Current Analytical Chemistry - Volume 12, Issue 2, 2016

In recent years, cloud point extraction (CPE) has become widely utilized for separation and preconcentration of trace metals. CPE uses the property of nonionic surfactants in aqueous solutions to create micelles and to become turbid when heated to particular temperature (so-called cloud point temperature). Above this temperature, the micellar solution separates into two phases: a surfactant-rich phase of a small volume, and a diluted aqueous phase (so-called equilibrium solution). Conventional CPE needs to be heated in water bath to realize cloud point phenomenon, which makes the solution turbid. This CPE procedure has many steps, which makes it quite time- and labor-consuming. Recently, researchers constantly looking for ways to improve conventional CPE in order to shorten procedure time and reduce steps needed or to improve selectivity. On the other hand, longer procedures such as the conventional CPE have been proposed to overcome troubles with organic solvents (which are used for the dissolution of the surfactant-rich phase). In this review, articles have been summarized in seven sub-titles including (I) cloud point extraction, (II) displacement cloud point extraction, (III) rapidly synergistic cloud point extraction, (IV) dual cloud point extraction, (V) ultrasound-assisted cloud point extraction, (VI) microwave-assisted cloud point extraction, and (VII) flow-based cloud point extraction.

This paper presents a comparison between a multiple response function (MR) proposed for optimization of analytical strategies involving multi-element determinations with the desirability function D, which was proposed by Derringer and Suich in 1980. The MR function is established by the average of the sum of the normalized responses for each analyte considering the highest value of these. This comparison was performed during the optimization of an spectrometer for quantification of six elements using inductively coupled plasma optical emission spectrometry (ICP OES). Four instrumental factors were studied (auxiliary gas flow rate, plasma gas flow rate, nebulizer gas flow rate and radio frequency power). A (24) two-level full factorial design and a Box Behnken matrix were developed to evaluate the performance of the two multiple response functions. The results found demonstrated great similarity in the interpretations obtained considering the effect values of the factors calculated using the two-level full factorial design employing the two multiple responses. Also a Box Behnken design was performed to compare the applicability of the two multiple response functions in quadratic models. The results achieved demonstrated high correlation (0.9998) between the regression coefficients of the two models. Also the response surfaces obtained showed great similarity in terms of formats and experimental conditions found for the studied factors. Thus, the multiple response (MR) is presented as a simple tool, easy to manipulate, efficient and very helpful for application in analytical procedures involving multi-response. An overview of applications of this function in several multivariate optimization tools as well as in various analytical techniques is presented.

This paper proposes a method for the determination of total selenium in eggs employing hydride generation atomic fluorescent spectrometry (HG AFS). The optimization step of the experimental conditions for quantification of selenium was performed using factorial design and Doehlert matrix involving the factors: pre-reduction time, pre-reducing volume, hydrochloric acid concentration and sodium tetrahydroborate concentration. The procedure of sample preparation was established using a digester block and a reflux system “cold finger” using nitric and hydrochloric acids and oxygen peroxide. Using the optimized conditions, this method allows the determination of selenium using external calibration technique with limits of detection and quantification of 0.04 and 0.13 ng g-1, for a sample mass of 0.2 g. The precision expressed as relative standard deviation is lower than 4.7%, and the accuracy was confirmed by analysis of a certified reference material of oyster tissue furnished by the National Institute of Standards and Technology, and also by development of addition/ recovery tests. The method was applied for determination of total selenium in egg samples of chicken, quail and paw, being that the total selenium content found varied from 0.35 to 0.88 μg g-1. The results achieved by proposed method were compared with those found employing inductively coupled plasma mass spectrometry (ICP-MS). A statistical method demonstrated that there is no significant difference between the results found by two methods.

