Experimental design in pesticide extraction methods: A review

Lipid-Based Nanocarriers for Ophthalmic Administration: Towards Experimental Design Implementation

Nanotherapeutics based on biocompatible lipid matrices allow for enhanced solubility of poorly soluble compounds in the treatment of ophthalmic diseases, overcoming the anatomical and physiological barriers present in the eye, which, despite the ease of access, remains strongly protected. Micro-/nanoemulsions, solid lipid nanoparticles (SLN) or nanostructured lipid carriers (NLC) combine liquid and/or solid lipids with surfactants, improving drug stability and ocular bioavailability. Current research and development approaches based on try-and-error methodologies are unable to easily fine-tune nanoparticle populations in order to overcome the numerous constraints of ocular administration routes, which is believed to hamper easy approval from regulatory agencies for these systems. The predictable quality and specifications of the product can be achieved through quality-by-design (QbD) implementation in both research and industrial environments, in contrast to the current quality-by-testing (QbT) framework. Mathematical modelling of the expected final nanoparticle characteristics by variation of operator-controllable variables of the process can be achieved through adequate statistical design-of-experiments (DoE) application. This multivariate approach allows for optimisation of drug delivery platforms, reducing research costs and time, while maximising the understanding of the production process. This review aims to highlight the latest efforts in implementing the design of experiments to produce optimised lipid-based nanocarriers intended for ophthalmic administration. A useful background and an overview of the different possible approaches are presented, serving as a starting point to introduce the design of experiments in current nanoparticle research.

An appraisal of experimental designs: Application to enantioselective capillary electromigration techniques

Enantioresolution processes are vital tools for investigating the enantioselectivities of chiral compounds. An analyst resolves to optimize enantioresolution conditions once they are determined. Generally, optimization is conducted by a one-factor-at-a-time (OFAT) approach. Although this approach may determine an adequate condition for the method, it does not often allow the estimation of the real optimum condition. Experimental designs are conducive for the optimization of enantioresolution methods via capillary electromigration techniques (CETs). They can efficiently extract information from the behavior of a method and enable the estimation of the real optimum condition. Furthermore, the application of the analytical quality by design (AQbD) approach to the development of CET-based enantioselective methods is a trend. This article (i) offers an overview of the application of experimental designs to the development of enantioselective methods from 2015 to mid-2020, (ii) reveals the experimental designs that are presently employed in CET-based enantioresolutions, and (iii) offers a critical point of view on how the different experimental designs can aid the optimization of enantioresolution processes by considering the method parameters.

Determination of benzotriazole and benzothiazole derivatives in marketed fish by double-vortex-ultrasonic assisted matrix solid-phase dispersion and ultrahigh-performance liquid chromatography-high resolution mass spectrometry

Benzotriazoles (BTRs) and benzothiazoles (BTs) are two groups of emerging concern and high production volume contaminants. Via the biomagnification of the food web, they could jeopardize human health. In this work, rapid determining the presence of five BTRs and two BTs in marketed fish was performed by a novel double-vortex-ultrasonic assisted matrix solid-phase dispersion (DVUA-MSPD) and UHPLC-electrospray ionization (+)-quadrupole time-of-flight mass spectrometry detection. Unlike traditional MSPD, we simplified the method without the use of mortar/pestle and SPE-column procedures. The DVUA-MSPD factors were screened by a multilevel categorical design, and then optimized by Box-Behnken Design plus with response surface methodology. The limits of quantification were 0.15-2 ng g^-1 (dry weight). The satisfactory average recovery ranged from 70% to 93% with RSDs less than 9%. The developed method was successfully applied for the rapid determination of selected BTRs and BTs in fish samples at trace-level.

A systematic approach for stability-indicating HPLC method optimization for Nilotinib bulk through design of experiments: Application towards characterization of base degradation products by mass spectrometry

A novel and reliable stability-indicating high-performance liquid chromatography method was developed using design of experiments. Under forced degradation conditions (hydrolysis, oxidative, photolytic and thermal) Nilotinib produced five major degradation products utilizing sodium hydroxide in base hydrolysis. The degradation products were separated by Hypersil ODS column (150×4.6mm i.d., 5μ) utilizing methanol and 10mM ammonium acetate (pH 3.0, adjusted with acetic acid) as mobile phase in gradient elusion mode at a flow rate of 1.2mL/min column temperature set at 35°C and UV detection at 263nm. Tandem mass spectrometry method was used to characterize the base degradation products by accurate mass measurements. The developed method was found to be linear, accurate, precise and selective for the separation of Nilotinib from its degradation products as per the International Conference on Harmonisation guidelines. The structures of the degradation products have been elucidated, of which three degradation products were reported for the first time.

