Magnetic graphene oxide modified with choline chloride-based deep eutectic solvent for the solid-phase extraction of protein

Four kinds of green deep eutectic solvents (DESs) based on choline chloride (ChCl) have been synthesized and coated on the surface of magnetic graphene oxide (Fe₃O₄@GO) to form Fe₃O₄@GO-DES for the magnetic solid-phase extraction of protein. X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Fourier transform infrared spectrometry (FTIR), field emission scanning electron microscopy (FESEM) and thermal gravimetric analysis (TGA) were employed to characterize Fe₃O₄@GO-DES, and the results indicated the successful preparation of Fe₃O₄@GO-DES. The UV–vis spectrophotometer was used to measure the concentration of protein after extraction. Single factor experiments proved that the extraction amount was influenced by the types of DESs, solution temperature, solution ionic strength, extraction time, protein concentration and the amount of Fe₃O₄@GO-DES. Comparison of Fe₃O₄@GO and Fe₃O₄@GO-DES was carried out by extracting bovine serum albumin, ovalbumin, bovine hemoglobin and lysozyme. The experimental results showed that the proposed Fe₃O₄@GO-DES performs better than Fe₃O₄@GO in the extraction of acidic protein. Desorption of protein was carried out by eluting the solid extractant with 0.005 mol L⁻¹ Na₂HPO₄ contained 1 mol L⁻¹ NaCl. The obtained elution efficiency was about 90.9%. Attributed to the convenient magnetic separation, the solid extractant could be easily recycled.     

Development of a new strategy for the synthesis of graphene oxide-alumina nanocomposite as an efficient adsorbent for dispersive solid-phase extraction of parabens

The present study investigates the synthesis and application of the graphene oxide-alumina nanocomposite as a new adsorbent for the dispersive solid-phase extraction of three parabens and their determination using high-performance liquid chromatography-ultraviolet detection. The characterization of the synthesized material was accomplished and its size, morphology, chemical composition, porosity, and thermal stability were studied. Application of the proposed strategy for the synthesis of the nanocomposite resulted in the incorporation of Al₂O₃ nanoparticles into graphene oxide nanosheets, further resulting in the exfoliation of graphene oxide nanosheets increasing their surface area. An orthogonal rotatable central composite design was used to optimize the extraction. Under the optimum conditions, the analytical performance of the method showed a suitable linear dynamic range (0.2–100.0 μg/L), reasonable limits of detection (0.03–0.05 μg/L), and preconcentration factors ranging from 128 to 173. Finally, the new validated method was applied for the determination of parabens in some real samples including wastewater, cream, toothpaste, and juice samples with satisfactory recoveries (88%–109%), and relative standard deviations less than 8.7% (n = 3). Results demonstrated that inserting alumina nanoparticles into graphene oxide nanosheets improved the extraction efficiency of parabens, as polar acidic compounds, by providing additional efficient interactions including hydrogen bonding, dipole-dipole, and Brønsted and Lewis acid-base interactions.     

Defluoridation in aqueous solution by a composite of reduced graphene oxide decorated with cuprous oxide via sonochemical

The World Health Organization (WHO) has recommended the fluoride level in drinking water (1.5 mg/L) and defluoridation of water is an essential to remove of fluoride from contaminated water. Hence, the effective and rapid adsorbent Cuprous oxide-reduced graphene oxide (Cu₂O-RGO) composite was developed to overwhelm this concern. Sonochemical approach was adopted for the synthesis of desirable composite which was further characterized by XRD, FTIR, SEM, and EDS. The optimized composite (30 mg) shown the significant adsorption capacity of 34 mg/g of F⁻ solution (pH = 9), 70% removal of F⁻ solution from real experiment and Freundlich model was fitted than Langmuir and Temkin isotherms. The experimental results corroborate that adsorbent is the most effective for removal of fluoride from its polluted water.     

