Speciation of Cr (III) and Cr (VI) via Reversed Phase HPLC with Inductively Coupled Plasma Emission Spectroscopic Detection (HPLC-ICP)24

Abstract

Chromium ions, viz., chromic (Cr^±3=III) and chromate (Cr^±6 = VI), can be reliably, conveniently, reproducibly, and quickly separated and detected by the use of conventional paired-ion, reversed phase (RP) high performance liquid chromatography (HPLC) together with refractive index (RI) and/or inductively coupled plasma emission spectroscopic (ICP) detection. A number of novel paired-ion approaches have now been developed, using PIC A (tetrabutylammonium hydroxide) or PIC B (sodium n-alkyl sulfonate) separately in the mobile phase. This allows for the retention of each Cr species depending on the particular ion pairing reagent being used, while the remaining Cr ion elutes in the solvent front. Changing the ion pairing reagent reverses the overall situation. The total time for each HPLC analysis is about 10 mins. ICP detection provides for a complete, overall method of speciation for both Cr (III) and Cr (VI) via two separate injections, together with quantitation for both species. This method of using paired-ion RP-HPLC can easily be applied to other mixtures of inorganic cations and anions, presumably with equally successful results. Minimum limits of detection are computed for chromate via direct-ICP, using at least two basic methods for such computations. It is suggested that virtually all chromatographic detection limits can be significantly improved by the application of newer, spectroscopic based methods of automated computation of detection limits.     

Simultaneous Determination of Inorganic Cations and Anion in Medical Electrolytes by Capillary Electrophoresis

Abstract

Capillary electrophoresis (CE) was developed in order to effect rapid, specific determination of potassium, calcium, sodium, and magnesium. Ions (4 cations, 1 anion) were measured continuously via shifting of samples from the inlet electrode to the outlet electrode; moreover, samples were subjected to indirect and direct ultraviolet (UV) techniques, respectively. For the measurement of cations, imidazole (5 mM) functioned as a UV absorber of indirect detection at 214 nm. Consequently, anions can be measured directly by UV at 214 nm. Separation times of cations and Cl^? anions were 10 min and 2 min, respectively; the detection limit of each ion (chloride, magnesium, sodium, calcium, and potassium) was 0.1 µmol/L. This approach is very simple; additionally, measurement time is extremely short. As a result, the proposed method is suitable for routine assay of electrolytes in pharmaceutical preparations.     

Determination of Toxic Organophosphorus Compounds by Specific and Nonspecific Detectors

Abstract

Sample preparation procedures and gas chromatography methodology are presented for the determination of tabun, sarin, soman, and VX in aqueous solutions. Extraction recoveries from chloroform were quantitative. Peak area ratios of organophosphorus compounds (OPs) to internal standard versus concentrations of OP were linear over the range of 10-1000 (μg/ml when determined by the flame ionization detector and 10-800 μg/ml when determined by the flame photometric detector. Imprecision occurring at low ng concentrations of VX was caused by its adsorption on the analytical column. Acceptable precision was regained by the addition of a weak base, such as atropine, to the sample extract prior to its injection onto the gas chromatograph (GC).     

A Comparison of Solid-Phase Extraction Techniques for Assay of Drugs in Aqueous and Human Plasma Samples

Abstract

Six commercially available solid adsorbent materials were evaluated for their applicability as effective tools for extraction of drugs from aqueous and human plasma samples. Ten model compounds were selected as representative of the acidic, basic, amphoteric, hydrophobic, and hydrophilic drug classes. Percent recovery and precision data for each model drug on each solid adsorbent material were calculated using spiked water and/or plasma samples. Octadecylsilane materials were the best overall choice for extraction of the different chemical classes of drugs from water and plasma samples, giving both highest recovery and best reproducibility data for a majority of the drugs studied. It was also determined that good extractability for basic drugs could be obtained using either XAD-2, Clin-eht® or cyanopropyl columns. In addition, XAD-2 gave good recoveries of amphoteric compounds and Clin-elut® was good for hydrophobic drugs.     

