Presence Of Rhodamine 6G Research Articles

Spectral analysis and dynamic properties of polyurethanes dyed with rhodamine 6G and rhodamine B as matrices of a solid-state laser element

A comparison was carried out of the nature of intermolecular interactions, elastic properties and gas permeability of the crosslinked polyurethanes doped with xanthene dyes and original polyurethane using IR spectroscopy, dynamic mechanical analysis (DMA) and electron paramagnetic resonance (EPR). The introduced dye can be considered as useful microimpurity which, however, can affect the efficiency of the laser. In IR spectra of polyurethanes the complex band of stretching vibrations of C=O groups is sensitive to the nature of intermolecular interaction of urethane groups. From the analysis of that band it is shown that in the presence of dyes, self-association of urethane groups within the hard segment predominates and the interaction of urethane groups with the oligoether component decreases, which can contribute to increasing the mobility of the flexible component. A decrease in the dynamic storage modulus (E’) and a decrease in the glass transition temperature (Tc) of polyurethanes in the presence of dyes is shown by the DMA method. The results of both DMA and IR spectroscopy indicate a greater increase in the mobility of the elastic component with the introduction of the rhodamine B dye, covalently bound to the polyurethane chain. According to nitroxyl paramagnetic probe data the introduction of both rhodamine B and rhodamine 6G dyes into polyurethanes increases their permeability to vapors of low-molecular weight compounds, but rhodamine 6G has a more prominent effect on this characteristic. This is consistent with DMA data indicating a greater increase in the Mc value in the presence of rhodamine 6G in polyurethane. The obtained results make it possible to determine the optimal composition of the active laser medium and are important in assessing the radiation resistance of the polymer matrix. Its increase is facilitated by a decrease in the storage modulus and an increase in the gas permeability of the polymer, leading to a decrease in pressure in the area of local heating.

Spectroscopic Insights of an Emissive Complex between 4'-N,N-Diethylaminoflavonol in Octa-Acid Deep-Cavity Cavitand and Rhodamine 6G.

Excited-state chemistry relies on the communication between molecules, making it a crucial aspect of the field. One important question that arises is whether intermolecular communication and its rate can be modified when a molecule is confined. To explore the interaction in such systems, we investigated the ground and excited states of 4'-N,N-diethylaminoflavonol (DEA3HF) in an octa acid-based (OA) confined medium and in ethanolic solution, both in the presence of Rhodamine 6G (R6G). Despite the observed spectral overlap between the flavonol emission and the R6G absorption, as well as the fluorescence quenching of the flavonol in the presence of R6G, the almost constant fluorescence lifetime at different amounts of R6G discards the presence of FRET in the studied systems. Steady-state and time-resolved fluorescence indicate the formation of an emissive complex between the proton transfer dye encapsulated within water-soluble supramolecular host octa acid (DEA3HF@(OA)2) and R6G. A similar result was observed between DEA3HF:R6G in ethanolic solution. The respective Stern-Volmer plots corroborate with these observations, suggesting a static quenching mechanism for both systems.

Water-stable Perovskite Quantum Dots-based FRET Nanosensor for the Detection of Rhodamine 6G in Water, Food, and Biological Samples

The practical application of perovskite quantum dots (QDs) for sensing in the aqueous phase has been restricted by their poor resistance to moisture and oxygen due to their highly ionic characteristic. In this work, we employed silica and phospholipid co-encapsulated water-stable all-inorganic CsPbBr3 QDs as a ratiometric fluorescence resonance energy transfer (FRET)-based fluorescence nanosensor for the detection of Rhodamine 6G (R6G) in food, water, and biological samples. The nanosensor on its own exhibits a strong green emission signal at 518 nm. However, in the presence of R6G, the original fluorescence signal at 518 nm decreases while a new emission peak at 565 nm increases, accordingly, indicating a typical ratiometric fluorescence relationship. The fluorescence intensity ratio (I565/I518) was found to be linearly correlated to the concentration of R6G present. The proposed R6G nanosensor has a linear operating range of 0 – 10 μg/mL and a detection limit of 0.01 μg/mL. In addition, the proposed nanosensor displayed good selectivity towards R6G when tested with other color additives and was also able to detect R6G in tap water, food, and biological samples that contain complex interfering background species. Overall, this work opens a new avenue for water-stable perovskite quantum dots for aqueous-phase sensing applications.

