Problems in Determining Compositional Heterogeneity of Copolymers by Size-Exclusion Chromatography and UV-RI Detection System

Abstract

The compositional heterogeneity of styrene-methylmethacrylate copolymer has been evaluated by a UV-RI dual-detector method and by a RI detector-pyrolysis-gas chromatographic method and problems associated with the determination of the chemical heterogeneity by a UV-RI method are discussed. The quotient of signals H(UV)/H(RI) of both the detectors (UV and RI) for polystyrene increased at the extreme parts of the molecular weight distribution owing to nonlinearity of UV response. The correction of the quotient of signals of both detectors for the copolymer was proposed. The UV and RI response factors for the copolymer were supposed to differ from those for homopolymers. Reproducibility for the detector responses influences the values of chemical heterogeneity much more than expected. To overcome these problems, the detection method to obtain each composition independently using different detectors will be preferable.     

The Quantitation of Heroin and Selected Basic Impurities via Reversed Phase HPLC. II. The Analysis of Adulterated Samples

Abstract

Methodology is presented for the quantitation of heroin, O⁶-monoacetylmorphine, acetylcodeine, noscapine and papaverine in adulterated illicit heroin samples. Reversed phase chromatography was employed using an HS-5 C18 column with a gradient system. This methodology used a multimode detection scheme which consisted of a photodiode array detector in series with a dual electrochemical detector in the parallel mode. Owing to its high specificity for O⁶-monoacetylmorphine, electrochemical detection via the oxidation mode proved necessary for the quantitation of this compound in samples highly adulterated with quinine. The use of relative retention times, UV spectra and dual electrochemical response ratios for the screening of adulterants in heroin is discussed.     

Characterization of PVC BY SEC. II. One Shot Chromatography of the Organic Components of PVC Compounds

Abstract

1,2,4-Trichlorobenzene at 90°C proved to be a universal solvent for the common organic components of PVC compounds except crosslinked impact modifiers. Size exclusion chromatography was carried out with 8 different components, with a PVC-U compound and plate out formed during its extrusion using both RI and IR detection. In the RI detector PVC shows a very low detector response. It is therefore possible to analyze the whole organic fraction of the compound without prior precipitation of PVC. Using RI/IR double detection, an “one shot” analysis of the PVC matrix and of all the soluble additives can be accomplished.     

The high-performance liquid chromatography and detection of phospholipids and triglycerides: Part 2. Comparison of an ultraviolet absorption and post-column reactor detector

A liquid chromatographic ultraviolet absorption detector (at 195 nm) and a novel postcolumn reactor detector are compared for use in the detection of triglyceride and phospholipid molecular species. The detection limit for the u.v. detector depends on the degree of unsaturation of the lipid sample (3 × 10^-6–2 × 10^-8 M in the detector cell for 0–3 double bonds per acyl group). The post-column reactor detector is responsive to equivalents of lipid and has detection limits of 5 × 10^-7 M for triglycerides and 2 × 10^-6 M for phospholipids. The log u.v./post-column reactor detector response ratios are linearly related to the log of the degree of unsaturation of the lipid, indicating the usefulness of both detectors for quantifying triglycerides and phospholipids.     

Reversed-Phase HPLC. Determination of Ionic Surfactants As UV-Absorbing Ion Pairs

Abstract

Ionic and amphoteric surfactants were separated on reversed-phase columns. Ultraviolet photometry and differential refractometry were employed so that ion pairing and nonpairing compounds could be distinguished. Analysis of ionic surfactants as ultraviolet (UV) absorbing ion pairs improved detection limits 100 fold compared to detection by differential refractometer (RI).     

The Quantitation of Heroin and Selected Basic Impurities Via Reversed Phase HPLC. I. The Analysis of Unadulterated Heroin Samples

Abstract

Methodology was developed employing reversed phase liquid chromatography for the simultaneous determination of heroin, O³-monoacetylmorphine, o⁶-monoacetylmorphine, acetylcodeine, noscapine and papaverine in unadulterated illicit powders. An HS-5 C18 column was used with a gradient system using methanol and a hexylamine phosphate buffer at pH 2.2. This method, suitable for automated analysis, used a multi-mode detection scheme via the use of a photodiode array detector. In order to arrive at the optimum chromatographic conditions in terms of selectivity and stability, a study was performed on the effect of various mobile phase parameters on log k′ for heroin, various impurities, and common adulterants. The mobile phase parameters included amine concentration, organic modifier type, and eluent pH.     