Selective separation and determination of the synthetic colorants in beverages by magnetic solid‐phase dispersion extraction based on a Fe3O4/reduced graphene oxide nanocomposite followed by high‐performance liquid chromatography with diode array detection

A facile adsorbent, a nanocomposite of Fe₃O₄ and reduced graphene oxide, was fabricated for the selective separation and enrichment of synthetic aromatic azo colorants by magnetic solid‐phase dispersion extraction. The nanocomposite was synthesized in a one‐step reduction reaction and characterized by atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X‐ray diffraction and Brunauer–Emmett–Teller analysis. The colorants in beverages were quickly adsorbed onto the surface of the nanocomposite with strong π–π interactions between colorants and reduced graphene oxide, and separated with the assistance of an external magnetic field. Moreover, the four colorants in beverages were detected at different wavelengths by high performance liquid chromatography with diode array detection. A linear dependence of peak area was obtained over 0.05–10 μg/mL with the limits of detection of 10.02, 11.90, 10.41, 15.91 ng/mL for tartrazine, allure red, amaranth, and new coccine, respectively (signal to noise = 3). The recoveries for the spiked colorants were in the range of 88.95–95.89% with the relative standard deviation less than 2.66%. The results indicated that the nanocomposite of Fe₃O₄ and reduced graphene oxide could be used as an excellent selective adsorbent for aromatic compounds and has potential applications in sample pretreatment.     

磁性石墨烯纳米粒子固相萃取与气相色谱-质谱相结合测定环境水样中的三嗪类除草剂

将磁性石墨烯作为磁性固相萃取的吸附剂与气相色谱-质谱(GC-MS)相结合建立了环境水样中7种三嗪类除草剂残留的测定新方法。对影响萃取效率的一些因素如吸附剂用量、萃取时间、样品溶液的pH值、离子强度和解吸条件等进行了优化。在优化的实验条件下,7种三嗪类除草剂的富集倍数在574~968之间。测定西玛津、扑灭津、嗪草酮、西草净、氰草津的线性范围为0.01~10.0 μg/L,莠去津的线性范围为0.05~10.0 μg/L,扑灭净的线性范围为0.01~8.0 μg/L。线性相关系数为0.9968~0.9998,检出限(S/N=3)为1.0~5.0 ng/L。将本方法应用于井水、自来水和湖水等实际水样的分析,在0.5 μg/L和2.0 μg/L下的加标回收率为79.8%~118.3%,相对标准偏差为3.6%~10.5%。该法操作简单、富集倍数高,可满足水样中三嗪类除草剂残留的检测要求。     

Preparation of magnetic chitosan and graphene oxide-functional guanidinium ionic liquid composite for the solid-phase extraction of protein

A series of novel cationic functional hexaalkylguanidinium ionic liquids and anionic functional tetraalkylguanidinium ionic liquids have been synthesized, and then magnetic chitosan graphene oxide (MCGO) composite has been prepared and coated with these functional guanidinium ionic liquids to extract protein by magnetic solid-phase extraction. MCGO-functional guanidinium ionic liquid has been characterized by vibrating sample magnetometer, field emission scanning electron microscopy, X-ray diffraction spectrometer and Fourier transform infrared spectrometer. After extraction, the concentrations of protein were determined by measuring the absorbance at 278 nm using an ultra violet visible spectrophotometer. The advantages of MCGO-functional guanidinium ionic liquid in protein extraction were compared with magnetic chitosan, graphene oxide, MCGO and MCGO-ordinary imidazolium ionic liquid. The proposed method has been applied to extract trypsin, lysozyme, ovalbumin and bovine serum albumin. A comprehensive study of the adsorption conditions such as the concentration of protein, the amount of MCGO-functional guanidinium ionic liquid, the pH, the temperature and the extraction time were also presented. Moreover, the MCGO-functional guanidinium ionic liquid can be easily regenerated, and the extraction capacity was about 94% of the initial one after being used three times.     

Magnetic graphene oxide as adsorbent for the determination of polycyclic aromatic hydrocarbon metabolites in human urine

