Comparison of magnesium sulfate and sodium sulfate for removal of water from pesticide extracts of foods

Water-miscible solvents, such as acetone and acetonitrile, effectively extract both polar and nonpolar pesticide residues from nonfatty foods. The addition of sodium chloride to the resulting acetonitrile-water or acetone-water extract (salting out) results in the separation of the water from the organic solvent. However, the organic solvent layer (pesticide extract) still contains some residual water, which can adversely affect separation procedures that follow, such as solid-phase extraction and/or gas chromatography. Drying agents, such as sodium sulfate or magnesium sulfate, are used to remove the water from the organic extracts. In the present study, we used nuclear magnetic resonance spectroscopy to study the composition of the phases resulting from salting out and to compare the effectiveness of sodium sulfate and magnesium sulfate as drying agents. The study showed that considerable amounts of water remained in the organic phase after phase separation. Sodium sulfate was a relatively ineffective drying agent, removing little or no residual water from the organic solvent. Magnesium sulfate proved to be a much more effective drying agent.     

Drying dissipative patterns of colloidal crystals of silica spheres in organic solvents

Drying dissipative structural patterns formed in the course of drying colloidal crystals of silica spheres (110 nm in diameter) in water, methyl alcohol, ethyl alcohol, 1-propyl alcohol, diethyl ether, and in the mixtures of ethyl alcohol with the other solvents above have been studied on a cover glass. The macroscopic broad rings were formed in the outside edges of the dried film for all the solvents examined. Furthermore, much distinct broad rings appeared in the inner area when the solvents were ethyl alcohol, methyl alcohol, and their mixtures. Profiles of the thickness of the dried films were sensitive to the organic solvents and explained well with changes in the surface tensions, boiling points, and viscosities of the solvents. The macroscopic and microscopic spoke-like crack patterns formed. The drying area (or the drying time) increased (or decreased) as the surface tension of the solvent decreased. However, the absolute values of these drying parameters are determined also by the boiling points of the solvents. Importance of the fundamental properties of the solvents is supported in addition to the characteristics of colloidal particles in the drying dissipative pattern formation.     

A cold silanization method for preparation of medium polarity capillary columns

Silane-coupling agents, commonly used for fiberglass reinforced plastics (FRP), were applied for deactivation of silanol sites in glass capillary columns prior to coating with mediumpolarity phases such as Carbowax and Superox. The columns, prepared in a two-stage process in the case of glass (acidic leaching and drying, dynamic cold silanization followed by static coating with the phase) or a one stage process in the case of fused silica, gave the best results when deactivation and hence wettability were induced by glycidoxypropyltrimethoxy silane.     

Influence of the Solvent on the “Casting” Methodology for MWCNT‐Modified Glassy Carbon and Platinum Electrodes

The choice of electrode material and surface preparation method are usually dictated by the suitability of the electrode to observe an electrochemical parameter, such as heterogeneous electron transfer rate, surface coverage, or redox potential. Thus, the glassy carbon (GC) and platinum (Pt) electrodes were modified with multiwalled carbon nanotubes (MWCNT) by direct “casting” modification using nine different aliquots of solvents. After drying at room temperature, the modified electrode showed distinct redox peaks corresponding to ferrocyanide oxidation/reduction. Using chemometrics, the cyclic voltammograms with higher current intensity were obtained for those in which ethanol, water and acetone as dispersing agents were used for GCE and dimethylformamide, water and acetone for Pt electrode modification.     

Preparation of rapid (chain-stopped) alkyds by incorporation of gum rosin and investigation of coating properties

In this study, the synthesis, characterization, and properties of a short oil length chain–stopped(rapid) alkyd resin is investigated. Gum rosin modified alkyd resin (RA-GR) was prepared using soybean oil, phthalic anhydride, glycerin and gum rosin acid. An alkyd modified with benzoic acid (RA-BA) was also prepared for comparison. FTIR analyses and GPC measurements of the alkyds were used for characterization. Other properties such as the viscosity, acid value, and solid content of the final resins were determined. Separately, the synthesized resins were used in paint formulations without any changes in other parameters such as filler, airdrying agents, solvents, etc. Paints were applied to metal and glass surfaces and the effect of gum rosin was investigated by looking at touch and hard drying times, adhesion to metals and gloss changes. Compared to the benzoic acid modified resin (RA-BA), gum rosin modified resin (RA-GR) exhibited remarkable positive effects on the paint with a better adhesion to the metals, and short drying times without any loses in the glosses.     

