Application of Multivariate Calibration Techniques to HPLC Data for Quantitative Analysis of a Binary Mixture of Hydrochlorathiazide and Losartan in Tablets

New multivariate approaches have been applied to high-performance liquid chromatography (HPLC) with multiwavelength photodiode-array (PDA) detection. Multivariate calibration techniques such as partial least squares (PLS), principal component regression (PCR), classical least squares (CLS), and inverse least squares (ILS) was subjected to HPLC data for simultaneous quantitative analysis of synthetic binary mixtures and a commercial tablet formulation containing hydrochlorothiazide (HCT) and losartan potassium (LST). The combined use of HPLC and multivariate calibrations has been denoted HPLC–CLS, HPLC–ILS, HPLC–PCR, and HPLC–PLS. Successful chromatographic separation of the two active compounds and enalapril maleate, used as internal standard (IS), was accomplished by means of a 4.6 mm i.d. × 250 mm, 5 m particle, Waters Symmetry C₁₈ reversed-phase column and a mobile phase consisting of 60:40 acetate buffer (0.2 M, pH 4.8)–acetonitrile (v/v, 60:40). HPLC data based on the ratio of analyte peak areas to IS peak area were obtained by PDA detection at five-wavelengths (250, 255, 260, 265, and 270 nm). The HPLC–CLS, HPLC–ILS, HPLC–PCR, and HPLC–PLS calibration plots for hydrochlorothiazide and losartan potassium were constructed separately by using the peak-area ratios corresponding to the concentrations of each active compound. The HPLC multivariate calibrations obtained were tested for different synthetic mixtures containing HCT and LST in the presence of the IS. These multivariate chromatographic methods were also applied to a commercial pharmaceutical dosage form containing HCT and LST. The results obtained from the multivariate calibrations were compared with those obtained by use of another, classical HPLC method using single-wavelength detection.Revised: 29 September 2004 and 4 January 2005     

Neutron activation analysis of low level lithium in water samples

For determining low level lithium concentrations in water, a neutron activation method based on the measurement of tritium radioactivity produced by⁶Li(n,)³H reaction has been developed. This method is specific and free from interference by other chemical elements. Using a low background liquid scintillation counter for tritium measurement, the detection limit is approximately 0.3 ppm during irradiation at a thermal neutron flux density of 1.1·10⁷n·cm^–2·s^–1 for 6 hours by a small nuclear reactor and liquid scintillation counting for 2000 minutes     

A specific HPLC-UV method for the determination of cysteine and related aminothiols in biological samples

We present a highly selective and sensitive method for the determination of cysteine (Cys) and related aminothiols that play important roles in health and disease. The key step in the analysis is treatment with 1,1′-thiocarbonyldiimidazole (TCDI) that rapidly and quantitatively reacts with both the amino and thiol groups to form stable cyclic dithiocarbamates with intense UV absorption. Cys, homocysteine (hCys), and cysteinylglycine in plasma (75 μl), urine (100 μl), or cerebrospinal fluid (100–500 μl) were determined by separating and measuring their cyclic derivatives by a high performance liquid chromatograph (HPLC) connected to a UV detector. The chromatograms obtained using TCDI contained fewer and better-resolved peaks than those produced by less selective reagents used previously. Using chemically similar 2-methylcysteine as the internal standard, high repeatability (variation of less than 5%) and adequate sensitivity to detect small increments (10–20%) in the concentrations of cysteinylglycine and hCys were achieved. The HPLC method can also be modified to measure -penicillamine (greater than 0.8 μM) in plasma (50 μl) providing a potential method to monitor plasma levels of this drug in patients.     

Multimeric high-performance liquid chromatography of plant sterols using UV detection

A method for the multimeric high-performance liquid chromatography of plant sterols is proposed which permits the separation of compounds close in structure with similar chromatographic properties. The first stage includes the chemical modification of the sterols with the aid of a bis(p-nitrophenyl) phosphate group. The phosphotriesters formed as the result of the reaction are separated by normal-phase HPLC. The compounds isolated are treated with ammonia, as a result of which the sterol phosphotriesters are converted into the corresponding phosphodiesters. These phosphodiesters are then subjected to reversed-phase HPLC. The chromatographic separation of UV-absorbing sterol derivatives using several variants of HPLC substantially increases the resolving power of the method.State Scientific-Research Institute on the Standardization and Control of Drugs, USSR Ministry of Health, Moscow. L. V. Lomonosov Moscow State University. Translated from Khimiya Prirodynkh Soedinenii, No. 6, pp. 831–836, November–December, 1988.     