Effect of the Cationic Head Group on Cationic Surfactant-Based Surfactant Mediated Gelation (SMG).

The surfactant-mediated gelation (SMG) method allows us to formulate hydrogels using a water-insoluble organogelator. In this study, we formulated hydrogels using three cationic surfactants, hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), and hexadecylpyridinium chloride (CPC)] and an organogelator (12-hydroxyoctadecanoic acid (12-HOA), and studied their structures and mechanical properties. A fiber-like structure similar to that found in the 12-HOA-based organogels was observed by optical microscopy. Small- and wide-angle X-ray scattering profiles showed Bragg peaks derived from the long- and short-spacing of the crystalline structures in the gel fibers and a correlation peak from the surfactant micelles in the small-angle region. Furthermore, the formation of micelles in the hydrogels was confirmed by UV-vis spectroscopic measurements of the gel samples in the presence of Rhodamine 6G. We concluded that the hydrogels prepared by the SMG method in the present systems are orthogonal molecular assembled systems in which two different molecular assembled structures coexist. Among the three surfactant systems, the CTAB system presented the lowest critical gelation concentration and highest sol-gel transition temperature and viscoelasticity. These differences in gel fiber formation and gel properties were discussed from the viewpoint of the degree of solubilization of the gelator molecules in micelles coexisting with gel fibers and diffusion of the gelator molecules in the gel formation process.

Optical characterization of graphene-f-o-phenylenediamine and charge transfer interaction with organic dyes

Carbon based nanomaterials can effectively be doped to tailor their electronic and optical properties for various applications. In this work, we have synthesized and characterized the o-phenylenediamine doped graphene (G-f-OPD) to study the charge transfer with a standard laser dye rhodamine 6G (R6G). A comparison with pristine graphene shows that the static quenching efficiency of the graphene is 25 times higher than that of the G-f-OPD. Time-resolved measurements reveal the absence of dynamic quenching of the dye in presence of graphene and its nitrogen doped derivative. Nonlinear optical characterization of G-f-OPD has also been done in presence of R6G by degenerate four wave mixing (DFWM) technique. The measured values of third order optical nonlinearity (χ(3)) reveals the fact that the dominant contribution to the optical nonlinearity is due to its real part at the probe wavelength (532 nm). Furthermore, the nonlinear optical study by Z-Scan technique shows that G-f-OPD-R6G composite can be suitable for passive mode-locking applications.

Mechanistic Studies on the Salicylate-Catalyzed Peroxyoxalate Chemiluminescence in Aqueous Medium.

The peroxyoxalate reaction is one of the most efficient chemiluminescence transformations known and the onlysystem occurring by an intermolecular chemically initiated electron exchange luminescence (CIEEL) mechanism with confirmed high quantum yields. The peroxyoxalate chemiluminescence (PO-CL) is mainly studied in anhydrous organic medium; however, for bioanalytical application, it should be performed in aqueous media. In the present work, we study the peroxyoxalate system in a binary 1,2-dimethoxyethane/water mixture with bis(2,4,6-trichlorophenyl) oxalate (TCPO), bis(4-methylphenyl) oxalate (BMePO) and bis[2-(methoxycarbonyl)phenyl] oxalate (DMO), catalyzed by sodium salicylate, in the presence of rhodamine 6G as activator. Reproducible kinetic results are obtained for all systems; emission decay rate constants depend on the salicylate as well as hydrogen peroxide concentration, and the occurrence of a specific base catalysis is verified. Although singlet quantum yields determined are lower than in anhydrous media in comparable conditions, they are still considerably high and adequate for analytical applications. The highest singlet quantum yields are obtained for the "ecologically friendly" derivative DMO indicating that this derivative might be the most adequate substrate for the use of the peroxyoxalate system in bioanalytical applications.

Fluorescent detection of cholesterol using p-Sulfonatocalix[4]arene functionalized carbon nanotubes and thermally reduced graphite oxide composites

In the present study, carbon nanotube (CNT), thermally reduced graphite oxide (TRGO), and CNT-TRGO were functionalized with p-sulfonatocalix[4]arene (SC4) and then investigated for fluorescent detection of cholesterol in the presence of rhodamine 6G (R6G). All of the composite samples show effective quenching of R6G fluorescent intensity without cholesterol, but the fluorescence intensity significantly increases with the addition of cholesterol. The results indicate a strong interaction between SC4 composites and cholesterol rather than between the SC4 composites and R6G, increasing R6G fluorescence intensity in the presence of cholesterol due to the release of R6G from the SC4 composites. Formation of the complex, made of the SC4 composite plus the cholesterol, enables the detection of cholesterol in the wide range of cholesterol concentration up to 109 µM. The binding constant between SC4 and cholesterol has been calculated, indicating that the SC4 composites display the maximum binding constant of 1.9 × 104 M−1 with cholesterol.