Use of a Drying Cartridge in On-Line Solid-Phase Extraction–Gas Chromatography–Mass Spectrometry

A drying cartridge was used and optimized for the in-line elimination of water from the desorption eluent in on-line solid phase extraction–gas chromatography (SPE–GC). The cartridge is essentially a small stainless-steel precolumn packed with a drying agent which can be regenerated by simultaneous heating and purging with a moisture-free gas. The drying cartridge was mounted on an additional valve instead of between the SPE–GC transfer valve and the on-column injector to enable regeneration of the cartridge during the GC run and, thus, to increase sample throughput. Three drying agents were tested, viz. sodium sulfate, silica, and molecular sieves. Although molecular sieves have the highest capacity, silica was preferred because of practical considerations. Large-volume injections were performed through the in-line drying cartridge using a mixture of 23 microcontaminants ranging widely in polarity and volatility. Four solvents were tested. With pentane and hexane, the more polar analytes were retained by the drying cartridge. Ethyl acetate and methyl acetate gave much better (and closely similar) recoveries for all analytes. Because water elimination on the silica cartridge proved to be less critical than with ethyl acetate, this solvent was finally selected. The entire SPE–drying cartridge–GC set-up was combined with mass spectrometric (MS) detection for the determination of a mixture of micropollutants in real-life water samples. With 10-ml tap water samples spiked at the 0.5 μg/l level, for the majority of the test compounds the analyte recoveries generally were 60–106%, and (full-scan) detection limits typically were 0.01–0.03 μg/l. Some very polar analytes such as, e.g. dimethoate, were (partially) sorbed onto the silica packing of the drying cartridge.     

Understanding the effect of skin formation on the removal of solvents from semicrystalline polymers

The effect of glassy skin formation on the drying of semicrystalline polymers was investigated with a comprehensive mathematical model developed for multicomponent systems. Polymers with high glass‐transition temperatures can become rubbery at room temperature under the influence of solvents. As the solvents are removed from the polymer, a glassy skin can form and continue to develop. The model takes into account the effects of diffusion‐induced polymer crystallization as well as glassy–rubbery transitions on the overall solvent content and polymer crystallinity. A Vrentas–Duda free‐volume‐based diffusion scheme and crystallization kinetics were used in our model. The polymer–solvent system chosen was a poly(vinyl alcohol) (PVA)–water–methanol system. The drying kinetics of PVA films were obtained by gravimetric methods with swollen films with known water/methanol concentrations. The overall drying behaviors of the polymer system determined by our model and experimental methods were compared and found to match well. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3191–3204, 2005     

Nonaqueous capillary electrophoresis: application possibilities and suitability of various solvents for the separation of basic analytes

Eleven organic solvents were tested for their suitability in the use of capillary electrophoresis (CE). In all cases, 25 mM ammonium acetate and 1 M acetic acid were used as electrolytes. Three basic therapeutical agents, propranolol, carteolol and imipramine, were used as analytes. Four solvents (2-propanol, ethylene glycol, propylene glycol, dichloromethane) were not suitable for use with CE under our conditions. Depending on the other solvents used, the analytes showed very different behavior. We observed that the epsilon/eta quotient alone is not sufficient for a characterization of the solvents. Further investigations with all the solvents as 1:1 mixtures with methanol were carried out. As a result some principal changes occurred compared to the pure solvents. Working with mixtures of different solvents proved to be advantageous because of the possibility to influence properties like high viscosity or low ionizing abilities by the addition of a suitable second solvent.     

High-Throughput GC-FID Method for the Determination of Residual Solvents in Early-Phase Drug Discovery Samples

Chromatographia - In drug discovery environment, determination of residual solvents is indispensable and requires rapid analysis covering a maximum number of commonly used solvents especially with...     

Chelate resin-iron(II) complex: Adsorption and desorption of nitrogen monoxide at the dry state

A chelate resin-immobilized iron(II) complex was prepared from iron(II) and poly(styrenecodivinylbenzene) which is functionalized by iminodiacetic acid group. It is activated by drying after having been washed with methanol. The resin complex can rapidly adsorb nitrogen monoxide, and the nitrogen monoxide adsorbed on the complex can be released by the treatment with heat. The adsorption of nitrogen monoxide proceeds through the 1:1 complex formation of the NO molecule with the iron(II) atom, and its complex formation constant was calculated as 8330 atm^?1 at room temperature from Langmuir plots. This value does not depend on the solvents used for washing. The activation of the resin complex by the treatment of washing with methanol is derived by increasing the amount of effective iron(II) ions due to the increase in the surface area. Moreover, this resin complex was revealed to have high complex formation constant with NO and high durability to dioxygen compared with an aqueous solution of ethylenediaminetetraacetato–iron(II) complex, which is the corresponding monomeric absorbent commonly used for nitrogen monoxide.     

