Fluorimetric characterization of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) are a family of structurally related artificial nanomaterials with unusual properties and many potential applications. Most SWCNTs can emit spectrally narrow near-IR fluorescence at wavelengths that are characteristic of their precise diameter and chiral angle. Near-IR fluorimetry therefore offers a powerful approach for identifying the structural species present in SWCNT samples. Such characterization is increasingly important for nanotube production, study, separation, and applications. General-purpose and specialized instruments suitable for SWCNT fluorimetric analysis are described, and methods for interpreting fluorimetric data to deduce the presence and relative abundances of different SWCNT species are presented. Fluorescence methods are highly effective for detecting SWCNTs in challenging samples such as complex environmental or biological specimens because of the methods’ high sensitivity and selectivity and the near absence of interfering background emission at near-IR wavelengths. Current limitations and future prospects for fluorimetric characterization of SWCNTs are discussed.     

Automated standard addition for fluorimetric steady-state and reaction-rate measurements

Instrumentation and methodology are described in which fluorescence measurements are made on a sample before and after a microcomputer-controlled injection of a standard-addition aliquot. From the two measurements an dother information, the analyte concentration in the sample is calculated and reported. The automated standard-addition procedure is shown to reduce measurement errors of 25–40% due to the presence of matrix quenchers or absorbers to less than 2% for fluorimetric steady-state measurements of quinine sulfate and in a fluorimetric reaction-rate method for determination of aluminum.     

The use of polarizers to improve detection limits in fluorimetric analysis

The use of variously-oriented film polarizers to reduce scattered light interference in fluorimetric analysis is reported. Single horizontally-oriented polarizers in the excitation beam (to obtain fluorescence spectra) or the emission beam (to obtain excitation spectra) are efficient at removing first-order Rayleigh scattered light signals. Crossed polarizers are necessary to remove substantial second-order signals. With the aid of polarizers, fluorimetric detection limits can be considerably improved, even when excitation and emission maxima are well separated, and when deproteinized blood plasma is analyzed. Polarizers are also effective in reducing scattered light signals from macromolecular solutes.     

Fluorimetric detector and sensor for flow analysis made of light emitting diodes

Two compact optoelectronic fluorimetric devices operating according to the paired-emitter-detector-diode concept have been developed. The fluorimetric detector, fabricated of three light emitting diodes only, has been applied for the development of fluorimetric optosensor by further integration with sensing solid phase. In these investigations as a model analyte and as a model sensing layer useful for solid phase spectrometry, riboflavin and C18-silica have been chosen, respectively. Both developed analytical devices have been applied for non-stationary fluorimetric measurements performed under conditions of flow injection analysis. The presented flow-through detector and sensor operating under given flow conditions offer riboflavin determination in mg L⁻¹ and μg L⁻¹ ranges of concentration, respectively.     

Organic analysis by luminescence methods

This review presents the major features of luminescence methods relating to the estimation of organic compounds in solution. A notation for reporting fluorimetric determinations is proposed. The outstanding factors affecting the fluorescence of solutions are briefly reviewed, and determinations of compounds offering a native fluorescence are illustrated by selected examples. Special attention is paid to functional fluorimetry and to the determination of non-fluorescent compounds by means of chemical reactions giving rise to fluorescent species. Some enzymatic reactions are described, as far as they allow the estimation of definite chemicals. Phosphorimetry and chemiluminescence are exemplified. An appendix presents some new functional fluorimetric determinations developed by the authors.     

Construction of a compact spectrofluorometer/spectrophotometer system using a flexible liquid core waveguide

A liquid-core waveguide made of Teflon AF-2400 has been used to construct a simple, sensitive and robust instrument capable of performing fluorimetric and spectrophotometric analyses on aqueous solutions. The instrument, which uses a CCD array detection system, is unique in that high performance is achieved for both measurement techniques with minimal changes in instrument configuration. The fluorimetric detection limits for quinine sulfate and chlorophyll-a are 0.06 nanomolar and 0.03 nanomolar, respectively. Absorbance measurements using the same instrument demonstrate nanomolar detection capacities for hydrogen sulfide and subnanomolar detection limits for methylene blue.     

Correction for quenching in fluorimetric determinations using steady state fluorescence

Quenching corrections in fluorimetric estimations are arrived at using time resolved fluorometry, where the reduction in the lifetimes of the fluorophore in the presence of quenchers is a measure of the correction. A novel procedure for the correction of quenching in fluorimetric determinations using steady state fluorescence spectroscopy is described here. The method is based on the variation in the slope of the fluorescence versus concentration plots, as the quencher concentration is changed. As a test case, the procedure for the determination of uranium has been demonstrated in the presence of a number of metal ion quenchers.     

