Ultra-Fast Analysis of Contaminant Residue from Propolis by LC/MS/MS Using SPE

Transcription

1 Ultra-Fast Analysis of Contaminant Residue from Propolis by LC/MS/MS Using SPE Matthew Trass, Philip J. Koerner and Jeff Layne Phenomenex, Inc., 411 Madrid Ave.,Torrance, CA USA PO _L_2

2 Introduction The rapid growth in the global economy has seen a dramatic increase in food imports from China, which has become a major exporter and consumer of agricultural products. Recent outbreaks of foodborne illnesses and the discovery of contaminated food and feed have generated significant media attention and highlighted the need for improved testing methods and procedures. Potentially harmful contaminants such as fluoroquinolone antibiotics have been found in a number of products intended for human consumption. In some instances the matrix of the contaminated product can make analysis very problematic. One such problematic matrix is propolis, a wax-like substance found in beehives that is used as a traditional medicine, for skin care and for a multitude of other purposes. We describe here a method for the analysis of contaminant residues in propolis, which utilizes liquid-liquid extraction of the resinous propolis matrix followed by SPE to further clean up and concentrate the sample prior to LC/MS/MS analysis.

3 Compound Structure Ofloxacin Norfloxacin Ciprofloxacin Enrofloxacin Difloxacin Sparfloxacin

4 Gemini -NX Ethane cross-linking stabilizes the silica particle, providing resistance to high ph attack while maintaining high efficiency and mechanical strength.

5 Sample Preparation Weigh out 1 g of beeswax propolis and transfer to a 50 ml conical-bottom centrifuge tube. Add 40 ml of methyl tert-butyl ether (MTBE). Shake contents vigorously by hand to mix, and then ultrasonicate for 30 minutes. Invert the tube at 5 minute intervals during the ultrasonication to assist in sample dispersion. Transfer 5 ml of the dissolved beeswax propolis solution to a 15 ml centrifuge tube. Add 5 ml of 10 mm monopotassium phosphate with 2 % trichloroacetic acid (TCA) buffer. Shake the samples for 20 minutes using a mechanical shaker. Centrifuge the suspension for 10 minutes at 4700 rpm at 15 C. Using a Pasteur pipette, transfer the lower fraction to a 15 ml test tube. Reserve the upper organic fraction. Add 5 ml of the monopotassium phosphate with 2 % TCA buffer to the reserved organic fraction from step 5. Shake samples using mechanical shaker for 20 minutes. Centrifuge the suspension for 10 minutes at 4700 rpm at 15 C. Discard the supernatant (including waxy substance in the bi-layer) and combine the aqueous fraction with the aqueous fraction from step 5. The beeswax propolis extract is now ready for SPE.

6 Solid Phase Extraction The extracted beeswax propolis is cleaned up and concentrated using solid phase extraction (SPE) Cartridge: Strata -X 200 mg/6 ml Part No.: 8B-S100-FCH Condition: 4 ml Methanol (1-2 ml/min) Equilibrate: 2 x 4 ml Water (1-2 ml/min) Note: Do not let sorbent run dry Load: 10 ml extracted beeswax propolis sample (1-2 drops/sec) Dry: >10 Hg for 5-10 minutes to remove residual water Elute: 2 x 3 ml 49/49/2 Acetonitile/Methanol/Acetic acid (ca. 1 drop/sec) Dry down: Nitrogen gas at 55 ºC Reconstitute: 0.5 ml of initial mobile phase

7 LC/MS/MS Conditions HPLC conditions: AB SCIEX API 4000 Column: Gemini-NX 3 μm C18 Dimensions: 50 x 2.0 mm Part No.: 00B-4453-B0 Mobile Phase: A: 0.1 % Formic acid in Water B: Methanol Ion source conditions: IS: 4500 TEM: 550 C Gas1: 50 Gas2: 50 Scan Type: MRM MRM conditions: Analyte Gradient: Time (min) B (%) Flow Rate: 0.4 ml/min Injection: 25 μl Temperature: 40 C Retention Time, min Q1 Q3 DP, V CE, V Ofloxacin Norfloxacin Norfloxacin-d5 (IS) Ciprofloxacin Ciprofloxacin-d8 (IS) Enrofloxacin Difloxacin Sparfloxacin

