A novel cyclohexane/water/ionic-liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6]) triphasic extraction system was studied for a possible fractional extraction of divalent metal cations with co-using 8-quinolinol (HQ) and tri-n-octylphosphine oxide (TOPO) as competitive extractants. In this system, Ni2+ was extracted into the [bmim][PF6] phase as a Q−-complex, whereas each of Mn2+, Zn2+, Cd2+ and Pb2+ was extracted into the cyclohexane phase as an ion-pair of a cationic TOPO-complex and PF6−. A suitable selection of extractants and ionic liquid can result in developing a powerful triphasic fractional extraction system.
Fluorometric determination techniques for mercury (Hg2+) assays have been very popular in recent years. This review focuses mainly on advances in the field of fluorescent sensors, concerning the detection of Hg2+ ion, that have been developed over the last few years. Based on a difference among the bearing functional fluorophores, these works are divided into two major sections. In the first section, rhodamine-derived Hg2+ ion sensors have been reviewed according to the essential mechanisms that work together with the spirolactam ring opening reaction. Various fluorescence Hg2+ ion sensors based on other functional fluorophores are discussed in the second section, divided by their recognition mechanisms that used for the signal responses.
The inactivation of a redox enzyme, bilirubin oxidase (BOD), by heat and guanidine hydrochloride (GuHCl) was studied by two bioelectrochemical methods. One is a conventional method, which measures the inactivation of BOD in solution, and the other is a method using a BOD-immobilized electrode (a membrane/BOD/GC electrode), which measures the inactivation of BOD in the immobilized state. The results for thermal inactivation revealed that BOD both in solution and in the immobilized state obeyed the same irreversible inactivation kinetics. The CD and absorption spectra of BOD confirmed that the irreversible thermal inactivation was accompanied by a change in the secondary structure and the dissociation of type-1 copper from BOD. The measurements in the presence of GuHCl demonstrated that the BOD activity was significantly decreased at 1 M GuHCl in both states, and that the decrease proceeded reversibly. The CD spectrum of BOD indicated that the secondary structure of BOD was little affected by GuHCl at this concentration. The effect of GuHCl on the thermal inactivation was studied and evaluated as the resulting values of the Arrhenius activation energy: ΔG≠, ΔH≠, and ΔS≠.
A gold electrode modified with diethylenetriaminepentaacetic acid (DTPA) has been fabricated to selectively detect dopamine (DA). The influences of experimental parameters were investigated and optimized. The anodic peak current is proportional to the concentration of DA in the range of 1.0 × 10−7 − 6.0 × 10−3 mol L−1 with a detection limit of 3.0 × 10−8 mol L−1 (S/N = 3). DA contents in the serum samples were determined; coexisting ascorbic acid (AA), uric acid (UA) and other oxidizable compounds did not cause interference to the determination. The response of AA and UA during the determination of DA could be suppressed due to the distinct charge discrimination between DA cations and the negative DTPA self-assembled layer in pH 7.4 phosphate-buffered solutions (PBS). The selectivity has been improved significantly; the response time, reproducibility and lifetime of the modified electrode are discussed.
Trifluoperazine is widely used in the treatment of psychotic patients for its neuroleptic and antidepressive action. In this study, the construction, evaluation and application of new potentiometric sensors for trifluoperazine hydrochloride (TFPH) are described. The sensing membranes incorporated either ion-pair complexes of the trifluoperazine cation and phosphotungstic acid (PTA) or phosphomolybdic acid (PMA) or sodium tetraphenyl borate (NaTPB) as electroactive materials in poly(vinyl chloride) matrix membrane. The plasticizers used were di-n-butyl phthalate (DBPH) and tri-n-butyl phosphate (TBP). After a series of experiments, the best electrodes were based on PTA or PMA as electroactive materials and DBPH as plasticizer. A linear concentration range between 1 × 10−5 − 1 × 10−2 M with a near Nernstian slope of 28.43 and 32.11 mV decade−1, respectively, was obtained. The electrodes were characterized in terms of the composition, usable pH range, life span and response time. The selectivity coefficient values were calculated for different inorganic cations and sugars. Validation of the method shows the suitability of the electrodes for the determination of TFPH in pharmaceutical formulations.