Photometric and fluorimetric kinetic determination of manganese by means of the oxidation of sodium 4,8-diamino-1,5-dihydroxyanthraquinone-2,6-disulphonate

Three kinetic methods for the determination of manganese, two of them by photometric monitoring and another by fluorimetric monitoring, based on the oxidation of sodium 4,8-diamino-1,5-dihydroxyanthraquinone-2,6-disulphonate are described. A critical comparative evaluation of both monitoring techniques and their effect on the analytical figures of merit of the methods has been made. Manganese contents between 6.5 and 21.7 ng ml can be determined with relative standard deviation of +/- 3.7%. Under appropriate working conditions, the fluorimetric method can be satisfactorily applied to the determination of manganese in environmental samples of tap water and workroom metallic fumes.     

Exploitation of synthetic surfactant vesicles for enhanced fluorescence of metal chelates

The use of synthetic surfactant vesicles as a means for enhancing the photoluminescence of metal chelates is illustrated and a sensitive fluorimetric determination of aluminium with quinolin-8-ol-5-sulphonic acid in vesicles of didodecyldimethylammonium bromide is given. The influence of different variables on the organized aluminium-quinolin-8-ol-5-sulphonic acid reaction is investigated and possible mechanisms of the observed enhancing effects are discussed. The limit of detection is 1 μg l^?1 of aluminium. The optimized fluorimetric method has been successfully applied to the determination of aluminium in tap waters and dialysis fluids.     

Fluorescence analysis in air pollution research

Luminescence phenomena are of value in the analysis of air pollutants. The problems arising in the use of excitation and emission spectra under various conditions are discussed. Phenomena such as solvent, pH, and photochemical effects are shown to play an important role in the fluorimetric analysis of air pollutants. Many of the fluorimetric methods used in the trace analysis of organic airborne particulates involve factors such as direct measurement of the separated pollutant on a chromatogram or pherogram, quenching phenomena, scanning, excimer formation, charge-transfer fluorescence, sensitized fluorescence, and photo-oxidation on adsorbent or in solution. In addition, fluorescence assay methods are discussed in terms of selectivity, sensitivity, speed, simplicity, accuracy, precision, interferences, and the relation between concentration and fluorescence intensity.     

Uronic acid determination by high performance liquid chromatography with postcolumn fluorescence derivatization

To develop a fluorimetric high performance liquid chromatography (HPLC) technique for uronic acid microanalysis, a saline mobile phase and the postcolumn fluorimetric determination were combined. The detection limits of D-glucuronic, D-galacturonic and D-mannuronic acids were 7.19, 23.88 and 7.08 pmol, respectively. The proposed method was successfully applied to uronic acid microanalysis in a polysaccharide hydrolysate and a drink.     

New Fluorimetric Detection Method of Corticosteroids after High-Performance Liquid Chromatography Using Post-Column Derivatization with Glycinamide

Abstract

Some biological corticosteroids were detected by a new fluorimetric method using post-column derivatization with glycinamide.

Urinary corticosteroids which are hydrolyzed and extracted from sample fluid are detected by the reaction with glycinamide in the presence of hexacyanoferrate (III) in weakly alkaline media of borate buffer solution of pH 9.8 at 90 [ddot]C for 5 min.

This method is highly sensitive and specific for some corticosteroids and the reaction is performed under mild condition, compared with the fluorimetric method using the reaction with sulfuric acid, so that this method can be used for fractional assay of urinary corticosteroids of patients for a steroid abnormal metabolism.     

3-Hydroxypyridine-2-aldehyde 2-pyridylhydrazone as an analytical reagent: Fluorimetric Determination of Aluminium in Natural Waters

The properties of 3-hydroxypyridine-2-aldehyde 2-pyridylhydrazone as a spectrophotometric and fluorimetric reagent are described. The four ionization constants are reported. A rapid procedure for the fluorimetric determination of 2—300 ppb(7.2 × 10^-81.1 × 10^-5 M) of aluminium in acetate-buffered medium is described (λ_ex = 390 nm, λ_em = 475 nm). Interferences have been evaluated, and the procedure has been applied satisfactorily to the determination of aluminium in potable, fresh and sea waters.     

Direct laser photo-induced fluorescence determination of bisphenol A

Classical photo-induced fluorescence methods are conducted in two steps: a UV irradiation step in order to form a photo-induced compound followed by its fluorimetric determination. Automated flow injection methods are frequently used for these analyses. In this work, we propose a new method of direct laser photo-induced fluorescence analysis. This new method is based on direct irradiation of the analyte in a fluorimetric cell in order to form a photo-induced fluorescent compound and its direct fluorimetric detection during a short irradiation time. Irradiation is performed with a tuneable Nd:YAG laser to select the optimal excitation wavelength and to improve the specificity. It has been applied to the determination of bisphenol A, an endocrine disrupter compound that may be a potential contaminant for food. Irradiation of bisphenol A at 230 nm produces a photo-induced compound with a much higher fluorescence quantum yield and specific excitation/emission wavelengths. In tap water, the fluorescence of bisphenol A increases linearly versus its concentration and, its determination by direct laser photo-induced fluorescence permits to obtain a low limit of detection of 17 μg L⁻¹.     

