Solventless injecction for packed column supercritical fluid chromatography

The adverse effects of injection solvent strength on microbore packed column SFC band broadening are demonstrated and a solventless injection system that eliminates these effects is introduced. The injection system removes solvent in a GC-like manner using a retention gap and an on-column capillary GC syringe. The analyte is delivered to the analytical column in a solvent-free plug of supercritical fluid mobile phase.     

Excited-state dipole moments from absorption/fluorescence solvatochromic ratios

The permanent dipole moments of excited molecules can be obtained from the ratio of the solvent shifts of absorption and fluorescence spectra. This ratio method eliminates the uncertain solute cavity radius parameter, as well as the solvent polarity function. In the case of the first excited singlet state of aniline the dipole moment is 5 D (versus 1.57 D in the ground state).     

Non-flammable preparative reversed-phase liquid chromatography of recombinant human insulin-like growth factor-I

Acetonitrile is used as an eluent for reversed-phase chromatography. However, because it is a flammable solvent, using acetonitrile on a large scale requires expensive equipment and facilities specially designed for flammable solvents. Using a non-flammable solvent as an eluent eliminates this expense. A method was developed to purify recombinant human insulin-like growth factor I by reversed-phase high-performance liquid chromatography using gradient elution with hexylene glycol, a non-flammable replacement for acetonitrile. The separation produced equivalent yield, purity and throughput as reversed-phase chromatography using elution with acetonitrile.     

A facile synthesis of substituted pyridines and pyrazolo[3,4‐b]pyridines

A facile, solvent free, ecofriendly approach for the synthesis of 2‐amino‐3(ethylcarboxy)‐4,6‐disubsti‐tuted pyridine 4 and pyrazolo[3,4‐b]pyridines 6 is herein described employing neat reaction conditions under microwave irradiation. This solventless methodology is environmentally benign as it completely eliminates the use of solvent from the reaction procedure. The observed reaction rate enhancement and high yield of products are due to the neat reaction conditions coupled with microwaves (MWs).     

Enhancement of ionization efficiency of mass spectrometric analysis from non-electrospray ionization friendly solvents with conventional and novel ionization techniques

Electrospray ionization mass spectrometry (ESI-MS) has significantly impacted the analysis of complex biological and petroleum samples. However ESI-MS has limited ionization efficiency for samples in low dielectric and low polarity solvents. Addition of a make-up solvent through a T union or electrospray solvent through continuous flow extractive desorption electrospray ionization (CF-EDESI) enable ionization of analytes in non-ESI friendly solvents. A conventional make-up solvent addition setup was used and a CF-EDESI source was built for ionization of nitrogen-containing standards in hexane or hexane/isopropanol. Factors affecting the performance of both sources have been investigated and optimized. Both the make-up solvent addition and CF-EDESI improve the ionization efficiency for heteroatom compounds in non-ESI friendly solvents. Make-up solvent addition provides higher ionization efficiency than CF-EDESI. Neither the make-up solvent addition nor the CF-EDESI eliminates ionization suppression of nitrogen-containing compounds caused by compounds of the same chemical class.     

Optimization of diffusion-filtered NMR experiments for selective suppression of residual nondeuterated solvent and water signals from 1H NMR spectra of organic compounds

Interpretation of 1H NMR spectra of organic compounds is sometimes hampered by the presence of strong peaks arising from residual nondeuterated solvent and water that obscure compound signals. Classical solvent suppression techniques such as presaturation or those based on pulsed field gradients are not effective in this regard because they also remove the compound resonances that overlap with the solvent signal being suppressed. Here, we propose an alternative scheme by using an optimized NMR diffusion filter that eliminates the nondesired peaks while retaining the signals of interest. This strategy has proved to be useful in three common deuterated solvents, namely, CDCl3, DMSO-d6, and CD3OD, resulting in clean spectra with no interference from solvent or water peaks.     

