Retention Time Measurements Research Articles

A Study of the Behavior of Alkyl Side Chains Phenols and Arenes in Polar and Nonpolar GC Stationary Phases

Gas chromatographic measurements of the relative retention times of alkyl-substituted arenes and phenols on capillary columns at temperatures of 125 – 140°C have shown that logarithms of retention times increase bilinearly with the number of carbon atoms in the molecule. It was found that in a high density stationary phase, the longer alkyl side chains of compounds in question are subject to cyclization as a result of the resistance force of this phase affecting molecules during their thermal and diffusion motion. Consequently, common conventional aromatic-aliphatic molecules become new molecules with quasi-alicyclic rings. In comparison with the conventionally conceived molecules, the resulting aromatic–quasi-alicyclic molecules are characterized by rather different, possibly even completely different non-covalent interactions between the molecules, which then affect the retention characteristics. Moreover, cyclization facilitates the mixing of n-alkyl arenes and n-alkyl phenols with high-molecular stationary phases, because the thermodynamic condition for mixing is better fulfilled.

Retention Time and Depolarization in Organic Nonvolatile Memories Based on Ferroelectric Semiconductor Phase-Separated Blends

Resistive switches have been fabricated using a phase-separated blend film of ferroelectric random copolymer poly(vinylidene fluoride-co-trifluoroethylene) with the organic semiconductor regio-irregular poly(3-hexylthiophene) (rir-P3HT). Spin-coated blend films have been contacted with symmetrical Ag top and Ag bottom electrodes, yielding switching diodes. The ferroelectric polarization modulates the injection barrier, yielding an injection-limited off-state and a space-charge-limited on -state. To study the effect of depolarization, an additional polyphenylenevinylene-type semiconductor layer with the highest occupied molecular orbital energy that is comparable to that of rir-P3HT has been inserted in the diode stack. When the ad-layer is the injecting contact, the current modulation ratio goes to unity. The origin is a decrease in the effective band bending at the contact with increasing ad-layer thickness. When the counter electrode at the blend interface is the injecting contact, the diode can be switched, but the on-state is only stable when an electric field that is larger than the coercive field is applied. Upon field removal, the ferroelectric depolarizes, and the current drops to that of an unpoled pristine diode. The depolarization is confirmed by capacitance-voltage and retention time measurements. To realize bistable diodes with excellent retention times, the thickness of the semiconducting wetting layer may not be at most 10 nm.

Is the second week post-race an adequate period to assess the effect of a long-term conditioning on digestive physiology in competing endurance horses?

In human athletes, the physiological effects of physical activity on digestion could differ depending on whether it is a bout of exercise or a long-term conditioning. When the aim is to investigate the effect of long-term endurance training on the digestive physiology in competing horses, animals need to be at complete rest during the digestibility and mean retention time (MRT) measurements. We hypothesized that the resting period allowed to horses post-race, and particularly the second week following an endurance race, could be an adequate period to assess digestive physiology and that measurements would still be representative of the pre-competition status. Nutrient total tract apparent digestibility, total MRT and faecal microbial composition and activity measured before a 90km endurance race were compared with the data obtained post-race, during the second week of the resting period. No differences in the digestibility coefficients, MRT, faecal pH, lactate concentrations and bacterial counts were observed before and after the endurance race. The propionate proportion was higher and the (C2 þ C4):C3 ratio was lower during the second week post-race than before the race. Carrying out measurements during the second week post-race provides data close to the prerace status, and avoids an a disturbed training schedule and unnecessary stress before the race in competing endurance horses.

Evolutionary Differences in Glycosaminoglycan Fine Structure Detected by Quantitative Glycan Reductive Isotope Labeling

To facilitate qualitative and quantitative analysis of glycosaminoglycans, we tagged the reducing end of lyase-generated disaccharides with aniline-containing stable isotopes (12C6 and 13C6). Because different isotope tags have no effect on chromatographic retention times but can be discriminated by a mass detector, differentially isotope-tagged samples can be compared simultaneously by liquid chromatography/mass spectrometry and quantified by admixture with known amounts of standards. The technique is adaptable to all types of glycosaminoglycans, and its sensitivity is only limited by the type of mass spectrometer available. We validated the method using commercial heparin and keratan sulfate as well as heparan sulfate isolated from mutant and wild-type Chinese hamster ovary cells, and select tissues from mutant and wild-type mice. This new method provides more robust, reliable, and sensitive means of quantitative evaluation of glycosaminoglycan disaccharide compositions than existing techniques allowing us to compare the chondroitin and heparan sulfate compositions of Hydra vulgaris, Drosophila melanogaster, Caenorhabditis elegans, and mammalian cells. Our results demonstrate significant differences in glycosaminoglycan structure among these organisms that might represent evolutionarily distinct functional motifs.