Development of a new analytical method for Pb preconcentration and its further determination in water and foodstuffs using relatively low-sensitivity flame atomic absorption spectrometry

ABSTRACTThe present study describes chelation of Pb(II) with ascorbic acid and formation of a charge-transfer sensitive ion-pair in the presence of Rhodamine 6G at pH 5.5, and then its extraction to the micellar phase of non-ionic surfactant, PONPE 7.5 by an ultrasound-assisted cloud point extraction method before analysis by FAAS. The various variables affecting ion-pair formation and extraction efficiency were studied and optimised. Under the optimised conditions, the good linear relationships in the ranges of 0.4–150 μg L−1 and 0.8–120 μg L−1 for solvent-based calibration and matrix-matched calibration curves, respectively, were achieved with a pre-concentration factor of 71.4 from pre-concentration of 50-mL sample. Moreover, the limits of detection with good sensitivity enhancements of 124 and 114.5 were 0.13 and 0.24 μg L−1, respectively, while the intra-day and inter-day precision (as RSD%, for five replicate measurements of 5 and 100 μg L−1 in the same day and three succeed days) were in range of 2.8–5.4% and 3.7–6.3%, respectively. The matrix effect on triplicate determination of 50 µg L−1 Pb(II) was also investigated. The accuracy of the method was statistically verified by the analysis of two certified reference materials (CRMs) after digestion with acid mixtures (HNO3-H2O2-HF and HNO3-H2O2) and dilution at suitable ratios. It has been observed that there is statistically not a significant difference between the certified- and found-values. The accuracy was also controlled using the pre-treated sample solutions spiked at different concentration levels, and the good spiked recoveries were obtained in range of 90–102.8%. The method was successfully applied to the determination of trace amounts of lead in water and food matrices with satisfactory results.

Cyclodextrin-carbon nanotube composites for fluorescent detection of cholesterol

The efficiency of cyclodextrin-carbon nanotube composites (CD-CNT) for cholesterol detection was investigated using their fluorescent yields in the presence of rhodamine 6G (R6G). The CD-CNT composites using α-, β- and γ-cyclodextrin (x-CD) all showed strong fluorescent responses to cholesterol when in the presence of R6G. The α-CD based composites, however, exhibit more dramatic fluorescent changes in response to cholesterol, over a wider range of cholesterol concentrations, and also display the highest binding constant of 2.98×105M−1 with cholesterol. The effectiveness of these fluorescent responses for the detection of cholesterol depends primarily on the concentration and cavity size of the CD.

Computational design and fabrication of core-shell magnetic molecularly imprinted polymer for dispersive micro-solid-phase extraction coupled with high-performance liquid chromatography for the determination of rhodamine 6G.

A novel core-shell magnetic nano-adsorbent with surface molecularly imprinted polymer coating was fabricated and then applied to dispersive micro-solid-phase extraction followed by determination of rhodamine 6G using high-performance liquid chromatography. The molecularly imprinted polymer coating was prepared by copolymerization of dopamine and m-aminophenylboronic acid (functional monomers), in the presence of rhodamine 6G (template). The selection of the suitable functional monomers was based on the interaction between different monomers and the template using the density functional theory. The ratios of the monomers to template were further optimized by an OA9 (3(4) ) orthogonal array design. The binding performances of the adsorbent were evaluated by static, kinetic, and selective adsorption experiments. The results reveal that the adsorbent possesses remarkable affinity and binding specificity for rhodamine 6G because of the enhanced Lewis acid-base interaction between the B(Ш) embedded in the imprinted cavities and the template. The nano-adsorbent was successfully applied to dispersive micro-solid-phase extraction coupled to high-performance liquid chromatography for the trace determination of rhodamine 6G in samples with a detection limit of 2.7 nmol/L. Spiked recoveries ranged from 93.0-99.1, 89.5-92.7, and 86.9-105% in river water, matrimony vine and paprika samples, respectively, with relative standard deviations of less than 4.3%.

