Alkyl pyrazine synthesis via an open heated bath with variable sugars, ammonia, and various amino acids.

BACKGROUND: Semi-quantitative characteristics of headspace volatile pyrazines which constituted around 1% by weight of the final product have been previously described. The influence of reactant concentration, reaction temperature, and reaction time on both the yield of total alkyl pyrazines and the distribution pattern of specific identified pyrazines has not been reported. RESULTS: The optimum synthetic conditions were 5 mol L-1 NH4 OH, 2 mol L-1 rhamnose, 0.5 mol L-1 leucine at 110°C for 2 h. The greatest total amount of pyrazines obtained was 17 280 µg of extracted product which translated into 31% 2,6-dimethyl pyrazine, 17% 2-methyl pyrazine, 15% 2-ethyl-6-methyl pyrazine, and 16% 2-isoamyl-6-methyl pyrazine. CONCLUSION: The yield of synthesized pyrazines increased at higher temperatures. Quantitative total and specific pyrazine results as opposed to analysis of only headspace volatiles are more representative of pyrazine synthesis. © 2016 Society of Chemical Industry.

Subcritical fluid chromatography of water soluble nucleobases on various polar stationary phases facilitated with alcohol-modified CO2 and water as the polar additive.

The separation of four water soluble nucleobases (thymine, uracil, adenine, and cytosine) via supercritical fluid chromatography with a CO(2)-based mobile phase containing an alcohol modifier and additive is described. Methanol, ethanol, 1-propanol, and 1-butanol were examined in conjunction with water as a neutral additive. Packed column stationary phases included silica bonded diol, cyanopropyl, and 2-ethyl pyridine. Thymine and uracil eluted with good peak shapes without additive, while adenine and cytosine yielded late eluting, severely tailing peaks. The addition of up to 5% water to each of the five alcohols gave rise to much sharper peaks that eluted under gradient conditions in less than 10 min with no baseline noise. Results with water under identical chromatographic conditions were compared with formic acid and ammonium acetate as additives. Water proved to be much superior to formic acid, and it was comparable to ammonium acetate. The role of water was speculated to not only enhance the solvating power of the binary mobile phase for water soluble analytes, but the common elution pattern exhibited by each of the three stationary phases suggested that water had altered the surface chemistry of the packed phase.

Analytical scale supercritical fluid fractionation and identification of single polar lipids from deoiled soybean lecithin.

The phosphatidylcholine (PC)-enriched fraction from soybean lecithin is of interest due to its critical role in both the pharmaceutical and industrial field. In this work, enhancement of the purity of the PC fraction along with other individual polar lipid fractions was achieved from crude soybean lecithin by using supercritical fluid extraction (SFE) with methanol-modified SC-CO(2). Neutral lipids were first removed from the crude sample using pure CO(2). Then, the effect of CO(2 )pressure, temperature, and modifier percentage on phospholipid (PL) fractionation from deoiled lecithin was compared with and without silica gel mixed with the lecithin. Pure fractions of phosphatidylethanolamine (PE) and PC were obtained by varying the modifier concentration of the extraction fluid at 460 atm and 40 degrees C with silica gel added to the deoiled lecithin. Without silica gel, coextraction of PE and PC was observed. A total of six components were isolated and tentatively identified in the extract of deoiled crude soybean lecithin.

Feasibility study of online supercritical fluid extraction-liquid chromatography-UV absorbance-mass spectrometry for the determination of proanthocyanidins in grape seeds.

Online coupling of supercritical fluid extraction (SFE) with liquid chromatography (LC)-UV absorbance-electrospray ionization (ESI)-mass spectrometry (MS) is evaluated for the determination of proanthocyanidins in grape seeds. The solid-phase intermediate trap is optimized in order to enhance the collection efficiency for the extracted polar components. Pure supercritical CO2 is used first to remove the oil in the seeds. Then methanol-modified CO2 is used to remove the polar components (e.g., phenolic compounds). Catechin and epicatechin (90%) are extracted out of the de-oiled after 240 min with 40% methanol as a modifier. Both singly-linked (B-type) and doubly-linked (A-type) procyanidins are identified by LC-ESI-MS, as well as their galloylated derivatives. The hyphenated system combines the extraction, separation, and detection in series. The experimental design minimizes the chance of analyte oxidation, degradation, and contamination. The traditional off-line SFE-LC method is also studied for comparison with the online method. Both advantages and disadvantages are observed for the online mode.