Detection of monohydroxy polycyclic aromatic hydrocarbons metabolites in urine is an advisable and valid method to assess human environmental exposure to polycyclic aromatic hydrocarbons. In this work, novel Fe₃O₄/graphene oxide composites were prepared and their application in the magnetic solid‐phase extraction of monohydroxy polycyclic aromatic hydrocarbons in urine was investigated by coupling with liquid chromatography and mass spectrometry. In the hybrid material, superparamagnetic Fe₃O₄ nanoparticles provide fast separation to simplify the analytical process and graphene oxide provides a large functional surface for the adsorption. The prepared magnetic nanocomposites were characterized by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and vibrating sample magnetometry. The experimental conditions were optimized systematically. Under the optimal conditions, the recoveries of these compounds were in the range of 98.3–125.2%, the relative standard deviations ranged between 6.8 and 15.5%, and the limits of detection were in the range of 0.01–0.15 ng/mL. The simple, quick, and affordable method was successfully used in the analysis of human urinary monohydroxy polycyclic aromatic hydrocarbons in two different cities. The results indicated that the monohydroxy polycyclic aromatic hydrocarbons level in human urine can provide useful information for environmental exposure to polycyclic aromatic hydrocarbons.     

Nanocomposite of bimetallic nanodendrite and reduced graphene oxide as a novel platform for molecular imprinting technology

In this present work, for the first time, we are reporting a green synthesis approach for the preparation of vinyl modified reduced graphene oxide-based magnetic and bimetallic (Fe/Ag) nanodendrite (RGO@BMNDs). Herein, the RGO@BMNDs acts as a platform for the synthesis of the pyrazinamide (PZA)-imprinted polymer matrix and used for designing of the electrochemical sensor. We have demonstrated how the change in morphology could affect the electrochemical and magnetic property of nanomaterials and for this the reduced graphene oxide-based bimetallic nanoparticle (Fe/Ag) was also prepared It was found that the combination of graphene and bimetallic nanodendrites shows improvement as well as enhancement in the electrocatalytic activity and adsorption capacity, in comparison to their respective nanoparticles. The application of imprinted-RGO@BMNDs sensor was explored for trace level detection of PZA (Limit of detection = 6.65 pg L⁻¹, S/N = 3), which is a drug used for the cure of Tuberculosis. This is lowest detection limit reported so far for the detection of PZA. The sensor is highly selective, cost-effective, simple and free from any interfering effect. The real time application of the sensor was explored by successful detection of PZA in pharmaceutical and human blood serum, plasma and urine samples.     

Metal-organic framework derived magnetic nanoporous carbon as an adsorbent for the magnetic solid-phase extraction of chlorophenols from mushroom sample

In this work, a metal-organic framework derived nanoporous carbon(MOF-5-C) was fabricated and modified with Fe_3O_4 magnetic nanoparticles. The resulting magnetic MOF-5-derived porous carbon(Fe_3O_4@MOF-5-C) was then used for the magnetic solid-phase extraction of chlorophenols(CPs) from mushroom samples prior to high performance liquid chromatography–ultraviolet detection. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and N_2 adsorption were used to characterize the adsorbent. After experimental optimization, the amount of the adsorbent was chosen as 8.0 mg, extraction time as 10 min, sample volume as 50 m L, desorption solvent as 0.4 m L(0.2 mL×2)of alkaline methanol, and sample p H as 6. Under the above optimized conditions, good linearity for the analytes was obtained in the range of 0.8–100.0 ng g~(-1)with the correlation coefficients between0.9923 and 0.9963. The limits of detection(S/N = 3) were in the range of 0.25–0.30 ng g~(-1), and the relative standard deviations were below 6.8%. The result showed that the Fe3O4@MOF-5-C has an excellent adsorption capacity for the analytes.     

Magnetic solid-phase extraction based on Fe3O4/graphene oxide nanoparticles for the determination of malachite green and crystal violet in environmental water samples by HPLC

This work describes a magnetic Fe₃O₄/graphene oxide (GO)-based solid-phase extraction (MSPE) technique for high performance liquid chromatography (HPLC) detection of malachite green (MG) and crystal violet (CV) in environmental water samples. Fe₃O₄/ GO magnetic nanoparticles were synthesised by a chemical co-precipitation method and characterised by scanning electron micrograph, transmission electron microscope, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and surface area analyser. The prepared Fe₃O₄/GO magnetic nanoparticles were used as the adsorbents of MSPE for MG and CV. By coupling with HPLC, a sensitive and cost-effective method for simultaneous determination of MG and CV was developed. The important parameters including the amount of Fe₃O₄/GO, pH of the sample solution, extraction time, salt effect, the type and volume of desorption solvent were investigated in detail. Under optimised conditions, the calibration curves were linear in the concentration range of 0.5–200 μg L^?1, and the limits of detection were 0.091 and 0.12 μg L^?1 for MG and CV, respectively. Finally, the established MSPE-HPLC method was successfully applied to determine MG and CV in environmental water samples with the recoveries ranging from 91.5% to116.7%.     