Liquid chromatography/tandem mass spectrometric bioanalysis using normal-phase columns with aqueous/organic mobile phases - a novel approach of eliminating evaporation and reconstitution steps in 96-well SPE

Bioanalytical methods using automated 96-well solid-phase extraction (SPE) and liquid chromatography with electrospray tandem mass spectrometry (LC/MS/MS) are widely used in the pharmaceutical industry. SPE methods typically require manual steps of drying of the eluates and reconstituting of the analytes with a suitable injection solvent possessing elution strength weaker than the mobile phase. In this study, we demonstrated a novel approach of eliminating these two steps in 96-well SPE by using normal-phase LC/MS/MS methods with low aqueous/high organic mobile phases, which consisted of 70-95% organic solvent, 5-30% water, and small amount of volatile acid or buffer. While the commonly used SPE elution solvents (i.e. acetonitrile and methanol) have stronger elution strength than a mobile phase on reversed-phase chromatography, they are weaker elution solvents than a mobile phase for normal-phase LC/MS/MS and therefore can be injected directly. Analytical methods for a range of polar pharmaceutical compounds, namely, omeprazole, metoprolol, fexofenadine, pseudoephedrine as well as rifampin and its metabolite 25-desacetyl-rifampin, in biological fluids, were developed and optimized based on the foregoing principles. As a result of the time saving, a batch of 96 samples could be processed in one hour. These bioanalytical LC/MS/MS methods were validated according to "Guidance for Industry - Bioanalytical Method Validation" recommended by the Food and Drug Administration (FDA) of the United States.     

大口径毛细管气相色谱检查药物中残留溶剂的方法研究

 以药物合成中常用的 16种有机溶剂为研究对象 ,建立了用大口径毛细管柱检查残留有机溶剂的气相色谱法 ,并考察了不同极性的色谱柱及不同提取溶剂对分离与检测的影响。实验表明 ,根据原料药合成中可能存在的残留溶剂 ,选用适当的提取溶剂 ,采用大口径毛细管气相色谱法检查 ,可获得较满意的结果。     

Dilute solution studies of pyrrone prepolymers

Data on dilute solutions of a pyrrone “prepolymer” are presented and the tendency of this polymer to aggregate in certain solvents commonly used in dilute solution studies is discussed. It is concluded that reliable molecular weights can be determined if solvents that interact with the prepolymer through hydrogen bonding are used.     

IOn-exchange behaviour of several elements in mixed solvents

The distribution coefficients between the cation- and anion-exchangers Dowex 50 and Dowex 1, and aqueous solutions containing nitric or hydrochloric acid and organic solvents with or without amines or complexing agents, have been obtained for a number of metals including uranium, thorium, cerium, iron, copper, and nickel. The organic solvents were methanol, acetone and dimethylformamide; the amines were tributylamine and tribenzylamine, and the complexing agents EDTA and citric acid. Both batch and column methods were used.     

Determination of chelating agents and metal chelates by capillary zone electrophoresis

Aminopolycarboxylic acids such as diethylenetriaminepentaacetic acid (DTPA) are commonly used as chelating agents in many pulp and paper industries, particularly as scavengers of metal ions which catalyze the decomposition of hydrogen peroxide used as a bleaching agent. Concern for the effect of waste DTPA in the aquatic environment has led to a need for the development of methods to determine its levels in waste water. This paper describes the determination of free DTPA and several metal-DTPA complexes in water and waste water by capillary zone electrophoresis. The optimization of separation conditions included the selection of an appropriate carrier electrolyte composition (pH, organic solvents, ion-pairing reagents) and the systematic investigations of selective complexation of free DTPA as well as metal exchange reactions for metal-DTPA complexes in order to achieve selective and sensitive direct UV detection. The determination of DTPA in waste water from a paper mill was possible in the low ppm range.     

0-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride as a sensitive derivatizing agent for the electron capture gas liquid chromatographic analysis of keto steroids.

0-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride was used to prepare oximes of steroids with keto groups in selected positions; 3,17 and 20-monoketo; 3,17 and 3,20-diketo. Some of the 3-keto steroids had hindered 17-hydroxyl groups which were not readily amenable to esterification with perfluoroanhydrides, the most commonly used derivatizing agents for electron capture gas chromatographic analysis of hydroxy steroids. The oximes were readily prepared from 5 ng of each of the compounds tested, and with testosterone it was demonstrated that the derivative could be prepared from as little as 0.1 ng. The derivatives were stable to gas chromatography and extremely sensitive to electron capture detection. The sensitivity ranged from 1.5 X 10(4) coulombs per mole of progesterone. Because of the ease of preparation of the derivatives, their stability in common solvents and analytical manipulative techniques, the reagent would be suitable for the micro analysis of biologically significant keto steroids by electron capture gas chromatography.     