A method for investigating migration of some of the most widely used polyolefin stabilizers into aqueous and ethanolic simulants is presented. Main advantage of the proposed approach is that concentrations down to 0.05 μg L-1 (Irganox 1010 and Irganox 1076) – 0.1 μg L-1 (Irgafos 168 and Irgafos 168ox) can be determined without any additional pre-concentration step. This is achieved via direct injection of 1000 μl of simulant onto the HPLC column. Due to the reduced number of working steps of the proposed protocol, this approach also helps to minimize the risk of contamination via contact with plastic material employed during analysis such as pipette tips or plastic SPE-cartridges. Large volume injection with either UV or MS2 detection allowed the sensitive determination of the selected stabilizers in food contact materials, whereby MS2 (employing electrospray ionization in the positive ion mode, nitrogen as collision gas and collision energies between 22 and 80V) provided slightly better LOD values. Migration of the selected stabilizers from polyolefin-based foils used for food storage and food processing into simulants could be verified down to levels of less than 10 ng per cm2 of foil.

Objective: The aim of this study was to prepare and assess the solubilization and antitumor activity of oleanolic acid lysinate. Methods: Oleanolic acid lysinate was prepared as a potential antitumor pro-drug by co-grinding or rotary evaporating method. Characterization of oleanolic acid lysinate was achieved by X-ray powder diffraction, infrared spectroscopy, and differential scanning calorimetry techniques. Solubilization of oleanolic acid lysinate was measured by an HPLC method and the antitumor activity was assessed by the MTT method. Results: The results confirmed the formation of oleanolic acid lysinate. The water solubility was increased significantly. The antitumor activity of oleanolic acid lysinate was 9 times on HCT-8 and 8 times on A549 than that of oleanolic acid. Conclusion: The satisfactory water solubility and antitumor activity of oleanolic acid lysinate will be potentially useful for its application as a new pharmaceutical formulation in cancer treatment in the future.

The cyanide anion (CN−) is known to be an extremely toxic anion and can directly lead to the death of human beings in several minutes because it strongly binds cytochrome-c, thereby disrupting the mitochondrial electron-transport chain and causing a decreased oxidative metabolism and oxygen utilization. A colorimetric sensor L1 bearing azosalicylic aldehyde of benzoyl hydrazone was designed and synthesized. The binding property of the sensor L1 with anions such as F−, Cl−, Br−, I−, CH3COO−, H2PO4−, HSO4−, ClO4−, CN− and SCN−, was examined by UV-vis and 1H NMR spectra. The result showed that sensor L1 has behaved good selectivity and high sensitivity for CN− in DMSO/H2O (5:5, v/v) binary solutions. When CN− was added to the solution containing L1, a dramatic color change from colorless to red was observed, while the other anions did not cause noticeable changes. And the detection limits were 1.0×10−5 mol•L-1 and 3.7×10−8 mol•L-1 of CN− from visual color changes and UV-vis spectrum changes respectively. Furthermore, test strips based on sensor L1 were fabricated, and sensor L1 could be served as practical colorimetric sensor to detect CN− for “in-the-field” measurement. In addition, test strips based on L1 were fabricated, which could serve as a practical colorimetric sensor to detect CN− in field measurements or in test kits.

This paper presents a comprehensive statistical evaluation of the conductivity performance of PEDOT/PSS films generated at various spin coating speeds (1000 to 5000 rpm) by correspondence analysis (CA), regression and ANOVA models. Poly(3,4-ethylenedioxythiophene) (PEDOT) is a highly conducting insoluble polymer which, when doped with poly(styrene sulfonic acid) (PSS) in water, results in a dispersion with good film forming properties. Our interest in PEDOT/PSS is in its application as an interfacial layer and gate electrode in organic photovoltaic and organic field effect transistor devices, respectively. The generation of a homogeneous spun-cast layer of PEDOT/PSS over the entire substrate for these intended applications is a function of the spin-coating speed which, in turn, affects the thickness of the film and, consequently, its conductivity measured by the four point probe. From correspondence analysis, we find that only the 1000 rpm spin-coating speed is strongly associated with high thickness and high resistivity (i.e. low conductivity), although further analysis of speeds 2000 - 5000 rpm shows that the spin-coating speed is still associated with the thickness of the films, and subsequently, their conductivities, such that the thinnest and most conductive films result from the highest spin-coating speed (5000 rpm). We also observed the phenomenon of the horseshoe effect from the CA displays and discussed the reasons for not resorting to detrending solutions for dealing with its presence. From multiple and nonlinear regression models, spin-coating speeds 1000 and 2000 rpm were found to produce films of less precise conductivity values as reflected in the absolute value of mean of residuals of nonlinear regression models while more precise and optimal conductivity values are obtained when the films are generated between 3000 and 5000 rpm. The ANOVA models showed that the means of conductivity of films obtained at 1000 rpm is statistically significantly different to those from higher spin coating speeds and that there is no significant difference between the conductivity of films generated using spin coating speeds 2000 and 3000 rpm and between spin coating speeds 4000 and 5000 rpm. Further, the conductivity of films from spin coating speeds 4000-5000 rpm are higher and more precise than those obtained at 2000-3000 rpm. Based on the results of this study, we have standardised conductivity measurements of PEDOT/ PSS films using the four-point probe by spin-coating at 4000-5000 rpm in order to obtain optimal and reproducible conductivity values.

