Determination of Dextromethorphan and its Metabolite Dextrorphan in Human Hair by Gas Chromatography–Mass Spectrometry

An analytical method has been developed for determination of dextromethorphan (DMP) and dextrorphan (DRP) in human hair by gas chromatography–mass spectrometry (GC–MS). Hair samples (30 mg) were washed with distilled water and acetone and cut into small fragments (<1 mm) before extraction with methanol. The extracts were evaporated to dryness and then derivatized by use of BSTFA containing 1% TMCS, for preparation of the trimethylsilyl (TMS) derivative of DRP. The extract (1 μL) was then injected into the GC–MS. Recoveries of DMP and DRP at 7.0 and 22.5 ng mg^?1 were in the range 90.6–97.2% with intra-assay and inter-assay precision of less than 5.7% and 4.7%, respectively. LOD and LOQ were, respectively, 0.67 and 2.13 ng mg^?1 for DMP and 0.14 and 0.47 ng mg^?1 for DRP. The responses were linear with correlation coefficients (r > 0.9995) for the drugs studied. The applicability of the method was proven by analysis of authentic hair samples.     

Performance of hollow-fiber flow field-flow fractionation in protein separation

Since hollow-fiber flow field-flow fractionation (HF FIFFF) utilizes a cylindrical channel made of a hollow-fiber membrane, which is inexpensive and simple in channel assembly and thus disposable, interests are increasing as a potential separation device in cells, proteins, and macromolecules. In this study, performance of HF FIFFF of proteins is described by examining the influence of flow rate conditions and length of fiber (polyacrylonitrile or PAN in this work) on sample recovery as well as experimental plate heights. The interfiber reproducibility in terms of separation time and recovery was also studied. Experiments showed that sample recovery was consistent regardless of the length of fiber when the effective field strength (equivalent to the mean flow velocity at the fiber wall) and the channel void time were adjusted to be equivalent for channels of various fiber lengths. This supported that the majority of sample loss in HF FIFFF separation of apoferritin and their aggregates may occur before the migration process. It is finally demonstrated that HF FIFFF can be applied for characterizing the reduction in Stokes' size of low density lipoproteins from blood plasma samples obtained from patients having coronary artery disease and from healthy donors.     

Calix[2]furano[2]pyrrole and related compounds as the neutral carrier in silver ion-selective electrode

The performance of calix[2]furano[2]pyrrole and related compounds used as neutral carriers for silver selective polymeric membrane electrode was investigated. The silver ion-selective electrode based on calix[2]furano[2]pyrroles gave a good Nernstian response of 57.1 mV per decade for silver ion in the activity range 1×10⁻⁶ to 1×10⁻² M. The present silver ion-selective electrode displayed very good selectivity for Ag⁺ ion against alkali and alkaline earth metal ions, NH₄⁺, and H⁺. In particular, the present Ag⁺-selective electrode exhibited very low responses towards Hg²⁺ and Pb²⁺ ions. The potentiometric selectivity coefficients of the silver ion-selective electrode exhibited a strong dependence on the solution pH. In particular, the response of the electrode to the Hg²⁺ activity was greatly diminished at pH 2.5 compared to that at pH 5.0. Overall, the performance of the present silver ion-selective electrode based on the ionophore, calix[2]furano[2]pyrrole, is very comparable to that of the electrode prepared with the commercially available neutral carrier in terms of slope, linear range, and detection limits.     

Biotin-avidin mediated competitive enzyme-linked immunosorbent assay to detect residues of tetracyclines in milk

Tetracycline (TC) antibiotics are widely used for prevention and control of disease because they inhibit the growth of bacteria. However, the presence of TC antibiotics residues in food causes harmful effects on consumer's health such as allergic reactions, liver damage and gastrointestinal disturbance, so that many countries have set MRLs (maximum residue levels). Therefore, it is necessary to detect tetracycline residues, to develop suitable analytical techniques to be used as routine screens and field detection.A new approach to the biotin-avidin mediated competitive ELISA is developed to determine tetracycline residues in milk. After optimization, the LOD and LOQ were 1.0 × 10^− 10 M (0.048 μg/L) and 1.0 × 10^− 9 M, respectively, and the working range from 3.16 × 10^− 10 M to 3.16 × 10^− 7 M toward TC in milk. No cross-reactivity was observed with the structurally similar compounds; chlortetracycline (13.7%), oxytetracycline (10%) and doxytetracycline (< 1%). Additionally percent recoveries of TC spiked in milk were quite satisfactory (∼ 90%). Comparing our results obtained in this work with others, it shows with the capability to detect TC ranging in MRLs (100 μg/L in milk) sufficiently with highly sensitivity in milk, and with simple pre-treatment. In addition, this method can apply to developing useful ELISA test kit for determination of TCs in milk.     