8 Results Figure 1. Representative chromatogram of a 0.5 µg/l extract Intensity, cps 2.2e5 2.1e5 2.0e5 1.9e5 1.8e5 1.7e5 1.6e5 1.5e5 1.4e5 1.3e5 1.2e5 1.1e5 1.0e5 9.0e4 8.0e4 7.0e4 6.0e4 5.0e4 4.0e4 3.0e4 2.0e4 1.0e ,3 4,5 6 7 Analyte list: 1. Ofloxacin 2. Norfloxacin 3. Norfloxacin-D5 4. Ciprofloxacin 5. Ciprofloxacin-D8 6. Enrofloxacin 7. Difloxacin 8. Sparfloxacin min 8 App ID Figure 2. Norfloxacin extracted calibration curve ranging from µg/l Analyte Area / IS Area Analyte Conc. / IS Conc.

9 Figure 3. Ciprofloxacin extracted calibration curve ranging from µg/l Analyte Area / IS Area Analyte Conc. / IS Conc.

10 Experimental Conditions for LC/MS/MS Analysis LC/MS/MS Condition (acid, base, and neutral probes): Column: Kinetex 2.6 µm C18 Dimensions: 50 x 2.1 mm Mobile Phase: A: 0.1 % Formic acid in Water B: 0.1 % Formic acid in Acetonitrile Gradient: A/B (95:5) to (5:95) in 2 min, hold for 0.5 min, equilibrate for 1.5 min Flow Rate: 0.5 ml/min Analysis condition for testosterone: Column: Kinetex 2.6 µm C18 Dimensions: 50 x 2.1 mm Mobile Phase: A: 0.1 % Formic acid in Water B: 0.1 % Formic acid in Acetonitrile A/B (30:70) Flow Rate: 0.5 ml/min

11 Table 2. Absolute recovery for entire extraction process Analyte Average recovery (n=3) Norfloxacin 82 % Ciprofloxacin 85 % Difloxacin 75 % Enrofloxacin 60 % Ofloxacin 61 % Sparfloxacin 72 %

12 Table 3. Quality Control Summary Analyte Expected Concentration Number of Values % CV % Accuracy Norfloxacin Norfloxacin Ciprofloxacin Ciprofloxacin Sparfloxacin Sparfloxacin Difloxacin Difloxacin Ofloxacin Ofloxacin Enrofloxacin Enrofloxacin

13 Results and Discussion Analyzing fluoroquinolones in propolis is problematic since both the analytes and the sample matrix are very hydrophobic. Because both the analyte and matrix are similar, an extended sample preparation procedure is required. Often, additional sample preparation steps can lead to decreased recovery. However, the described protocol acquired very acceptable recoveries ranging from % (Table 2). Following sample preparation, chromatographic separation was achieved using a Gemini-NX column (Figure 1). The run time is less than 3 minutes with baseline or nearly baseline resolution between each of the analytes. MS/MS acquisition in multiple reaction monitoring (MRM) mode provided unique parent/daughter ion combinations for each analyte, allowing for accurate quantitation for any slightly co-eluting peaks. Calibration curves for each of the fluoroquinolones were generated over the concentration range µg/l (Figures 2 & 3). To investigate the accuracy and reproducibility of the method, QC samples were prepared at two concentrations, 1.5 and 7.5 µg/l, in dissolved propolis and multiple replicates analyzed (n=7-8). The results are summarized in Table 3 and demonstrate good reproducibility (% CV) and accuracy.

14 Conclusions Due to the increasing use of antibiotics worldwide, there is a significant risk that products intended for human consumption have been contaminated with compounds such as fluoroquinolones. Therefore, testing for fluoroquinolones and related compounds is becoming more prevalent. When analyzing compounds in a complex matrix such as propolis, a sample cleanup method is important as it reduces the amount of contamination that the LC/MS/MS system is exposed to. SPE with Strata -X in conjunction with the outlined sample preparation method is an effective way of concentrating and cleaning up propolis samples for fluoroquinolones analysis by LC/MS/MS. Chromatographically, the Gemini-NX reversed phase HPLC column gives adequate resolution, allowing for an easily integrated peak with low detection limits. Trademarks Gemini is a registered trademark of Phenomenex, Inc. Strata-X is a trademark of Phenomenex, Inc. API 4000 is a trademark of AB Sciex Pte. Ltd. AB SCIEX is being used under license Phenomenex, Inc. All rights reserved.