Determination of Copper in Food and Water by Dispersive Liquid-Liquid Microextraction and Flame Atomic Absorption Spectrometry

Development of two highly sensitive and selective sensor-assisted fluorescence immunoassays for trace determination of copper residues in food samples

This study describes the development of two highly sensitive and selective sensor-assisted fluorescence immunoassays for the trace determination of copper ions, Cu(ii) residues, in food samples. These assays were the microwell-based fluoroimmuoassay (FIA) and the kinetic exclusion assay (KinExA). FIA and KinExA were assisted by a microplate reader and a KinExA™ 3200 immunosensor, respectively. Both FIA and KinExA were developed utilizing the same antibody, capturing reagent, and fluorescence signal-generating reagent. The antibody was a mouse monoclonal antibody, designated as 8D66, that specifically recognized the Cu(ii)-ethylenediaminetetraacetic acid complex (Cu(ii)-EDTA) but did not recognize Cu(ii)-free EDTA. The capturing reagent was Cu(ii)-EDTA covalently linked to bovine serum albumin protein (Cu(ii)-EDTA-BSA). The fluorescence-generating reagent was an anti-mouse IgG conjugated with fluorescein isothiocyanate (IgG-FITC). Both FIA and KinExA involved competitive binding reactions between Cu(ii)-EDTA complexes, formed in the sample solution, and Cu(ii)-EDTA-BSA conjugate which has been immobilized onto microwell fluorescence assay plates (in FIA) or polymethylmethacrylate beads (in KinExA) for a limited quantity of binding sites of 8D66 antibody. The conditions of both FIA and KinExA were investigated, and the optimum procedures were established. Both FIA and KinExA were validated, and all validation parameters were acceptable. Many different metal ions that are commonly encountered in food samples did not interfere with Cu(ii) analysis by both FIA and KinExA. Both assays were applied to the determination of Cu(ii) in food samples with satisfactory accuracy and precision. Both assays were compared favorably with inductively coupled plasma atomic emission spectroscopy. Comparative evaluation of FIA and KinExA revealed that KinExA had higher sensitivity and better precision than FIA, whereas, both assays had comparable accuracy. Both FIA and KinExA were superior to the existing atomic spectrometric methods for Cu(ii). The proposed FIA and KinExA are anticipated to effectively contribute to assessing Cu(ii) concentrations and controlling the exposure of humans to its potential toxicities.

Determination of Ultra-Trace Amounts of Copper in Environmental Water Samples by Dispersive Liquid-Liquid Microextraction Combined with Graphite Furnace Atomic Absorption Spectrometry

A new method of dispersive liquid-liquid microextraction (DLLME) combined with graphite furnace atomic absorption spectrometry (GFAAS) was proposed for the determination of ultra-trace copper. It was based on the reaction of Cu(II) with the laboratory-prepared chelating agent 2-(5-bromo-2-pyridylazo)-5-dimethylaminoaniline (5-Br-PADMA) in a HAc-NaAc buffer solution at pH 5.0 to form stable hydrophobic chelates, which were separated and enriched by DLLME with chlorobenzene (C6H5Cl) and acetonitrile (CH3CN) as extraction and disperser solvents, respectively. The sedimented phase containing the chelates was then determined with GFAAS. Various operating variables that may be affected by the extraction process such as the pH of the solution, the concentration of the chelating agent 5-Br-PADMA, the types and volumes of extraction and disperser solvents, the extraction time, and the centrifugation time were investigated. Under optimum conditions, the calibration curve was linear in the range from 0.02 ng/mL to 0.16 ng/mL of copper with a correlation coefficient of r = 0.9961, and the detection limit was 0.01 ng/mL based on 3Sb. The relative standard deviation for six replicate measurements of 0.05 ng /mL of copper was 3.9%. An enrichment factor (EF) of 110 was obtained. The method has the advantages of low detection limit, high sensitivity, simple operation, less consumption of organic solvents, higher enrichment factor, and environmental friendliness and was applied to the determination of trace copper in environmental water samples with satisfactory results.

Development and Validation of a Method for the Analysis of Zinc Oxide in Cosmetic Matrices by Flame Atomic Absorption Spectroscopy

