Enantiomeric analysis of rivastigmine in pharmaceuticals by cyclodextrin-modified capillary zone electrophoresis

Chiral separation method development is usually very time-consuming due to the diversity in chemical structures of pharmaceutical drug substances as well as the suitable separation conditions and the problem to choose the appropriate chiral selector. This paper shows capillary zone electrophoresis (CZE) which was developed for chiral separation of a basic compound - rivastigmine (RIV) using 30 cm × 50 μm i.d. polyacrylamide (PAA)-coated fused-silica capillary (effective length 20 cm), amine-modified phosphate buffer of pH 2.5 and sulfated-β-CD (S-β-CD) as chiral selector. Other selected native or derivatized cyclodextrins (CDs) were also tested: β-CD (5, 30 mM), carboxymethyl-β-CD (5, 30 mM), dimethyl-β-CD (15 mM), hydroxypropyl-β-CD (5, 30 mM), hydroxypropyl-α-CD (5, 30 mM) and hydroxypropyl-γ-CD (5, 30 mM). Complete enantiomeric separation of RIV was achieved at 20 kV, 18 °C and detection at 200 nm within 8 min with R.S.D. for the absolute migration time reproducibility of less than 2.1%. Rectilinear calibration range was 5.0-500.0 μM of each enantiomer (r = 0.9994-0.9995). The CZE method proposed was used for the control of chiral purity of pharmaceutically active S-RIV and for the analysis of Exelon caps preparation.     

Capillary Zone Electrophoresis of Eleven Priority Phenols with Amperometric Detection

A scheme for separation and detection of eleven priority phenols using capillary zone electrophoresis (CZE) coupled with amperometric detection is described. With a capillary of I.D. 50 μm and length 62.5 cm at 9 kV and an electrophoretic buffer of 20 mM CHES (pH 10.1), complete separation of the eleven compounds was achieved in less than 17 min. Amperometric detection was carried out using a carbon fiber microelectrode of diameter 9 μm inserted into the end of the detection capillary. Linearity over two orders of magnitude was generally obtained for the eleven priority phenols. With an electrode potential+1.10 V (vs. Ag/AgCl reference), the concentration limits of detection were in the sub-ppm (10^?6 M) level. This method was successfully applied to analysis of priority phenols in industrial waste water.     

合并带流动注射分光光度法研究硫羟乳酸掩蔽性能

本文运用合并带流动注射分析技术，建立了以Ｙｂ＾３＋ＸＯ显色体系为参考体系研究硫羟乳酸掩蔽性能的方法，在ｐＨ５．６硫羟乳酸能掩蔽Ｓｎ＾４＋，Ｂｉ＾３＋，Ｔｌ＾３＋，Ｈｇ＾２＋，Ｃｕ＾２＋，Ｃｒ＾３＋和Ｃｄ＾２＋测定Ｙｂ＾３＋的线性范围为１．３６×１０＾－６～２．７２×１０＾－５ｍｏｌ／Ｌ，采样频率可达１２０次／ｈ。     

Multi-configuration electron-hole potential method for excited states

The recently proposed electron-hole potential (EHP) method for excited states is extended to the multi-configurational case. The variation equation is solved using the quadratic convergence method. The EHP methods are shown to be approximations to the complete singly excited configuration interaction (CSECI) in the variational sense. Extended Brillouin theorems are proved for the EHP methods. The excitation energies and wave functions obtained by one and two configurational EHP methods agree well with those of the CSECI method. The EHP methods have clear advantage in the computer time requirement over the CI method and are especially suited for a calculation of approximate excited states of large molecules. The EHP methods are applicable to excited states which belong to the same irreducible representation as the ground state.     

Chiral Recognition of Phenylacetic Acid Derivatives by Aminated Cyclodextrins

Chiral recognition of mandelic acid ( 1), acetylmandelic acid ( 2), 1-methoxyphenylacetic acid ( 3), phenylsuccinic acid ( 4), 2-phenylpropanoic acid ( 5) and ibuprofen ( 6) in their anionic forms by protonated 6A-amino-6A-deoxy--cyclodextrin (mono-NH3+--CD) and 6A,6D-diamino-6A,6D-dideo xy--cyclodextrin (di-NH3+--CD) has been studied by means of capillary zone electrophoresis (CZE) and 1H NMR spectroscopy. Both methods show the preferable guests for mono-NH3+--CD to be the (R)-enantiomers of 1, 3 and 5 and the (S)-enantiomers of 2, 4 and 6. Cooperative work of Coulomb interactions and inclusion is essential for chiral recognition of these anionic guests.     