A new approach to extraction and preconcentration of Ce(III) from aqueous solutions using magnetic reduced graphene oxide decorated with thioglycolic-acid-capped CdTe QDs

In the present study, a nanocomposite consisting of magnetic reduced graphene oxide decorated with thioglycolic-acid-capped CdTe quantum dots (TGA/CdTe QDs/Fe₃O₄/rGO) was synthesised using simple ‘hydrothermal method’ and applied as a nanosorbent for extraction and preconcentration of cerium (Ce)(III) from aqueous solutions prior to inductively coupled plasma-optical emission spectroscopy detection. Under the optimised extraction conditions, the calibration graph for Ce(III) was linear in a concentration range of 0.1–511.0 μg L^?1 with a correlation coefficient of 0.9986. A detection limit of 0.1 μg L^?1 Ce(III) with an enrichment factor of 125 was obtained. Precisions, expressed as relative standard deviation for single-sorbent repeatability and sorbent-to-sorbent reproducibility, were 3.6% and 9.1% (n = 5), respectively. Finally, spiked sea, mineral and tap waters were analysed to evaluate the performance of the proposed method. The high recoveries indicated that the suggested protocol was acceptable for determination of Ce(III) ions in the water samples. The use of QDs and study of their ability for preconcentration of metal ions is an important achievement towards designing novel adsorbents with high efficiency.     

C18 functionalized graphene oxide as a novel coating for solid-phase microextraction

A novel C18 functionalized graphene oxide (GO) coated solid-phase microextraction fiber was prepared by a novel protocol. Based on the strong van der Waals interaction present in GO and abundant oxygenous groups in GO sheets, a simple layer-by-layer self-assembly method was used in the preparation process and then C18 was successfully self-assembled on GO via C-O-Si bonding. Coupled with gas chromatography, extraction performance of the fiber was tested with polycyclic aromatic hydrocarbons (PAHs) as model analytes. The fiber not only exhibited excellent extraction efficiency and selectivity, but also showed many advantages including high rigidity, long service life and well stability toward organic solvent, acidic and alkali solutions, and high temperature. The relative standard deviations for single-fiber repeatability and fiber-to-fiber reproducibility were less than 7.26 and 17.25%, respectively. The detection limits to the PAHs were less than 0.08 μg L(-1) and the calibration curves were linear in a wide range for all analytes. The as-established Solid-phase microextraction GC method was also successfully used for determination of PAHs in two real water samples.     

Effective extraction and simultaneous determination of Sudan dyes from tomato sauce and chili‐containing foods using magnetite/reduced graphene oxide nanoparticles coupled with high‐performance liquid chromatography

A simple, effective, and robust magnetic solid‐phase extraction method was developed using magnetite/reduced graphene oxide nanoparticles as the adsorbent for the simultaneous determination of Sudan dyes (I, II, III, and IV) in foodstuffs. The magnetite/reduced graphene oxide nanoparticles were characterized by X‐ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The extraction parameters including extraction time, elution solution, and elution time and volume were investigated in detail. Such magnetite/reduced graphene oxide nanoparticles based magnetic solid‐phase extraction in combination with high‐performance liquid chromatography and variable wavelength detection gave the detection limits of 3–6 μg/kg for Sudan I–IV in chili sauce, tomato sauce, chili powder, and chili flake samples. The recoveries were 79.6–108% at three spiked levels with the intra‐ and inter‐day relative standard deviations of 1.2–8.6 and 4.5–9.6%, respectively. The feasibility was further performed by a comparison with commercial alumina‐N. This method is suitable for the routine analysis of Sudan dyes due to its sensitivity, simplicity, and low cost.     