A catalytic method for the determination of Nickel

The catalytic effect of nickel on the decomposition of permanganate in alkaline solution in the presence of acctodiphosphonic acid is used as a basis for a method for the determination of 0.1–0 7 p.p.m. of nickel. A solvent extraction procedure eliminates the interferences of silver, cobalt, copper and iron, and can be used to concentrate lower concentrations of nickel.     

A solvent recirculation trapping device for supercritical fluid extraction of polyaromatic hydrocarbons

A new device has been developed for the trapping of volatile pollutants in trapping solvents. The device allows solvent recirculation and cryogenic trapping of evaporated volatiles to minimize the stripping effect and any losses of volatile analytes. Due to solvent recirculation, the trapping solvent column height remains constant during the extraction without any need for replenishment. Also mass transfer conditions are favorable due to the flattened shape of bubbles of CO2 and the longer extraction time. The bubbles have higher interfacial area and they have to pass a three times longer distance in the solvent column. The device produces more concentrated extracts, reduces solvent consumption, and reduces or eliminates its evaporation to the environment. The cryotrapping part reduces losses of volatile analytes and the stripping effect. It also enables single-phase extraction into much smaller solvent volumes. Due to constant and favorable extraction conditions, the precision of the method was also greatly improved (RSDs decreased from 2.2 to 0.8%). As proved by a set of rapid spiked-sample extractions of highly volatile compounds at very high flow rates, the relative standard deviation of the experiments performed in the new device is 3.5 times lower.     

Systematic studies on mechanochemical synthesis: Schiff bases from solid aromatic primary amines and aldehydes

A versatile and robust mechanochemical route to Aldehyde–Schiff base conversions has been established for a broad range of aldehydes via a simple cogrinding in mortar with a pestle under a solvent‐free, as well as solvent‐assisted, environment. The extent of amines reactivity under these conditions has also been explored, along with an examination of the possible connection between reactivity and electronic substituent effects. Results obtained demonstrated that the solvent‐free mechanochemical conversion of p‐toluidine and aromatic aldehydes to the corresponding Schiff bases proceeded more smoothly than the corresponding synthesis with 4‐aminobenzonitrile. The present approach not only provides good to excellent yields but also eliminates the disadvantages of the traditional synthesis of Schiff bases, such as the use of hazardous solvents, more or less demand of expensive catalysts, and looking for optimization on reaction conditions.     

A novel approach for solid-liquid extraction laser-excited time-resolved Shpol'skii spectrometry

A new procedure is presented for the analysis of polycyclic aromatic hydrocarbons by solid–liquid extraction (SLE) and laser-excited time-resolved Shpol'skii spectrometry (LETRSS). Microliters of Shpol'skii solvent are spiked on the surface of the extraction membrane and LETRSS is directly performed on the organic layer above the surface of the solid substrate. Fluorescence measurements are easily performed with a fiber-optic cell specifically designed for cryogenic measurements at 77 and 4.2 K. In comparison to the SLE–LETRSS procedure previously reported (Environ. Sci. Technol. 35 (2001) 2566), the spiking procedure eliminates the eluting step, reduces solvent consumption and improves limits of detection for at least one order of magnitude.     

Determination of residual monomer in polymer latex by full evaporation headspace gas chromatography

This study demonstrated a full evaporation (FE) headspace gas chromatographic technique for the determination of residual monomer in methyl methacrylate (MMA) polymer latex. A very small amount (approximately 10-30 mg) of latex was added to a sealed headspace sample vial (20 ml). A near-complete monomer mass transfer from both liquid (aqueous phase) and solid phase (polymer particles) to the vapor phase (headspace) is achieved within 5 min at a temperature of 110 degrees C. The method eliminates sample pretreatment procedures such as the solvent extraction. Thus, it avoids the risk of polymer deposition on the GC system caused by a directly injection of extraction solvent in the conventional GC monomer analysis. The present method is simple, rapid, and accurate.     

