Current Analytical Chemistry - Volume 15, Issue 6, 2019

Background and Objectives: A rapid, simple and environmental friendly supramolecular solvent (SUPRAS) based liquid-liquid microextraction method for preconcentration of ciprofloxacin (CIPRO), danofloxacin (DANO) and enrofloxacin (ENRO) from wastewater was developed. Methods: This microextraction technique was coupled with high-performance liquid chromatography equipped with a diode array detector (HPLC-PDA) for detection and separation of the antibiotics. The SUPRAS composed of decanoic acid and tricaprylymethylammonium chloride. Optimum conditions for the extraction and preconcentration of all the antibiotics were obtained using surface response methodology (RSM) based on Box-Behnken design. Results: Under optimum conditions, the limits of detection (LOD) and limit of quantification (LOQ) ranged from 0.06-0.14 μg L−1 and 0.22-0.47 μg L−1, respectively with the preconcentration factors ranging from 153-241. The linear dynamic ranges were between LOQ and 850 μg L−1 with correlation coefficients ranging from 0.9928 to 0.9999. The intra-day (n = 15) and inter-day (n = 5) precisions (expressed in terms of %RSD) for 50 μg L−1 of CIPRO, DANO and ENRO were in the range of 3.3–4% and 4.1–5.8%, respectively. Conclusion: Lastly, the developed method was used for the extraction, preconcentration and quantification of selected CIPRO, DANO and ENRO in influent and effluent wastewater samples.

Background: In recent times many new uses have been found for nanomaterials that have undergone homogenous immobilization within porous supports. For this paper, immobilization of SNPs on a thiol-functionalized silica monolith using a fast, easy, environmentally friendly and costeffective process was performed. This was achieved by modifying the surface of a silica-based monolith using thiol groups, and then we fabricated green SNPs in situ, reducing an inorganic precursor silver nitrate solution (AgNO3) by employing tangerine peel extract as a reducing reagent, with Ag-thiol bonds forming along the monument. Doing this allows monoliths to be prepared in such a way that, as TEM analysis demonstrated, SNPs are evenly distributed along the rod's length. Once the materials had been fabricated, they were employed as a sorbent by being placed in a centrifuge. The SNP-thiol functionalized silica monolith was then tested using a standard protein (HSA). Methods: The process involves creating monolithic materials by employing a two-part sol-gel technique before modifying the surface of the silica-based monolith using thiol groups for hosting purposes. Homogenous surface coverage was achieved through the use of a non-toxic "green" reducing reagent (tangerine peel extract) to reduce a silver nitrate solution in place to create SNPs joined to the pore surface of a thiol-functionalized silica monolith, employing bonds of Ag-thiol. Once these materials were synthesized, they were classified by utilizing a number of methods based on SEM coupled with EDAX, TEM, AFM and BET analysis. The silica-based monolith, embedded with constructed SNPs, was employed as a sorbent in the preconcentration of human serum albumin (HSA). Results: The performance of the fabricated materials was measured against a silica-based monolith with no SNPs. Also, a silica monolith with constructed SNPs embedded was employed to capture HSA within a sample of human urine mixed with a double detergent concentrate (SDS). Such a monolith containing functionalized SNPs can be a highly effective sorbent for preconcentration of proteins in complex samples. Conclusion: It was shown to have superior performance compared to a bare silica-based monolith. Additionally, it was shown that a monolithic column modified by SNPs could preconcentrate spiked HSA in urine samples.

Background: The unnatural levels of dopamine (DA) result in serious neurological disorders such as Parkinson’s disease. Electrochemical methods which have the obvious advantages of simple operation and low-cost instrumentation were widely used for determination of DA. In order to improve the measurement performance of the electrochemical sensor, molecular imprinting technique and graphene have always been employed to increase the selectivity and sensitivity. Methods: An electrochemical sensor which has specific selectivity to (DA) was proposed based on the combination of a molecular imprinting polymer (MIP) with a graphene (GR) modified gold electrode. The performance and effect of MIP film were investigated by differential pulse voltammetry (DPV) and cyclic voltammetry (CV) in the solution of 5.0 x 10-3 mol/L K3[Fe(CN)6] and K4[Fe(CN)6] with 0.2 mol/L KCl at room temperature. Results: This fabricated sensor has well repeatability and stability, and was used to determine the dopamine of urine. Under the optimized experiment conditions, the current response of the imprinted sensor was linear to the concentration of dopamine in the range of 1.0x10-7 ~ 1.0x10-5 mol/L, the linear sensor was linear to the concentration of dopamine in the range of 1.0x10-7 ~ 1.0x10-5 mol/L, the linear equation was I (μA) = 7.9824+2.7210lgc (mol/L) with the detection limit of 3.3x10-8 mol/L. Conclusion: In this work, a highly efficient sensor for determination of DA was prepared with good sensitivity by GR and great selectivity of high special recognization ability by molecular imprinting membrane. This proposed sensor was used to determine the dopamine in human urine successfully.