The use of graphene as an adsorbent for the extraction of permethrin from urine

A nonmagnetically modified graphene was employed as the adsorbent in the dispersive solid-phase extraction (d-SPE) for the isolation of permethrin from urine samples that were further analyzed by the HPLC/UV method. The following four key factors influencing permethrin extraction efficacy were studied: 1. graphene suspension volume, 2. adsorption time, 3. desorbent (acetonitrile) volume, and 4. desorption time. Under the optimized conditions of the d-SPE (graphene) procedure the main validation parameters of the analytical method were determined as follows: extraction recovery (%) 71.2, 63.5, and 95.4; intra-day repeatability (%RSD) 14.7, 11.5, and 15.2; inter-day repeatability (%RSD) 16.2, 11.9, and 19.1 for 0.125, 0.250, and 1.0 µg/mL permethrin concentration levels, respectively. Limits of detection (LOD) and quantification (LOQ) were 0.045 and 0.125 µg mL^?1, respectively. The proposed method may be useful for the monitoring of permethrin in human urine taken from people dressed in uniforms disinfected with this pesticide.     

Dispersive solid-phase extraction based on mesoporous melamine-formaldehyde polymer for sensitive determination of five chlorinated herbicides residues in water by high-performance liquid chromatography

ABSTRACT

In this work, a low-cost melamine-formaldehyde polymer with large-surface-area mesoporous structure was prepared and applied as an efficient solid sorbent for pre-concentration of five kinds of chlorinated herbicides including fomesafen, atrazine, pyrithiobac-sodium, benazolin and acifluorfene from water samples. Extraction parameters such as pH of the sample solution, amount of mesoporous melamine-formaldehyde polymer (mMFP), extraction time, type of desorption solv-ent and volume of the sample were systematically investigated. Combining dispersive solid-phase extraction with high-performance liquid chromatography (HPLC), the detection limits (S/N = 3) of the five herbicides were ranged from 0.04 to 0.18 μg L^?1 with good linearity (R² ≥ 0.9908). Then the tap water and river water samples were analysed by the developed method, and the obtained results indicated that this method provides acceptable recoveries and precisions. mMFP can be prepared through one-pot catalyst-free polymerisation from low-cost starting materials, so that they could be easily scaled up for the sample pre-treatment and have the powerful potentiality in purification of contaminated water.     

Metal-organic framework-templated synthesis of magnetic nanoporous carbon as an efficient absorbent for enrichment of phenylurea herbicides

Nanoporous carbon with a high specific surface area and unique porous structure represents an attractive material as an adsorbent in analytical chemistry. In this study, a magnetic nanoporous carbon (MNC) was fabricated by direct carbonization of Co-based metal-organic framework in nitrogen atmosphere without using any additional carbon precursors. The MNC was used as an effective magnetic adsorbent for the extraction and enrichment of some phenylurea herbicides (monuron, isoproturon, diuron and buturon) in grape and bitter gourd samples prior to their determination by high performance liquid chromatography with ultraviolet detection. Several important experimental parameters that could influence the extraction efficiency were investigated and optimized. Under the optimum conditions, a good linearity was achieved in the concentration range of 1.0–100.0 ng g⁻¹ for monuron, diuron and buturon and 1.5–100.0 ng g⁻¹ for isoproturon with the correlation coefficients (r) larger than 0.9964. The limits of detection (S/N = 3) of the method were in the range from 0.17 to 0.46 ng g⁻¹. The results indicated that the MNC material was stable and efficient adsorbent for the magnetic solid-phase extraction of phenylurea herbicides and would have a great application potential for the extraction and preconcentration of more organic pollutants from real samples.     

Graphene oxide and reduced graphene oxide as novel stationary phases via electrostatic assembly for open‐tubular capillary electrochromatography

We present here the application of graphene oxide (GO) and reduced graphene oxide (GOOH) sheet as novel stationary phases for open‐tubular CEC (OTCEC) separation based on electrostatic assembly. The inner walls of a bare capillary column was first modified by ionic assembly of poly (diallyldimethylammonium chloride) (PDDA), and then negatively charged GO or GOOH was easily assembled on a positively charged interior walls of the capillary by electrostatic force. Scanning Electron Microscope images showed that GO and GOOH can still maintain sheet‐layer‐like structure when coated onto the capillary via electrostatic assembly. The chromatographic properties of the GO and GOOH coated columns were evaluated via OTCEC separations of various kinds of analytes, including three acid nitrophenol isomers, three basic nitroaniline isomers, and four neutral PAHs. Efficient separations of all the analytes were achieved with optimized buffer pH and organic additive. The reproducibility and stability of the GO or GOOH coated columns were investigated. Our results indicate the capability of application GO or GOOH sheet in OTCEC separation, which can be coated on the inner wall of fused‐silica capillary via electrostatic assembly.     

