Comparison of HPLC-DAD and LC-MS/MS for the determination and validation of pyriproxyfen in water solutions

Abstract

High-performance liquid chromatography with diode array (HPLC-DAD) is a widely method used for the analyses of pyriproxyfen. Although the method has been remarkably improved, tandem mass spectrometry (LC-MS/MS) systems with significant advantages have gradually replaced HPLC-DAD in many analyses. The aim of this study is to evaluate the two methods for linearity, limit of detection (LOD), limit of quantification (LOQ) selectivity and repeatability for the determination of pyriproxyfen in water solutions. Using HPLC-DAD, the obtained LOD was 0.01 μg/ml with the LOQ of 0.03 μg/ml. The linearity was over 0.99 for the concentrations with the repeatability RSD less than 11.7%. The LC-MS/MS method showed high reproducibility. It exhibits linearity for the concentrations with the repeatability RSD less than 12.7%. The obtained LOD and LOQ were 0.1 ng/ml and 1.0 ng/ml, respectively. The HPLC-DAD performed well in terms of various validation parameters, but showed a very high LOD and LOQ compared to LC-MS/MS.

Headnote

Abstract

Pyriproxyfen is an insect growth regulator that affects the physiology of morphogenesis, reproduction and embryogenesis of insects. The molecule of pyriproxyfen bears little resemblance to endogenous insect juvenile hormone (JH), but it affects JH and ecdysteroid titers in a variety of arthropods. High-performance liquid chromatography with diode array (HPLC-DAD) method is a widely used method for the analyses of pyriproxyfen. Although the methods have been remarkably improved, tandem mass spectrometry (LC-MS/MS) systems with significant advantages have gradually replaced HPLC-DAD in many analyses. The aim of this study, was the evaluation of the two methods for linearity, limit of detection (LOD), limit of quantification (LOQ) selectivity and repeatability for the determination of pyriproxyfen in water solutions. Using HPLC-DAD the obtained LOD was 0.01 µg/ml with the LOQ of 0.03 µg/ml. The linearity was over 0.99 for the concentrations from 0.1 to 1.0 µg/ml with the repeatability RSD less than 11.7%. The LC-MS/MS method showed high reproducibility, as evident from the RSD values for intra-day and inter-day variability being 1.0-6.8% and 2.0-7.7%. The LC-MS/MS method exhibits linearity (R2>0.99) for the concentrations from 1.0 to 100.0 ng/ml with the repeatability RSD less than 12.7%. The obtained LOD and LOQ was 0.1 ng/ml and 1.0 ng/ml, respectively. The HPLC-DAD performed well in terms of various validation parameters, but showed a very high LOD and LOQ (considering low concentration level of pyriproxyfen used in mosquito treatment) compared to LC-MS/MS.

Keywords - HPLC-DAD, LC-MS/MS, pyriproxyfen, water solution

1. Introduction

Pyriproxyfen is the ISO common name for 4-phenoxyphenyl (RS)-2-(2-pyridyloxy)propyl ether (IUPAC), wit the structure shown in Figure 1. Pyriproxyfen is an insecticide that belongs to the class of juvenile hormone mimics with the mode of action - suppression of embryogenesis and inhibition of metamorphosis and reproduction in insects [3]. Owing to its mode of action and safety to nontarget organisms, it is classified as unlikely hazardous category by the World Health Organization [14]. Researchers found that pyriproxyfen is a few hundred times more toxic for mosquito larvae, with LC5o=0.011 pg/L and LC90=0.376 pg/L [12] than the most commonly used larvicide temephos. Applied concentration of pyriproxyfen, representative of IGR's, which is sufficient to inhibit the emergence of adult insect genus Aedes, in the research is less than 1 ppb [2, 7, 8, 11]. In addition, WHO is committed to its implementation, because the concentration that is sufficient for the inhibition of development of mosquito larvae does not affect the quality of drinking water even if it is found in it [13].

High-performance liquid chromatography with diode array (HPLC-DAD) method is a widely used method for the analyses of pyriproxyfen [4-6]. Although the methods have been remarkably improved, tandem mass spectrometry (LC-MS/MS) systems with significant advantages have gradually replaced HPLC-DAD in many analyses, also in the determination of pyriproxyfen [15]. In the literature data the use of ultra performance liquid chromatography - tandem mass spectrometry (UPLCMS/MS) in the analysis of this insecticide can be found [9].

The aim of this study, was the evaluation of the two methods for linearity, limit of detection (LOD), limit of quantification (LOQ) selectivity and repeatability for the determination of pyriproxyfen in water solutions.

2. Material and methods

A. Instrumentation. Agilent 1100 Series HPLC system with Zorbax SB-C18 (5pm, 3.0 x 250 mm) column and DAD. For LC analysis, an Agilent 1200 (Agilent Technologies, USA) HPLC system with a binary pump was used. This was equipped with a reversed-phase C8 analytical column of 150><4.6mm and 5 pm particle size (Agilent Zorbax Eclipse XDB). For the mass spectrometric analysis, an Agilent 6410 Triple-Quad LC/MS system was used. Agilent MassHunter Data Acquisition, Qualitative Analysis and Quantitative Analysis software were applied for method development and data acquisition.

B. Chemicals. The analytical standard of pyriproxyfen of 99.50% purity (Bayer), water of HPLC purity, acetone (GLC-pesticide residue grade, Fisher Chemical, UK), methanol and acetonitrile (HPLC gradient grade, J.T.Backer), HCOOH p.a. (Carlo Erba) were used.