Rhodamine 6G assisted adsorption of metanil yellow over succinamic acid functionalized MCM-41

The adsorption properties of succinamic acid functionalised MCM-41 (SA-MCM-41) towards dyes aqueous solution, such as rhodamine 6G (R6G), methylene blue (MB) and metanil yellow (MY), were studied. SA-MCM-41 was synthesised using a three step synthesis strategy, starting with the preparation of MCM-41 through a sol–gel methodology. Succinamic acid functionality was introduced through a ring opening reaction of succinic anhydride (SA) over the propyl amine functionality of A-MCM-41 in presence of trimethylamine. The materials at each synthesis step were characterised by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, N2 adsorption–desorption isotherms, Fourier transform infrared spectroscopy, and 29Si and 13C nuclear magnetic resonance spectroscopies. SA-MCM-41 exhibited good adsorption capacity towards R6G and MB but poor adsorption for MY from the individual dye solutions. The competitive adsorption from binary and ternary dye mixtures showed that SA-MCM-41 can remove MY effectively in the presence of R6G. The adsorption behaviour of R6G and MY over SA-MCM-41 from binary and ternary mixtures highlight the possibility of multilayer adsorption. The MY removal efficiency of pristine MCM-41 from R6G-MY binary mixture was also tested.

Florescent silica PVA hybrids via sol–gel processing

A cost-effective, one-pot synthesis approach is reported to fabricate Rhodamine 6G (R6G) silica hybrid xerogels. Polyvinyl alcohol (PVA) is used as a non-ionic surfactant to homogeneously trap the dye in silica matrix. Presence of R6G in silica matrix is confirmed through Fourier Transform Infrared (FTIR) spectroscopy and Thermo Gravimetric Analysis (TGA) studies. Hybrids containing larger amount of PVA are found to exhibit better thermal stability than the hybrids with lesser PVA content. Optical properties of the hybrids are analyzed via UV–visible spectroscopy, and it is discovered that hybrids containing larger amounts of PVA do not form aggregates. Uniform distribution of fluorophores in silica matrix helps to minimize formation of J-aggregates in the hybrids, therefore making them ideal candidates for use in dye lasers. The resultant hybrids can be ascribed as stable multicomponent systems that exhibit excellent monodispersity and brightness.

Kinetics and mechanism of ionic intercalation/de-intercalation during the formation of α-cobalt hydroxide and its polymorphic transition to β-cobalt hydroxide: reaction–diffusion framework

We study the kinetics and mechanism of intercalation and de-intercalation of small anions during the formation of crystalline α-Co(OH)2 and its transformation to β-Co(OH)2 within a reaction–diffusion framework. We therein use fluorescence spectroscopy with Rhodamine 6G (Rh6G) as a probe as well as other spectroscopic and imaging techniques. The method is based on the reaction and diffusion of hydroxide ions into a gel matrix containing the Co(II) ions, the conjugate anions to be intercalated and Rh6G. The advantage of this simple method is that it allows us to separate throughout space the various stages during the formation of α-Co(OH)2 and its transformation to β-Co(OH)2, thus enabling fluorescence measurements of the those stages by simply focusing on different areas of the tube. It also permits us to extract with ease the solids for characterization and image analysis. The macroscopic evolution of the system, which consists of a leading blue front designating the formation of α-Co(OH)2 followed by a sharp blue/pink interface designating the transformation to the pink β-Co(OH)2, exhibits different dynamics depending on the anion present in the gel. At a certain stage, the blue/pink interface stops its propagation and only the blue front continues. This represents clear evidence of the dependence of the kinetics of intercalation and de-intercalation on the nature of the anion. The coexisting polymorphs were collected and characterized using XRD, FTIR, Raman and UV-Vis. The fluorescence images of the α-Co(OH)2 reveal clearly the presence of Rh6G between its layers, whereas images from the β polymorph indicate the opposite. Moreover, the fluorescence of Rh6G is monitored during the formation of α-Co(OH)2 and its conversion to β-Co(OH)2. During the formation, the fluorescence intensity and lifetime are significantly increased whereas the opposite happens during the transformation to the β phase. We are able to calculate the activation energies associated with the intercalation and de-intercalation of anions and show using SEM that the polymorphic transformation is accompanied by an Ostwald ripening mechanism whereby the smaller crystals of α-Co(OH)2 dissolve to reappear as larger crystals of β-Co(OH)2. We find that the activation energies of de-intercalation are systematically smaller than those of intercalation. Our results confirm many aspects of the results of Du et al. on the conversion of a chloride-intercalated α-Co(OH)2 to β-Co(OH)2.

