Re-equilibration Time Research Articles

An experimental study of the grain-scale processes of peridotite melting: implications for major and trace element distribution during equilibrium and disequilibrium melting

The grain-scale processes of peridotite melting were examined at 1,340°C and 1.5 GPa using reaction couples formed by juxtaposing pre-synthesized clinopyroxenite against pre-synthesized orthopyroxenite or harzburgite in graphite and platinum-lined molybdenum capsules. Reaction between the clinopyroxene and orthopyroxene-rich aggregates produces a melt-enriched, orthopyroxene-free, olivine + clinopyroxene reactive boundary layer. Major and trace element abundance in clinopyroxene vary systematically across the reactive boundary layer with compositional trends similar to the published clinopyroxene core-to-rim compositional variations in the bulk lherzolite partial melting studies conducted at similar P–T conditions. The growth of the reactive boundary layer takes place at the expense of the orthopyroxenite or harzburgite and is consistent with grain-scale processes that involve dissolution, precipitation, reprecipitation, and diffusive exchange between the interstitial melt and surrounding crystals. An important consequence of dissolution–reprecipitation during crystal-melt interaction is the dramatic decrease in diffusive reequilibration time between coexisting minerals and melt. This effect is especially important for high charged, slow diffusing cations during peridotite melting and melt-rock reaction. Apparent clinopyroxene-melt partition coefficients for REE, Sr, Y, Ti, and Zr, measured from reprecipitated clinopyroxene and coexisting melt in the reactive boundary layer, approach their equilibrium values reported in the literature. Disequilibrium melting models based on volume diffusion in solid limited mechanism are likely to significantly underestimate the rates at which major and trace elements in residual minerals reequilibrate with their surrounding melt.

High-performance liquid chromatography–tandem mass spectrometry for the analysis of bile acid profiles in serum of women with intrahepatic cholestasis of pregnancy

A simple, sensitive, and specific high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) method for the analysis of the bile acid profile has been developed. Fifteen bile acids, including free and conjugated bile acids, were separated and detected by HPLC–MS/MS. The MS detection was performed by electrospray ionization (ESI) in negative ion mode. Quantification was achieved in multiple reaction monitoring (MRM) mode with external standard curve methods. Total analysis time was 15 min for one sample including re-equilibration time of the column. The assay was linear in the range 0.02–100.0 μmol/L with correlation coefficients of standard curves for all bile acids better than 0.999. The detection limits ranged from 0.001 to 0.006 μmol/L for different bile acids. The precisions for each bile acid were CVs < 3.8% for within-day and CVs < 6.1% for between-day. The average recoveries for all bile acids studied were in the range of 86–110.0%. The developed method was applied to the analysis of clinic samples consisting of 53 women with healthy pregnancies and 43 women with intrahepatic cholestasis of pregnancy (ICP). The results revealed that the bile acid profile was markedly different between women with ICP and women with healthy pregnancies.

Aging in a free-energy landscape model for glassy relaxation. II. Fluctuation-dissipation relations

Several fluctuation-dissipation relations are investigated for a simple free-energy landscape model designed to describe the primary relaxation in supercooled liquids. The calculations of the response and of the correlation functions are performed for a quench from a high temperature to a low temperature. In the model, all dynamical quantities reach equilibrium after long times, but for times shorter than the re-equilibration time they do not exhibit time-translational invariance and the fluctuation-dissipation theorem is violated. Two measures for these violations are considered. One such measure is given by the slope in a plot of the integrated response versus the correlation function and another one by the so-called fluctuation-dissipation ratio. It is found that these measures do not coincide and furthermore are not independent of the dynamical variable considered in the calculation. We propose to determine the fluctuation-dissipation ratio experimentally via measurements of the deuteron spin-lattice relaxation rate and the dielectric loss.