On-line coupling of supercritical CO2 extraction with reversed-phase liquid chromatography for the quantitative analysis of analytes in aqueous matrices.

The first report of on-line coupled supercritical fluid extraction (SFE) with reversed-phase liquid chromatography for the quantitative analysis of analytes in aqueous matrices is described. Two commercial systems (e.g. SFE and HPLC) were connected via a single six-port injection valve. By using water to eliminate residual decompressed CO2 gas in the solid-phase extraction trap, quantitative extraction and transfer were achieved for the target analytes (progesterone, phenanthrene, and pyrene) spiked in water, as well as in real samples (urine and environmental water). During each extraction, no restrictor plugging was realized. Extraction temperature and pressure were optimized. Different amounts of salt were added to the aqueous matrix to enhance ionic strength and thus extraction efficiency. Methanol and 2-propanol were used as CO2 modifiers. Compared with dynamically mixing modifier with the CO2 extraction fluid, pre-spiking the same amount of modifier in the extraction vessel enhanced the recovery approximately 30% for progesterone, phenanthrene, and pyrene due to a "co-extraction effect".

Increasing UV detection sensitivity in the supercritical fluid chromatographic analysis of alcohol polyethers.

Alcohol ethoxylates (AEOs) that contain a wide distribution of oligomers pose a challenge for ultraviolet (UV) absorbance detection due to the fact that the AEOs absorb strongly only in the range of commercial UV detectors between 190 and 200 nm. Most mobile phase components, with the exceptions of water and carbon dioxide, also absorb in this region. Ethoxylated hexadecanol and octadecanol were derivatized with disilazane-chlorosilane mixtures for the formation of phenyl containing silylethers. Derivatized samples were analyzed by supercritical fluid chromatography (SFC) coupled with both electrospray ionization mass spectrometry and UV absorbance detection. An increase in the number of phenyl groups incorporated into the derivatives increased the number of oligomers observed by UV detection. An increase in the number of oligomers detected increased the calculated average molar ethoxylate values. The average molar oligomer values calculated by SFC-UV for these alcohols were consistent with the nominal reported values.

Separation of derivatized alcohol ethoxylates and propoxylates by low temperature packed column supercritical fluid chromatography using ultraviolet absorbance detection.

Supercritical fluid chromatography (SFC) is capable of separating oligomers of alcohol ethoxylates (AEOs) and propoxylates (APOs) samples with pure carbon dioxide. The instrumental conditions, however, needed for separation necessitate both high temperature and high pressure. Derivatization of alcohol polyether samples with an UV absorbing agent has been achieved with a phenylated disilazane in hopes of employing a solvent-modified CO2 mobile phase in conjunction with both lower CO2 pressure and lower temperature for oligomer separation. A silylether containing a single phenyl group was formed via the derivatization of the hydroxyl termini of AEO and APO samples. The derivatized polyethers were detected at 215 nm with little or no interference from the mobile phase. Octadecylsilica (ODS) and a polar embedded alkyl bonded silica stationary phase were studied with the organic solvent-modified CO2 mobile phase. The combination of an ODS phase and the polar embedded phase, tandemly stacked, produced the best chromatographic separation of oligomeric species. Data from SFC-UV separations combined with peak assignments from SFC with electrospray ionization-mass spectrometric (ESI-MS) detection produced average molar oligomer values for each surfactant sample.

Determination of alcohol polyether average molar oligomer value/distribution via supercritical fluid chromatography coupled with UV and MS detection.

Supercritical fluid chromatography (SFC) was used for the analysis of ethoxylated and propoxylated surfactants. Samples were derivatized to phenylated silyl ethers with a disilazane-chlorosilane mixture. Addition of a phenyl group to the surfactant allowed UV-absorbance detection of each oligomer. Acetonitrile and methanol were evaluated as mobile phase modifiers. Better peak shape was realized with methanol-modified CO2 on an octadecyl silica bonded phase than with acetonitrile-modified CO2. Peak assignments were made via SFC coupled with electrospray ionization-mass spectrometry (ESI-MS) in the positive ion mode. A sulfonamide-embedded alkyl stationary phase was also evaluated for separation of the derivatized samples. SFC-UV and SFC-ESI-MS data were jointly used for calculation of average molar oligomer values which were then compared to values calculated from 1H NMR data of non-derivatized samples. The derivatization or separation method using the sulfonamide embedded phase required no preliminary cleanup and yielded reproducible oligomer values that were consistent with those of the manufacturer's nominal values.