Flow condensation heat transfer characteristics of hydrocarbon refrigerants and dimethyl ether inside a horizontal plain tube

Flow condensation heat transfer coefficients (HTCs) and pressure drop of R22, propylene, propane, DME and isobutane are measured on a horizontal plain tube. The main test section in the experimental flow loop is made of a plain copper tube of 8.8 mm inner diameter and 530 mm length. The refrigerant is cooled by passing cold water through the annulus surrounding the test section. Tests are performed at a fixed refrigerant saturation temperature of 40 ± 0.2 °C with mass fluxes of 100, 200, and 300 kg/m² s and heat flux of 7.3–7.7 kW/m². The heat transfer and pressure drop data are obtained in the vapor quality range of 10–90%. Test results show that for a given mass flux the flow condensation HTCs of propylene, propane, DME and isobutane are higher than those of R22 by up to 46.8%, 53.3%, 93.5% and 61.6%, respectively. Also well-known correlations developed based upon conventional fluorocarbon refrigerants predict the present data within a mean deviation of 33%. Finally, the pressure drop increases as the mass flux and quality increase and isobutane shows the highest pressure drop due to its lowest vapor pressure among the fluids tested.     

Development of pH sensor based on aromatic polyurethane matrix

The synthesized aromatic polyurethane (APU)-based all-solid-state (ASS) pH sensor was developed with the same APU-based reference site in an ASS multi sensing electrode. The best analytical performance (the linear range of pH 3.0–11.5, slopes of 57 mV pH⁻¹) was obtained with the membrane composition of 33:66:1 (wt.%) of APU/plasticizer (NPOE)/ionophore (N,N-dioctadecylmethylamine) with the addition of lipophilic additive (KTpClPB, 5 mol.%). This ASSE exhibits more advantages of increasing stability, reducing membrane resistance and reducing anion interference.     

Competitive enzyme-linked immunosorbent assay for the determination of catecholamine, dopamine in serum

A competitive enzyme-linked immunosorbent assay for dopamine (DA) has been optimized and characterized. DA is sensitive to oxygen and light according to a function of the pH on the DA oxidation process. The phenolic groups in DA are readily oxidisable to a quinoid form and thus, free DA deteriorates in alkaline media. Thus, effect of factors such as pH, enzyme-label with substrate, ionic strength and reaction time was considered on performance of ELISA. Assay was performed with 5 μg mL⁻¹ of BSA-DA and 1/7500 dilution of anti-DA antibody. A dose-response curve was constructed, and a limit of detection and a dynamic range for DA were accomplished to 1.0 × 10⁻⁹ M (0.19 μg L⁻¹) and five orders (3.2 × 10⁻⁸ M to 3.2 × 10⁻³ M) of magnitude, respectively. The correlation diagram of the absorbance obtained both in buffer and in serum has shown good agreement with correlation coefficient (R² = 0.9947): Abs. (in serum) = 0.6128 × Abs. (in buffer) + 0.2926. The cross-reactivity was examined with the structurally similar compounds. And the results demonstrated that epinephrine and 3-methoxytyramine showed cross-reactivity (18.9% each), whereas 3,4-dihydroxyphenylacetic acid and homovanillic acid showed low cross-reactivity (<1%). And percent recoveries of DA in serum were quite satisfactory. This provides usefulness of the present assay to monitor DA in serum.     

Selective solid-phase extraction of catecholamines by the chemically modified polymeric adsorbents with crown ether

A simple and selective one-step solid-phase extraction procedure using chemically modified polymer resin (Amberlite XAD-4) with crown ether was investigated for the measurement of urinary catecholamines. After loading the urine samples (adjusted to pH 4) on the synthesized adsorbent cartridge, the column was washed with methanol followed by water and then the adsorbed catecholamines were eluted by 1.0 mL of 6.0 M acetic acid. The effectiveness of sample clean-up method was demonstrated by reversed-phase ion-pair high-performance liquid chromatography with electrochemical detection. Under optimal condition, the recoveries of epinephrine, norepinephrine, and dopamine from spiked urine sample were >86% for all catecholamines. The detection limits (n=5) for epinephrine, norepinephrine, and dopamine were 37, 52, and 46 nmol/L, respectively.     

Electrodeposition of Silver Vanadate Films: A Tale of Two Polymorphs

Two polymorphs of AgVO₃, namely the α- and β- forms, were prepared and their physical, structural, optical, electrochemical, and photoelectrochemical characteristics were compared using a battery of experimental and theoretical tools. A two-step method, previously developed in the our laboratory for the electrodeposition of inorganic semiconductor films, was applied to the electrosynthesis of silver vanadate (AgVO₃) films on transparent, conducting oxide surfaces. In the first step, silver was cathodically deposited from a non-aqueous bath containing silver nitrate. In the second step, the silver film was anodically stripped in an aqueous medium containing ammonium metavanadate. The anodically generated silver ions at the interface underwent a precipitation reaction with the vanadate species to generate the desired product in situ. Each of these steps were mechanistically corroborated via the use of electrochemical quartz crystal microgravimetry, used in conjunction with voltammetry and coulometry. As-deposited films were crystalline and showed p-type semiconductor behavior. Theoretical insights are provided for the electronic origin of the α→β phase transformation in AgVO₃ and the disparate optical band gaps of the two polymorphs. Finally, implications for the application of this material in solar cells are provided.     

Anion-Selective Membrane Electrodes Based on Polymer-supported Metalloporphyrins

Prepared polystyrene pyridine copolymer supported metallo-protoporphyrin IX structures (MPPIX-PSP4) were applied as an ionophore for ion selective electrodes.