Reversed-phase high-performance liquid chromatography purification of methyl esters of C 16–C 28 polyunsaturated fatty acids in microalgae, including octacosaoctaenoic acid [28:8(n-3)

A preparative reversed-phase (RP; C 18) high-performance liquid chromatography (HPLC) method with gradient elution using acetonitrile (MeCN)–chloroform (CHCl 3) (or dichloromethane (DCM)) and evaporative light-scattering detection (ELSD) with automatic multiple injection and fraction collection was used to purify milligram quantities of microalgal polyunsaturated fatty acids (PUFA), separated as methyl esters (ME). PUFA-ME purified included methyl esters of docosahexaenoic acid (DHA; 22:6(n-3)), eicosapentaenoic acid (EPA; 20:5(n-3)) and the unusual very long-chain (C 28) highly unsaturated fatty acid (VLC-HUFA), octacosaoctaenoic acid [28:8(n-3)(4, 7, 10, 13, 16, 19, 22, 25)] from the marine dinoflagellate Scrippsiella sp. CS-295/c. Other PUFA purified from various microalgae using this RP-HPLC method to greater than 95% purity included 16:3(n-4), 16:4(n-3), 16:4(n-1) and 18:5(n-3). The number of injections required was variable and depended on the abundance of the desired PUFA-ME, and resolution from closely eluting PUFA-ME, which determined the maximum loading. The purity of these fatty acids was determined by electron impact (EI) GC–MS and the chain length and location of double bonds was determined by EI GC–MS of 4,4-dimethyl oxazoline (DMOX) derivatives formed using a low temperature method. Advantages over silver-ion HPLC for purifying PUFA-ME is that separation occurs according to chain length as well as degree of unsaturation enabling separation of PUFA-ME with the same degree of unsaturation but different chain length (i.e. between 18:5(n-3) and 20:5(n-3)). In addition, PUFA-ME are not strongly adsorbed, but elute earlier than their more saturated corresponding FAME of the same chain length. This method is robust, simple, and requires only a short re-equilibration time. It is a useful tool for preparing milligram quantities of pure PUFA-ME for bioactive screening (as free fatty acids), although many multiple injections may be required for minor PUFA-ME. It also enabled dose–response and structure–activity studies to be carried out. It can be used for the enrichment of low levels of VLC-HUFA-ME to facilitate elucidation of their chemical structure and so is a useful adjunct to EI GC–MS of DMOX derivatives and other techniques such as NMR, which requires milligram quantities of purified compounds.

Simultaneous separation and quantitation of amino acids and polyamines of forest tree tissues and cell cultures within a single high-performance liquid chromatography run using dansyl derivatization

The objective of the present study was to develop a rapid HPLC method for simultaneous separation and quantitation of dansylated amino acids and common polyamines in the same matrix for analyzing forest tree tissues and cell cultures. The major modifications incorporated into this method as compared to previously published HPLC methods for separation of only dansyl amino acids include: use of a 10 cm column to reduce the total run time by approximately 15 min; modification of the dansyl derivatization process and gradient profile to elute amino acids and common polyamines within the same run; addition of steps for column cleaning within each run; shorter re-equilibration time; and finally, column cleaning and physically reversing the column at the end of a loop of samples. These changes improved peak resolution and increased column longevity by several-fold. Over 1000 foliar samples from mature forest trees could be analyzed with the same column as compared to only 200–250 samples before the incorporation of these changes. This method eluted 22 amino acids within 40 min plus all three common polyamines between 44 and 47 min. The total run time is 53.6 min for amino acids only and 55.6 min for both amino acids and polyamines.

Capacitively coupled hot-electron nanobolometer as far-infrared photon counter

We show theoretically that hot-electron nanobolometers consisting of a small piece of normal metal, capacitively coupled to a superconducting antenna through a pair of normal metal–insulator–superconductor (NIS) tunnel junctions may be used as far-infrared photon counters. To make the device most effective at high counting rates, we suggest the use of the bolometer in the simplest configuration, when the NIS tunnel junctions are used as both an electron cooler and thermometer. The absorbtion of the photon in the normal metal produces a pulse in the electron temperature, which is measured by the NIS junctions. The counter may resolve photons up to 0.3–0.4 mm wavelength and has a typical re-equilibration time constant of about 20 ns.