Sensitization of fluorescence of dye molecules in nanoparticles of metal complexes

We studied the dependence of absorption and fluorescence spectra of complexes of Al, In, Sc, Y, and La with dibenzoylmethane and naphthoyltrifluoroacetone, as well as the dependence of sensitized fluorescence of dyes in nanoparticles of these complexes, in relation to the water pH, the ratio between ions and diketones, and the ion selection. We showed that the ability of complexes of ions to form nanoparticles that efficiently sensitize dye molecules incorporated into them is determined by stability constants of these ions with organic ligands and by their ability to compete with the formation of hydroxy complexes of these ions. We found that nanoparticles consist of diketonates of different compositions and that Nile red incorporated into nanoparticles is an indicator of the dependence of the composition of nanoparticles on the selection of the central ion of complexes and conditions of their formation. We revealed that complexes M(diketone)(OH)2 self-assemble into nanoparticles with an admixture of dye molecules and efficiently sensitize dyes upon excitation into absorption bands of complexes. We showed that, at concentrations of rhodamine 6G in water smaller than 50 nM, the use of a solution that contains 50 μM of Al(III), In(III), or Sc(III) + 50 μM of naphthoyltrifluoroacetone makes it possible to increase the sensitivity of the luminescence analysis by 20-fold for the presence of rhodamine 6G in an aqueous solution.

Analysis of parabens in cosmetics by low pressure liquid chromatography with monolithic column and chemiluminescent detection

This paper presents an application of chromatographic separation based on an ultra-short monolithic column and chemiluminescent detection in an FIA type instrument manifold for the determination of four paraben mixtures: methylparaben (MP), ethylparaben (EP), propylparaben (PP) and butylparaben (BP). The separation is achieved in 150 s using two consecutive carriers: first 12% ACN:water that changes 75 s after injection to 27% ACN:water. The detection is based on the oxidation of the hydrolysis product of parabens, p-hydroxybenzoic acid, with Ce(IV) in the presence of Rhodamine 6G which evokes chemiluminescence of sufficient intensity to enable a sensitive determination of these species. After optimization of the variables involved, the analytical method is characterized, displaying the following values for concentration ranges, detection limits and precision, as relative standard deviation at low concentration (0.15 mg l −1)—MP: from 9.9 × 10 −7 to 3.3 × 10 −4 M; 1.9 × 10 −8; 5.6%; EP: from 9.0 × 10 −7 to 3.3 × 10 −4 M; 2.8 × 10 −8; 3.5%; PP: from 8.3 × 10 −7 to 9.9 × 10 −5 M; 2.3 × 10 −8; 4.2%; and BP: from 7.7 × 10 −7 to 9.9 × 10 −5 M; 4.2 × 10 −8 M; 6.2%. The method was applied and validated satisfactorily for the determination of these parabens in cosmetic samples, comparing the results against a liquid chromatography reference method.

A study of quenching and enhancing effects of some amino acids on peroxyoxalate chemiluminescence of rhodamine 6G

The quenching effect of l-cysteine, l-methionine on strong chemiluminescence of bis(2,4,6-trichlorophenyl)oxalate–H 2O 2 system in the presence of rhodamine 6G was studied. The chemiluminescence parameters were evaluated from computer fitting of the resulting intensity–time plots. These systems resulted in Stern–Volmer plots in the quencher concentration range of 4.0 × 10 −6 to 4.0 × 10 −5 M, with K Q values of 1.64 × 10 4 and 8.0 × 10 4 M −1 for l-metionine and l-cysteine, respectively. Also, this study describes the employment of l-histidine as a highly potent signal enhancer in peroxyoxalate chemiluminescence in the presence of rhodamine 6G.

Interfacial Recognition of Acetylcholine by an Amphiphilic p-Sulfonatocalix[8]arene Derivative Incorporated into Dimyristoyl Phosphatidylcholine Vesicles.

