Enhancement of the fluorescence intensity of Se-2,3-diaminonaphthalene complex in aqueous solution by adding organic solvents

Effects of Microenvironmental Changes on the Fluorescence Signal of Alternariol: Magnesium Induces Strong Enhancement in the Fluorescence of the Mycotoxin

Alternariol (AOH) is an emerging mycotoxin produced by Alternaria molds. It occurs as a contaminant e.g., in oilseeds, cereals, grapes, and tomatoes. Chronic exposure to AOH may cause genotoxic and endocrine disruptor effects. Our recent studies demonstrated that the fluorescence signal of AOH can be strongly affected by the environmental pH as well as by the presence of serum albumin or cyclodextrins. In the current study, we aimed to characterize the most optimal circumstances regarding the highly sensitive fluorescent detection of AOH. Therefore, the further detailed investigation of the microenvironment on the fluorescence signal of the mycotoxin has been performed, including the effects of different buffers, organic solvents, detergents, and cations. Organic solvents (acetonitrile and methanol) caused only slight increase in the emission signal of AOH, while detergents (sodium dodecyl sulfate and Triton-X100) and Ca2+ induced considerably higher enhancement in the fluorescence of the mycotoxin. In addition, Mg2+ proved to be a superior fluorescence enhancer of the AOH. Spectroscopic and modeling studies suggest the formation of low-affinity AOH-Mg2+ complexes. The effect of Mg2+ was also tested in two HPLC assays: Our results show that Mg2+ can considerably increase the fluorescence signal of AOH even in a chromatographic system.

A ratiometric fluorescence nanosensor for highly selective and sensitive detection of selenite

We herein developed a ratiometric fluorescent nanosensor for accurate and on-site sensing of SeO₃²⁻ by linking the recognition molecules 3,3′-diaminobenzidine (DAB) onto the surface of carboxyl group modified CdTe@SiO₂.

A new spectrophotometric method for determination of selenium in cosmetic and pharmaceutical preparations after preconcentration with cloud point extraction

A simple, rapid, and sensitive spectrophotometric method for the determination of trace amounts of selenium (IV) was described. In this method, all selenium spices reduced to selenium (IV) using 6 M HCl. Cloud point extraction was applied as a preconcentration method for spectrophotometric determination of selenium (IV) in aqueous solution. The proposed method is based on the complexation of Selenium (IV) with dithizone at pH < 1 in micellar medium (Triton X-100). After complexation with dithizone, the analyte was quantitatively extracted to the surfactant-rich phase by centrifugation and diluted to 5 mL with methanol. Since the absorption maxima of the complex (424 nm) and dithizone (434 nm) overlap, hence, the corrected absorbance, Acorr, was used to overcome the problem. With regard to the preconcentration, the tested parameters were the pH of the extraction, the concentration of the surfactant, the concentration of dithizone, and equilibration temperature and time. The detection limit is 4.4 ng mL⁻¹; the relative standard deviation for six replicate measurements is 2.18% for 50 ng mL⁻¹ of selenium. The procedure was applied successfully to the determination of selenium in two kinds of pharmaceutical samples.

Simultaneous determination of catecholamines and amino acids by micellar electrokinetic chromatography with laser-induced fluorescence detection

A selective and sensitive method was developed for separation and simultaneous determination of catecholamines and amino acids by MEKC with LIF. Interestingly enough, such work has been firstly performed on catecholamines derivatized with 4-chloro-7-nitro-2,1,3-benzoxadiazole and the detailed derivatization mechanism was discussed. After derivatization at 60 degrees C for 20 min, NBD-labeled catecholamines and amino acids were separated in a buffer system containing 10 mM sodium tetraborate-Na2HPO4, 20 mM SDS, and 10% v/v ACN at pH 9.75. SDS micelles were employed to improve the fluorescence intensity of catecholamine derivatives efficiently. Under optimum conditions, two catecholamines and 11 amino acids were separated in a short 13 min analysis time and the RSDs for migration time and peak area were less than 0.60 and 6.50%, respectively. The method was successfully applied for the quantification of catecholamines and amino acids in Portulaca oleracea L., human urine sample, and mixed injection sample.

Successive determinations of platinum(II) and selenium(IV) with 1,4-dibromo-2,3-diaminonaphthalene in aqueous micellar solutions

Highly sensitive successive determinations for PtII and SeIV ions have been developed based upon reactions with 1,4-dibromo-2,3-diaminonaphthalene (Br2DAN), which forms a near-infrared (NIR) absorbing complex (epsilon = 1.2 x 10(5) l mol-1 cm-1 at 800 nm) and an emissive complex (ex. 386 nm, em. 604 nm) for PtII and SeIV ions, respectively, in acidic aqueous micellar solutions. In the presence of a cationic surfactant, cetyltrimethylammonium chloride, the detection limits for PtII and SeIV ions are 1.2 ng ml-1 (3 sigma) and 0.98 ng ml-1 (S/N = 3), respectively. Hydrobromic acid plays a key role to enhance the color development of the NIR-absorbing PtII complex. The influences of CuII and ZnII ions at the normal human serum levels are readily tolerated, and interference from FeIII ion at 35 mumol l-1 is circumvented by the addition of 50 mumol l-1 of polyaminocarboxylates, such as EDTA.

Response of sediment bacterial assemblages to selenate and acetate amendments

We followed the response of bacterial assemblages in slurries of estuarine sediments to amendments of 100 microM sodium selenate and 10 mM sodium acetate. Selenate was removed from the dissolved phase in all slurries after an initial lag that varied depending on the source of the sediment used in the slurry. Subsequent selenate amendments were removed without a lag but with the appearance of transient peaks of selenite. We documented changes in the composition of bacterial assemblages in the slurries using PCR/DGGE and RT-PCR/DGGE of 16S rDNA and rRNA. Bands of interest were sequenced to identify organisms responding to selenate amendments. The composition of communities from the two sampling sites was different and changed but did not converge during incubations with selenate. Selenate-reducing assemblages had broad phylogenetic diversity. Most bands were related to groups of bacteria known to contain organisms capable of selenate or selenite reduction, except for Acinetobacter species which dominated one of the samples and has not previously been associated with selenium oxyanion reduction.

Nonaqueous capillary electrophoresis with laser induced fluorescence detection

This paper describes the use of nonaqueous capillary electrophoresis (NACE) with laser induced fluorescence (LIF) to improve detection sensitivity. The nonaqueous medium is conducive to lower detection limits due to the minimization of quenching effects. The nonaqueous solvent, N-methylformamide, produced the best detection limit with a 2-fold enhancement using NACE-LIF as compared to aqueous CE. N-methylformamide also gave the best fluorescent signal enhancement (6-fold) among the five nonaqueous solvents tested using steady-state fluorescence. The extent (or degree) of enhancement in fluorescence intensity seems to be related to the viscosity and/or polarity of the solvent.