Studies on Iodinated Compounds. IV. High Performance Liquid Chromatographic Determination of Iodide with a Complex of Primary Ammonium Ion - Crown Ether

Abstract

Determination of iodide (I^?) was performed using a complex of primary ammonium ion - crown ether as the counter ion on reversed-phase high performance liquid chromatography (HPLC)_° Retention of the I^? in the present system increased more than the corresponding counter ion system, using the only primary ammonium ion_° The rate of increase of the retention was dependent on pHs', concentration of crown ether and organic solvents of the eluent. Determination of I^? was investigated with hexylamine and 18-crown-6 with a UV detector at 225 nm_° The calibration curve was linear from 25 pmoles to 25 nmoles, and the least detection of I^? was 1 pmole.     

Azothia- and Azoxythiacrown Ethers as Ion Carriers. Part I. Cationic Response of Membrane Electrodes

13-Membered azothia- and azoxythiacrown ethers have been applied as ion carriers in ion-selective membrane electrodes. Their sensitivity and selectivity were studied towards alkali, alkaline earth, transition and heavy metal cations. It was found that membranes doped with the azoxythiacrown ether (A) show higher affinity towards Pb²⁺ than Cu²⁺ (log K_Cu,Pb ^pot = 1.7), whereas membranes with the azothiacrown ether (B) are more selective towards Cu²⁺ than Pb²⁺ (log K_Cu,Pb ^pot = -2.4). The discrimination of alkali and alkaline earth cations was found to be greater for B than for A. Electrodes with both ionophores suffered from strong interference by Ag⁺ and Hg²⁺. The relation between the carrier structure and electrode properties has been discussed.     

A New Reagent for Determination of Isocyanates in Working Atmospheres by HPLC Using UV or Fluorescence Detection

Abstract

A new liquid chromatographic method with increased sensitivity has been developed for the determination of isocyanates common in industrial environments. The isocyanates are converted to stable urea derivatives by reaction with 9-(N-methylaminomethyl)-anthracene. These derivatives were analyzed using high performance liquid chromatography on a bonded octadecylsilyl phase using isocratic elution with acetonitrile/water and detected either by a UV or a fluorescence detector. The method was applied to toluene 2, 4- and 2, 6-diisocyanate (2, 4- and 2, 6-TDI), hexamethylene diisocyanate (HDI) and 4, 4-diphenylmethane diisocyanate (MDI).

The influence of various salts on the retention of the reagent amine was studied, as well as the separation of the urea derivatives on different C₁₈-phases. The detection limit is about 1 · 10^?4 mg/m³ for the isocyanates investigated, using either UV or fluorescence detection. This means that the new method is ten to twenty times more sensitive than the previously described reversed phase LC method, which utilized N-4-nitrobenzyl-N-n-propylamine as reagent.     

Characterization and Assessment of the Microjet Electrode as a Detector for HPLC

The microjet electrode (MJE) is characterized as a detector for high performance liquid chromatography (HPLC). Voltammetric measurements of the oxidation of hydroquinone (HQ) allow mass transport to be determined for the MJE detector configuration, and the factors controlling the conversion efficiency of the device to be well understood. The current‐time response to the flow injection analysis of volumes of solution in the 10–80 μL range has been established, and the limit of detection of this method has been determined. The latter was found to approach that of UV absorbance measurements, which is particularly encouraging, given that HQ has a relatively strong chromophore (ε=2 290.8 cm^?1 mol^?1 L). This detection system is a robust and simple arrangement with the capability of analyzing large volumes of eluent at typical analytical HPLC flow rates.     

Minimizing UV noise in supercritical fluid chromatography. I. Improving back pressure regulator pressure noise

Pressure fluctuations and resulting refractive index changes, induced by the back pressure regulator (BPR) can be a significant source of UV detector noise in supercritical fluid chromatography (SFC). The refractive index (RI) of pure carbon dioxide (CO(2)) changes ≈0.2%/bar at the most commonly used conditions in supercritical fluid chromatography (SFC) (40 °C and 100 bar), compared to 0.0045%/bar for water (CO(2) IS 44× worse). Changes in RI cause changes in the focal length of the detector cell which results in changes in UV intensity entering the detector. The change in RI (ΔRI/bar) of CO(2) decreases 8-fold at 200 bar, compared to 100 bar. A new back pressure regulator (BPR) design representing an order of magnitude improvement in the state of the art is shown to produce peak to peak pressure noise (PN(p-p)) as low as 0.1 bar, at 200 bar, and 20Hz, compared to older equipment that attempted to maintain PN(p-p)<1bar, at <5Hz. With this lower PN(p-p), changes in baseline UV offsets could be measured as a function of very small changes in pressure. A pressure change of ±1 bar at 100 bar, common with some older BPR's, produced a UV baseline offset >0.5 mAU. A pressure change of ±0.5 bar representing the previous state-of-the-art, resulted in a UV offset of 0.3m AU. Baseline noise <0.05 is required to validate methods for trace analysis. The new BPR, with a PN(p-p) of 0.1 bar, demonstrated UV peak to peak noise (N(p-p))<0.02 mAU with a >0.03 min (10Hz) electronic filter under some conditions. This new low noise level makes it possible to validate SFC methods for the first time.     