Zeta potential time dependence reveals the swelling dynamics of wood cellulose nanofibrils

In this paper, we present the swelling dynamics of individual wood cellulose nanofibrils (CNFs) following solvent substitution into various organic solvents and drying, by employing the time dependence of the zeta potential (ζ). We succeeded in smoothly redispersing the coaggregating CNFs dried in solvents, including acetone, acetonitrile, DMSO, ethanol, and t-butanol into water. ζ-t plots of the redispersed CNFs measured in a 1 mM KCl solution indicated different values of Δζ (volume fraction of hydration capacity), corresponding to the dielectric constant of the substituted solvents. Differential scanning calorimetry confirmed that the redispersed CNFs swell to different degrees, corresponding to Δζ. This swelling behavior is characterized by expansion of hemicelluloses, the amorphous polysaccharides located on the CNF surface, with a different degree of aggregation during drying. The specific swelling ratio, radius, and diameter of the CNFs in water were calculated using the values of ζ(0) and ζ(∞) by introducing surface chemical analysis. The calculated diameters of the CNFs at t = 0 coincided well with the median diameters measured directly by transmission electron microscope. Swellability of hemicelluloses exponentially increased with the decrease in dielectric constant of solvent during drying. The analysis method combining zeta potential time dependence and a surface chemical approach proved useful for specifically evaluating the swelling dynamics of polymers on a bulk surface.     

Photocleavable peptide hydrogel arrays for MALDI-TOF analysis of kinase activity

We have developed an acrylamide copolymerization strategy to immobilize acrylamide labeled peptides and proteins into a hydrogel surface and detect their modifications using MALDI-TOF mass spectrometry. Copolymerization into hydrogels is robust, compatible with "off-the-shelf" chemistry, and yields materials and surfaces that are stable to aqueous or organic solvents, drying, high or low temperature, high or low pH, oxidizing agents, sonication, mechanical contact, etc. The use of acrylamide hydrogels allows immobilization of substrates in a hydrated environment that can be used both as a biological reaction matrix and as a MALDI target. In our strategy, a substrate peptide was designed in a modular fashion to include both modification site and affinity domains. It was labeled with an acrylamide functionality using a generalized chemistry and covalently attached to the surface with a photocleavable linker, allowing for aggressive washing to remove any fouling, followed by selective release for MALDI-TOF analysis. Using this system we were able to analyze and compare v-Abl (truncated) and c-Abl (full-length) kinase activity on a peptide substrate with an affinity domain specific for the full-length kinase, observing excellent overall reproducibility in the extent of phosphorylation detected. This work serves as proof of principle for modular substrate design strategies for mass spectrometry-readable biosensors.     

固相微萃取-气相色谱法测定食品包装材料中残留有机溶剂

提出了一种以固相微萃取与气相色谱-氢火焰联用技术为基础的测定食品包装材料中15种常用有机溶剂(苯类、醇类、酮类、酯类等)的方法。选择聚二甲亚砜作为固相微萃取的萃取相,采用DB-624毛细管色谱柱进行分离。在优化的试验条件下,15种有机残留溶剂在20min内能很好地分离,15种溶剂的测定下限(10S/N)为0.08～0.69μg.dm-2。加标回收率为60.0%～115.0%,相对标准偏差(n=5)为2.17%～8.34%。     

Layer-by-layer nanoassembly of polyelectrolytes using formamide as the working medium

Formamide, in its pure state, has been used as a working solvent for layer-by-layer (LbL) polyelectrolyte self-assembly. Polystyrene sulfonate (PSS) and polyallylamine hydrochloride (PAH) polyelectrolyte films were deposited onto planar substrates and colloidal particles. Film deposition was confirmed using quartz crystal microbalance and zeta potential measurements. Formamide was used as an alternative to the water-based working solvents commonly used for LbL self-assembly. Few LbL self-assembly studies using nonaqueous solvents have been reported. Most studies performed with nonaqueous solvents have required the addition of small volumes of water to dissolve the polyelectrolytes. Conversely, the high dielectric constant of pure formamide led to the dissolution and transport of PSS and PAH. Using formamide, it is possible to deposit nanometer thick polyelectrolyte films onto water-sensitive surfaces. Formamide can be thus be used for encapsulating water sensitive hydrogen storage materials within polyelectrolyte films.