Highly sensitive spectrofluorimetric determination of trace amounts of lecithin

A new spectrofluorimetric method was developed for the determination of trace amounts of lecithin using the ciprofloxacin (CIP)–terbium (Tb³⁺) ion complex as a fluorescent probe. In a buffer solution at pH=5.60, lecithin can remarkably reduce the fluorescence intensity of the CIP–Tb³⁺ complex at λ=545 nm. The reduced fluorescence intensity of the Tb³⁺ ion is proportional to the concentration of lecithin. Optimum conditions for the determination of lecithin were also investigated. The linear range and detection limit for the determination of lecithin were 1.0×10⁻⁶–3.0×10⁻⁵ mol L⁻¹ and 3.44×10⁻⁷ mol L⁻¹, respectively. This method is simple, practical, and relatively free of interference from coexisting substances. Furthermore, it has been successfully applied to assess lecithin in serum samples.      

香草醛缩氨基硫脲-铅高灵敏荧光反应的研究及其应用

合成了新荧光试剂香草醛缩氨基硫脲 ,并研究了此试剂与铅荧光反应的最佳条件。在λex em=368 45 0nm处 ,测定铅的线性范围为 3.0～ 45 .0 μg L ,检测限为 0 .72 μg L ,该方法已用于猪肝粉和小麦粉中痕量铅的测定。     

Highly sensitive spectrofluorimetric determination of cysteine by Cu2+-morin complex

p-Toluenesulfonylamide was immobilized on silica gel and on nm-sized silicium dioxide (SiO₂). Their adsorption efficiency toward metal ions was investigated by the batch equilibrium technique. Although silica gel and nm-SiO₂ have the same composition (silicon and oxygen), the difference in their sizes and surface structures results in distinct chemical activity and selectivity. At pH 4, the adsorption capacity of modified silica gel adsorbent was found to be 4.9, 5.0, 33.2, and 12.6 mg g⁻¹ for Cr(III), Cu(II), Pb(II) and Zn(II), respectively. However, the adsorption capacity of nm-SiO₂ adsorbent toward Cr(III) was 26.7 mg g⁻¹ under ultrasonic dispersing. The potential application of p-toluenesulfonylamide-modified silica gel for simultaneous preconcentration of trace chromium, copper, lead and zinc from two standard reference materials and two food samples was performed with satisfactory results. Correspondence: Xijun Chang, Department of Chemistry, Lanzhou University, Lanzhou 730000, P.R. China     

Highly sensitive spectrofluorimetric determination of trace amounts of lead with a new fluorescent reagent, 2-hydroxy-1-naphthaldehydene-8-aminoquinoline

A new fluorescent reagent, 2-hydroxy-1-naphthaldehydene-8-aminoquinoline (HNAAQ), was synthesized. The fluorescent reaction of this reagent with lead was also studied. Based on this chelation, a highly sensitive spectrofluorimetric method was developed for the determination of trace amounts of lead in a water-ethanol (5 + 1, v/v) medium at pH = 9.4. Under these conditions, the Pb-HNAAQ complex has excitation and emission maxima at 398 and 450 nm, respectively. The linear range of the method is from 0 to 100 microg l(-1) and detection limit is 0.28 microg l(-1) of lead. Interference of other ions was studied. In strongly basic media most interfering metal ions form precipitates of hydroxides or oxides and can be removed efficiently through filtration while the residual cations can be removed with a cation-exchange resin. Hence, the selectivity of the method can be increased considerably. The procedure can easily be performed and affords good precision and accuracy. The method was successfully applied to the determination of lead in wheat and rice flour.     

Flow injection kinetic spectrofluorimetric determination of trace amounts of osmium

A flow injection (FI) kinetic spectrofluorimetric method is described for the determination of osmium(IV) and the possible mechanism of catalytic reaction is discussed. The method is based on the fluorescence enhancing reaction of o-vanillin furfuralhydrazone (OVFH) with potassium bromate, which is catalyzed by Os(IV) in water medium at pH 6.10 and 45 degrees C. OVFH is newly synthesized and its ionization, IR and elemental analysis are established. Under these experimental conditions, the oxidized product of OVFH has excitation and emission maxima at 337 and 490 nm, respectively. The linear range of this method is 0-600 ng ml(-1) with the R.S.D. of 1.2%. The detection limit is 1.0 ng ml(-1) of Os(IV). A high analysis rate of 24 samples h(-1) is obtained by the FI method. The proposed method is applied successfully to determine Os(IV) in synthetic mixture and mineral samples, and the results are well consistent with the standard values.     