Quantitation of free polyethylene glycol in PEGylated protein conjugate by size exclusion HPLC with refractive index (RI) detection

In this study, size exclusion high performance liquid chromatography was evaluated for its application in separation and quantitation of free polyethylene glycol (PEG) and its PEGylated-protein-conjugate (PEG-conjugate). Although the large mass of the free PEG (2-fold greater than the protein) made separation difficult, chromatographic conditions were identified enabling resolution and quantitation of the free PEG, PEG-conjugate and non-PEGylated protein with Shodex Protein KW803 and KW804 columns in series and refractive index detection. The optimum resolution of 1.7 and 2.0 was achieved for the free PEG and PEG-conjugate as well as the free PEG and non-PEGylated protein using 20 mM HEPES buffer at pH 6.5. Under this condition, the plot of log 10MW of all the pertinent analytes against retention time showed a linear relationship with a correlation coefficient of 1. Limited assay performance evaluation demonstrated that the method was linear in the concentration range of 10 to 250 μg/mL of free PEG with correlation coefficients of ≥0.99. When free PEG in this concentration range was spiked into PEG-conjugate samples at 1 mg/mL, the recovery was in the range of 78%–120%. Detection and quantitation limits were determined to be, respectively, 10 and 25 μg/mL for free PEG. The R.S.D. for intra- and inter-day precision was 0.09% or less for retention time measurements and 2.9% or less for area count measurements. Robustness testing was performed by deliberately deviating ±0.2 pH units away from the desired pH as well as by increasing the flow rate. These deviations resulted in no significant impact on area percent distribution of all species. However, separation was found to be sensitive to high ionic strength and buffer species.

Retention and Retention of Effect of Topical Formulations in Dry Eye Subjects

It was the purpose of this investigation to examine both retention time (RT) and retention of effect of two ophthalmic formulations in the same dry eye subjects. This was a randomized, subject-masked cross-over study. Dry eye subjects, characterized by sub-type, were recruited. For direct RT measurement, fluorescein isothiocyanate (FITC)-dextran, 70 kDa molecular weight, was admixed at 0.1% wt/vol concentration into buffered saline (active control) and a viscous marketed artificial tear formulations (test formulation). RT in minutes was estimated directly as the return to baseline intrinsic fluorescence with an objective scanning fluorometer. Retention of effect was measured with a xeroscope as non-invasive breakup time (NIBUT) and by use of a numerical rating scale for comfort. Eleven subjects, with most being classified as having non-inflammatory meibomian gland dysfunction, completed the study. The RTs averaged 17.7 (+/-10.0) and 26.8 (+/-16.5) minutes for the saline and test formulations, respectively. The averages for NIBUT were 8.73 (+/-6.1) and 19.5 (+/-4.9) minutes, for saline and the test formulations, respectively. Return to baseline for the numerical rating scale comfort averages were 9.91 (+/-4.1) and 20.21 (+/-6.4) minutes for the saline and test formulations, respectively. When residence time was subtracted from the retention of effect measures, no statistical significance was found for the polymeric solution (vs. comfort, p = 0.153; vs. NIBUT, p = 0.109). However, statistical differences were found for direct retention compared against comfort (p = 0.01) and NIBUT (p = 0.004) for buffered saline. It seems that these two retention of effect measures are much shorter than RT measured directly. Future work should aim to confirm these findings in additional dry eye sub-types and in those with more severe disease manifestations.

