Combination of In Situ Surfactant-based Solid Phase Extraction and Central Composite Design for Preconcentration and Determination of Manganese in Food and Water Samples

A review of the use of central composite design in the optimization of procedures aiming at food chemical analysis

Design of experiments is a branch of chemometrics that encompasses the study and application of experimental matrices to study and optimize systems, procedures, and processes to improve their performances. The central composite design (CCD) stands out among the experimental matrices available for this task. This design has been widely applied in various areas of human knowledge due to its flexibility and robustness. This review addresses the use of CCD as a matrix to optimize analytical methods to improve their characteristics in determining analytes in food samples. Its principles and characteristics, its association with the response surface methodology, and recent applications of this matrix in developing analytical methods aimed at food analysis will also be addressed.

In situ Surfactant-based Solid Phase Microextraction of p-cresol in Human Plasma Prior to HPLC Analysis

Background:

Uremia is the outcome of the remaining of nitrogenous waste products that are normally removed by the kidneys. Para-cresol (4-methylphenol) can be regarded as a proteinbound uremic toxin. The p-cresol determination in sera is necessary since it is a marker of cardiovascular risk and overall mortality in hemodialysis patients. Among the reported methods, chromatographic ones especially HPLC techniques due to the high sensitivity, selectivity and reproducibility have been extensively exploited in analysis of p-cresol in complex mixtures. However, an appropriate sample preparation prior to analysis is necessary for obtaining accurate and precise results.

Methods:

In this study, the appropriate precipitating agent for p-cresol determination in plasma samples was investigated. Then, in situ surfactant-based solid phase microextraction followed by HPLCFL detection was developed and validated for the quantification of p-cresol in plasma samples.

Results:

According to the results, HCl/heat precipitation method was used for p-cresol microextraction from from plasma samples. In situ surfactant-based solid phase microextraction using cetyltrimethylammonium bromide as extraction medium was proposed for pretreatment of plasma samples prior to analysis. The separation was achieved by isocratic elution with sodium acetate buffer (pH 3.8) and acetonitrile (20:80, v/v). Linearity was found to be acceptable over the concentration ranges of 0.5 to 8 μg mL-1 with the limit of detection and quantification of 0.324 and 0.422 μg mL-1, respectively. The variations for intra-day and inter-day precisions were both less than 8.2% and the extraction recoveries were more than 97%.

Conclusion:

A validated ISS-SPME followed by HPLC-FL detection reported to determine the total p-cresol concentration of human plasma samples. The traditional liquid-liquid extraction techniques are normally time consuming and require the use of large amounts of toxic organic solvents. In addition, the evaporation of extraction solvent and dissolving the analyte in the mobile phase is commonly used before HPLC analysis. Such a requirement makes the sample preparation process even more tedious and time consuming. ISS-SPME that is the developed ISS-SPE in micro scale, is a simple, rapid and effective sample preparation technique that is appropriate for HPLC-FL analysis.

Performance of metal-organic framework as an excellent sorbent for highly efficient and sensitive trace determination of anthracene in water and food samples

Polycyclic aromatic hydrocarbons are a class of highly toxic and unremitting organic pollutants that are widely distributed in the natural environment. In this work, a metal-organic framework (MOF) designated as HKUST-1 [Cu₃(BTC)₂] was synthesized, characterized, and applied as a solid-phase extraction sorbent for the determination of a trace polycyclic aromatic hydrocarbon, anthracene (Ant) as model compound, in various real samples by spectrofluorimetry. The synthesized MOF exhibited large surface areas and high extraction ability, making it excellent candidate as sorbent for enrichment of trace anthracene. The effects of influential parameters on the performance of the dispersive micro-solid-phase extraction (Dμ-SPE) process, such as the initial anthracene concentration, pH, sorbent dosage, and shaking time, were investigated and optimized by the experiment design method. Under the optimized experimental conditions, good linearity in the range of 3-85 ng mL^-1 with correlation coefficient 0.997 and good sensitivity with low detection limit 0.5 ng mL^-1 for Ant was achieved. The method has been validated in the analysis of real tap water, soft drink, and vegetable juice samples with recoveries in the range of 86.33-103.00% and relative standard deviations in the range of 1.94-3.77%. The as-prepared HKUST-1 was used for at least four times without any obvious decline of extraction capability. The results of this study show the great potential of MOFs as sorbents in Dμ-SPE procedures for the separation and determination of trace Ant in complicated matrices.

Preconcentration of Cu(II), Co(II), and Ni(II) using an Optimized Enrichment Procedure: Useful and Alternative Methodology for Flame Atomic Absorption Spectrometry

In this paper, a new solid phase extraction procedure is described for Cu(II), Co(II), and Ni(II). Silica gel which was coated with N,N'-bis(4-methoxysalicylidene) ethylenediamine (MSE) is used as a sorbent. Three independent variables were optimized using central composite design (CCD) for sorption and elution of metal ions. The optimum values of sorption and elution variables allowed simultaneous preconcentration of the ions in same conditions as follows, for sorption, pH 6.9, flow rate 5.4 mL min(-1), sample volume 50.0 mL, and for elution, flow rate 2.6 mL min(-1), eluent concentration 1.0 mol L(-1), eluent volume 5.0 mL. The detection limits (LOD) were found to be 1.1 µg L(-1) for Cu(II), 7.4 µg L(-1) for Co(II), and 7.5 µg L(-1) for Ni(II) and preconcentration factor was 200 for each of the ions. The accuracy of the method was tested with Lake Ontario water and multi-element standard solution. The proposed method was also applied to various water samples. The proposed method can be alternatively suggested as accurate, precise, easy, and a cheap method for Cu(II), Co(II), and Ni(II) determination.