Optimization of double-vortex-assisted matrix solid-phase dispersion for the rapid determination of paraben preservative residues in leafy vegetables

The extensive use of preservatives during the growth, transport and storage of vegetables has been a concern because of their known or suspected toxicity that jeopardizes human health. This paper reports the development of a technique that rapidly determines the presence of five paraben preservative residues in leafy vegetables using double-vortex-assisted matrix solid-phase dispersion (DVA-MSPD) and UHPLC-electrospray ionization(-)-quadrupole time-of-flight mass spectrometry detection. We simplified the original MSPD technique by eliminating the use of mortar/pestle and SPE-column procedures. The DVA-MSPD factors were screened by a multilevel categorical design, and then optimized by Box-Behnken Design plus response surface methodology. The limits of quantification were 1.2-1.8 ng g-1 (dry weight). The satisfactory average recoveries were 85-104% with RSDs less than 10%. The developed method was successfully employed for the rapid determination of selected paraben residues at trace-level in leafy vegetable samples.

Eco-Efficient Green Seaweed Codium decorticatum Biosorbent for Textile Dyes: Characterization, Mechanism, Recyclability, and RSM Optimization

Biosorption using natural waste has emerged as a potential and promising strategy for removal of toxic dyes from wastewaters in comparison to conventional ones. Herein, the Codium decorticatum alga (CDA) was biologically identified and used as a biosorbent for anionic and cationic dyes from aqueous solutions. SEM analysis showed a rough surface with an irregular edge and shape while hydroxyl, amine, sulfur and carboxyl functional groups were identified using FTIR analysis. TGA/DTG confirmed the stability of CDA and the adsorption process. Batch studies were conducted to investigate the effect of operational factors such as initial pH, biosorbent dosage, temperature, initial concentration, and solid/liquid contact time on the biosorption of crystal violet (CV) and Congo red (CR) dyes. For both CV and CR dyes, the biosorption kinetics was accurately described by the pseudo-second-order model and the Langmuir isotherm was found to be best fitted for equilibrium data. Maximum uptake capacities have attained up to 278.46 mg/g for CV and 191.01 mg/g for CR. The CV and CR dye biosorption mechanism was ultimately manifested through the electrostatic interactions. The regeneration study showed that the CDA presents excellent reuse performance up to four consecutive cycles. The process optimization was performed using the response surface methodology based on Box-Behnken design (RSM-BDD). Accordingly, the optimum predicted removal efficiencies using RSM-BBD for CV and CR were obtained, respectively, at 96.9 and 89.8% using a CDA dose of 1.5 g/L, dye concentration of 20 mg/L, pH of 10 for CV, and pH of 4 for CR. Overall, CDA behaves as an efficient, recyclable, cheap, and eco-friendly adsorbent for cleaning-up of dyed effluents.

Sol-gel fabrication and performance evaluation of graphene-based hydrophobic solid-phase microextraction fibers for multi-residue analysis of pesticides in water samples

Widespread use of organophosphorus pesticides poses serious environmental threats, and hence calls for effective analysis methods for these classes of compounds. In this study, a lab-made graphene-based solid-phase microextraction (SPME) fiber was fabricated by the sol-gel method and combined with a gas chromatography-flame photometry detector (GC-FPD) to realize the detection of trace OPPs in water samples. Compared to the commercial fiber coatings, the new sol-gel graphene fiber coatings showed advantages of good durability and solvent resistance, which were attributed to the hydrophobic and antibacterial properties of the functionalized graphene and 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride (QAS). A headspace SPME method in combination with a GC-FPD was established to evaluate the performance of the novel fibers. The proposed method showed a good linear relationship for the eight OPPs (R²≥ 0.9957) in the concentration range of 1 to 1000 μg L^-1, with limits of quantification of 0.11-3.37 μg L^-1 and limits of detection of 0.03-1.01 μg L^-1. Furthermore, the developed method also exhibited good recoveries for the analysis of OPPs both in rainwater and lake water, which demonstrates that this method is an alternative choice for multi-residue analysis of OPPs, and it has the potential for broader applications in the future.