A study of polyethoxylated alkylphenols by packed column supercritical fluid chromatography.

Alkylphenol polyethoxylates (APEs) are a widely used group of nonionic surfactants in commercial production. Characterization of the composition of APE mixtures can be exploited for the determination of their most effective uses. In this study sample mixtures contain nonylphenol polyethoxylates and octylphenol polyethoxylates. The separation of individual alkylphenols by ethoxylate units is performed by supercritical fluid chromatography (SFC)-UV as well as normal-phase high-performance liquid chromatographic (HPLC)-UV employing packed columns. The stationary phase and column length are varied in the SFC setup to produce the most favorable separation conditions. Additionally, combinations of packed columns of different stationary phases are tested. The combination of a diol and a cyano column is found to produce optimal results. An advantage of using packed columns instead of capillary columns is the ability to inject large amounts of sample and thus collect eluted fractions. In this regard, fractions from SFC runs are collected and analyzed by flow injection analysis-electrospray ionization-mass spectroscopy in order to positively identify the composition of the fractions. In comparing the separation of APE mixtures by SFC and HPLC, it is found that SFC provides shorter retention times with similar resolution. In addition, less solvent waste is produced using SFC.

Feasibility of enhancing high-performance liquid chromatography using microwave radiation.

High-performance liquid chromatography (HPLC) is the most versatile of the chromatographic techniques because it is applicable to a wide variety of analytes. Unfortunately, liquid mobile phases have relatively low diffusivities. A novel approach is presented for increasing the diffusivity of a liquid mobile phase. The method advocated in this study is the first process that has been described by which it is possible to increase the diffusivity of a liquid while having essentially no effect on other physical properties of the liquid, such as the temperature or solvating power. It is demonstrated that it is possible to sharpen peaks, in an HPLC separation, by the application of microwave radiation.

Packed column supercritical fluid chromatography of hydrophilic analytes via water-rich modifiers.

The use of additives to dramatically extend the range of solute polarity amenable to CO(2) based supercritical fluid chromatography (pcSFC) was predicted over 20 years ago. At that time additives were predicted to have multiple functions such as enhancement of mobile phase solvating power, ion suppression, and ion pairing. The adsorption of mobile phase components on the stationary phase causing a modification of its surface was predicted, but the implications for separations were not defined. Reports published in the late 1980s showed that while water could not function as a primary modifier due to it poor solubility in carbon dioxide, its use as an additive was more promising. The past decade has seen very little published work concerning water and pcSFC. Now reports are beginning to appear that demonstrate enhanced selectivity with water, and application of the technology to polypeptide salts, drug molecules, and nucleobases. This review attempts to bridge the past with the present. As evidenced by the studies described in this review, water may offer much potential as an additive in that it could (a) enhance the solvating power of the mobile phase, (b) introduce HILIC-like analyte partitioning, (c) simplify preparative purifications, and (d) offer a more mass spectrometrically compatible interface.

Enhancement of volatile aglycone recovery facilitated by acid hydrolysis of glucosides from Nicotiana flower species.

