Chiral resolution of the insecticide fipronil enantiomers and the simultaneous determination of its major transformation products by high-performance liquid chromatography interfaced with mass spectrometry

Simultaneous Determination of Fipronil, Permethrin, and Their Key Related Substances in a Topical Drug Product by a Single Stability-Indicating High-Performance Liquid Chromatography Method

BACKGROUND

The topical veterinary drug product containing fipronil and permethrin provides an effective repellent protection and high insecticidal efficacy for dogs.

OBJECTIVE

The objective of this study was to develop a stability-indicating high-performance liquid chromatography (HPLC) method for simultaneous detection and quantification of fipronil, permethrin, their key degradation products, and butylated hydroxytoluene (BHT) in a topical drug product.

METHOD

The two active ingredients, their degradation products, and the antioxidant (BHT) were separated by a gradient elution on a Phenomenex Kinetex C18 column (150 × 3 mm, 2.6 µm particle size) maintained at 37°C with H2O acetonitrile isopropyl alcohol 85% H3PO4 (65.5 + 32.5 + 4/0.0053, v/v/v/v) as mobile phase A and acetonitrile (100%) as mobile phase B. The flow rate was 0.9 mL/min, and analytes were detected and quantified at 235 nm.

RESULTS

The specificity of the method was demonstrated by adequate separation of fipronil, permethrin, their degradation products, and BHT in the forced degraded finished product. The linearity of the method was demonstrated in the range of 0.2% to 150% of target analytical concentration of both active ingredients and 50% to 150% for BHT. Excellent recoveries of fipronil, permethrin, and BHT in placebo spiked active ingredient solutions in the linearity range showed sufficient accuracy of the method. The LOQ and LOD of the method were determined to be 0.2% and 0.07% of the analytical concentration. A robustness study did not identify any critical parameter that adversely affected the separation and quantification.

CONCLUSIONS

Here, we report the development and validation of a robust, stability-indicating HPLC method for identification and assay of fipronil, permethrin, and BHT, including estimation of fipronil's and permethrin's degradation products in a topical drug product for dogs.

HIGHLIGHTS

The new HPLC method permits the acquisition of data for all analytes of interest for a topical finished drug product containing fipronil, permethrin, and BHT.

Stereoselective analysis of chiral pesticides: a review

Chiral organic pollutants, including pesticides, herbicides, medicines, flame retardants, and polycyclic musk, represent a significant threat to both the environment and human health. The presence of asymmetric centers in the structure of chiral pesticides introduces stereoisomers with distinct distributions, fates, biomagnification capacities, and cytotoxicities. In aquatic environments, pesticides, as persistent/pseudo-persistent compounds, have been detected in substantial quantities, posing severe risks to non-target species and, ultimately, public health through water supply and food exposures. In response to this environmental challenge, stereoselective analytical methods have gained prominence for the identification of pesticide/drug enantiomers in recent years. This review examines the environmental impact of chiral pesticides, emphasizing the distinct biological activities and distribution patterns of their stereoisomers. By highlighting the advancements in liquid chromatography for enantiomeric analysis, the review aims to underscore the urgent need for a comprehensive understanding of these pollutants to facilitate informed remediation strategies and ensure the safer dispersal of chiral organic pollutants in the environment, thereby addressing the potential risks they pose to ecosystems and human health. Future research should focus on developing sustainable and efficient methodologies for the precise analysis of stereoisomers in complex matrices, particularly in sewage water, emphasizing the importance of sewage processing plants in ensuring water quality.

An electrochemical immunosensor based on a carboxylated multiwalled carbon nanotube-silver nanoparticle-chitosan functional layer for the detection of fipronil

Fipronil (FP) is a very effective phenylpyrazole insecticide and is now widely used in agriculture. At the same time, the water and soil in the environment are polluted by FP. For the rapid detection of FP toxicants in food and the environment, we have designed an entirely novel electrochemical immunosensor that employs the combined functionalities of a cMWCNTs-AgNPs-CS-FAb-BSA layer to modify an SPCE by the freeze-drying technique. The high porosity of chitosan (CS) coupled with an excellent electron transfer enabled by the cMWCNTs and AgNPs increased the surface area for anti-fipronil (FAb) antibody immobilization and enhanced the current signal of the immunosensor. Cyclic voltammetry (CV) was applied for the quantitative determination of FP under optimized conditions (0.1 M PBS, pH 7.5, 35 °C incubation temperature, and 40 min incubation duration). The modified electrochemical immunosensor displayed excellent analytical performance, including a wide linear concentration range from 0.1 to 1000 ng mL-1 with a very low limit of detection of 0.021 ng mL-1 and good reproducibility (RSD = 2.58%, n = 6), stability (80.4% sensitivity after 5 days), and selectivity. Not only could the modified electrochemical immunosensor be applied in the FP residue analysis of agricultural products, but the present immobilization strategy can also potentially be applied to different biomolecules.

Rapid discrimination of enantiomers by ion mobility mass spectrometry and chemical theoretical calculation: Chiral mandelic acid and its derivatives

Because R/S-mandelic acids (MA) and their derivatives are critical starting materials or intermediates in the synthesis of chiral drugs, their chirality discrimination is important. In this study, R/S-MA and its derivatives, including R/S-2-phenylpropionic acid (2-PPA), R/S-methoxyphenylaceticacid (MPA), and R/S-2-hydroxy-4-phenylbutyric acid (HPBA), were accurate simultaneous mobility-discriminated by forming diastereomer complexes for the first time, which were obtained by simply mixing with cyclodextrins (α, β, γ-CD) and transition-metal ions (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺). The mass spectra revealed non-covalent diastereomer complexes formed by CD, enantiomers, and metal ions, and ion-mobility spectrometry (IMS) was performed for 109 pairs of complexes. Significant chiral discrimination was observed in the formed diastereomeric complexes, and their separation peak-to-peak resolution (R_p-p) for the enantiomers depended on the transition metal ion type. In most cases, the R_p-p value gradually increases with CD size, with quaternary complexes having the largest R_p-p value. The greatest chiral distinctions of 2-PPA, MA, MPA, and HPBA were obtained by the diastereomeric complex ions of [(2-PPA)(α)₂+Zn²⁺-H]⁺, [(MA)(α)₂+Zn²⁺-H]⁺, [(MPA)₂(β)+Co²⁺-H]⁺, and [(HPBA)(α)₂+Fe²⁺-H]⁺, with R_p-p values of 1.35, 1.57, 1.70, and 0.71, respectively. Furthermore, the favorable conformation and collisional cross section (CCS) value of the different [CD + R/S-MA + Cu-H]⁺ complexes were measured using chemical theoretical calculations to detail their intermolecular interaction, revealing that [α-CD + R/S-MA + Cu-H]⁺ has two favored gas complexes, and the CCS calculated were consistent with the TIMS observed. In addition, R² > 0.99 was obtained for the relative quantification of the chiral enantiomers. Overall, the proposed method provides a promising strategy for distinguishing the enantiomers of MA and their derivatives, with the advantages of simplicity, speed, and accuracy, without the need for complex chemical derivatization or chromatographic separation.