Systematic HPLC Study of a New Series of 4-Methyl-1,4-dihydropyridines with Antitrombotic Activity

Abstract

A systematic study of a new series of 4-methyl-1,4-dihydropyridine derivatives by HPLC by both photodiode array and electrochemical detectors is reported.

The optimum mobile phase was acetonitrile 0.05 M phosphate buffer pH 3 (55/45, v/v) at a flow-rate of 1.5 mL/min.

Compounds I–VIII were determined with UV detection at 250 nm and by electrochemical detection at + 1200 mV.

Retention times varied between 3.0 and 14.0 minutes in the optimal experimental conditions.

Good linear relationships between the peak areas and concentration were found, with limits of quantification ranging between 1 x 10^?8 M and 1 x 10^?6 M. Repeatability studies showed average variation coefficients lower than 1% for a photodiode array detector. No significant differences between the detectors in sensitivity and selectivity were found.

Also, we used different degradation trials to test the selectivity of the methods. Results of these experiments revealed that the developed methods exhibited a good selectivity.     

Cyclodextrin Bonded Phase for Liquid Chromatographic Separation and Analysis of Some Oral Contraceptives

Abstract

A specific and sensitive analytical HPLC procedure was described for quantitative determination of ethinylestradiol and norethisterone acetate (Anovlar 1) and ethinylestradiol and norgestrel (Primovlar) in tablet formulation. These steroids were extracted from the tablets with methanol. The steroids were then determined with high performance liquid Chromatograph-Cyclobond 1 column using mobile phase phosphate buffer pH 7.0: methanol (60:40), flow rate 0.5 ml min^?1 and the detection was effected spectrophotometrically at 280 nm, using variable wavelength UV detector.

There was > 99.3% recovery from synthetic mixtures and the coefficient of variation was < 2.0% for the formulations investigated. The method is highly quantitative and reproducible.     

Spiropyran‐Conjugated Pluronic as a Dual Responsive Colorimetric Detector

Novel spiropyran‐conjugated Pluronic [polyethylene oxide (PEO)‐b‐polypropylene oxide (PPO)‐b‐polyethylene oxide (PEO)] micelles are developed as a new colorimetric detector showing photo‐ or thermo‐switchable behavior. Facile conjugation of spiropyran to Pluronic was confirmed by ¹H NMR, UV–Vis, and Fluorescence spectroscopy. A switchable photoluminescence is found depending on the irradiation with either UV or visible light, and temperature resulting from structural isomerization of spiropyran between spiropyran (SP) and merocyanine (MC) form. Cytotoxicity of the spiropyran‐conjugated Pluronic (SP‐PL) was evaluated following an MTT assay, whereas photo responsiveness of spiropyran within the micelles was determined by confocal laser scanning microscopy.     

Frequency-selective absorbance detection: Refractive index and turbidity compensation with dual-wavelength measurement

A frequency-selective absorbance detection approach and its applications are described. First, a digital signal processor-lock-in amplifier (DSP-LIA)-based absorbance detector was evaluated. Compared to a simple operational amplifier (TL082CP)-based detector, the DSP-LIA-based detector showed lower noise levels, but the relative advantage was reduced under very low photocurrent levels (down to few nA). A 7 cm pathlength flow cell with this commercial LIA-based detector exhibited excellent Beer's law linearity (r² = 0.9999) and a noise level of 7 micro absorbance units (μAU). The limit of detection (LOD, S/N = 3) for methyl orange (MO) was 7 nM with this detector. Finally, as a more affordable alternative to an LIA, a balanced demodulator integrated circuit chip was used to fabricate a dual wavelength-frequency-selective LED-based absorbance detector. This device successfully compensated refractive index (RI) effect and turbidity effect in test flow systems. The LOD for MO with this system was 8 nM.     