Four different Nicotiana flowers (Nicotiana alata (alata), Nicotiana sylvestris (Sy), Nicotiana suaveolens (Su), and Nicotiana tabacum cv. Flue-Cured (FC)) from farms in Virginia and North Carolina were harvested and promptly quenched with liquid nitrogen and hand-ground prior to analysis. Each Nicotiana flower was pre-extracted with hexane to remove unbound volatiles. Fifteen standard compounds that were thought to be in the pre-extract were employed to aid in GC-MS identification and quantification. Glucosides were then chromatographically isolated and next hydrolyzed via 2 M sulfuric acid for 24 h at 75 °C. For each flower, the products of hydrolysis were extracted in tandem with hexane and dichloromethane (DCM) prior to analysis by GC-MS. The mixture of hexane and DCM extracts of the flowers after hydrolysis were then analyzed for each of 15 external standards via GC-MS to determine the concentration of any isolated flower-derived aglycone. Quantitative results for each of the possible 15 free volatile compounds extracted before and after hydrolysis were compared. Benzyl alcohol, phenethyl alcohol, and cis-3-hexenol were found in all Nicotiana both before and after acid hydrolysis. Enormous increases in the mass of benzyl alcohol and phenethyl alcohol were obtained with all flowers as a result of acid hydrolysis. With selected Nicotiana flowers, significant increases were observed for eugenol and cinnamaldehyde. The significant increases observed in cinnamaldehyde and eugenol upon mild acid hydrolysis strongly indicate that this approach could be a viable alternative process for the production scale isolation of these important natural flavor compounds.

Purification of pharmaceutical excipients with supercritical fluid extraction.

Supercritical fluid extraction (SFE), with carbon dioxide as the solvent, was tested for its ability to remove common reactive impurities from several pharmaceutical excipient powders including starch, microcrystalline cellulose (MCC), hydroxypropylcellulose (HPC), polyethylene oxide (PEO), and polyvinylpyrrolidone (PVP). Extraction of the small molecule impurities, formic acid and formaldehyde, was conducted using SFE methods under conditions that did not result in visible physical changes to polymeric excipient powders. It could be shown that spiked, largely surface-bound, impurities could be removed effectively; however, SFE could only remove embedded impurities in the excipient particles after significant exposure times due to slow diffusion of the impurities to the particle surfaces. Attempts at hydrogen peroxide extraction were hindered by its low solubility in CO2, thereby effectively precluding SFE for removal of hydrogen peroxide from excipients. This work suggests that SFE will only be commercially useful for removal of low molecular weight impurities in polymeric excipients when migration of the impurities to the particle surfaces is sufficiently rapid for extraction to be completed in a reasonable time frame.

Air/light-free hyphenated extraction/analysis system: supercritical fluid extraction on-line coupled with liquid chromatography-UV absorbance/electrospray mass spectrometry for the determination of hyperforin and its degradation products in Hypericum pertoratum.

Hyperforin, which is a major active constituent of the antidepression herbal medicine-Hypericum pertoratum (St. John's wort), is very sensitive to oxygen and light. Our paper reports for the first time an air/light-free extraction-separation-detection hyphenated system and its application to St. John's wort. It involves on-line coupling of supercritical fluid extraction with liquid chromatography-UV absorbance/electrospray ionization mass spectrometry (SFE-LC-UV/ESI-MS). Mass spectral data on the extract that was produced on-line suggested the presence of the major degradation compound of hyperforin-furohyperforin and two of its analogues. Thus, some degradation process must have already occurred in our sample during plant drying or storage. The feasibility of quantitative extraction and analysis of hyperforin by on-line SFE-LC was made possible by optimizing the extraction pressure, temperature, and CO(2) modifier content. High recovery ( approximately 90%) relative to liquid-solid extraction was achieved under optimized conditions.

Design for on-line coupling of supercritical fluid extraction with liquid chromatography: quantitative analysis of polynuclear aromatic hydrocarbons in a solid matrix.

Supercritical fluid extraction (SFE) was directly coupled with high-performance liquid chromatography (LC) via the simplest interface--only one six-port injection valve. By using water to eliminate decompressed CO2 gas in the solid-phase octadecylsilica trap, high extraction recovery (> or = 95%) of polynuclear aromatic hydrocarbons (PAHs) from a sand matrix was achieved under optimized conditions. The volume of rinse water had little influence on the recovery, due to the very low solubility of PAHs in water and the sorption properties of the C-18 trap. Different amounts of sand matrix with a fixed mass of analytes have also been tested. No decrease in recovery was found when the matrix (sand) increased from 1 to 10 g. Methanol and acetone were used as a CO2 modifier to enhance the extraction efficiency. Finally, PAHs in naturally contaminated soil were successfully extracted and quantitatively determined by this hyphenated system. Compared to the EPA method (Soxhlet extraction following by GC/MS), on-line SFE-LC gave precise results in a much shorter time.