Ytterbium triflate catalysed Meerwein-Ponndorf-Verley (MPV) reduction

Ytterbium triflate was shown to be effective in promoting the reduction of substituted aromatic and aliphatic aldehydes and ketones using isopropanol as the solvent and the reducing agent. The whole process furnished the desired adducts in 22-98% yield.     

Mixed Valence Tungsten (IV,V) Compounds with Layered Structures (Part IV): Syntheses,Crystal Structures,and Conductivity of BiX2[W2O2X6] (X = Cl,Br)

The reaction of metallic bismuth with either tungsten tetrachlorideoxide WOCl₄ at 650 K or tungsten tetrabromideoxide WOBr₄ at 670 K, respectively, leads to BiX₂[W₂O₂X₆] (X = Cl, Br) as black, lustrous crystal needles. The crystal structure determinations (triclinic, P$\bar{1}$ ) show the two isotypic structures to be closely related to Hg_0.55[W₂O₂Cl₆] with the presence of 1D‐polymeric W₂O₂X₆ double strands. Dinuclear [Bi₂X₄]²⁺ cations are embedded in the host structure via secondary W–X ··· Bi bonds. Unlike the other members of theM_y[W₂O₂X₆] structure family, which crystallize monoclinic and show crystallographic equivalent tungsten atoms, BiX₂[W₂O₂X₆] has independent tungsten sites. Nevertheless, an assignment of an individual oxidation state to the tungsten atoms within the W₂ group (W–W 2.8321(4) Å for X = Cl, 2.8985(4) Å for X = Br) is not possible and a dynamic intervalent state W(IV, V) is assumed. Electrical conductivity measurements for BiCl₂[W₂O₂Cl₆] show semi‐conductive behavior with a very small band gap of 70 meV and a high conductivity of around 0.5 Ω^–1cm^–1 at temperatures above 220 K. A temperature dependence of the activation energy of charge transport is present and interpreted by the Varshni model.     

Synthesis,structural characterization,and properties of two new polyoxovanadates based on decavanadate [V10O28]6−

Two new decavanadate metal compounds, [Co(pyim)₃]₂[V₁₀O₂₈]·7H₂O (1) and [Ni(pyim)₃]₂[H₂V₁₀O₂₈]·4H₂O (2) (pyim?=?2-(2-pyridyl)-imidazole), have been synthesized under hydrothermal conditions and characterized by elemental analysis, single-crystal X-ray diffraction analysis, infrared spectra, powder X-ray diffraction analysis, and thermogravimetric analysis. Crystallographic analysis reveals that 1 is constructed from [V₁₀O₂₈]^6?, metal cation [Co(pyim)₃]³⁺, and water. [V₁₀O₂₈]^6? clusters are connected by waters through O–H?O hydrogen bonds to form a sheet structure which is further connected by N–H?O hydrogen bonds to form a 3-D supermolecular framework. In 2, although [Ni(pyim)₃]²⁺ is similar to [Co(pyim)₃]³⁺ in 1, the M?O cluster anion is protonated [H₂V₁₀O₂₈]^4?.     

Coordination-driven synthesis of Ag(I) compounds based on a double emission ligand consisting of 1,3,4-oxadiazole and cyclotriphosphazene units

A new ligand (L) which consists of cyclotriphosphazene and 1,3,4-oxadiazole units is reported. Two new Ag(I) coordination compounds {[Ag(L)SO₃CF₃] _n (1) and Ag₂L₂(NO₃)₂ (2)} based on L and Ag(I) salts are obtained. Compound 1 features a 1-D chain, in which the ligand L adopts a divergent trans-conformation, whereas 2 is a discrete binuclear Ag(I) molecule in which L adopts convergent cis-conformation. Compounds 1 and 2 are fully characterized by ¹H-NMR, Infrared, elemental analysis, X-ray powder, and single-crystal diffraction. Luminescent properties of 1 and 2 are investigated.