Evaluation of a magnetic polysulfone microcapsule containing organic modified montmorillonite as a novel solid-phase extraction sorbent with chlorophenols as model compounds

A porous polysulfone microcapsule containing organic modified montmorillonite and magnetic nanoparticles (OMMT-Fe₃O₄@PSF) has been successfully prepared by a phase-inversion method and evaluated as a magnetic solid-phase extraction (MSPE) sorbent for clean-up and enrichment of 4-chlorophenol (4-CP) and 2-chlorophenol (2-CP) in aqueous samples. Compared with a microcapsule containing the conventional extraction sorbent C18 (C18-Fe₃O₄@PSF), OMMT-Fe₃O₄@PSF had much lower cost, a faster adsorption rate, and superior uptake amounts for the investigated analytes. The proposed microcapsule has been developed for the extraction of 4-CP and 2-CP from environmental water samples and their analysis by high-performance liquid chromatography with UV detection (HPLC-UV). Various parameters, such as pH, extraction time, the mass of sorbent, and the desorption conditions, have been evaluated and the calibration curves of the chlorophenols were linear (R² ≥ 0.9985) in the range from 1.01 to 104.5 ng mL⁻¹. The limits of detection at a signal-to-noise (S/N) ratio of 3 were 0.22 and 0.17 ng mL⁻¹ and the limits of quantification calculated at S/N = 10 were 1.52 and 1.07 ng mL⁻¹ for 2-CP and 4-CP, respectively. The recoveries of 2-CP and 4-CP from natural water and the treated wastewater samples were in the range of 84.4-115% with relative standard deviations (RSDs) lower than 7.0%. The results have demonstrated the suitability of the MSPE approach for the analysis of trace chlorophenols in aqueous samples.     

Ionic‐liquid‐functionalized magnetic particles as an adsorbent for the magnetic SPE of sulfonylurea herbicides in environmental water samples

In this paper, a new ionic‐liquid‐functionalized magnetic material was prepared based on the immobilization of an ionic liquid on silica magnetic particles that could be successfully used as an adsorbent for the magnetic SPE of five sulfonylurea herbicides (bensulfuron‐methyl, prosulfuron, pyrazosulfuron‐ethyl, chlorimuron‐ethyl and triflusulfuron‐methyl) from environmental water samples. The main parameters affecting the extraction efficiency such as desorption conditions, sample pH, extraction time and so on, were optimized using the Taguchi method. Good linearities were obtained with correlation coefficients ranging from 0.9992 to 0.9999 in the concentration range of 0.1–50 μg L^?1 and the LODs were 0.053–0.091 μg L^?1. Under the optimum conditions, the enrichment factors of the method were 1155–1380 and the recoveries ranged from 77.8 to 104.4%. The proposed method was reliable and could be applied to the residue analysis of sulfonylurea herbicides in environmental water samples (tap, reservoir and river).     

Carboxylated graphene oxide/polyvinyl chloride as solid-phase extraction sorbent combined with ion chromatography for the determination of sulfonamides in cosmetics

A carboxylated graphene oxide/polyvinyl chloride (CGO/PVC) material was prepared as a sorbent for the selective extraction of sulphonamides from complex sample. After being dispersed in buffer solution, sample was transferred into the prefabricated solid-phase extraction (SPE) column, which integrated extraction and cleanup into one single-step. A multi-response optimization based on the Box-Behnken design was used to optimize factors affecting extraction efficiency. Compared with the commonly commercial sorbents including MCX, WCX and C₁₈, CGO/PVC hybrid material had higher extraction selectivity and capacity to sulphonamides. The limits of detection and quantification for seven target compounds were in the range of 3.4–7.1 μg/L and 11.4–23.7 μg/L, respectively. The self-assembly SPE cartridge was successfully used to enrich seven analytes in anti-acne cosmetics prior to ion chromatography detection with good recoveries of 87.8–102.0% and relative standard deviations of 1.2–6.4%, implying that this method was suitable for routine analysis of cosmetics.