six blank samples at each of three concentration levels 5, 10, and 20 µg kg -1 with lincomycin compounds. The samples were analysed on the same day with the same instrument and the same operators, and the coefficient of variations (CV) was calculated. The within-laboratory reproducibility was determined by fortifying other two sets of blank samples at the same concentration levels of analysed compound as for the repeatability and analysing on two different days with the same instrument and the different operators. The overall CVs were calculated. The percentage recovery was evaluated in the same experiment as repeatability by comparing the mean measured concentration with the fortified concentration of the samples. The CCα and CCβ were determined by the matrix calibration curve procedure. CCα was calculated with a statistical certainty of 1-α (α ), whereas CCβ was calculated with a statistical certainty of 1-β (β ). Results The optimal conditions for the detection and confirmation of lincomycin by mass spectrometry are listed in Table 1. The best product ions were obtained choosing collision energy at the level of 40 V for the first transition 407>126 (detection) and the collision energy at the level of 27 V for the second transition 407>359 (confirmation). Dwell times were 200 ms for the both transitions.

3 207 (a) (b) (c) Fig. 1. Chromatograms (a) lincomycin standard solution at concentration level of 20 ng ml -1, (b) honey sample spiked with lincomycin at concentration level of 10 µg kg -1, (c) blank honey sample.

4 208 Analyte Table 1 Multiple reaction monitoring (MRM) mode for the detection and confirmation of lincomycin RT (min) Precursor (m/z) Products 1/2 (m/z) DP (V) FP (V) CE (V) CXP (V) Ion ratio Lincomycin / /27 8/ RT retention time, DP declustering potential, FP focusing potential, CE collision energy, CXP cell exit potential. Parameters Compound Table 2 Results of validation of analytical procedure for the determination of lincomycin in honey Linear regression equation, (y=ax+b) Results Lincomycin y=0.39x+0.75 Correlation coefficient Linearity (working range), µg kg Decision limit, µg kg Detection capability, µg kg Level of spiked samples, µg kg Recovery, % Repeatability, CV% Reproducibility, CV% The specificity of the procedure is demonstrated by the comparative chromatograms depicted in Fig. 1. The choice of suitable chromatographic conditions allowed eliminating any interferences at the retention time of the investigated analyte. The optimal condition for sample preparation was obtained after comparative studies of different extraction solutions coupled with different SPE cartridges. The preliminary studies indicated that mean recovery of lincomycin from Strata X and Oasis HLB was 80% and 65%, respectively. The cleaning up of the Strata X cartridge followed by the extraction with phosphate buffer (ph 9) was found to be the most effective. The procedure was satisfactory sensitive, the limit of detection was established at the level of 2.5 µg kg -1, and the limit of quantification 5.0 µg kg -1. The whole procedure was validated and results are listed at Table 2. Discussion Sample preparation strategies for the determination of antibacterial compounds in honey involve the isolation with water or buffer solution coupled with clean up with SPE technique. Chemically, lincomycin is a lincoside that has tertiary amine moiety, therefore to suppress ionisation and achieve an acceptable recovery, honey samples are treated with buffer solution with high ph (1, 3, 11). Lincomycin is amenable to SPE using traditional packings (octyl, octadecyl, etc.) giving good recoveries from various matrices (4-6). However, these packings were not found suitable for the cleanup of extracts obtained from honey samples because of the insufficient separation of the analyte from endogenous compounds of matrix. In our preliminary study, we compared clean up efficacy after the use of two polymeric packings: Oasis HLB and Strata X. As it was found, the use of Strata X was more efficient because of the higher recoveries and larger amount of the clean extract. Therefore we decided to use this kind of sorbent for optimisation of the honey sample preparation before analysing lincomycin by LC- MS/MS. The use of Strata X cartridge was previously described (9) for simultaneous determination of lincomycin and sixteen other antibacterial compounds in honey samples. However, the authors of this procedure described the use of water as extraction solution, but water is not too good extractant for lincomycin because of base character of the analyte (recoveries were from 65% to 79%). Additionally, the use of hexane for the elimination of the honey endogenous compounds adsorbed on the column bed can modify recoveries of analytes. In our procedure we applied phosphate buffer (ph 9) for setting lincomycin on bed of cartridge. The