Major human plasma lipid classes determined by quantitative high-performance liquid chromatography, their variation and associations with phospholipid fatty acids

An HPLC method with evaporative light-scattering detection (ELSD) was optimized and validated for the simultaneous quantitation of cholesteryl esters (CEs), triacylglycerols (TGs), free cholesterol (FC) and phosphatidylcholine (PC) in human plasma. The separation of CEs from TGs, the most variable plasma lipid class, was improved by speeding up the gradient steps and by increasing the re-equilibration time between runs. The calibrations were made at levels of 0.14–14 μg lipid/injection. The intra- and inter-day precision values of the method ranged between 1.9 and 4.5 and 2.3–7.2% (RSD, n=6), respectively, including determinations at two concentration levels. In comparison to other lipid classes, quantitation of PC proved to be equally repeatable despite its lowest detector response. The relative recoveries varied from 97.0 to 110.3%, showing good accuracy of the method. The methodological variation of the lipid classes covered 0.6–3.1% of their total variation in the study population ( n=48). The CE/FC ratio showed an even closer relationship with phospholipid linoleic acid (18:2 n−6; r=0.65, P<0.001) than with serum cholesterol levels, while eicosapentaenoic acid (20:5 n−3) was significantly associated with PC ( r=0.41, P<0.01). The CE/FC ratio increased ( P<0.01) during soyabean oil substitution and the level of PC increased ( P<0.01) during cold-pressed rapeseed oil substitution.

Ion-exchange HPLC of Cheese-related Organic Acids in Comparison with Reverse-phase HPLC

Sixteen cheese-related organic acids were analysed by an ion-exchange HPLC protocol developed in this study. The proposed technique was compared to a typical reverse-phase separation of the same organic acid mixture to establish the most satisfactory HPLC methodology. The ion-exchange method yielded best results for the concentration of compounds analysed, resolution, duration of separation and ease of analysis. A number of compounds co-eluted with the proposed ion-exchange HPLC protocol but could be individually distinguished and quantified using spectral array UV detection and three-dimensional Spectacle software. Isoplot graphs were found to be valuable for the more detailed analysis of HPLC chromatograms. The reverse-phase method succeeded in eluting all the polar and more non-polar organic acids in a single chromatographic run with the aid of a buffer–methanol gradient. However, resolution was not as good as with the ion-exchange method. The reverse-phase methodology was found to be more laborious, requiring column re-equilibration and longer run time, and could not accomplish analysis of diacetyl.

Example of gradient elution in normal-phase liquid chromatography

Only a small fraction of all separations by high-performance liquid chromatography are performed at normal-phase conditions and especially on silica. Plain silica has the reputation that it is inconvenient to use due to long equilibration times. At least for solvents of low and moderate polarity this is not true, as is shown here with the reproducible separation of ten compounds with gradient elution; solvents are hexane and dichloromethane or hexane and tert.-butyl methyl ether. Short re-equilibration times could especially be obtained with hexane-dichloromethane gradients.

Separation and determination of amino acids, creatinine, bioactive amines and nucleic acid bases by dual-mode gradient ion-pair chromatography

A simple and fast high-performance liquid chromatography method for the analysis of amino acids and biological bases such as creatinine was developed using a technique termed “dual-mode gradient ion-pair chromatography”. A butyl-silica reversed-phase column and water-acetonitrile eluent containing sodium dodecyl sulfate (SDS) and perchloric acid were used for the separation. A concentration gradient of acetonitrile from 15 to 35% provided a good separation of such organic cations. Since change in concentration of acetonitrile causes change in distribution equilibrium of SDS between mobile and stationary phases, a complete regeneration of the column to the initial state is required for the reproducible separations. Completion of the reequilibrium was indicated by a system peak appearing in the UV chromatogram and by conductivity measurements. The formation mechanism of the system peak was revealed. A flow-rate gradient from 1 to 2 ml/min was introduced in addition to the concentration gradient to shorten the cycle time of the chromatography. More than twenty kinds of amino acids, creatine and creatinine were simultaneously separated within 50 min and the cycle time was 80 min including the reequilibration time. A post-column derivatization fluorescence detection system was usable as well as UV detection. This elution system was also useful for the separation of bioactive amines and nucleic acid bases. The developed method was applied to the simultaneous determination of urinary creatinine and diagnostic amino acids due to inherited metabolic disorders.