Fluorimetry compared to spectrophotometry for uranium evaluation in liquid waste

Uranium concentration levels in surface waters are of great importance because uranium presents both chemical and radiological hazard to the environment. The subject of this article is to establish that spectrophotometric method for uranium evaluation in effluents collected from liquid waste treatment generated during fabrication of nuclear fuel elements could be replaced by the optical fluorimetric technique. Both methods are briefly described. The comparison of the two methods was carried out with regard to international standards and national regulations offering from a statistical point of view a useful approach to compare two analytical measurement techniques. This methodology can be applied to any other measurement procedures. A discussion about the compliance of the fluorimetric analytical method with the mandatory discharge level of uranium concentration in surface waters is also presented.     

The fluorescence properties of metal complexes of alkyl derivatives of aromatic schiff bases

Seventeen alkylated salicylidene-o-aminophenol derivatives were tested as fluorimetric reagents for aluminium, gallium, indium, scandium and beryllium. The aluminium, gallium and beryllium complexes are intensely fluorescent, and the scandium and indium complexes weakly fluorescent. The fluorescence properties of the aluminium, gallium and beryllium complexes were studied and conditions for the fluorimetric determination of these metals were established. 2-Hydroxy-4-methylaniline-N-2-hydroxy-4-methyl-benzylidene is a good reagent because of the reproducibility and sensitivity of the fluorescence. The optimal ranges for determination are 0.005–3 mg Al/25 ml, 0.1–7 μg Ga/25 ml and 0.02–7 μg Be/25 ml. In all cases, 1:1 metal—ligand complexes are formed. Optimal reaction conditions and interference studies are reported.     

Validated spectrophotometric and fluorimetric methods for analysis of clozapine in tablets and urine

Five spectrophotometric methods and one fluorimetric method have been developed and validated for the analysis of clozapine. The spectrophotometric methods were based on the charge-transfer complexation reaction between clozapine as electron donor and each of iodine as sigma-acceptor or 7,7,8,8-tetracyanoquinondimethane (TCNQ), 2,3-dichloro-5,6-dicyano-1,4-benzo-quinone (DDQ), tetracyanoethane (TCNE), and p-chloranilic acid (pCA) as pi-acceptors. The obtained complexes were measured spectrophotometrically at 365, 843, 460, 414, and 520 nm for iodine, TCNQ, DDQ, TCNE, and pCA, respectively. The fluorimetric method was based on the oxidation of clozapine in the presence of perchloric acid by cerium (IV), and subsequent measuring the fluorescence of the produced cerium (III) fluorimetrically at lambda(excitation) 260 and lambda(emission) 355 nm. Under the optimum assay conditions, Beer's law was obeyed at concentrations ranged from 4-200 microg mL(-1) for the spectrophotometric methods and from 24-250 ng mL(-1) for the fluorimetric method. The limits of detection for the spectrophotometric methods were 1.12, 1.76, 2.22, 0.95, and 13.26 microg mL(-1) for iodine, TCNQ, DDQ, TCNE, and pCA, respectively. The limit of detection for the fluorimetric method was 6.69 ng mL(-1). The proposed methods were successfully applied to the analysis of clozapine in tablets with good recoveries. The fluorimetric method could also be applied to the analysis of clozapine in spiked urine samples. The molar ratios and the reaction mechanisms were investigated.     

Enhancement of the Fluorimetric Properties of Some Carboxyl Substituted Anthracenes by Complexation with Bovine Serum Albumin

Abstract

A study has been conducted of the fluorimetric properties of substituted anthracenes, following complexation with bovine serum albuinin(BSA). It was found that although protein binding of the ligands enhances their fluorimetric properties, it fails to do so for their phosphorimetric properties. BSA would serve well in post column reactors for HPLC detectors, but not in pre-column systems.     

Development and comparison of different fluorimetric HPLC-methods with standard methods for the determination of formaldehyde in the atmosphere

Summary Three different fluorimetric methods for the measurement of atmospheric formaldehyde are described. The relatively unknown 2-diphenylacetylindan-1,3-dionhydrazine (DAIH) method was developed and optimized with an improved limit of detection of 2 ppbv corresponding to a sample volume of 7.5 L. Separation of lutidines necessary for the Nash method was successfully carried out and the separation time was reduced by a factor of 5. The detection limit of the Nash method was improved to 1 ppbv. In comparison, the N,N-diphenyl-1-naphthylamine-5-sulfonhydrazine (DNSH) method performed in a similar manner, reached an LOD of 0.5 ppbv. Finally, measurements made in candle smoke using the three different fluorimetric methods and three standard methods yielded very similar results.