C. Standard solutions. The standard solutions were prepared by dissolving 10 mg ±0.1 of the basic standard in 10 ml of acetone while the working standards were obtained by diluting the basic standard in water. The prepared basic standards were kept in a freezer at -12°C whereas the working solutions were kept in a freezer at 5 °C [10].

D. Instrumentation and chromatographic conditions for HPLC-DAD

The HPLC-DAD conditions were: the mobile phase consisted of water:acetonitrile (70:30 v/v) at 1.0 mL/min, the injection volume 30 pL and the column temperature at 40°C. The detection was carried out at 254 nm.

E. Instrumentation and chromatographic conditions for LC-MS/MS

LC separation was performed on an Agilent 1100 series HPLC system (Agilent Technologies, USA). The system was equipped with a binary solvent pump, an autosampler, and a MS detector coupled with an analytical work station. The MS detector consisted of a multi source that can be configured as APCI (atmospheric pressure chemical ionization) or ESI (electospray ionization). The chromatographyc separation was carried out on a Zorbax Eclipse XDBC18 column (4.6x100 mm; 1.8 pm) protected by a security guard cartridge C18 (4.6x12,5 mm; 5 pm), both from Agilent Technologies, USA. The separation was performed using gradient elution with methanol as mobile phase A, and water as mobile phase B, both containing 0.1% formic acid. Gradient started with 20% B and it was linearly decreased to 5% B in 10 min and held constantly for 2 min. The flow rate was maintained at 0.5 mL/min.

MS analysis was performed in positive ion modes.The ESI source values were as follows: capillary voltage, 3.5 kV; source gas temperature, 325 °C; vaporizer temperature, 220 °C; desolvation gas (nitrogen, 99.99% purity) flow, 5 L/min. The ideal fragmentation conditions were accomplished varying fragmentation and collision energies for pyriproxifen.

F. Validation parameters. The method was validated in according to SANCO/12495/2011 [10].

The detection limit (LOD) was determined as the lowest concentration giving a response of three times the average baseline. The limit of quantification (LOQ) was determined as the lowest amount of a given pesticide giving a response of ten times the average baseline. LOQ was set based on the regulations and confirmed experimentally by spiking the water sample with pyriproxyfen standard so as to obtain the final mass concentration of 0.03 pg/mL for HPLC. The ratio signal/sound in the obtained chromatograms for the LOQ was calculated on the computer and the LOD values were calculated mathematically. The linearity was checked using matrix matched standards (MMS) at concentrations of 0.1, 0.25, O.5., 0.75 and 1.0 pg/mL for HPLC analysis and 1.0, 2.0, 5.0, 10 and 20 ng/mL for LC-MS/MS.

3. Results

The comparison of chromatographic methods for the determination particularly low mass concentrations of pyriproxyfen in water solutions, was ceried out on the basis of the optained basic validation parameters.

A. HPLC-DAD. The linearity was over 0.9984 for the concentrations from 0.1 to 1.0 pg/mL with the was 0.01 pg/mL with the LOQ of 0.03 pg/mL. The retención time of this insecticide is 1.37 min (Figure 2). 0.1 ng/mL and 1.0 ng/mL, respectively B. LC-MS/MS.

Table 1 lists the precursor, product ions and the ratio of abundances among both ion transitions as well as the optimized fragmentation energies and collision energies used for MRM. For the detection of pyriproxyfen the precursor ion was m/z 322.1, the product ions selected m/z werw 185.1 and 96.2 (Table 1). Based on the confirmation of parent ions, at least two product ions should be selected in accordance with relevant EU recommendation 2002/657/EC [1] which corresponds to four identification points (one precursor ion and two product ions). Figure 3

shows a LC-MS/MS chromatogram of pyriproxyfen standard solution concentración 10 ng/mL. The LC-MS/MS method showed high reproducibility as it is evident from the RSD values for intra-day and inter-day variability being 1.0-6.8% and 2.0-7.7%. The LC-MS/MS method exhibits linearity (R2 = 0.9983) for the concentrations from 1.0 to 20.0 ng/mL (Figure 4) with the repeatability RSD less than 12.7%. The obtained LOD and LOQ were repeatability RSD less than 11.7%. The obtained LOD

4. Discussions

Based on the validation parameters LC-MS/MS method with extremely low LOD and LOQ is more reliable compared with HPLC-DAD (<0.001 pg/mL) considering the fact that the applied concentrations of pyriproxyfena could not be detected by this method. The linearity is the same for the both methods (R2 = 0.9984 for the HPLC-DAD and 0.9983 the LCMS/MS). On the other hand, the efficacy of the method which does not decrease by the increase of the flow was taken into account. The principle advantage LC-MS/MS compared with HPLC are a better resolution, nerrow peaks, a higher relation of a signl to noice and the impoved confirmation of the target pesticide. The only advantage of HPLC-DAD is the speed of the analysis it self in wich the retention time of pyriproxyfen is 1.37 min and with LC-MS/MS is 9.11 min which brings obout the decrese of run time.

5. Conclusions

Considering very low concentration level of pyriproxyfen used in mosquito treatment (0.0001 pg/ml), a special treatment of mosquito larvae in water, the use of HPLC-DAD is not an adequate technique. On the other hand the use of LC-MS/MS is justified in such research work. The HPLC-DAD performed well in terms of various validation parameters, but showed a very high LOD and LOQ compared to LC-MS/MS.

6. Acknowledgments

The authors acknowledge the financial support of the Ministry of Education and Science, Republic of Serbia, Project Ref. TR43005.

References

7. References

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