A very simple and sensitive method for the simultaneous analysis of naphthalene and p-dichlorobenzene in human whole blood and urine by headspace capillary gas chromatography-mass spectrometry (GC-MS) is presented. The advantages of the method were that as much as 1 mL of headspace vapor could be injected into a GC port in the splitless mode, and that the addition of deuterated naphthalene and p-dichlorobenzene as internal standards resulted in much better headspace extraction efficiencies, which resulted in high sensitivity. The detection limits for both naphthalene and p-dichlorobenzene were 1 ng mL−1 for whole blood and 0.5 ng mL−1 for urine. Validation data, such as the linearity of calibration curves, reproducibility and recovery rates, were all satisfactory. Using this method, both compounds could actually be detected from whole blood samples of a male volunteer after the inhalation of each gas of the compounds.
We have developed and validated a new and reliable gradient reversed-phase high-performance liquid chromatography (RP-HPLC) method with a diode array detector (DAD) for the simultaneous separation and determination of 23 frequently prescribed selected drugs belonging to different therapeutic groups in human urine samples. For the drugs listed below, this method of analysis for human urine was also successfully applied to determine urine concentrations of these drugs in samples from treated patients: enalapril (ENA), paracetamol (PAR), sotalol (SOT), dipyrone (DIP), vancomycin (VAN), captopril (CAP), fluconazole (FLU), cefazolin (CEF), metoprolol (MET), aspirin (ASP), ticlopidine (TIC), prednisolone (PRE), propranolol (PRO), digoxin (DIG), sildenafil (SIL), furosemide (FUR), dexamethasone (DEX), carvedilol (CAR), ketoprofen (KET), nifedipine (NIF), terbinafine (TER), acenocoumarol (ACE) and spironolactone (SPI). Separation of the analytes was achieved by RP-HPLC-DAD with a mobile phase composed of acetonitrile, methanol and 0.05% trifluoroacetic acid in water using a gradient elution program. Good linear relationships over the investigated concentration ranges were observed with values of r2 higher than 0.998 for all of the drugs. The intra-day and inter-day precisions of this method were evaluated with RSD values less than 4.26 and 5.42%, respectively. The relative recoveries of the 23 investigated compounds ranged from 93.60 to 106.00% with RSD values less than 4.46%. An expanded uncertainty budget was constructed for all investigated drugs in human urine samples.
A novel β-cyclodextrin (β-CD) derivative modified with a degradable and biocompatible oligo(lactic acid) (OLA) group, 6-oligo(lactic acid)cyclomaltoheptaose (6-OLA-β-CD), was successfully synthesized and used as a chiral selector for the capillary electrophoretic (CE) resolution (Rs) of several basic analytes. The primary purpose of the research was to explore the capability of the 6-OLA-β-CD as a chiral selector for comparisons with β-CD and HP-β-CD. Substitution with the oligo(lactic acid) group at the sixth hydroxyl sites of the CD is aimed at influencing the magnitude and selectivity of the analyte-CD interactions. The chiral resolution was strongly influenced by the concentration of the CDs and buffer pH. The effects of the substitution degree (DS) and the chain length (n) of the 6-oligo(lactic acid) groups of 6-OLA-β-CD on separations were also investigated.