Phase Equilibria and Nonequilibrium Structures in the Sodium Di-2-Ethylhexyl Phosphate–Decane–Water System

Phase equilibria and nonequilibrium structures in the sodium di-2-ethylhexyl phosphate (NaSDEHP)–decane–water system were studied. It was found that, at a certain component ratio, a microemulsion and a liquid crystal phase are present in the system. The phase diagram was plotted, describing two- and three-phase equilibria: NaSDEHP and water solution in decane–microemulsion, microemulsion–liquid crystals, NaSDEHP and water solution in decane–microemulsion–liquid crystals, and NaSDEHP and water solution in decane–liquid crystals. The viscosity of NaSDEHP microemulsion was measured. It was shown that the viscosity increases significantly with an increase in the ratio of sodium hydroxide and di-2-ethyhexyl phosphoric acid molar concentrations from 0.6 to 1.0. Formation of the third liquid (microemulsion) phase in the vicinity of the oil–water interface was found upon the transfer of NaSDEHP from one phase to the other.     

Knudsen effusion mass spectrometric determination of mixing thermodynamic data of liquid Ag–In–Sn alloy

The vaporisation of a liquid Ag–In–Sn system has been investigated at 1273–1473 K by Knudsen effusion mass spectrometry (KEMS) and the data fitted to a Redlich–Kister–Muggianu (RKM) sub-regular solution model. Nineteen different compositions have been examined at six fixed indium mole fractions, X_In = 0.10, 0.117, 0.20, 0.30, 0.40 and 0.50. The ternary L-parameters, the thermodynamic activities and the thermodynamic properties of mixing have been evaluated using standard KEMS procedures and from the measured ion intensity ratios of Ag⁺ to In⁺ and Ag⁺ to Sn⁺, using a mathematical regression technique described by us for the first time. The intermediate data obtained directly from the regression technique are the RKM ternary L-parameters. From the obtained ternary L-parameters the integral molar excess Gibbs free energy, the excess chemical potentials, the activity coefficients and the activities have been evaluated. Using the temperature dependence of the activities, the integral and partial molar excess enthalpies and entropies were determined. In addition, for comparison, for some compositions, also the Knudsen effusion isothermal evaporation method (IEM) and the Gibbs–Duhem ion intensity ratio method (GD-IIR) were used to determine activities and good agreement was obtained with the data obtained from fitting to the RKM model.     

Simultaneous determination of DTPA,EDTA, and NTA by UV–visible spectrometry and HPLC

In this study, UV–visible spectrophotometry (UV–Vis) and high-performance liquid chromatography (HPLC) were used for simultaneous analysis of chelating agents diethylenetriamine pentaacetic acid (DTPA), ethylenediamine tetraacetic acid (EDTA), and nitrilotriacetic acid (NTA), as their metal chelates in dishwashing detergents, natural waters, and pulp mill water. The total amounts of the chelating agents in dishwashing detergents were verified by potentiometric titration with Fe(III) solution. Nickel(II) chelates were determined by UV–Vis and iron(III)chelates by HPLC and titration. Recoveries of DTPA, EDTA, and NTA from a standard mixture of analytes by UV–Vis were 107±7, 101±12 and 94±13%, respectively, and the recovery of the total amount of complexing agents was 99±4%. The limits of detection for DTPA, EDTA, and NTA were 667, 324, and 739 mol L^–1, respectively. In HPLC measurements the optimized mobile phase contained 0.03 mol L^–1 sodium acetate, 0.002 mol L^–1 tetrabutylammonium bromide, and 5% methanol at pH 3.15 and the detection was by UV–Vis detection at 254 nm. All three complexing agents could be separated from each other in a simultaneous analysis in less than 5 min. The limits of detection were 0.34, 0.27, and 0.62 mol L^–1 for DTPA, EDTA, and NTA, respectively. The total amounts of the analytes measured in the dishwashing detergents by the three techniques were found to be highly comparable (ANOVA: F=0.04, P=0.96). R² values were 0.99 for EDTA, 0.99 for NTA, and 0.99 for all the results when UV–Vis and HPLC determinations were compared using regression lines. The UV–Vis and HPLC methods were proved to be viable also for analyses of natural and pulp mill waters. The absence of matrix interferences was verified by the standard addition technique.     

Preparation of tritium-labeled prostaglandin E3

Conditions for the biosynthesis of PGE₃ from eicosa-5,8,11,14,17-pentaenoic acid using an enzyme system isolated from ram seminal vesicles have been worked out. Tritium-labeled PGE₃ has been obtained in good yield with a molar radioactivity sufficient for performing many biological investigations.Institute of Molecular Genetics, Academy of Sciences of the USSR, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 319–322, May–June, 1985.     