The adsorption and inhibition behaviors of an organic corrosion inhibitor (C12) on the surface of the carbon steel in chloride solution were systematically investigated by using electrochemical measurements. The results indicated that C12 exhibited inhibition and curative effects on the depassivation steel in the presence of chloride. The inhibition efficiency (IE) of C12 was also studied at different temperature. It was seen that the IE was enhanced with an increase in C12 concentration. The Gibbs free energy (ΔG) calculated based on the proposed isothermal adsorption formula for the adsorption process showed that the absorption of inhibitor on steel surface including stably chemisorption. XPS and AFM analyses suggested that after C12 being incorporated, the C12 molecular was tightly adsorbed on the steel surface, resulting in a dense layer formation. This study provides an insight into better understanding of corrosion inhibiting mechanism of C12 in the chloride solution.

The special properties of platinum group of elements (PGE's), particularly platinum, palladium, rhodium, ruthenium, iridium and gold have many applications in anthropogenic activities. The importance of PGE's and gold led to the development of sensitive analytical methods to quantify them in different types of samples. The performance of an axial viewing 40.68 MHz inductively coupled plasma atomic emission spectrometry (ICP-AES) was examined by optimization of the operating conditions. Four parameters which influence the atomization process of the inductively coupled plasma (ICP) were studied, namely the radiofrequency power, the nebulizer gas flow rate, the auxiliary gas flow rate and the liquid uptake flow rate. Response Surface Methodology (RSM) with a Central Composite Design (CCD) and Derringer’s type Desirability Function were employed to construct prediction mathematical models and optimize intensity. Second order polynomials were eventually calculated and their power for prediction was evaluated. Response surfaces and Pareto charts illustrated the effects of each of the examined parameters and also of their interactions on the determination of the six analytes. The Desirability Function was employed for first time in such analytical methodology and proved to be an effective chemometric tool to typical tedious optimization procedures. Furthermore, it limited the necessity to arbitrary compromise the optimum settings for simultaneous multi-elemental, providing thus a reliable solution to this type of problem.

Context: Homocysteine (Hcy) is an amino acid that occurs in the body as an intermediate in the metabolism of methionine and cysteine. Hcyinplasma is a disease risk factor associated with both atherosclerosis and depression. The relation between Hcy balance and complication of atherosclerosis and depression remains unclear. Determination of Hcy in plasma is important and necessary for the research on comorbidities of atherosclerosis and depression. Objective: To establish an LC/ESI-MS/MS method for measuring plasma Hcy levels in rats and to compare plasma Hcy levels in rats exposed to high-fat diet, unpredictable mild stress or its combination. Materials and Methods: Forty rats were randomized into control group, high-fat group (HFD), chronic unpredictable mild stress group (CMS) and CMS+HFD group (n=10 in each group). 8 weeks later, the rats were sacrificed and plasma was collected for determining Hcy by LC/ESI-MS/MS. All data were analyzed by using SPSS13.0 software. Results: Compared to the plasma Hcy levels of control group, neither HFD group nor CMS group had statistical significance. However, CMS+HFD group showed a significantly higher level of plasma Hcy than the other three groups. Conclusions: Only when exposed to both high fat diets and chronic unpredictable mild stress, rats showed a remarkably elevated Hcy level in their plasma, however, when exposed alone to either high fat diet or chronic unpredictable mild stress, rats had a normal Hcy level in their plasma. Our findings indicate that Hcy is increased in comorbidity of atherosclerosis and depression.