Bi-chromophoric compounds linked to linear polyether N,N′-[oxybis(3-oxapentamethyleneoxy-2-phenyl)]-bis(1-anthracenecarboxamide) (14) and its analogues (15, 24 and 25) were synthesized. Their photochemical properties and complexation actions were investigated in acetonitrile. These fluoroionophores have shown weak emissions in the absence of guest ions, resulting in a twisted intramolecular charge transfer (TICT) quenching process (off state) of an anthracene aromatic amide moiety. After the formation of a complex with alkaline earth metal ions, a large enhancement of fluorescent intensities was obtained (on state). The efficiencies of controlling an off-on fluorescent signal using 14 and its analogues (15, 24 and 25) were larger than that of the 9-positioned analogue. These results suggested that the TICT relaxation process was effectively able to control using 14 and its analogues (15, 24 and 25) by complex formations.
A novel nanoparticles-based fluorescence detection method has been developed by taking advantage of magnetic separation and amplified fluorescence detection. This DNA sensor relies on a "sandwich" hybridization strategy, in which the DNA targets are first hybridized to captured oligonucleotide probes immobilized on magnetic nanoparticles, and then hybridized with thiol-modified oligonucleotide probes immobilized on gold nanoparticles. Subsequently, the amplified DNA signals are detected in the form of bio-bar-code DNA using a chip-based fluorescence detection method. The result showed that the detection limit of target DNA probes is 1 pM. Complementary and mismatched sequences were clearly distinguished, and the ratio of the background-subtracted fluorescence values for complementary and single-base mismatched oligonucleotide was 2.12:1. This new system can be applied to both DNA detection and immunoassay, and has broad potential applications in disease diagnosis and immunoassay.
The binding of sinafloxacin to DNA has been studied by fluorescence spectroscopy and UV-vis absorption spectroscopy. The variations in the spectroscopic characteristics of sinafloxacin upon addition of DNA were observed. Salt concentration effect, KI quenching, fluorescence polarization, DNA denaturation experiments, melting temperature (Tm) curves and viscosity measurements were studied to investigate the binding mechanism. It was proved that the fluorescence quenching of sinafloxacin is a result of the formation of sinafloxacin-DNA complex. Quenching constants were determined using the Stern-Volmer equation. From the experiment evidence, the major binding mode of sinafloxacin with DNA was evaluated to be the groove binding.
The resolution method for overlapped peaks based on fractional-order differentiation (FOD) of the Gaussian function is described. Its main idea stems from a variation of the maximum and the zero-crossing of the Gaussian peaks signal at different differential orders. I obtained two kinds of estimators for estimating the characteristic parameters of the Gaussian peak based on the above relationship. The resolution of several kinds of overlapped peaks simulated by computer has been performed and discussed in detail. The proposed method has been used to resolve overlapped voltammetric peaks obtained in the analysis of binary mixtures of Cd(II) and In(III) metal ions. The results indicate that the proposed method can be used to resolve overlapped peaks which can be modeled by the Gaussian peaks both effectively and satisfactorily.
A technique for the selective measurement of diffusive gradients in thin-films (DGT) for free Cu2+ ions was developed using a 0.030 M solution of polyvinyl alcohol (PVA) as the liquid binding phase with the liquid-type DGT devices (PVA DGT). The PVA DGT had a substantial binding capacity at pH 5.6 − 8.6 and concentrations of competitive Na+ up to 0.7 M. The measurements of PVA DGT and cupric ion selective electrode (Cu-ISE) for free Cu2+ in synthetic river water (recovery = 97.51 ± 2.58% for PVA DGT and recovery = 98.25 ± 1.46% for Cu-ISE), in spiked river water (recovery = 24.99 ± 3.55% for PVA DGT and recovery = 26.32 ± 3.33% for Cu-ISE) and in spiked industrial wastewater (recovery = 4.21 ± 3.13% for PVA DGT and recovery = 5.10 ± 2.78% for Cu-ISE) were equivalent. The results showed that PVA DGT could measure selectively the free Cu2+ ion concentrations in water samples.