Simultaneous analysis of different classes of phytohormones in coconut (Cocos nucifera L.) water using high-performance liquid chromatography and liquid chromatography-tandem mass spectrometry after solid-phase extraction

Coconut (Cocos nucifera L.) water, which contains many uncharacterized phytohormones is extensively used as a growth promoting supplement in plant tissue culture. In this paper, a high-performance liquid chromatography (HPLC) method was developed for the simultaneous determination of various classes phytohormones, including indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), abscisic acid (ABA), gibberellic acid (GA), zeatin (Z), N⁶-benzyladenine (BA), α-naphthaleneacetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D) in young coconut water (CW). The analysis was carried out using a reverse-phase HPLC gradient elution, with an aqueous mobile phase (containing 0.1% formic acid, pH adjusted to 3.2 with triethylamine (TEA)) modified by methanol, and solute detection made at 265 nm wavelength. The method was validated for specificity, quantification, accuracy and precision. After preconcentration of putative endogenous phytohormones in CW using C₁₈ solid-phase extraction (SPE) cartridges, the HPLC method was able to screen for putative endogenous phytohormones present in CW. Finally, the identities of the putative phytohormones present in CW were further confirmed using independent liquid chromatography–tandem mass spectrometry (LC–MS/MS) equipped with an electrospray ionization (ESI) interface.     

Isothermal vapor–liquid equilibrium at 333.15 K and excess molar volumes at 298.15 K for the ternary system di-isopropyl ether + n-propyl alcohol + toluene and its binary subsystems

Isothermal vapor–liquid equilibrium data at 333.15 K are reported for the ternary system di-isopropyl ether (DIPE) + n-propyl alcohol + toluene and the binary subsystems DIPE + n-propyl alcohol, DIPE + toluene and n-propyl alcohol + toluene by using headspace gas chromatography. The excess molar volumes at 298.15 K for the same binary and ternary systems were also determined by directly measured densities. The experimental binary and ternary vapor–liquid equilibrium data were correlated with different G^E models and the excess molar volumes were correlated with the Redlich–Kister equation for the binary systems and the Cibulka equation for the ternary system, respectively.     

A multi-residue method for characterization and determination of atmospheric pesticides measured at two French urban and rural sampling sites

The extensive use of pesticides to protect agricultural crops can result in the transfer of these compounds into the atmosphere and their diffusion towards urban areas. Precise evaluation of the geographic impact of this type of pollution is important environmentally. In this paper, analytical methods for the sampling, characterization, and determination of agricultural pesticides in air were developed; the methods were then applied in the Paris and Champagne regions. Sixteen pesticides belonging to nine chemical families were monitored. Sampling was carried out in urban (Paris) and rural (Aube district) sites, utilizing either a high-volume pump (12.5 m³ h^–1) (urban site) or a low-volume pump (2.3 m³ h^–1) for the rural site. Quartz filters and polyurethane foams (PUF) were used for sampling in all cases. After extracting the samples and concentrating the recovered solutions, high-performance liquid chromatography (HPLC) analysis with UV detection was performed. Identification of the pesticides was confirmed by applying to the HPLC measurements a novel UV-detection procedure based on the normalized absorbance variation with wavelength (Noravawa procedure). The presence of metsulfuron methyl, isoproturon, linuron, deltamethrin (and/or malathion), and chlorophenoxy acids (2,4-D and MCPP) was found at the urban sampling site at levels ranging from about 1 to 1130 ng m^–3 of air, depending on the compound and sampling period. On the rural sampling site residues of isoproturon, deltamethrin (and/or malathion), MCPP, and 2,4-D were generally detected at higher levels (19–5130 ng m^–3) than on the urban site, as expected. The effects of the weather conditions and agricultural activity on the atmospheric concentrations of pesticides are discussed, as are long-range atmospheric transfer processes for these pesticides.     