Study of charge storage characteristics of memory devices embedded with metallic nanoparticles

The structural and electrical properties of thin silicon dioxide and hafnium oxide dielectric stacks with embedded gold nanoparticles obtained by electron-beam evaporation are reported. Transmission electron microscopy shows that the nanoparticles have a mean diameter of 2.6 nm and a sheet density of 3.3×10 12 cm −2. High-frequency and quasi-static capacitance–voltage measurements of MOS capacitors reveal that charge injection and storage takes place in the nanoparticle dielectric stack at low gate voltages. Efficient charge trapping occurs only in the case of holes injected from the substrate. Programming and retention time measurements indicate that the fabricated nanoparticle dielectrics are attractive for low-voltage non-volatile memory applications.

Precision in differential field‐flow fractionation: A chemometric study

In the present paper, the capabilities of differential field-flow fractionation, i. e., the determination of an incremental quantity of a colloidal species, e. g., an uptake adsorbed mass, determined by the joint use of two independent FFF measurements, over a species and the same modified species respectively, are considered. The different error types, those related to the retention time determinations and those coming from the operating parameter fluctuations were considered. The different components were computed with reference to SdFFF determinations of bare polystyrene (PS) submicronic particles and the same PS particles covered by IgG. Comparison was made between theoretically computed precision and experiments. The error coming from the experimental measurement of retention times was identified to be the main source of errors. Accordingly, it was possible to make explicit the detection limits and the confidence intervals of the adsorbed mass uptake, as a function of experimental quantities such as the retention ratio, the detector calibration ratio, the injected quantity, the baseline noise, and the void time relative error. An experimentally determined and theoretically foreseen dependence of both the experimental detection and confidence limits (approximately +/- 10(-17) g) on the square root of the injected concentration, for constant injected volume, was found.

HPLC‐chip‐mass spectrometry for protein signature identifications

This work investigates the use of an HPLC-chip microfluidic device interfaced to an IT mass spectrometer to search for biomarker signatures. To that end, the identification of autoantigens is chosen as a model. It not only constitutes a proof of concept model but also the growing interest in autoantibodies and autoantigens as new markers of diseases provides a practical application at the same time. The peptides are separated by the HPLC-chip system allowing suitable resolution and reproducibility. The determination of two parameters that characterize a peptide sequence during LC-MS/MS analyses, retention time (RT) and m/z ratio, improves the identification of a number of peptides derived from protein digests. These findings illustrate that accurate RT measurement obtained in a microfluidic device is useful to obtain mass/retention time (MRT) pairs for a given peptide, which can contribute to the definition of biomarker signatures.

Usefulness of an integrated microfluidic device (HPLC‐Chip‐MS) to enhance confidence in protein identification by proteomics

Nanoflow liquid chromatography/mass spectrometry (nanoLC/MS) has become a current tool in proteomics applications increasingly used in the search for new biomarkers. A new integrated microfluidic device (HPLC-Chip), coupled to ion trap mass spectrometry (ITMS), appears as an innovative and robust tool for improving the identifications commonly performed by nanoLC/MS/MS. We tested this device for the identification of proteins obtained from two-dimensional gel electrophoresis or chromatography. The chip allows the measurement of reproducible retention times that, in association with m/z ratios, was found useful for identifying peptide sequences without ambiguity. A sensitivity increase of a factor of at least 5-fold is obtained compared to the results obtained previously in our laboratory by conventional nanoLC/MS/MS on the same ion trap. We conclude that this recently available microfluidic device can be a valuable tool during biomarker discovery programs, particularly identifying low-abundance proteins.

06/01394 Calculating latent frequencies of systems with local damping: Kolonits, F. Nuclear Engineering and Design, 2005, 235, (17–19), 2003–2008