The efficient synthesis of carbon–carbon double bonds via Knoevenagel condensation using red mud packed in a column

Abstract

Red mud (RM) is generated as a by-product during the production of alumina from bauxite ore. In this study, RM packing in a column is used as a catalyst for carbon–carbon double bond formation via Knoevenagel condensation. The reactants are added to the top of the column and then eluted with solvent. The products are collected in high yields and short time. RM packed in a column eliminates a catalyst separation step from the reaction mixture in this work.     

Friedel-Crafts酰基化法制备聚苯乙烯型阴离子交换树脂

提出了一种合成聚苯乙烯型阴离子交换树脂的新方法：通过Ｆｒｉｅｄｅｌ－Ｃｒａｆｔｓ酰基化反应在交联聚苯乙烯上引入乙酰基，然后经溴化、胺化反应制备阴离子交换树脂。该方法避免了使用氯甲醚等致癌物质，并消除了二次交联等副反应。讨论了溶剂，催化剂，试剂和反应温度及时间等因素对各步反应的影响。测定了产物的基本性能并对所得结果进行了讨论。     

A mild, clean, and simple synthesis of symmetrical carboxylic anhydrides from carboxylic acides using a polymer supported tosyl chloride

The use of polymeric reagents simplifies routine acylation of carboxylic acid because it eliminates the traditional purification. We describe the use of readily available cross-linked poly(4-vinylpyridine) supported tosyl chloride, [P₄VP].TsCl, in the suspended solution phase synthesis of symmetrical anhydrides from carboxylic acids in the presence of K₂CO₃ in high yields and purity. The products can be obtained by filtration and evaporation of the solvent.     

An advanced solventless column test for capillary GC columns

Manufacturing skills for capillary GC columns have improved to a point where the commonly used tests no longer distinguish between "adequate" and "excellent" columns. A more stringent test mixture, coupled with a more exacting procedure, was proposed for testing capillary columns in 2004. The solutes were less sterically hindered and less retained, permitting the test to be run isothermally at lower temperatures where sorptive forces are stronger. To avoid masking active sites by solvent flooding, the test used a higher boiling solvent that eluted last. This test mixture, used under the prescribed conditions, differentiated adequate from excellent columns, but removal of the late-eluting solvent prolonged run times to as long as 1 h. The new test uses the same probes proposed in 2004, but entirely eliminates the solvent. Injections utilize a plunger-in-needle microvolume syringe, and the "gas saver" feature of a contemporary gas chromatograph. The latter serves as a dynamic diluter to deliver nanogram quantities of undiluted solutes to the column. The test can be conducted isothermally at a lower temperature in less than 15 min for most of the columns. This paper summarizes the analytical approach used, and presents method performance data and test results obtained on contemporary capillary columns from leading manufacturers.     

A simple,inexpensive, rapid,sensitive and solventless technique for the analysis of accelerants in fire debris based on SPME

The current method of choice for the extraction of flammable or combustible liquid resides from fire debris samples is passive headspace concentration using activated charcoal strips (ACS) for adsorption of the liquid residues followed by elution with carbon disulfide or other suitable solvent. Presently, we report a new technique based on headspace solid-phase microextraction which has been successfully applied to the identification of a wide range of accelerants commonly seen in arson analysis. The SPME technique developed is simple, inexpensive, rapid, and eliminates the use of the highly flammable and toxic solvent carbon disulfide. Results using this SPME method have been directly compared to results obtained via the ACS technique for light, medium, and heavy petroleum distillates as well as gasoline. All of the accelerants studied were accurately identified by the SPME method with equal or greater sensitivity compared to the ACS method.     

Molecular imprinting made easy

A simple method of molecular imprinting is presented that uses a single cross-linking monomer N,O-bismethacryloyl ethanolamine (NOBE) along with template, initiator, and solvent. This formulation eliminates the need for additional functional monomers and empirical optimization of relative ratios of functional monomers, cross-linkers, and template. In fact, utilization of NOBE alone often provides molecularly imprinted polymers (MIPs) with higher performance than MIPs incorporating functional monomer (e.g., methacrylic acid).     