Flow-injection hydride generation atomic absorption spectrometric study of the automated on-line pre-reduction of arsenate, methylarsonate and dimethylarsinate and high-performance liquid chromatographic separation of their -cysteine complexes

An automated on-line pre-reduction of arsenate, monomethylarsonate (MMA) and dimethylarsinate (DMA) using flow injection hydride generation atomic absorption spectrometry (FI-HGAAS) is feasible. The kinetics of pre-reduction and complexation depend strongly on the concentration of -cysteine and on the temperature in the following increasing order: inorganic As(V)<DMA<MMA. Arsenate is pre-reduced/complexed within less than 50 s at 70–100°C compared to 1 h at room temperature, while MMA and DMA require 1.5–2 min at 70–100°C and up to 1–2 h at room temperature. The characteristic masses and concentrations for 100 μl injections are 0.01 ng and 0.1 μg l⁻¹ in integrated absorbance and 0.2 ng and 2 μg l⁻¹ in peak height measurements, and the limits of detection are ca. 0.5 ng and 5 μg l⁻¹, respectively. In a high-performance liquid chromatography (HPLC)–HGAAS system, the -cysteine complexes of inorganic As(III), MMA and DMA are best separated within 7 min by HPLC on a strongly acidic cation exchange column such as Spherisorb S SCX 120×4 mm (5 μm) with a mobile phase containing 12 mmol l⁻¹ phosphate buffer (KH₂PO₄/H₃PO₄)–2.5 mmol l⁻¹ -cysteine, pH 3.3–3.5. Upon dilution to -cysteine levels below 10 mmol l⁻¹, which are compatible with HPLC separations, the DMA–cysteine complex is unstable on storage. No baseline separations are possible with anion exchange and reverse phase C₁₈ HPLC columns. The limits of detection with 50 μl injections in peak area mode are ca. 0.5 ng and 10 μg l⁻¹, respectively.     

Direct quantitative analysis of peptides using matrix assisted laser desorption ionization

The protocol and various matrices were examined for quantification of biomolecules in both the low ca. 1200 amu and mid mass 6000–12000 amu ranges using an internal standard. Comparative studies of different matrices of MALDI quantitative analysis showed that the best accuracy and standard curve linearity were obtained for two matrices: (a) 2,5-dihydroxybenzoic acid (DHB) combined with a comatrix of fucose and 5-methoxysalicylic acid (MSA) and (b) ferulic acid/fucose. In the low mass range, the quantitative limit was in the 30 fmol range and in the mid mass range the quantitative limit was in the 250 fmol range. Linear response was observed over 2–3 decades of analyte concentration. The relative error of the standard curve slope was 1.3–1.8% with correlation coefficients of 0.996–0.998.The main problem for quantitative measurement was suppression of the signal of the less concentrated component (analyte or internal standard) by the more concentrated component. The effect was identified with saturation of the matrix by the analyte. The threshold of matrix saturation was found to be in the range of 1/(3000–5000) analyte/matrix molar ratio. To avoid matrix saturation the (analyte+internal standard) to matrix molar ratio should be below this threshold. Thus the internal standard concentration should be as low as possible.DHB/MSA/fucose and ferulic acid/fucose matrices demonstrated good accuracy and linearity for standard curves even when the internal standard had chemical properties different from the analyte. However, use of an internal standard with different chemical properties requires highly stable instrumental parameters as well as constant (analyte+internal standard)/matrix molar ratio for all samples.     

Current state of the liquid column chromatography of coumarins

Literature information for the period 1983–1990 on the use of high-performance liquid chromatography (HPLC) in the phytochemical, biochemical, toxicological, and pharmaceutical analysis of coumarin derivatives has been generalized and systematized. Conditions for the separation of complex mixtures of coumarins are considered, and questions of the use of coumarins in the HPLC analysis of natural and synthetic organic compounds are discussed.Kemerov State Medical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 171–188, March–April, 1993.     

Aqueous solubilities and enthalpies of solution of adenine and guanine

A generator column—liquid chromatographic technique was used to determine the aqueous solubility of adenine from 20 to 30°C, and of guanine from 15 to 40°C. The 95% confidence limits of the solubilities and molar enthalpies of solution at 25°C are: 8.7±0.1×10^–3M and 33.5±0.5 kJ-mol^–1 for adenine; 3.9±0.1×10^–5M and 49.2±0.6 kJ-mol^–1 for guanine. the adenine enthalpy value includes a small correction for association in the saturated solutions. The previously undetermined molar enthalpy of the second ionization step of guanine (to form the doubly-charged guanine anion) is estimated from our data combined with other measurements to equal 33.8±2.9 kJ-mol^–1.     