The retention characteristics of 18 ethane-based chlorofluorocarbon, bromochlorofluorocarbon and fluorocarbon fluids have been studied as a function of temperature on a stationary phase consisting of a 5% (mass/mass) coating of a low-molecular-mass polymer of hexafluoropropylene epoxide on a graphitized carbon black adsorbent. Measurements were made at −20, 0, 20 and 40°C for hexafluoroethane (R-116), pentafluoroethane (R-125), 1,1,2,2-tetrafluoroethane (R-134), 1,1,1,2-tetrafluoroethane (R-134a), 1,1,2-trifluoroethane (R-143), 1,1,2-tri-fluoroethane (R-143a), 1,1-difluoroethane (R-152a), and fluoroethane (R161). Measurements were made at 40, 60, 80 and 100°C for 1,2-dichlorotetrafluoroethane (R-114), 1,1-dichlorotetrafluoroethane (R-114a), chloropentafluoroethane (R-115), 2,2-dichloro-1,1,1-trifluoroethane (R-123), 2-chloro-1,1,1- trifluoroethane (R-133a), 1,1-dichloro-1-fluoroethane (R-141b), 1-chloro-1,1-difluoroethane (R-142b), and 1-chloroethane (R-160). Measurements were performed at 60, 80, 100 and 120°C for 1-bromo-2-chlorotetrafluoroethane (R-114B1). Net retention volumes, corrected to a column temperature of 0°C, were calculated from retention time measurements, the logarithms of which were fitted against reciprocal thermodynamic temperature. The relative retentions, also as a function of temperature, were calculated with respect to the retention of tetrafluoromethane and hexafluoroethane. Qualitative features of the data are examined, and trends are identified. In addition, the data were fitted to linear models for the purpose of predicting retention behavior of these compounds to facilitate chromatographic analysis.

A comparison of the effect of forage type and level of feeding on the digestibility and gastrointestinal mean retention time of dry forages given to cattle, sheep, ponies and donkeys

Four cattle, sheep, ponies and donkeys were fed dehydrated lucerne, early-cut hay, later-cut hay or barley straw in a Latin square-based design for four periods of 35 d. In the first sub-period animals were fed the diets ad libitum (1-21 d) and in the second sub-period they were fed the same diet restricted to 0.75 of ad libitum intake (days 22-35). Measurements of forage intake, apparent digestibilities and gastrointestinal mean retention times (MRT) were made in the last 7 d of each sub-period. Differences between species in voluntary DM intake (VDMI; g/kg live weight (LW)(0.75) and g/LW) were greatest on the lucerne and least on barley straw. Cattle VDMI (g/kg LW(0.75)) compared with intake of the other species was > ponies > sheep > donkeys on lucerne. On barley straw VDMI (g/kg LW(0.75)) of cattle compared with intake of the other species was = donkey = ponies > sheep. VDMI of hays were intermediate between the lucerne and straw forages. Apparent digestibilities of DM, organic matter (OM), neutral-detergent fibre (NDF) and acid-detergent fibre (ADF) of the lucerne and hays were higher in the ruminants than in the equids. Effect of feeding level was not significant. Gastrointestinal MRT was shorter in the equids than in the ruminants. On straw diets donkeys showed similar apparent digestibilities of feed components to those of the cattle, whilst apparent digestibility of the straw diet by the ponies was lowest. Results are discussed in relation to evolutionary differences in feeding and digestion strategy associated with fore- or hind-gut fermentation in ruminants and equids.

Helium exhaust experiments on JET with Type I ELMs in H-mode and with Type III ELMs in ITB discharges

An analysis of helium exhaust experiments on JET in the MkII-GB divertor configuration is presented. Helium is pumped by applying an argon frost layer on the divertor cryo pump. Measurement of the helium retention time, , is performed in two ways: by the introduction of helium in gas puffs and measurement of the subsequent decay time constant of the helium content, ; and by helium beam injection and measurement of the helium replacement time, . In ELMy H-mode, with plasma configuration optimized for pumping, is achieved, where is the thermal energy replacement time. For quasi-steady internal transport barrier (ITB) discharges, the achieved is significantly lower. The achieved helium recycling coefficient, confirmed by an independent measurement to be Reff ≈ 0.91, is the same in both scenarios. None of the discharges are dominated by core confinement. The difference in is instead due to the confinement properties of the edge plasma, which is characterized by Type I ELMs for the H-mode discharges studied, and Type III ELMs for the quasi-steady ITB discharges. This difference is quantified by an independent measurement of the ratio of the helium replacement time with a helium edge source to the energy confinement time.

Fluorous Columns are Superior to Cyclodextrin Columns for Demixing in Fluorous Mixture Synthesis: When and Why to Use Fluorous Silica Gel

Measurements of retention times of assorted fluorous and non-fluorous compounds on both fluorous (FluoroFlash PF-C8) and cyclodextrin (Sumichiral OA 7500) columns show that the fluo­rous column is superior to the cyclodextrin column for separating fluorous compounds. Guidelines for when and why to use fluorous columns are suggested.