Rapid and sensitive spectrofluorimetric determination of trace amounts of Hg(II) with o-vanillin-8-aminoquinoline

The fluorimetric determination of mercury ions with o-vanillin-8-aminoquinoline (OVAQ) in aqueous solutions was investigated. Hg(II) could react with the fluorescent reagent OVAQ (λ_ex/em = 278/314 nm) to form a nonfluorescent complex in an ethanol-water medium of pH 6.00. The linear range of the proposed method was from 2.5 to 80 μg/L, and the detection limit was 0.80 μg/L. The interferences of 24 foreign ions were also studied. The method was successfully applied to the determination of Hg(II) in sludge. The text was submitted by the authors in English.     

Spectrofluorometric determination of trace amounts of coenzyme II using norfioxacin-terbium complex as a fluorescent probe.

When terbium ion (Tb3+)-norfloxacin (NFLX) complex is issued a fluorescent probe, in a buffer solution of pH = 7.6, NADP can remarkably enhance the fluorescence intensity of the Tb3+ -NFLX complex at lambda = 545 nm. The enhanced fluorescence intensity of Tb3+ is in proportion to the concentration of NADP. The dynamic range for the determination of NADP is 1.11 x 10(-7) - 6.16 x 10(-5) mol l(-1), with a detection limit of 4.31 x 10(-8) mol l(-1). This method is simple, practical and relatively free of interference from coexisting substances, so it can be successfully applied to determination of NADP in synthetic water samples.     

Highly selective and sensitive spectrophotometric determination of trace amounts of silver ion in surfactant media using 2-mercaptobenzoxazole

A simple and accurate spectrophotometric method for determination of trace amounts of silver ion in tap and wastewater solution and photographic solutions has been described. The spectrophotometric determination of silver ion using 2-mercaptobenzoxazole (MBO) in the presence of Triton X-100 as nonionic surfactant has been carried out. The Beer's law is obeyed over the concentration range of 0.1-9.0 microg mL(-1) of Ag+ ion with the detection limits of 1.6 ng mL(-1). The influence of type and amount of surfactant, pH, complexation time and amount of ligand on sensitivity of method were optimized. Finally the repeatability, accuracy and the effect of interfering ions on the determination of silver ion were evaluated. There is a good agreement between results of proposed method and atomic absorption spectrometry.     

Highly sensitive spectrofluorimetric determination of ephedrine hydrochloride in pharmaceutical preparations

A sensitive and specific spectrofluorimetry method was developed and validated for the quantification of ephedrine (EP) in pharmaceutical preparations. The method is based on the fluorescent enhancing reaction of EP with 7-chloro-4-nitrobenzofurazan (NBD-C1; derivatization reagent), in borate buffer of pH 9 to yield a yellow, fluorescent product. Under these experimental conditions, the derivatized product of EP had excitation and emission wavelength maxima at 458 and 516 nm, respectively. The linear range of this method was 20-2500 ng/mL. The detection limit was 7.3 ng/mL EP. Intra- and interday precisions of the assay at 3 concentrations within this range were 0.037-1.77%. The low relative standard deviation values indicate good precision, and high recovery values indicate excellent accuracy of the method. The proposed method was applied to the determination of the examined drugs in pharmaceutical formulations, and the results indicate that the method is equally as accurate, precise, and reproducible as the official method.     

Highly sensitive spectrofluorimetric determination of L-cysteine based on inhibition of hemoglobin

A highly sensitive spectrofluorimetric method for the determination of L-cysteine based on its inhibitory action on hemoglobin (Hb) activity was developed. The optimal conditions were studied. A linear calibration graph was obtained over the range 2.00 x 10(-7)-1.50 x 10(-6) mol l(-1) for L-cysteine. The relative standard derivation was 1.30% at L-cysteine concentration of 8.00 x 10(-7) mol l(-1) (n=11). Further experimental results revealed that the inhibition of L-cysteine on this system was of the competitive type. The method was applied to determine L-cysteine in protein hydrolysate and cystine electrolyte samples with satisfactory results.     