Background: The concept of green analytical chemistry prevails due to the growing environmental pollution. Objective: Our attempts are to develop simple and eco-friendly method which is non-harmful to the environment by producing minimal waste. In this context, a green liquid chromatographic method was applied for the simultaneous determination of chlorpheniramine maleate, pseudoephedrine hydrochloride and propyphenazone in their combined dosage form. Methods: Separation was carried out using X select HSS RP C18 analytical column (250 x 4.6 mm, 5μm) using methanol - 0.02 M phosphate buffer pH 3 - triethylamine (60:40: 0.1, by volume) as a mobile phase. The separated peaks were detected at 215 nm at a flow rate 1.0 mL/min. Results: Quantification was done over the concentration ranges of 1-25 μg/mL for chlorpheniramine maleate, 5-35 μg/mL for pseudoephedrine hydrochloride and 10-120 μg/mL for propyphenazone. The suggested method was validated with regard to linearity, accuracy and precision according to the International Conference on Harmonization guidelines with good results. Conclusion: It could be used as a safer alternative for routine analysis of the mentioned drugs in quality control laboratories.

Background: Fatty acids and other metabolites containing a carboxyl group are of high interest in biomedicine because of their major role in many metabolic pathways and, particularly in the case of oxidised fatty acids, their high biological activity. Tagging carboxylic acid compounds with a permanent positive charge such as a quaternary ammonium compound could increase the LC-MS detection sensitivity and selectivity. This paper describes a new and novel strategy for analysing carboxylcontaining compounds in biological samples by ESI-MS through coupling to choline. Methods: Coupling of carboxylic acid derivatives in biological samples was performed by coupling to 2-Fluoro-1, 3 dimethyl –pyridinium (FDMP). The variation in the fatty acid profile of five different plasma samples was studied and was illustrated by using principal components analysis (PCA) to group the samples. Orthogonal partial least squares discriminant analysis (OPLS-DA) modelling was then applied to identify the fatty acids that were responsible for the variation. Results: The test results showed that choline coupling reactions were successful in detecting fatty acids, oxidised fatty acids and other compounds containing carboxylic acid groups in biological samples. The PCA results showed loadings of different fatty acids according to the plasma sample allowing identification of the fatty acids responsible for the observed variation. Conclusion: A new and easy tagging method was developed to detect carboxylic acids in plasma samples. The method proved to be precise and reproducible and can quantify fatty acid compounds to 50 ng/ml.

Background: 8-Hydroxy-2’-deoxyguanosine (8-OHdG) has been regarded as a typical stable biomarker of DNA oxidative damage, and its level is one of the criteria for early diagnosis of various diseases. Considering the significance of 8-OhdG, various analytical techniques have been used for assaying 8-OHdG but all of them suffer from basic limitations like highly expensive instrumentation, large amount of sample requirement, complicated sample pre-treatment, tedious and time-consuming procedures etc. However, electroanalytical sensors provide a faster, easy and sensitive means of analyzing. Methods: The chitosan (CS) film provided the high electrode activity and stability which is required for detecting 8-OHdG though direct electrochemical oxidation. Zirconia was employed because it has some unique properties, such as high redox activity and selectivity etc. High-performance composite was easily detected by differential pulse voltammetry at a working voltage of 0. 51 V (vs. Ag/AgCl). A rapid and sensitive electrochemical sensor based on CS and metal oxide nanocrystalline for the determination of 8-OHdG was established. Results: Under optimized experimental conditions, the peak currents of differential pulse voltammetry increased as the concentrations of 8-OHdG increased from 10 to 200 ng·mL-1. The detection limit was 3.67 ng·mL-1 which was calculated by the S/N ratio of 3. The recoveries of the real spiked samples are in the range between 93.2 to 105.3%. Conclusion: The electrochemical sensor for direct 8-OHdG determination using a new CS/zirconia composite for GCE modification was developed and showed excellent reproducibility, stability and sensitivity for the specific determination of 8-OHdG in real urine specimen.

Background: Polybrominated diphenyl ethers (PBDEs) are dangerous for the environment and human health because of their persistent organic pollutant (POP) characteristics, which have attracted extensive research attention. Raman spectroscopy is a simple highly sensitive detection operation. This study was performed to obtain environmentally friendly non-POP PBDE derivatives with simple detection-based molecular design and provide theoretical support for establishing enhanced Raman spectroscopic detection techniques. Methods: A three-dimensional quantitative structure-activity relationship (3DQSAR) pharmacophore model of characteristic PBDE Raman spectral was established using 20 and 10 PBDEs as training and test sets, respectively. Full-factor experimental design was used to modify representative commercial PBDEs, and their flame retardancy and POP characteristics were evaluated. Results: The pharmacophore model (Hypo1) exhibited good predictive ability with the largest correlation coefficient (R2) of 0.88, the smallest root mean square (RMS) value of 0.231, and total cost of 81.488 with a configuration value of 12.56 (#130;17).74 monosubstituted and disubstituted PBDE derivatives were obtained based on the Hypo 1 pharmacophore model and full-factor experimental design auxiliary. Twenty PBDE derivatives were screened, and their flame-retardant capabilities were enhanced and their migration and bio-concentration were reduced (log(KOW) <5), with unchanged toxicity and high biodegradability. The Raman spectral intensities increased up to 380%. In addition, interference analysis of the Raman peaks by group frequency indicated that the 20 PBDE derivatives were easily detected with no interference in gaseous environments. Conclusion: Nine pharmacophore models were constructed in this study; Hypo 1 was the most accurate. Twenty PBDE derivatives showed Raman spectral intensities increased up to 380%; these were classified as new non-POP environmentally friendly flame retardants with low toxicity, low migration, good biodegradability, and low bio-concentrations. 2D QSAR analysis showed that the most positive Milliken charge and lowest occupied orbital energy were the main contributors to the PBDE Raman spectral intensities. Raman peak analysis revealed no interference between the derivatives in gaseous environments.