Gradient elution in micellar liquid chromatography II. Organic modifier gradients

The application of organic modifier gradients in micellar liquid chromatography (MLC) is discussed. The equation derived by Snyder and co-workers describing gradient elution in hydro—organic reversed-phase LC was verified for organic solvent gradients in the presence of micelles. It is also demonstrated that the use of these gradients require little re-equilibration time due to the limited range of organic modifier concentration used in the gradient. This would result in shorter analysis time. Lastly, a practical application of the use of propanol and acetonitrile gradients in MLC is described.

Preferential water loss from synthetic fluid inclusions

A fundamental question in most fluid inclusion studies is whether inclusions behave as compositionally closed systems after trapping, and, thus, represent samples of the fluid phase(s) present in the system at the time of their formation. This question was addressed in high-temperature laboratory experiments with synthetic fluid inclusions in quartz and it was found that at 825°C the inclusions exhibited open-system behavior with respect to water. Synthetic salt-water fluid inclusions in quartz were reequilibrated for 12 hours to 35 days at 825° C in a dry argon atmosphere under 1.5 kbar confining pressure. These conditions created initial internal overpressures (Pint> Pconf) of 1.5–4 kbar in the inclusions and differential water fugacities in the same sense i.e., fH2OfH2O. After 108 hours of reequilibration, preferential water loss had resulted in salinity increases as large as 22 wt% salt (e.g., from 57 to 79 wt% NaCl, as determined from measured temperatures of salt dissolution). Also, following reequilibration, a strong inverse correlation between salinity and inclusion volume was observed, and this trend became more pronounced with increasing reequilibration time. These observations, together with a lack of evidence for selective H2O removal via hydration reactions, suggest that water loss occurred by a diffusion-related mechanism. Fluxes of ≈4x10-11 g/cm2-s and diffusion coefficients on the order of 10-9 cm2/s are calculated for water loss from the inclusions. The calculated H2O diffusion coefficient is consistent with the determination of Blacic (1981) derived from hydrolytic weakening experiments, but is much larger than the value obtained by Giletti and Yund (1984) for volume diffusion of oxygen in isotope exchange experiments. These observations suggest that the mechanism of water loss from our synthetic fluid inclusions may have been pipe diffusion along dislocations, subgrain boundaries or other structural defects rather than bulk volume diffusion.

Evaluation of the portable pressure transducer technique for measuring field tensiometers

The use of a portable pressure transducer system which couples to tensiometers via a syringe needle and septum stopper was assessed. Changes that occurred to pressure within the tensiometer on insertion of the needle were significant and up to 120 min was sometimes required before complete re-equilibration to the original tensiometric pressure was achieved. Tensiometer readings with less than 5% error were attained by allowing 3-4 min re-equilibration time at soil matric potentials between -1 and -25 kPa, but up to 35 min was required at -40 kPa. As well as increasing with decreasing initial pressure in the tensiometer, re-equilibration time was dependent on soil properties. The re-equilibration times reported are specific to the volume of air left in the tensiometer below the septum stopper (1.2 cm3). A larger air bubble will decrease re-equilibration time but could cause undesirable thermal errors during field use. Transducer readings should be made after allowing time for complete re-equilibration of the tensiometer following insertion of the needle. However, for practical field measurement of low matric potentials, it will be necessary to read the portable transducer before full re-equilibration and correct the reading based on previously determined re-equilibration patterns. These re-equilibration patterns should be specific to each tensiometer and should cover a range of matric potentials. It is also important that the air bubble below the septum stopper be maintained constant for each reading, and that the septum stoppers be replaced regularly. With careful use, these systems are convenient for monitoring large numbers of tensiometers spaced apart in the field.