Homogeneous liquid-liquid extraction method for the selective spectrofluorimetric determination of trace amounts of tryptophan

Twenty-one amino acids were derivatized with fluorescamine (FLA) under basic conditions (pH 9) and the extraction of the amino acid-FLA derivatives was investigated using a homogeneous liquid-liquid extraction with perfluorooctanoic acid (HPFOA) based on phase separation under strongly acidic conditions. Under the optimum concentration conditions for the reagents ([PFOA]T = 3 x 10(-3) mol dm-3, [acetone]T = 3 vol.%, [HCl]T = 1.8 mol dm-3), the concentration factor was approximately 1000-fold (i.e., 30 microliters of the sedimented liquid phase was produced from 33 ml of the homogeneous aqueous solution). The percentage extraction (E) was determined for the 21 amino acid-FLA derivatives; the value for the tryptophan (Trp)-FLA derivative was 80.9%, whereas the other derivatives were not almost extracted (E < 0.4%). The Trp-FLA derivative was selective for the extraction using the homogeneous liquid-liquid extraction method with HPFOA. After the sedimented liquid phase containing Trp-FLA has been placed on a polytetrafluoroethylene filter-paper, the fluorescence intensity was determined using a spectrofluorimeter with filter-paper as the solid-sample holder. The calibration graph of Trp was linear over the range 1.0 x 10(-8)-1.5 x 10(-6) mol dm-3. The relative standard deviation for the central value of the calibration graph was 4.5% (five determinations) and the detection limit (S/N = 3) was 8.9 x 10(-9) mol dm-3. When the proposed method was applied to the highly sensitive spectrofluorimetric determination of Trp in animalin-L syrup, the results were satisfactory.     

催化荧光光度法测定砷的研究

在硫酸介质中，痕量砷对碘酸钾与罗丹明6G的氧化还原反应有催化作用，使罗丹明6G的荧光减弱，据此建立了催化荧光法测定痕量砷的新方法。方法检出限为0.26ng/mL，测定范围4.12ng/mL-82.4ng/mL。已用于环境和生物样品测定。     

Highly sensitive spectrofluorimetric kinetic determination of ultratrace amounts of vanadium(V) based on the oxidation of 1,8-diaminonaphthalene by bromate

A highly sensitive catalytic quenching spectrofluorimetric method was described for the determination of V(V) based on its catalytic effect on the oxidation of 1,8-diaminonaphthalene by potassium bromate with Tiron as an activator in weakly acidic medium and the reaction mechanism was investigated. The reaction was followed spectrofluorimetrically by measuring the fluorescence intensity of 1,8-diaminonathphlene (DAN) (λ_ex=356 nm, λ_em=439 nm) at a fixed time of 5 min from initiation of the reaction. Under the optimum conditions, vanadium(V) can be determined in the range 0.05-50.0 ng ml⁻¹ with a S.D.=0.024 for 15 times measurements. The detection limit of the method was down to 0.0088 ng ml⁻¹ and the catalytic reaction activation energy was found to be 43.92 kJ mol⁻¹. The proposed method was tested for the determination of vanadium(V) in rice and natural water samples.     

A sensitive flow-injection method for determination of trace amounts of nitrite

A new sensitive colour reaction for nitrite determination is presented. In acidic medium, nitrite was reacted with safranine to form a diazonium salt which caused the reddish-orange dye colour of the solution to change to blue. The carrier stream, into which the sample solution was injected, was doubly distilled water. The reagent solution stream, which contained safranine dye, hydrochloric acid and potassium chloride, was mixed with the carrier in a 3-m length of silicon tubing (bore 0.5 mm) maintained at 30°C in a thermostatic bath. The absorbance intensity was measured at 520 nm. The detection limit was 20 ng ml⁻¹ and the RSD% of 20 injections of 1 μg ml⁻¹ of nitrite was 0.65%. Analysis can be done at a rate of up to 30 h⁻¹. Under the optimum conditions in the concentration range of 30–4000 ng ml⁻¹ of nitrite ion, a linear calibration graph was obtained (r=0.9999). The method was applied successfully to the determination of nitrite in sausages.     

Synthesis and characterization of a novel cross-linking complex of beta-cyclodextrin-o-vanillin benzoylhydrazone and its selective spectrofluorimetric determination of trace amounts of zinc

A novel host inclusion complex of beta-cyclodextrin-o-vanillin benzoylhydrazone (beta-CDP-OVBH) was prepared and characterized by IR and 1H-NMR spectra. A highly selective and sensitive fluorescent determination of trace amounts of zinc was proposed based on the reaction between Zn(2+) and beta-CDP-OVBH in sodium hydroxide-ammonium acetate buffer medium of pH 8.3. The molar ratio of beta-CDP-OVBH to Zn(2+) was 1:1.The maximum excitation and emission wavelengths were 396 and 486 nm, respectively. The linear range of this method was 2.5-500 microg l(-1) with a detection limit of 0.60 microg l(-1). The effect of interferences in the determination of zinc was investigated, the results showed that the host reagent had a quite high identifying capacity on Zn(2+). This method was successfully applied to the determination of trace amounts of Zn(2+) in tea and human hairs.     