Solvent-free functionalization of carbon nanotubes

A fundamentally new single-walled and multiwalled carbon nanotube sidewall functionalization technique has been developed in which solvent is not required and the reaction times are greatly shortened (1 h at 60 degrees C). Exploiting the long linear dimension of the nanotube ropes by macroscopic mechanical deformation, reactive sites are generated merely by mechanically deforming the tubes using a stir bar. This approach eliminates the need for large volumes of solvent ( approximately 2 L/g), which were formerly considered essential due to the insolubility of carbon nanotubes. Using a series of 4-substituted anilines and a nitrite, the aryl diazonium intermediates were generated in situ and permitted to react with the tubes. Raman, IR, and UV spectroscopies, coupled with thermogravimetric analyses and solubility studies, support the assignments.     

Rapid narrow band elution for on-line SPE using a novel solvent plug injection technique

Determination of trace constituents in biological and environmental samples usually requires a pre-concentration step. While solid-phase extraction (SPE) has been widely used, it is slow, labor intensive and adversely affected by analytical errors from handling. On-line SPE eliminates some of the flaws but often suffers from solvent compatibility problems with the subsequent chromatography separation. In this study, we are presenting a technical solution for overcoming some of these compatibility issues, by utilizing a fully automated, focused SPE sample transfer technique utilizing narrow-band solvent plugs, for seamless hyphenation with high-performance liquid chromatography (HPLC) or flow injection mass spectrometry (MS). A wide range of pharmaceutical compounds was studied in different sample matrices. Short plugs of high elution strength solvent were generated by means of an electrically actuated sample loop and enrichment and transfer steps monitored using on-line SPE-MS. The impact of the solvent plugs on chromatographic separation was studied using hyphenated SPE-LC-MS. By carefully examining elution profiles of solvent plugs of different compositions, optimum conditions for quantitative elution within well-defined volumes were found for all substances. In addition, the highly focused elution bands resulted in excellent retention time and peak area reproducibilities when injected on-line onto HPLC columns. Finally, to demonstrate proof-of-principle, the fully integrated on-line SPE-LC-MS system was applied to the analysis of spiked urine and river water samples.     

Automation and optimization of liquid-phase microextraction by gas chromatography

Several fully automated liquid-phase microextraction (LPME) techniques, including static headspace LPME (HS-LPME) (a drop of solvent is suspended at the tip of a microsyringe needle and exposed to the headspace of the sample solution), exposed dynamic HS-LPME (the solvent is exposed in the headspace of sample vial for different time, and then withdrawn into the barrel of the syringe. This procedure is repeated a number of times), unexposed dynamic HS-LPME (the solvent is moved inside the needle and the barrel of a syringe, and the gaseous sample is withdrawn into the barrel and then ejected), static direct-immersed LPME (DI-LPME) (a drop of solvent is suspended at the tip of a microsyringe needle and directly immersed into the sample solution), dynamic DI-LPME (the solvent is moved inside the needle and the barrel of a syringe, and the sample solution is withdrawn and ejected), and two phase hollow fiber-protected LPME (HF-LPME) (a hollow fiber is used to stabilize and protect the solvent), auto-performed with a commercial CTC CombiPal autosampler, are described in this paper. Critical experimental factors, including temperature, choice of extraction solvent, solvent volume, plunger movement rate, and extraction time were investigated. Among the three HS-LPME techniques that were evaluated, the exposed dynamic HS-LPME technique provided the best performance, compared to the unexposed dynamic HS-LPME and static HS-LPME approaches. For DI-LPME, the dynamic process can enhance the extraction efficiency and the achieved method precision is comparable with the static DI-LPME technique. The precision of the fully automated HF-LPME is quite acceptable (RSD values below 6.8%), and the concentration enrichment factors are better than the DI-LPME approaches. The fully automated LPME techniques are more accurate and more convenient, and the reproducibility achieved eliminates the need for an internal standard to improve the method precision.