5 209 use of buffers with higher ph did not have statistically influence on recoveries of the analyte from SPE cartridge. In this procedure, two additional washing steps with 5 ml of 5% and 30% methanol in water were used for the separation of the analyte from other compounds adsorbed on the cartridge bed. As it was found, the use of water and methanol-water solutions for washing cleaned SPE sorbents was satisfactory. As it was previously described (1, 3), lincomycin can be eluted with alkalised methanol; however in our procedure, only methanol was used, giving good results. The elimination of alkalised methanol did not have negative effect on recovery of the analyte, and additionally allowed getting more clean eluted solutions. Initial results obtained with the use of classical octyl or octadecyl analytical columns with a variety of eluent conditions generated little to no retention of lincomycin leading to matrix interference. In addition, peak tailing was observed due to interaction between the silanol groups on the surface and positively charged basic compound. This phenomenon is commonly seen with basic compounds on reverse phase column. The use of Luna column increased analyte retention, while reducing or eliminating ionisation enhancement and matrix interference. Even under isocratic conditions, Luna provided excellent retention and separation from matrix components, while providing baseline resolution of lincomycin. Furthermore, the addition of formic acid to the eluent to promote source ionisation increased the overall sensitivity, provided good peak shape, and improved the reproducibility of the analyte retention time. Liquid chromatography coupled with mass spectrometry is rapidly becoming the method of choice for determination of antibiotics residues in foods. As demonstrated in the analytical procedure described herein, LC-MS/MS permits the rapid and sensitive detection of lincomycin in honey samples. The whole procedure was successively validated according to the European Decision 657/2002/EC and included the routine control of the lincomycin residues in honey imported from the third countries. References 1. Adams S.J., Fussell R.J., Dickinson M., Wilkins S., Sharman M.: Study of the depletion of lincomycin residues in honey extracted from treated honeybee (Apis mellifera L.) colonies and the effect of the shook swarm procedure. Anal Chim Acta 2009, 637, Anon.: Commission Decision 2002/657/EC of August 2002 implementing Council Directive 96/23/EC concerning the performance of analytical methods and the interpretation of results. O J 2002, L221, Benetti C., Piro R., Binato G., Angeletti R., Biancotto G.: Simultaneous determination of lincomycin and five macrolide antibiotic residues in honey by liquid chromatography coupled to electrospray ionization mass spectrometry (LC-MS/MS). Food Add Contamin 2006, 23, Chiu M.H., Yang H.H., Liu C.H., Zen J.M.: Determination of lincomycin in urine and some foodstuffs by flow injection analysis coupled with liquid chromatography and electrochemical detection with a preanodized screen-printed carbon electrode. J Chromatogr B 2009, 877, Sin D.W.M., Ho C., Wong Y.C., Ho S.K., Ip A.C.B.: Simultaneous determination of lincomycin and virginiamycin M1 in swine muscle, liver and kidney by liquid chromatography electrospray ionization tandem mass spectrometry. Anal Chim Acta 2004, 517, Sin D.W.M., Wong Y.U., Ip A.C.B.: Quantitative analysis of lincomycin in animal tissues and bovine milk by liquid chromatography electrospray ionization tandem mass spectrometry. J Pharmac Biomed Anal 2004, 34, European Union, Rapid Alert System for Food and Feed (RASFF), archive_en.htm, 8. Hammel Y.A., Mohamed R., Gremaud E., LeBreton M.H., Guy P.A.: Multi-screening approach to monitor and quantify 42 antibiotic residues in honey by liquid chromatography tandem mass spectrometry.j Chromatogr A 2008, 1177, Lopez M.I., Pettis J.S., Smith I.B., Chu P.S.: Multiclass determination and confirmation of antibiotic residues in honey using LC-MS/MS. J Agric Food Chem 2008, 56, Regulation (EC) No. 470/2009 of the European Parliament and of the Council of 6 May 2009 laying down community procedures for the establishment of residue limits of pharmacologically active substances in foodstuffs of animal origin, repealing Council Regulation (EEC) No. 2377/90 and amending Directive 2001/82/EC of the European Parliament and of the Council and Regulation (EC) No. 726/2004 of the European Parliament and of the Council. 11. Thompson T.S., Noot D.K., Calvert J., Pernal S.F.: Determination of lincomycin and tylosin residues in honey using solid-phase extraction and liquid chromatography-atmospheric pressure chemical ionization mass spectrometry. J Chromatogr A 2003, 1020,