Separation of Sulfur Species in Water by Co-Electroosmotic Capillary Electrophoresis with Direct and Indirect UV Detection

Co-electroosmotic capillary electrophoresis (co-CZE) with both direct and indirect UV detection was investigated for the separation of sulfur species. With direct UV detection, the separation of S₂O^2? ₃, S₂O^2? ₄ was possible using 20 mM phosphate electrolyte containing 0.75 mM tetradecyltrimethylammonium bromide (TTAB) and 15% acetonitrile. To obtain optimal peak shape and sensitivity using indirect UV detection, a range of background electrolytes (BGEs), including benzoate, phthalate, 2,6-pyridinedicarboxylate (2,6-PDCA) and trimellitate, were examined as the BGEs. Of all the BGEs, 2,6-PDCA gave high selectivity and indirect UV response due to its mobility matching to that of sulfur species and its high absorptivity. Detection limits in range of 3-6 μM were obtained using either direct UV or indirect UV detection. The proposed CZE methods were used for the determination of sulfur species in water samples, and provided fast separation of sulfur species in less than 5 min.     

Zn(II)-containing metallo-supramolecular polymers: synthesis,photophysical and electrochemical properties

Abstract

Two novel building blocks M1, M2 with different electronic structures, were synthesized based on 2,2′:6′,2″-terpyridine modified with cyano-p-phenylenevinylene (CN-PV) and carbazole moieties through Knoevenagel condensation and Suzuki coupling, respectively. Directed by transition metal ion Zn²⁺, the metallo-homopolymers P1, P2 and metallo-copolymer P3 were obtained via self-assembly polymerization. The structures of the monomers and metallo-supramolecular polymers were fully characterized by MS, ¹H-NMR and ¹³C-NMR. Meanwhile, the UV–vis absorption, photoluminescence (PL) and electrochemical properties of these compounds were systematically investigated. With respect to that of the monomers, both the UV–vis absorption and PL spectra of the polymers are significantly red-shifted. The resulting metallo-supramolecular polymers show similar double absorption peaks (342, 418?nm for P1, 339, 410?nm for P2, and 332, 412?nm for P3), which is caused by the π–π* transition and intramolecular charge transfer (ICT). Further, all the polymers display red-orange emission in toluene and narrow electrochemical energy gaps of 1.46, 1.65 and 1.48?eV for P1, P2, and P3, respectively.     

Synthesis,characterization, and DNA binding of two copper(II) complexes as DNA fluorescent probes

[Cu(DAPT)₂Cl]Cl·H₂O and [Cu(DBM)(DAPT)Cl] [DAPT = 2,4-diamine-6-(pyrazin-2-yl)-1,3,5-triazine] were synthesized and characterized by IR and UV spectroscopy, elemental analysis, TG–DTA, molar conductivity, and LC–MS. The interaction with calf thymus DNA (ct-DNA) of the two complexes has been studied using UV spectra, fluorescent spectra, cyclic voltammetry, and viscosity measurements. The complexes interact with ct-DNA through classical intercalation. Fluorescence intensity changes of 1 and 2 in the absence and presence of ct-DNA have been investigated for quantitative determination of ct-DNA with the limit of detection of 3.8 and 7.7 ng mL^?1, respectively. From the result, the two complexes are potentially sensitive DNA fluorescent probes.     

The Quantitative Separation of Alkyl and Phenethyl Halides by HPLC

Abstract

A method is described for the quantitative separation of alkyl and phenethyl halides in mixtures containing benzene or toluene. This method involves the isocratic chromatography separation of the mixture, using a ODS column and the detection of the compounds by means of a RI detector.     

Multiresidue Analysis of Pesticides in Environmental Waters by Capillary Electrophoresis Using Simultaneous UV and Electrochemical Detection

A rapid multiresidue method has been developed for the analysis of eight pesticides (triazines, triazinones and ureas) in environmental waters. A simple end‐column electrochemical detector was used in combination with an available commercial capillary electrophoresis instrument with UV detection. The determination of these pesticides using micellar electrokinetic capillary chromatography (MEKC) with dual electrochemical and UV detection is the first time reported. In both detection systems, a linear range was obtained for the eight pesticides, concentrations lower than 5.0×10^?5 mol L^?1, in 0.020 mol L^?1 boric acid at pH 8.3 and containing 0.025 mol L^?1 of sodium dodecylsulfate, to obtain selectivity in the additional separation by micellar distribution process. Under these conditions a lower detection limit than 2.0×10^?6 mol L^?1 (0.15 pmol of pesticide) was achieved for the most of them. The eight pesticides are resolved in less than 14 min.