Background: Melamine, contains 67% nitrogen by mass, and is adulterated in foods to uplift false protein. There is an urgent requirement to develop fast screening techniques for monitoring melamine in foods. Objectives: To develop rapid, high throughput detection techniques for melamine in the food matrix. Methods: IgY antibodies were developed against melamine in the hen, isolated and used for detection of melamine. The detection by colorimetric and chemiluminescent methods was compared. Results: The detection range for melamine was 1 ng-25 μg by the colorimetric method and 10 fg/mL-25 ng/mL by the chemiluminescent method. There was a very low matrix effect, where the recovery was 86 to 106 % by colorimetric method and 71 to 98 % by the chemiluminescent method. Conclusion: Both colorimetric and chemiluminescent methods could be employed for the fast and consistent melamine detection in the food matrix.

Background: High uric acid serum level, hyperuricemia, is now associated with many diseases such as gout, chronic kidney disease, hypertension, coronary artery disease and diabetes. Febuxostat is a novel selective xanthine oxidase inhibitor approved for the treatment of hyperuricemia. Objective: The aim of this study was to develop a first analytical method for the simultaneous determination of febuxostat and uric acid. Methods: An unmodified boron-doped diamond electrode provided concurrent quantitation of drug at low levels and uric acid, which has clinical significance in the diagnosis and therapy of hyperuricemia, at relatively high concentrations. The direct square-wave voltammetric method was applied to the analysis of both analytes in human serum samples. Results: Under the optimized conditions, the linear response of peak current on febuxostat concentration was achieved in the range from 7.5 x 10-7 to 3 x 10-5 M, while uric acid showed two linear ranges of 5 x 10-6 - 5 x 10-5 M and 5 x 10-5 - 2 x 10-4 M. The method was successfully utilised for quantification of both analytes in human serum samples. Good recoveries were obtained without interference from common inorganic cations and anions as well as glucose, dopamine, ascorbic and folic acids at concentrations expected in physiological conditions. Conclusion: The great benefits of developed method are fast analysis (only 7.5 s for run), low cost and simplicity of performance.

Background: Determination of the accurate mass of glucose generated from high-solids biomass saccharification is vital but problematic due to the uncertainty of liquid volume and slurry density. Methods: Herein, a new multiple-dilution-assays method was established to deduce the accurate glucose mass from the hydrolyzing biomass slurry. Results: This method was applicable for slurries of pretreated corn stover with a solids consistency up to 30 wt%, showing a high accuracy and good reproducibility. Dryness did not interfere with the accuracy. Ethanol at a high level, e.g. 10%, caused only a small negative error (<2%). This method can be used in either single- or fed-batch high-solids biomass saccharification, allowing to quantify the maldistribution of glucose in the slurry. Conclusion: The significant advantage of the present method was that only one single variable, glucose concentration, was to be determined, rendering it unnecessary to wash the insoluble or to measure the changing liquid density.

Background: Alpha-lipoic acid (ALA) has become a common ingredient in food supplements and multivitamin formulas. ALA is widely used as therapy for preventing diabetic polyneuropathies, scavenges free radicals, and restores intracellular glutathione levels. This study aimed to develop a simple and fast analytical method to determine ALA content in dietary supplements using highperformance liquid chromatography with pulsed amperometric detection (HPLC PAD). Methods: ALA was analyzed by HPLC in a mobile phase composed of 25 mmol/L potassium phosphate in 50% (v/v) acetonitrile (pH 4.0) and PAD at a gold electrode (vs. solid-phase hydrogen reference electrode). The PAD cycle was performed by applying a detection potential (E1) of +0.7 V for 0.4 s, an oxidation potential (E2) of +1.0V for 0.4 s and a reduction potential (E3) of -0.2 V for 1.2 s. Results: The runtime method was shown a rapid procedure for the analysis of α-lipoic acid. The sampling rate of 8 injections per hour was attained and measurements of the reproducibility of successive injections (20 μL) showed an RSD of 1.89% for 16 successive injections. The method presented low quantification limit of 0.21 mg/L. The industrialized ALA-based supplements ranged from to 97.8 to 104.1%, while manipulated capsules ranged from 69.2 to 95.4%. Conclusion: Electrochemical detector has been presented as an effective alternative for ALA determination, which has weakly UV-absorbing. This detection has the benefits of sensitivity, simplicity and low costs. The developed HPLC-DAD method proposes to be analytical tool applicable to quality control of ALA supplements.