Measurements of Protein-Protein Interactions by Size Exclusion Chromatography

A method is presented for determining second virial coefficients (B2) of protein solutions from retention time measurements in size exclusion chromatography. We determine B2 by analyzing the concentration dependence of the chromatographic partition coefficient. We show the ability of this method to track the evolution of B2 from positive to negative values in lysozyme and bovine serum albumin solutions. Our size exclusion chromatography results agree quantitatively with data obtained by light scattering.

An atmospheric pressure chemical ionization mass spectrometer (APCI-MS) combined with a chromatographic technique to measure the adsorption enthalpy of acetone on ice

An atmospheric pressure chemical ionization mass spectrometer (APCI-MS) has been developed to investigate the adsorption properties of atmospheric trace gases on ice using a chromatographic method. The APCI-MS system is presented and discussed as an analytical technique to monitor the gas-phase concentration of trace species by proton transfer reaction and ligand switching reactions involving protonated water clusters as reagent ions. The chromatographic method used relies on temperature-dependent retention time measurements of trace gases within a column packed with ice or snow. The adsorption enthalpy of a trace gas, Δ H ads, is readily obtained from its retention time as function of temperature. The study of the adsorption enthalpy of acetone on ice is chosen due to its recent importance to the atmospheric chemistry community. The measured Δ H ads on a packed column filled with ice spheres (400 μm< Ø<500 μm) (−54.4±7.6 kJ mol −1, 2 σ) and on a packed column filled with aged snow (−56.0±2.8 kJ mol −1, 2 σ) are in agreement with the literature values obtained using other analytical techniques, i.e., low pressure ice-coated wall flow tube reactors and volumetric methods. The possibility for the APCI-MS to measure Δ H ads of acetone with different ice surfaces, and Δ H ads of other species of atmospheric interest, is also discussed.

Estimation of Octanol‐Water Partition Coefficients for Polycylic Aromatic Hydrocarbons Using Reverse‐Phase HPLC

Retention time measurements on reverse phase HPLC columns at isocratic conditions are used to estimate the octanol‐water partition coefficient for 16 polycyclic aromatic hydrocarbons (PAHs). The log K ow values for PAHs ranged from 3.32 (napthalene) to 6.30 (Indeno(1,2,3‐cd)pyrene). The estimated values obtained from the present study were in good agreement with the literature values. This is a simple and rapid method for simultaneous determination of octanol‐water partition coefficients for different PAHs.

Immobilized artificial membrane chromatography with mass spectrometric detection: a rapid method for screening drug-membrane interactions.

A high-performance liquid chromatography (HPLC)/electrospray ionization mass spectrometry method for measuring drug-membrane interactions was developed using immobilized artificial membrane (IAM) fast-screening mini-columns. The HPLC mobile phase consisted of phosphate-buffered saline (i.e., 5.0 mM phosphate buffer at pH 7.4, 1.35 mM KCl, and 68.5 mM NaCl) and acetonitrile. This method facilitated the measurement of IAM retention time of over ten compounds in one experiment, significantly reducing analysis time compared with the earlier IAM-HPLC method. The particular electrospray source used demonstrated the ability to tolerate the high salt-containing nonvolatile buffer used for retention time measurement.

P‐33: A Novel TFT‐LCD Characterization Method Using Retention Measurement

AbstractWe have developed an optical measurement system for TFT‐LCD cells which measures not only conventional optical characteristics such as voltage‐transmittance, flicker and response time but also retention time. By using specific TFT driving condition, retention time measurement can address the cause of various current leakage problems.

A convenient method for routine estimation of dead time in gas chromatography.

A set of retention times (tR) of n-alkanes at different temperatures and the primary dead times (tM) are used to determine the 4 numerical constants (a, b, c, and d) of an equation. This equation is rearranged into a second equation, used in turn for routine calculation of the secondary dead time (tMS) of each chromatogram from any member of the n-alkane series. Equation 2 can be used to calculate the tMS of both packed and capillary columns. The calculated tMS values are in good agreement with those of the tM values. The greatest difference is 3.38%, but it is speculated that the percent difference would be lower when more tR data are collected for the determination of the 4 numerical constants of Equation 1. Error in measurement of retention time undoubtedly would affect the accuracy of the estimated dead time, but it is attenuated by a factor of 1 + e(a + bN + c/T + dN/T).