A novel molecular imprinting-chemiluminescence (MI-CL) method for the determination of sorbic acid (SA) was established, taking the molecularly imprinted polymer (MIP) as recognition material and a novel rhodanine derivative as chemiluminescence reagent. The MIP was prepared by a self-assembly technique with SA as template molecule, methacrylic acid (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as cross-linker. It was found that 3-o-methoxyphenyl-5-(2′-sulfono phenylazo) rhodanine (2MORASP) significantly enhanced the luminescence intensity of the SA-potassium permanganate-hydrochloride acid system. The method was proved to be selective and sensitive. Under the optimized experimental conditions, the system exhibits an excellent linear relationship over the range of 3.0 × 10−7 − 6.0 × 10−4 g mL−1. The detection limit of the proposed method was 2.2 × 10−8 g mL−1. This method was successfully applied to the determination of SA in milk and fruit juice samples.
Common buckwheat (Fagopyrum esculentum Moench) was foliarly sprayed with a water solution containing 10 mg Se(VI) L−1 at the beginning of flowering. The total Se content in plant parts in the untreated group was low, whereas in the Se-sprayed group it was approximately 50- to 500-fold higher, depending on the plant part (708 − 4231 ng Se g−1 DM−1 (DM: dry matter)). We observed a similar distribution of Se in plant parts in both control and treated groups, with the highest difference in Se content being in ripe seeds. Water-soluble Se compounds were extracted by enzymatic hydrolysis with protease XIV, resulting in above 63% of soluble Se from seeds, ∼14% from stems, leaves and inflorescences and less than 1% from husks. Se-species were determined in enzymatic extracts using HPLC-UV-HG-AFS (HPLC-hydride generation-atomic fluorescence spectrometry with UV treatment). The main Se species found in seeds was SeMet (∼60% according to total Se content), while in stems, leaves and inflorescences the only form of soluble Se present was Se(VI) (up to 10% of total Se). In husks no Se-species were detected. We observed an instability of Se(IV) in seed extracts as a possible consequence of binding to the matrix components. Therefore, special care concerning sample extraction and the storage time of the extracts should be taken.
To functionalize chitin surfaces using proteins, we developed a glucose oxidase (GOD)-chitin/platinum-modified glassy carbon paste electrode (GCPE) as a model. In a weakly acidic solution, negatively charged GOD were immobilized by the protonated acetylamide groups on chitin. When the electrode was immersed in a solution containing GOD, the enzyme was readily immobilized due to the electrostaic interaction. In addition, measurements were performed using electrodes made with powders of different sizes because sensor performance depends on the particle sizes of glassy carbon powder.
A capillary chromatography system was developed using an open capillary tube and a water-acetonitrile (hydrophilic)-ethyl acetate (hydrophobic) mixture carrier solution. In this study, we examined the effects of the inner-wall characteristics of a fused-silica capillary tube on the separation performance in this system. Untreated (silanol group-intact) and inactivated (silanol group-end-blocked) fused-silica capillary tubes were used. The mixture analyte of 1-naphthol and 2,6-naphthalenedisulfonic acid was injected into two types of capillary tubes. They were eluted from both tubes in this order with water-acetonitrile-ethyl acetate (volume ratio 2:7:4) mixture carrier solution, and eluted in reverse order with water-acetonitrile-ethyl acetate (volume ratio 15:3:2). The peak shapes observed here were analyzed while considering the inner-wall characteristics of the capillary tubes from the viewpoint of the tube radial distribution of the carrier solvents in the tubes.
The simultaneous LC/MS analyses of hexachlorobenzene (HCB) and pentachlorophenol (PCP), two dioxin precursors were studied by both atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization mass spectrometry (APPI/MS). The optimum LC/MS conditions of the simultaneous analysis were determined for these two compounds with different polarity. Ionization by APPI was found to be more effective than by APCI, and is thus a better ionization method for analysis of the two compounds. Using LC/APPI/MS we can achieve the simultaneous analysis of HCB and PCP at ppb levels.