Detection of Beet Sugar Adulteration of Orange Juice by Liquid Chromatography/Pulsed Amperometric Detection with Column Switching

Abstract A recently reported method for the quantitation of extraneous beet sugar In orange juice is based on the monitoring of unique oligosaccharides present in beet medium invert sugar (BMIS). Modifications are reported here that expedite the method and render it better suited for monitoring a large number of samples on a routine basis. A switching valve that allows the simple sugars to go to waste after the first column prevents overloading of the analytical column and detector. Furthermore, the retention and column re-equilibration times were significantly reduced. Results of spiking studies of BMIS In orange juice are reported. The estimated limit of detection is 5% BMIS, with a coefficient of variation of 0.1 %.

Rapid separation of creatine, phosphocreatine and adenosine metabolites by ion-pair reversed-phase high-performance liquid chromatography in plasma and cardiac tissue

A rapid ion-pair reversed-phase high-performance liquid chromatographic method has been developed for the simultaneous detection of creatine, phosphocreatine, hypoxanthine, inosine, adenosine, AMP, ADP, ATP, 8-azaguanine, 2-chloroadenosine, and 2'-O-methyladenosine. This method has proven useful for measuring changes in nucleotide concentrations in both heart tissue and plasma samples. Separation of the compounds of interest is achieved in less than 8 min with re-equilibrium in 7 min, making the total run time 15 min. Separation is performed on a 3-μm Ultrasphere ODS column employing tetrabutylammonium phosphate as the ion-pair agent and dipotassium hydrogenphosphate as the counter ion. The accuracy, rapid separation, and re-equilibration time make this method particularly useful for the routine analysis of a large number of samples.

Assessment of the biotransformation of the cardiotonic agent piroximone by high-performance liquid chromatography and gas chromatography-mass spectrometry

14C-labelled piroximone was administered to rats at a dose of 10 mg/kg body weight. Of the total radioactivity administered, 74.9 ± 7.9% ( n=4) and 87.8 ± 1.7 ( n=3) were recovered in the 8-h urine collection after oral and intravenous administration, respectively. Two major metabolites, M 1 and M 2, were detected in methanol extracts and accounted for 7.1 ± 1.2% ( n=4) (M 1 and 4.3 ± 0.4% ( n=4) (M 2) in response to oral administration and 5.7 ± 0.8% ( n=3) (M 1) and 6.7 ± 2.0% ( n=3) (M 2) in response to intravenous administration. In addition, three minor metabolites were detected; M 3 and M 4 in the 8-h urine collection and M 5 in the 12-h urine collection. Separation of piroximone and metabolites was achieved by high-performance liquid chromatography on a C 18 column by gradient elution with 0.05 M ammonium acetate (pH 7) using 0–60% methanol over 20 min at a flow-rate of 1 ml/min, followed by isocratic elution with 60% methanol for 10 min. M 1 and M 2 were isolated by fraction collection following the addition of 1 m M tetrabutylammonium acetate in the mobile phase. Between each injection a column re-equilibration time of 45 min was necessary to achieve optimum collection of M 1 and M 2 fractions. Gas chromatography-mass spectrometry of M 1 provided evidence for a molecular structure consistent with isonicotinic acid methyl ester. Corroborative evidence for this identification was obtained by comparison with a synthetic standard. Isonicotinic acid is assumed to be the actual metabolite while esterification with methanol had occurred as a result of the work-up procedure. In vitro studies carried out with rat liver microsomes resulted in a mean total metabolite formation rate of 94.3 pmol/mg microsomal protein/min.

Gradient elution with shorter equilibration times in reversed-phase ion-pair chromatography

To reduce the re-equilibration time needed between gradient runs in reversed-phase ion-pair chromatography (RP-IPC), various chromatographic conditions were studied. Five pairing ions of different size (and sorption kinetics), viz., trifluoroacetate, heptafluorobutyrate, octylsulphonate, dodecyl sulphate and tetrabutylammonium, each at two different concentrations, and three types of gradient (acetronitrile, salt and mixed gradients) were examined. Some common nucleotides, such as adenosine-5′-monophosphate, adenosine-5′-diphosphate and adenosine-5′-triphosphate, and some primary amines, such as dopamine, α-methyldopamine and serotonin, were used as analytes. The “efficiency” of the various gradient systems was tested in terms of the “speed” of re-equilibration and the average decrease in retention time achieved. Without solving the general problem of slow equilibration in ion-pair gradient elution, chromatographic conditions are recommended under which 1–3 column volumes of solvent A can be sufficient for re-equilibration between gradient runs, i.e., for obtaining reproducible retention times in gradient RP-IPC.