Development of a simple method to quantify fipronil and its intermediates in soil

A simple and reproducible method was developed and validated for simultaneous quantification of the pesticide fipronil and its intermediates fipronil desulfinyl, fipronil sulfone and fipronil sulfide, in soil. The analytes were extracted by ultrasonic bath and the ratio of solvents (hexane/acetone), number and time of cycles were optimized by Box-Behnken design with a triplicate central point. The optimal extraction conditions were achieved through a response surface analysis. The clean-up step was conducted by cartridges of solid phase extraction (SPE) containing silica (Florisil®) and aluminum oxide. Gas chromatography with electron capture detection (GC-ECD) was employed for separating fipronil and its intermediates with a suitable resolution and runtime of 20 minutes. The best quantification was achieved with 1 : 1 (v/v) acetone/hexane and 2 ultrasound cycles of 15 minutes each. The recovery values were between 81 to 108%, with relative standard deviation (RSD) lower than 6%, with no effect of the used matrix. Analytical curves presented regression coefficients values above 0.9908 for a concentration range from 0.005 to 0.6 μg g-1. Limits of detection (LOD) from 0.002 to 0.006 μg g-1 and limits of quantification (LOQ) from 0.006 to 0.020 μg g-1 were reached for all analytes. This method can be used to monitor and quantify fipronil and its intermediates in soil.

Development of selective preconcentration/clean-up method for imidazolinone herbicides determination in natural water and rice samples by HPLC-PAD using an imazethapyr imprinted poly(vinylimidazole-TRIM)

The development of a novel molecularly imprinted solid-phase extraction (MISPE) method for simultaneous preconcentration of imazapyr (IMP), imazapic (IMZ) and imazethapyr (IMT) with determination by HPLC-PAD (High performance liquid chromatography - photodiode-array detector) is proposed. The polymer synthesis was performed using imazethapyr as template molecule and 1-vinylimidazole as functional monomer. The method is based on preconcentration of 100.0 mL of sample through 200.0 mg of molecularly imprinted poly(vinylimidazole-TRIM) (MIP-1VN) at pH 4.0, followed by elution with 2.0 mL of MeOH:CH₂Cl₂:HAc (34:62:4, v/v). The range of analytical curve (0.29-200.0, 0.21-200.0 and 0.15-200.0 µg L^-1), limits of detection (0.09, 0.06 and 0.04 µg L^-1) and preconcentration factors (92, 96 and 98) determined for the herbicides, IMP, IMZ and IMT, respectively, were greatly superior when compared with those ones obtained with commercial adsorbents. The analytical method was successfully applied to spiked surface water and rice samples with good results of recovery values (86-107%).

Reuse and recycle solutions in refineries by ozone-based advanced oxidation processes: A statistical approach

Fresh water sources are under pressure globally by the increasing population and consequently increasing production, which increases the water demand day by day. Thus, decreasing the industrial fresh water demand and wastewater production became crucial both for the water availability in the future and for its impact to the environment. This study examined the ozone-based treatments as the possible solution to a refinery to treat the effluent already treated by the traditional techniques to reach the final requirements for reuse and recycle purposes. The screening tests performed by fractional factorial design revealed that the significant parameters for the treatment were ozone feed ratio, H₂O₂ amount and processing time while pH was found insignificant for this case. Based on the box-Behnken response surface methodology for effluent collected after biological treatment, the significant parameters were optimized as the ozone ratio of 0.9 g/h, H₂O₂ amount of 47 mg/L and 60 min duration. However, in case of increasing the H₂O₂ amount to 80 mg/L the duration can be minimized to 37.5 min decreasing the energy and reagent consumption costs by a 37%, reaching a final total organic carbon (TOC) under 4 mg/L, that is the target for reuse possibilities.

Analytical protocol for determination of endosulfan beta, propham, chlorpyrifos, and acibenzolar-s-methyl in lake water and wastewater samples by gas chromatography-mass spectrometry after dispersive liquid-liquid microextraction

This study describes the development of a sensitive and accurate dispersive liquid-liquid microextraction strategy for the preconcentration and determination of selected pesticides in wastewater and lake water samples by gas chromatography-mass spectrometry. Determination of these pesticides at high accuracy and precision is important because they can be still be found in environmental samples. The type of extraction solvent and type of disperser solvent were optimized using the univariate approach. Furthermore, a Box-Behnken experimental design was used to set up a working model made up of 18 combinations of three variables, tested at three levels. The parameters fitted into the design model were volume of extraction solvent, disperser solvent volume, and mixing period. Analysis of variance was used to evaluate the experimental data to determine the significance of extraction variables and their interactions, before selecting optimum extraction conditions. The method was then applied to aqueous standard solutions between 2.0 and 500 μg L^-1, and the limit of detection (LOD) and quantification (LOQ) values obtained for the analytes were between 0.37-2.8 and 1.2-9.4 μg L^-1, respectively. The percent recoveries were calculated in the range of 92-114 and 96-110% for wastewater and lake water, respectively. These results validated the accuracy and applicability of the method to the selected matrices.