Determination of rimantadine in pharmaceutical preparations by capillary zone electrophoresis with indirect detection or after derivatization

Summary Rimantadine is synthetic analog of amantadine; both are antiviral agents used for prophylaxis and treatment of influenza A. A capillary zone electrophoretic (CZE) procedure for the determination of rimantadine has been developed. As the direct determination of rimantadine is poorly sensitive because the compound is almost transparent in the UV/Vis range, several indirect methods were studied. Two were found to be the particularly useful: (a) indirect detection using 5 mM 4-methylbenzylamine in 1:4 methanol-water as absorbing background electrolyte, with detection at 210 nm, and (b) derivatization of rimantadine with 1,2-naphthoquinone-4-sulfonic acid in alkaline medium and subsequent determination of the derivative by CZE (40 mM tetraborate, pH 9.2, detection at 280 nm). Uncoated capillary tubing, 44 cm length ×75 μM i.d., was used for both determinations. The detection limits were 0.1 and 2 ppm for methods a and b, respectively. The methods were used to determine rimantadine in pharmaceutical products and for dissolution testing of Flumadin^? tablets.     

A quick method for the simultaneous determination of ascorbic acid and sorbic acid in fruit juices by capillary zone electrophoresis

A method of quickly determining ascorbic acid and sorbic acid by capillary zone electrophoresis with ultraviolet detection was developed. The choice of background electrolyte, wavelength, injection time and applied voltage were discussed. Ascorbic acid and sorbic acid were well separated in 80 mmol L⁻¹ boric acid-5 mmol L⁻¹borax (pH = 8.0) in 5 min at the detecting wavelength of 270 nm. Under the optimum condition, the method has linear ranges of 2.54-352.00 mg L⁻¹ for ascorbic acid and 1.08-336.39 mg L⁻¹ for sorbic acid with the detection limit of 1.70 mg L⁻¹ for ascorbic acid and 0.54 mg L⁻¹ for sorbic acid, respectively. Other organic acids in fruit juices have no effect on the detection. This method is very feasible and simple and can be used to detect ascorbic acid and sorbic acid in fruit juices.     

Imaging Magnetic Domain Structures with Soft X-Ray Microscopy

The current achievements in magnetic transmission soft X-ray microscopy will be reviewed. The magnetic contrast is given by X-ray magnetic circular dichroism (X-MCD), i.e., the dependence of the absorption coefficient of circularly polarized X rays on the projection of the magnetization in a ferromagnetic system onto the photon propagation direction. X-MCD contrast can reach, e.g., at L_2,3 edges in transition metals, large values up to 50%. Combined with a soft X-ray microscope where Fresnel zone plates acting as optical elements provide a lateral resolution down at 25 nm, it allows for imaging magnetic microstructures. Specific features of this photon-based technique are the recording of images in varying external magnetic fields, an inherent chemical specificity, a high sensitivity to thin magnetic layers, due to the large contrast, and the possibility to distinguish between in-plane and out-of plane contributions. In this report, recent results obtained with the XM-1 microscope at the ALS (Berkeley/CA) demonstrate the broad applicability of this novel experimental technique to both fundamental and technological relevant issues in nanomagnetism. The future potential will be briefly outlined.     

Capillary zone electrophoresis of alpha-helical diastereomeric peptide pairs with anionic ion-pairing reagents

The present study uses an unique capillary electrophoresis (CE) approach, that we have termed ion-interaction capillary zone electrophoresis (II-CZE), for the separation of diastereomeric peptide pairs where a single site in the centre of the non-polar face of an 18-residue amphipathic alpha-helical peptide is substituted by the 19 L- or D-amino acids. Through the addition of perfluorinated acids at very high concentrations (up to 400 mM), such concentration levels not having been used previously in chromatography or CE, to the background electrolyte (pH 2.0), we have been able to achieve baseline resolution of all 19 diastereomeric peptide pairs with an uncoated capillary. Since each diastereomeric peptide pair has the same sequence, identical mass-to-charge ratio and identical intrinsic hydrophobicity, such a separation by CZE has previously been considered theoretically impossible. Excellent resolution was achieved due to maximum advantage being taken of even subtle disruption of peptide structure/conformation (due to the presence of D-amino acids) of the non-polar face of the amphipathic alpha-helix and its interaction with the hydrophobic anionic ion-pairing reagents. In addition, due to the excellent resolution of diastereomeric peptide pairs by this novel CZE approach, we have also been able to separate a mixture of these closely-related alpha-helical peptides.