Drug matrix effect on the determination of residual solvents in bulk pharmaceuticals by wide-bore capillary gas chromatography.

A wide-bore capillary gas chromatographic method has been developed to study the drug matrix effect on the determination of residual solvents in bulk pharmaceuticals. A selective method is achieved on a Restek wide-bore (0.53-mm i.d. x 30 m) open-tubular fused-silica column coated with a 5-micron film of 95% dimethyl-5% diphenyl polysiloxane protected by a phenyl-methyl siloxane deactivated, uncoated fused-silica guard column. Utilizing this method, several common process solvents in weakly acidic, weakly basic, and neutral drug matrices are evaluated by recovery and linearity studies to show whether or not a drug matrix effect exists in their determination.     

Possibilities and pitfalls in analyzing (upgraded) pyrolysis oil by size exclusion chromatography (SEC)

The applicability of size exclusion chromatography (SEC) to analyze (upgraded) pyrolysis oil samples has been studied using model compounds, pyrolysis oils and hydrodeoxygenated pyrolysis oils. The assumptions needed for the conversion of the chromatogram to the M_w-distribution were validated. It was shown that the conversion of elution volume to molecular weight (based on polystyrene calibration curves) can introduce substantial errors in the prediction of the molecular weight. The conversion of RID response to W(log M) (as plotted on the y-axis of the M_w-distribution) is based on the assumption of a compound independent RID response factor and linear response to concentration. While the latter was shown to be true within the concentration range studied, the former was not true: the RID response factor depends on the type of (upgraded) pyrolysis oil. It was shown that within a single pyrolysis oil sample, the RID response for the low molecular weight fraction was a factor 3 lower than the high molecular weight fraction. Furthermore long term column fouling can influence SEC results that cannot be corrected with regular polystyrene recalibrations.Based on the results we recommend SEC not to be used as a quantitative method for characterization (upgraded) pyrolysis oil samples, but as a tool to compare (upgraded) pyrolysis oil samples, preferably prepared using incremental operating conditions and expected to have similar molecular composition. This work has further shown that (i) the ∫UVDdv/∫RIDdv ratio can be used as an indication of the sum of the relative aromaticity and conjugated double bond content for (upgraded) pyrolysis oil, and (ii) the negative peak area appearing in the low molecular weight part of the chromatogram can be used to estimate the water content of (upgraded) oil samples.     

180° -turns in integrated optics

Integrated optic devices, such as directional couplers, typically have a length to width ratio of 1:1000. Therefore economical use of quadratic substrate areas requires 180° wave guide turns to cover the whole substrate with a complex circuit in a zick-zack manner. For 180° -turns only curved guides have been considered. Radii of > 1 cm are necessary to avoid loss, and therefore are useless. A new concept for 180° -turns is proposed consisting of a halved 3 stage Δβ-reversal coupler with mirrors at one end. It is demonstrated that these 180° -turns may be fabricated providing high efficiency.     

Correlation of solute retention in gas chromatography with properties of the anion for tetra-n-butylammonium salts

Variations in the molar retention volume of organic solutes on thirteen tetra-n-butyl-ammonium salts with a common liquid temperature range are correlated with the properties of the anion. The anions studied include the chloride, bromide, nitrate, nitrite, methanesulfonate, trifluoromethanesulfonate, ethanesulfonate, 4-toluenesulfonate, sulfamate, thiocyanate, picrate, pentacyanopropenide, and tetra-n-butylborate. The high melting points and poor thermal stabilities of camphorsulfonate, dihydrogenphosphate, hydrogensulfate, and perrhenate precluded their use. The properties of the anions have only smallinfluences on the magnitudes of dispersive, orientative, and proton-donor interactions with the test solutes. Orientative interactions are strong for polar solutes but vary little with anion structure. There was no correlation between the dipole moment of the tetra-n-butylammonium salts and the retention of polar solutes. The structures of the anion do, however, have large influences on the retention of proton-donor solutes. for these solutes, a good correlation was found between molar retention volume and the basicity of the anions, represented by their pK_a values in aqueous solution.     