Simultaneous Determination of Pesticides and Veterinary Pharmaceuticals in Environmental Water Samples by UHPLC–Quadrupole-Orbitrap HRMS Combined with On-Line Solid-Phase Extraction

Pesticides and veterinary pharmaceuticals are used for effective crop production and prevention of livestock diseases; these chemicals are released into the environment via various pathways. Although the chemicals are typically present in trace amounts post-release, they could disturb aquatic ecosystems and public health through resistance development toward drugs or diseases, e.g., reproductive disorders. Thus, the residues of pesticides and veterinary pharmaceuticals in the environment must be managed and monitored. To that end, we developed a simultaneous analysis method for 41 target chemicals in environmental water samples using ultra-high-performance liquid chromatography (UHPLC)–quadrupole-orbitrap high-resolution mass spectrometry (HRMS) coupled with an on-line solid-phase extraction system. Calibration curves for determining linearity were constructed for 10–750 ng∙L−1, and the coefficient of determination for each chemical exceeded 0.99. The method’s detection and quantitation limits were 0.32–1.72 ng∙L−1 and 1.02–5.47 ng∙L−1, respectively. The on-line solid-phase extraction system exhibited excellent method reproducibility and reduced experimental error. As the proposed method is applicable to the monitoring of pesticides and veterinary pharmaceuticals in surface water and groundwater samples acquired near agricultural areas, it allows for the management of chemicals released into the environment.

Mesoporous silica supported orderly-spaced gold nanoparticles SERS-based sensor for pesticides detection in food

In this study, a novel sensor fabricated with compactly arranged gold nanoparticles (AuNPs) templated from mesoporous silica film (MSF) via air-water interface has been confirmed as a promising surface-enhanced Raman scattering (SERS) substrate for detecting trace levels of 2,4-dichlorophenoxyacetic acid (2,4-D), pymetrozine and thiamethoxam. The densely arranged AuNPs@MSF had an average AuNPs size of 5.15 nm with small nanogaps (<2nm) between AuNPs, and exhibited a high SERS performance. SERS spectra of pesticides were collected after their adsorption on the AuNPs@MSF. The results showed that the concentration of 2,4-D, pymetrozine and thiamethoxam gave a good linear relationship with SERS intensity. Moreover, the designed SERS-based sensor (AuNPs@MSF) was stable for 3 months with ca. 3% relative standard deviation (RSD) and was applied successfully for the analysis of 2,4-D extraction from both environmental and food samples. The proposed SERS-based sensor was further validated by HPLC and showed satisfactory result (p > 0.05).

Electrochemical mineralization of uric acid with boron-doped diamond electrode: Factor analysis and degradation mechanism

In the present study, the mineralization performance and pathway of uric acid (UA) on boron-doped diamond (BDD) anodes were investigated. The oxidation behavior of UA on BDD surface was firstly tested through cyclic voltammetry measurements. The individual and joint effects of four quantitative parameters (applied current density, NaHCO₃ concentration, NaCl concentration and flow rate) on UA mineralization were then examined with Doehlert experimental design. The results acquired by statistical analysis revealed that NaCl concentration and applied current density displayed the most dominant roles on UA degradation, while the influences of NaHCO₃ concentration and flow rate were statistically insignificant. As a result, the following optimal conditions were reached: applied current density of 7.80 mA cm^-2, NaHCO₃ concentration of 6.0 mM, NaCl concentration of 9.0 mM and flow rate of 600 mL min^-1, which gave a TOC decay of 89.4%, a specific energy consumption of 125.36 KWh kg^-1 TOC, a combustion current efficiency of 15.0% and an electrical energy per order of 35.79 KWh m^-3 order^-1 within 30 min of electrolysis. Further results from LC/MS analysis confirmed the ring rupture of UA during the electrolysis, due to the attack of hydroxyl radicals and active chlorine species. Accordingly, two plausible degradation pathways of UA in bicarbonate and chloride media on BDD anode were proposed respectively.

Multivariate response surface methodology assisted modified QuEChERS extraction method for the evaluation of organophosphate pesticides in fruits and vegetables cultivated in Nilgiris, South India

An effective, simple and sensitive analytical method has been developed employing liquid chromatography coupled with tandem mass spectrometry and validated for estimation of five organophosphate pesticides at trace levels in six fruits and twelve vegetables. Plackett-Burman design and central composite design was used to screen and optimize the significant factors in modified QuEChERS (quick, easy, cheap, effective, rugged and safe) extraction method. The method evaluation was done by matrix-matched calibration with linearity ranging from 5 to 500 µg/L with a correlation coefficient more than 0.990. The detection and quantification limit ranged from 0.1 to 1.0 µg/kg and 0.5 to 5 µg/kg, respectively. The mean recoveries were in the range of 76.89-110.30 % with the relative standard deviation less than 13.26% for all pesticides. Further, the method developed was applied to analyze real samples cultivated in the hill areas of Nilgiris, South India.