Some effects of collection equipment, glycerolation, and post-thaw re-equilibration times on the motility and survival of bovine spermatozoa

Forty ejaculates, from two Holstein bulls, were collected in one-piece combination liner-collection cones. Aliquots of spermatozoa were evaluated at each step of semen handling and processing. Similar differences in progressive motility and percent unstained cells associated with both glycerol level and equilibration time were highly significant ( P < 0.0001). Two h equilibration with mean losses in motility of 46, 39, and 42% for 2.7, 3.0, and 3.3% glycerol was superior ( P < 0.01) to 4 h equilibration with 51, 44, and 46% losses, respectively. Progressive motility survival was better ( P < 0.01) at both 3.0 and 3.3% glycerol levels than at 2.7%; however, only 3.0% glycerol and 2 h equilibration was superior ( P < 0.01) to the standard 8.0% glycerol and 2 h equilibration. In Experiment 2, post-thaw progressive motility of spermatozoa collected with polyethylene liner-collection cones was better than that of cells collected over rubber ( P < 0.001), but survival at 3% glycerol was not significantly different from survival at 8% glycerol. Spermatozoan survival half-life at 46.5 °C was longer for cells collected in polyethylene than in rubber liner-collection cones, and optimal re-equilibration time for maximum survival was directly related to glycerol concentration, 10 min for 3% glycerol vs 20 min for 8% glycerol, regardless of liner-collection cone type. Liner-collection cone type was the primary factor ( P < 0.0001) affecting the initial progressive motility of spermatozoa subjected to the thermal stress. However, both the linear and quadratic components of polynomials fitted to decreases in motility, differed ( P < 0.0001) in association with liner type, re-equilibration time, and some interactions involving liner type, re-equilibration time, and glycerol level.

Reduction of reequilibration time following gradient elution reversed-phase liquid chromatography

A simple and convenient method for the reduction of column reequilibration time following gradient elution reversed-phase liquid chromatography is described. This method utilizes the addition of a constant volume of 3% 1-propanol to the mobile phase throughout the solvent gradient to provide consistent solvation of the reversed-phase stationary phase. Reductions in reequilibration time of up to 78% have been observed. The effect of alkyl chain bonding density on reequilibration volume is also examined. A maximum in the mobile phase volume necessary to reequilibrate the column is found at a bonding density of about 2.9 mumol/m2. The relationship of reequilibration volume to bonding density supports the partitioning model of retention for reversed-phase liquid chromatography.

Surfactant-mediated hydrophobic interaction chromatography of proteins: gradient elution

Addition of 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulphonate (CHAPS) to mobile phases in gradient elution hydrophobic interaction chromatography (HIC) on SynChropak Propyl causes changes in observed elution times for nine globular proteins. The nine proteins showed different percentage reductions in capacity factor, k′, demonstrating the ability of CHAPS to change the selectivity of the separations. Three basic types of gradient experiments have been explored for surfactant-mediated gradient elution HIC. Type I gradients are conducted with constant salt and variable surfactant concentration. Type II gradients with variable salt and constant surfactant concentration, and Type III gradients with variable salt and surfactant concentrations. By the criterion of a linear relationship between gradient time and retention time the linear solvent strength condition applies to Type II and Type III gradients. Type III gradients, with the fastest re-equilibration time, are preferable for repetitive analyses. Type I gradients are relatively ineffective in making use of the solvent strength of CHAPS, and Types I and II gradients require long equilibration times due to large changes in surface concentration of CHAPS which occur during elution. The presence of CHAPs had a negligible effect on peak shapes of the proteins examined, except for bovine serum albumin which yielded a narrower, less distorted peak in the presence of CHAPS.