Highly sensitive spectrofluorimetric assay of glutathione in vegetables

A highly sensitive and simple spectrofluorimetric method for the determination of reduced glutathione based on the fluorescence quenching effect of glutathione on the hemoglobin-catalyzed reaction of H₂O₂ with L-tyrosine was developed. The concentration of glutathione is linear with the fluorescence quenching (??F) of system under the optimal experimental conditions. The calibration graph is linear in the range 6.25 × 10^?9 to 3.75 × 10^?6 M with the detection limit of 2.23 × 10^?9 M. This method can be used for the determination of glutathione in vegetables with satisfactory results.     

Spectrofluorimetric determination of trace heparin using lomefloxacin-terbium probe

A new spectrofluorimetric method was developed for determination of trace amount of heparin (Hep). Using lomefloxacin (LOM)-terbium ion (Tb3+) as a fluorescent probe, in the buffer solution of pH 8.70, Hep can remarkably enhance the fluorescence intensity of the LOM-Tb3+ complex at lambda = 545 nm and the enhanced fluorescence intensity of Tb3+ ion is in proportion to the concentration of Hep. Optimum conditions for the determination of Hep were also investigated. The linear range for the determination of Hep was 0.6-2.0 microg/ml and the detection limit was 45.22 ng/ml. This method is simple, practical and relatively free of interference from coexisting substances and can be successfully applied to assess Hep in biological samples. By the Rosenthanl graphic method, the association constant of Hep with the probe is 4.56 x 10(4) l/mol and binding numbers is 18.2. Moreover, the enhancement mechanism of the fluorescence intensity in the LOM-Tb3+ system and the LOM-Tb3+-Hep system have also been discussed.     

Highly sensitive biotin-labelled hybridization probe

A simple chemical method for introducing biotin into nucleic acids has been developed for the synthesis of nonisotopic hybridization probes. The method is based on the reaction of biotin hydrazide with amino residues of nucleic acids by using glutaraldehyde as a bifunctional coupling reagent. Biotin-labelled deoxyribonucleic acid (DNA) was detected by the use of alkaline phosphatase-labelled avidin, and alkaline phosphatase activity was measured by colorimetric and chemiluminescence methods. The chemiluminescence method using the nicotinamide adenine dinucleotide phosphate (NADP)/alcohol/alcohol dehydrogenase/microperoxidase/isoluminol system gave the highest sensitivity. A few picograms of lambda-phage DNA coated on a microtiter plate well could be detected by this method.     

Highly sensitive optical humidity probe

A highly sensitive optical humidity probe based on reflectance measurements has been developed using Nafion^®-crystal violet (CV) films. This sensor can be used to calibrate relative humidity (RH) in the range 0-0.25% with a detection limit (blank signal + 3σ_b, where σ_b = the standard deviation (S.D.) of the blank signal) of 0.018% RH (∼4.37 ppm) and exhibited low hysteresis. The sensor films were fully reversible in dry nitrogen and reversal times were shown to be dependent on exposure time and % RH. The response to 1% RH was highly reproducible (S.D. = 1.67%, number of samples (n) = 5). Hydrogen chloride gas did not interfere with the response of the sensor to RH but did reduce sensor reversal times. This sensor displayed sufficient sensitivity that it could be used to detect ppm levels of moisture in process gases such as nitrogen and HCl.     

Highly sensitive spectrophotometric determination of trace amounts of platinum(IV) with the molybdate-basic dyes-poly(vinyl alcohol) system

Three highly sensitive spectrophotometric methods for the determination of platinum(IV) have been developed, based on its colour reactions with molybdate and basic dyes (BD) in aqueous solution in the presence of poly(vinyl alcohol). Platinum(IV) reacts with molybdate and BD to form ion — association complexes of composition (BD)₂[Pt (MoO₄)₃]. The molar absorptivities are between 6.83 × 10⁵ and 9.51 × 10⁵ dm³mol^–1cm^–1, the highest value being found with nile blue. Suitable conditions for the reactions and the effects of foreign ions were investigated. The methods can be applied to the spectrophotometric determination of trace amounts of platinum(IV) in some catalysts and ores.