Adsorption mechanism of arsenate by zirconyl-functionalized activated carbon

Arsenate [As(V)] and arsenite [As(III)] sorption at the solid-water interface of activated carbon impregnated with zirconyl nitrate (Zr-AC) was investigated using X-ray absorption spectroscopy (XAS) and surface complexation modeling. The XAS data at the Zr K-edge suggest that the structure of the zirconyl nitrate coating is built from chains of edge-sharing ZrO8 trigonal dodecahedra bound to each other through two double hydroxyl bridges. The 8-fold coordination of each Zr atom is completed by four O atoms, which share a bit less than the two theoretically possible bidentate nitrate groups. On impregnation, two of the O atoms may lose their nitrate group and be transformed to hydroxyl groups ready for binding to carboxylic or phenolic ligands at the AC surface. As K-edge XANES results showed the presence of only As(V) on adsorption regardless of the initial As oxidation state. Oxidation to As(V) is probably mediated by available carbon species on the AC surface as found by batch titration. Zr K-edge EXAFS data indicate that arsenate tetrahedra form monodentate mononuclear surface complexes with free hydroxyl groups of zirconyl dodecahedra, whereby each bidentate nitrate group is exchanged by up to two arsenate groups. The inner-sphere arsenate binding to the Zr-AC surface sites constrained with the spectroscopic results was used in the formulation of a surface complexation model to successfully describe the adsorption behavior of arsenate in the pH range between 4 and 12. The results suggest therefore that Zr-AC is an effective adsorbent for arsenic removal due to its high surface area and the presence of high affinity surface hydroxyl groups.     

Surface states and the charge of a dust particle in a plasma

We investigate electron and ion surface states of a negatively charged dust particle in a gas discharge and identify the charge of the particle with the electron surface density bound in the polarization-induced short-range part of the particle potential. On that scale, ions do not affect the charge. They are trapped in the shallow states of the Coulomb tail of the potential and act only as screening charges. Using orbital-motion limited electron charging fluxes and the particle temperature as an adjustable parameter, we obtain excellent agreement with experimental data.     

Evaluation of the Performance of Small Diode Pumped UV Solid State (DPSS) Nd:YAG Lasers as New Radiation Sources for Atmospheric Pressure Laser Ionization Mass Spectrometry (APLI-MS)

The performance of a KrF^* bench top excimer laser and a compact diode pumped UV solid state (DPSS) Nd:YAG laser as photo-ionizing source in LC-APLI MS is compared. The commonly applied bench-top excimer laser, operating at 248 nm, provides power densities of the order of low MW/cm² on an illuminated area of 0.5 cm² (8 mJ/pulse, 5 ns pulse duration, beam waist area 0.5 cm², 3 MW/cm²). The DPSS laser, operating at 266 nm, provides higher power densities, however, on a two orders of magnitude smaller illuminated area (60 μJ/pulse, 1 ns pulse duration, beam waist area 2 × 10^–3 cm², 30 MW/cm²). In a common LC-APLI MS setup with direct infusion of a 10 nM pyrene solution, the DPSS laser yields a significantly smaller ion signal (0.9%) and signal to noise ratio (1.4%) compared with the excimer laser. With respect to the determined low detection limits (LODs) for PAHs of 0.1 fmol using an excimer laser, LODs in DPSS laser LC-APLI MS in the low pmol regime are expected. The advantages of the DPSS laser with respect to applicability (size, cost, simplicity) may render this light source the preferred one for APLI applications not focusing on ultimately high sensitivities. Furthermore, the impact of adjustable ion source parameters on the performance of both laser systems is discussed in terms of the spatial sensitivity distribution described by the distribution of ion acceptance (DIA) measurements. Perspectives concerning the impact on future APLI-MS applications are given.