Volumetric properties of tetraphenylporphine,their metallo-complexes and some substituted tetraphenylporphines in benzene solution

Densities, apparent molar volumes and partial molar volumes of benzene solutions of tetraphenylporphine, H₂TPP, tetraphenylporphine metallo-complexes, MTPP (where M=Ni,Cu,Zn,Pd,Ag, and Cd), and some substituted tetraphenylporphines H₂T(i-R)PP (where i=2–4 and R=–Cl,–CH₃,–OCH₃) H₂T(i-F)PP (where i-2,3), H₂T(3-Br)PP, and H₂T(3-I)PP were determined at 25°C. It was found that the partial molar volumes of the studied compounds correlate linearly with the first ionization potential of the corresponding metal atom. The calculated values of the surface and volume accessible to the solvent, and the solvent-excluded volume for different conformations of H₂TPP, were compared with experimental data. The volume per molecule for different crystalline forms of H₂TPP and MTPP were compared with the partial molar volumes of the corresponding compounds in benzene solutions. The correlation between the partial molar volumes of H₂T(3-R)PP and their Van der Waals volumes are presented for R=–H, –F,–CH₃,–Cl,–Br,–OCH₃, and –I. The experimental data are rationalized in terms of differences in the conformational states of the molecules.     

Chemical characterization of complexation behavior of pertechnetate with cysteine

The labeling behavior of cysteine with⁹⁹TcO ₄ ^– ion and/or^99mTcO ₄ ^– ion at different cysteine concentrations reductant and pH values has been studied by chromatography, and the labeling yield was calculated. Three major Tc-complexes, yellow, reddish brown and green can be separated by gel filtration chromatography (GFC). Thin layer chromatography (TLC), high performance liquid chromatography (HPLC) and ion-exchange chromatography (IC) were used to separate the complexes collected from GFC. The TLC, HPLC data show the pertechnetate accompanied with a yellow complex; the green and purple complex contain more than two complexes. Electrophoresis and IC data show that the complexes carry a negative charge. The conductivity, UV-VIS, flow beta-detector with HPLC and autoradiography are also applied to analyze complex formation.     

High-Performance Liquid Chromatography with Electrospray Mass Spectrometry for Rapid and Sensitive Determination of Sanguinarine and Chelerythrine in Exogenously Contaminated Honey

A simple, rapid, and sensitive high-performance liquid chromatographic (HPLC) method coupled with electrospray mass spectrometry (ESI-MS) has been used to determine sanguinarine and chelerythrine in exogenously contaminated honey. Sample extracts were separated on a C₈ reversed-phase HPLC column with acetonitrile–acetate buffer (40:60) as mobile phase. After ESI the abundance of protonated molecules was recorded by selected-ion recording (SIR) of m/z 332.5, 348.5, and 356.5 for sanguinarine, chelerythrine, and the internal standard, tetrahydropalmatine, respectively. The internal standard technique was used to construct calibration plots for quantitation of sanguinarine and chelerythrine; the linear ranges were 5.25–1050 and 3.75–750 ng mL^–1, respectively, with correlation coefficients of 0.9993 and 0.9989, respectively. The limits of detection for sanguinarine and chelerythrine were 1.60 and 1.11 ng mL^–1, respectively.     

Palladium(II) and platinum(II),(IV) complexes of 2-aminopyrimidine derivatives

Palladium(II) and Platinum(II),(IV) complexes with 2-aminopyrimidine derivatives (L1)–(L3), prepared by reacting the corresponding metal halide with the ligand in the required stoichiometric ratio, were characterised by chemical analyses and physical measurements. The structures have been assigned on the basis of i.r. spectroscopy, electronic reflectance spectra and molar conductivities.     

Thermodynamics of Aqueous Diethylenetriaminepentaacetic Acid (DTPA) Systems: Apparent and Partial Molar Heat Capacities and Volumes of Aqueous H2DTPA3−, DTPA5−, CuDTPA3−, and Cu2DTPA− from 10 to 55°C

Apparent molar heat capacities and volumes have been determined for aqueous solutions of the mixed electrolytes Na₅DTPA + NaOH, Na₃CuDTPA + NaOH, and NaCu₂DTPA + NaOH, and the single electrolyte Na₃H₂DTPA (DTPA=diethylenetriaminepentaacetic acid) at temperatures from 10 to 55°C. The experimental results have been analyzed in terms of Young's rule with the Guggenheim form of the extended Debye–Hückel equation and the Pitzer ion-interaction model. These calculations led to standard partial molar heat capacities and volumes for the species H₂DTPA^3–(aq), DTPA^5–(aq), CuDTPA^3–(aq), and Cu₂DTPA^–(aq) at each temperature. The partial molar properties at 0.1 m ionic strength were also calculated. The standard partial molar properties were extrapolated to elevated temperatures with the revised Helgeson–Kirkham–Flowers (HKF) model. Values for the partial molar heat capacities from the HKF model have been combined with the literature data to estimate the ionization constants of H₂DTPA^3–(aq) and the formation constant of the CuDTPA^3–(aq) copper complex at temperatures up to 300°C.