A fast and simple method for the extraction and Flame Atomic Absorption Spectroscopy (FAAS) quantification of ZnO in different cosmetic matrices, including lipsticks, water-in-oil foundations, and oil-in-water creams, was developed and validated, according to the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) and the United States Pharmacopeial Convention guidelines. The sample preparation consisted of an ultrasound-assisted ethanolic extraction of ZnO followed by digestion with 1 M nitric acid (HNO₃). Samples were analyzed by Flame Atomic Absorption Spectroscopy (FAAS). Specificity, linearity, the limit of detection (LOD), the limit of quantification (LOQ), sensitivity, precision, and accuracy parameters were studied. The robustness of the method was evaluated with a five-variable Youden-Steiner model. The method was specific for ZnO, and the extraction procedure did not affect the stability of the signal compared to the background. The method was linear in the range 0.2-1.0 mg/L with LOD/LOQ values equal to 0.0156 (mg·L^-1)/0.0473 (mg·L^-1), 0.0098 (mg·L^-1)/0.0297 (mg·L^-1), 0.0113 (mg·L^-1)/0.0341 (mg·L^-1), and 0.0131 (mg·L^-1)/0.0397 (mg·L^-1), respectively, for raw material, lipstick, liquid foundation, and emulsion matrices. Regarding precision, the %RSD values were below 3.0% for repeatability and intermediate precision. Global reproducibility RSD was below 8.0% for all matrices. The percentage of recovery was not statistically different from 100% in all cases. The final concentration was found to be a critical variable for all matrices except for the raw material. The variables associated with the extraction step (ethanol volume, bath temperature, and extraction time) were critical in the extraction of liquid foundations and cream emulsions. The method reduces the number and concentration of mineral acids spent on the digestion of ZnO, and its application is extendable to raw materials. This development is an adequate tool for routine analysis and cosmetic quality control of chemically different products that contain ZnO as ultraviolet radiation (UV) filter, to guarantee regulatory compliance and ensure the safety and efficacy of products delivered to consumers.

An accurate and sensitive effervescence-assisted liquid phase microextraction method for the determination of cobalt after a Schiff base complexation by slotted quartz tube-flame atomic absorption spectrophotometry in urine samples

In this study, an accurate analytical method development for cobalt determination in urine samples was described. The method is based on the mass transfer of the target analytes to the organic phase from the aqueous phase by the dispersing extractant throughout the solution with the aid of CO₂ bubbles prior to sample measurement by using a slotted quartz tube flame atomic absorption spectrophotometer. An extractor (1-decanol) dropped effervescent tablet (anhydrous sodium carbonate and sodium dihydrogen phosphate dihydrate mixture) was used in order to separate/preconcentrate cobalt after complexation of cobalt ions in aqueous solution with the Schiff base ligand. The parameters affecting the extraction output such as complexing conditions (pH, ligand concentration, and volume) and extraction conditions (extraction solvent type and volume, extraction temperature, and heating duration, NaOH volume and mixing period) were optimized to lower the detection limit. The limit of detection and quantification values under optimized experimental and instrumental conditions were determined as 3.7 μg L^-1 and 12 μg L^-1, respectively with high linearity with respect to the dynamic range between 15 and 300 μg L^-1. The enhancement factor obtained with the developed method was calculated as 83 fold. The pretreatment process was applied to urine samples in order to test the convenience of the developed method in urine samples for the determination of cobalt at low levels. The high percentage recovery results of 96-97% for four different concentrations of spiked urine samples indicated the proposed method's sufficient sensitivity for analyte determination in such a complex matrix.

Extraction and determination of heavy metals in soil and vegetables irrigated with treated municipal wastewater using new mode of dispersive liquid-liquid microextraction based on the solidified deep eutectic solvent followed by GFAAS

BACKGROUND

In this research, a new extraction method based on dispersive liquid-liquid microextraction and the solidification of deep eutectic solvent has been developed for the determination of heavy metals in soil and vegetables prior to their analysis by graphite furnace atomic absorption spectrometry (GFAAS). In this method, a green solvent consisting of 1-decyl-3-methylimidazolium chloride and 1-undecanol was used as an extraction solvent, yielding the advantages of material stability, low density and a suitable freezing point near room temperature.

RESULTS

Under optimal conditions, enrichment factors are in the range of 114-172. The calibration graphs are linear in the range of 0.02-200 µg kg^-1 and limits of detection are in the range of 0.01-0.03 µg kg^-1 . Repeatability and reproducibility of the method based on seven replicate measurements of 0.80 µg kg^-1 of Hg and 0.20 µg kg^-1 of Pb and Cd in analyzed samples were in the range of 2.3-4.1% and 3.7-6.6%, respectively.

CONCLUSION

A new deep eutectic solvent consists of two parts: 1-decyl-3-methylimidazolium chloride and 1-undecanol in a molar ratio of 1:2. The accuracy of the proposed procedure was also assessed by determining the concentration of the studied metal ions in a polluted farmland soil standard reference material. © 2018 Society of Chemical Industry.

Triethylenetetramine modified multiwalled carbon nanotubes for the efficient preconcentration of Pb(ii), Cu(ii), Ni(ii) and Cd(ii) before FAAS detection

Triethylenetetramine modified multiwalled carbon nanotubes (TETA-MWCNTs) were prepared and used as an efficient adsorbent for the solid phase extraction of heavy metal ions.