Dodecyl ether derivatives 1-3 of p-sulfonatocalix[n]arene were incorporated into dimyristoyl phosphatidylcholine (DMPC) vesicles, and their binding abilities for acetylcholine (ACh) were examined by using steady-state fluorescence/fluorescence anisotropy and fluorescence correlation spectroscopy (FCS). For the detection of ACh binding to the DMPC vesicles containing 5 mol % of 1-3, competitive fluorophore displacement experiments were performed, where rhodamine 6G (Rh6G) was used as a fluorescent guest. The addition of Rh6G to the DMPC vesicles containing 3 resulted in a decrease in the fluorescence intensity of Rh6G with an increase of its fluorescence anisotropy, indicating that Rh6G binds to the DMPC-3 vesicles. In the case of DMPC-1 and DMPC-2 vesicles, significant changes in the fluorescence spectra of Rh6G were not observed. When ACh was added to the DMPC-3 vesicles in the presence of Rh6G ([3]/[Rh6G]=100), the fluorescence intensity of Rh6G increased with a decrease in its fluorescence anisotropy. From the analysis of fluorescence titration data, the association constants were determined to be 7.1×105 M-1 for Rh6G-3 complex and 1.1×102 M-1 for ACh-3 complex at the DMPC-3 vesicles. To get a direct evidence for the binding of Rh6G and its displacement by ACh at the DMPC-3 vesicles, diffusion times of the Rh6G were measured by using FCS. Binding selectivity of the DMPC-3 vesicles for ACh, choline, GABA, l-aspartic acid,l-glutamic acid, l-arginine, l-lysine, l-histamine and ammonium chloride was also evaluated using FCS.

Nanostructured Hybrid Systems with Rhodamine 6G

We synthesized hybrid materials by sol-gel process, using: methyltriethoxysilane, tetraetylorthosilicate and vinyltriethoxysilane, in the presence of Rhodamine 6G. It was synthesized as well organic-inorganic hybrids with addition of tetraisopropyl orthotitanate and maleic anhydride UV-VIS spectra of dye show two absorption peaks at 499 nm (dimer) and 530 nm (monomer). Evaluating FTIR spectra of hybrid films, it was observed a band at 1077 cm−1, characteristic of the asymmetric Si-O-Si stretching vibration in oligomer. Fluorescence spectra show that tetraisopropyl orthotitanate presence in the composites modifies the nature of the inorganic matrix and affects the interaction with the added dye.

Biomimetic Synthesis of Inorganic Nanospheres

The synthesis of silica, silver bromide, and composite nanospheres made in the presence of block copolypeptide vesicles is reported. Hollow silica nanospheres of controllable size can be made with Lys:Phe 1:1 block copolypeptides, whereas at higher block ratios, uniform silica nanospheres are formed that are not hollow. Silver bromide nanospheres of controllable size in the range of 25−250 nm can also be formed, as well as silver bromide/silica core−shell particles. The silver bromide nanospheres can also be assembled into hollow rods in the presence of rhodamine 6G, and this process is reversible. The unique feature of this work is the ability to translate the information of an individual biomimetic supramolecular structure (e.g., vesicle) as a template into an inorganic material. The results show that block copolypeptides offer unique opportunities for assembling nanostructured materials.

Determination of hydrochlorothiazide in pharmaceutical preparations by time resolved chemiluminescence

A novel chemiluminescence method for the determination of hydrochlorothiazide (HCT) has been developed based on the reaction between Ce(IV) in acid medium with this diuretic agent in the presence of rhodamine 6G as sensitizer. The method described is based on the recording of the whole chemiluminescence intensity-versus-time profile that enables the use of other measured parameters such as the total area that is proportional to the analyte concentration. The optimum chemical conditions for the chemiluminescence emission were investigated. Two determination approaches, intensity and area, were proposed. The calibration graphs were linear for the concentration range from 0.5 to 30 μg ml −1. The detection limits, according to Clayton et al. [Anal. Chem. 59 (1987)], were 0.34 and 0.16 μg ml −1, for intensity and area measurements, respectively. For analysis of 10 solutions of 7.5 and 20 μg ml −1 HCT, if error propagation theory is assumed, the relative error was less than 2%. The present chemiluminescence procedures were applied to the determination of HCT in Spanish pharmaceutical formulations, with excellent recoveries, as the determination is free from interference from common excipients and other drugs which also be present in the formulation.