Theoretical investigation of the spatial progression of temporal statistical moments in linear chromatography

Migration and dispersion in chromatography are modeled by analogy to an effective eddy diffusion process. On the basis of this model, the spatial rates of temporal statistical moment change are derived for general chromatography in linear media. In most practical cases, these equations can be simplified so that temporal statistical moments can be calculated by solving a system of ordinary differential equations that depend only on the local HETP, solute velocity, and initial values of the temporal statistical moments. The calculations of temporal centroid, temporal variance, temporal skew, and temporal excess are demonstrated for the case of linear solvent strength gradients. It is shown for the case of temporally invariant separation environments, such as isocratic liquid chromatographic systems and isothermal gas chromatographic systems, that temporal variance contributions are spatially additive and that the temporal third normalized central moment is unaffected by spatial variations in the medium. A refined explanation is given for how peak symmetry is improved in gradient forms of chromatography.     

Capillary electrochromatography of cholesterol and its ester derivatives

Separation of cholesterol and its ester derivatives using micellar electrokinetic chromatography is a challenge due to the extreme hydrophobicity of these compounds. In this work, an isocratic capillary electrochromatography (CEC) method has been developed to separate a complex mixture of cholesterol and its 12-ester derivatives. The proportions of mobile phase (tetrahydrofuran, acetonitrile, water), as well as the effects of acid modifiers, buffer concentrations, voltage, and temperature on the separation of cholesterol derivatives were investigated. Addition of a polymeric surfactant, poly(sodium N-undecanoyl-L-glycinate), to the mobile phase reduced migration time and improved resolution of the analytes. The CEC method developed allows baseline separation of a complex mixture of cholesterol and 12 ester derivatives in less than 40 min. Finally, the method is applied to the characterization of cholesterol, cholesterol linoleate, and cholesterol oleate extracted from atherosclerotic plaque deposits in the arterial walls of a human aorta.     

Postprandial metabolism and endocrine status in veal calves fed at different frequencies

Veal calves fed by bucket often develop postprandial insulin resistance, hyperglycemia, and glucosuria during fattening. Automatic feeding systems allow feed intake for 24 h, and small ingested portions are expected to decrease postprandial glucose loads. We have studied metabolic and endocrine traits in calves that were either 1) fed identical daily amounts of whole milk plus milk replacer by a computer-programmed automatic feeder (> or =6 portions from 0800 to 2400 h) (GrA) or 2) fed by bucket at 0800 and 1630 h (GrB). Calves started at a body weight of 118 kg, and the experiment lasted for 3 wk. During wk 3, lactose was supplemented to stress postabsorptive glucose homeostasis. Feed intake and average daily gains in GrA and GrB were similar. Plasma concentrations during an 8-h period of glucose (in part), lactate, urea, and somatostatin (in wk 3), and of glucagon and insulin (wk 2 and 3) were smaller in GrA than in GrB, whereas growth hormone, insulin-like growth factor I, insulin-like growth factor binding protein-1 (wk 2), and prolactin concentrations (wk 2 and 3) were higher. Lactose supplementation in wk 3 enhanced transient postprandial hyperglycemia and hyperinsulinemia. Thus, there were marked metabolic and endocrine differences when calves sucked their feed in six or more portions during a 16-h period from an automatic feeder compared with twice daily drinking from a bucket. Ingestion of small portions by calves avoided marked hyperglycemia and lactate increments, and lower plasma urea concentrations mirrored enhanced nitrogen utilization, possibly mediated by the altered growth hormone, IGF-I and insulin status.     

Characterization of chicken antisera raised against Aspergillus spp. by enzyme linked immunosorbent assay

Enzyme linked immunosorbent assays of three Aspergillus species have been developed. Laying hens were immunized with the exoantigens from Asp. flavus, Asp. ochreaus and Asp. versicolor. All test chickens except for one produced antisera raised against the exoantigens. The antisera production process and ELISA titer were analysed. Fourteen days after the first injection, the antisera began to produce largely, on the 35th day reached to the peak, and maintained a stable level until the 42nd day. The maximum ELISA titer of the antisera to the exoantigens from Asp. flavus, Asp. ochreaus and Asp. versicolor was 1:8,000, 1:10,000 and 1:10,000, respectively. The cross-reactivities of antisera were determined with seventeen species of Aspergillus, ten species of fungi from other genera and the buffer-extracts of grain. The antisera did not cross-react with the exoantigens from other genera and the buffer-extracts of grain. The antiserum to exoantigen from Asp. ochreaus was species-specific, whereas the antisera against Asp. flavus and Asp. versicolor tended to cross-react with other Aspergillus species to varying degrees. The results suggest that exoantigens immunoassays can be developed to indentify and detect Aspergillus genus in grains.     

Tests of the fidelity of lake sediment core records of mercury deposition to known histories of mercury contamination

There has been recent controversy over the discrimination between natural and anthropogenic loadings of mercury to lakes. Sediment core profiles have been interpreted as evidence that inputs to lakes have increased. Some investigators have argued, however, that mercury may be sufficiently mobile in sediments to generate profiles that are misinterpreted as historical records. This argument can be tested where the histories of inputs of mercury are known independently from other kinds of information. We have such cases in Canadian lakes and we have been able to assemble sediment core records for comparison with known source histories. Three cases are represented by Clay Lake in Ontario where the source was a chlor-alkali plant with a known history of mercury discharges, Giauque Lake in the Northwest Territories where mercury was used at a gold mine to extract gold from ore, and Stuart Lake in British Columbia where a mercury mine operated for a known period at Pinchi Lake, the lake immediately upstream from Stuart Lake. In these cases lake sediment cores were dated using lead-210 and cesium-137 and then slices were analysed for mercury. The histories of mercury deposition derived from the cores agreed well with the known histories of inputs.     

Parametric cure models of relative and cause-specific survival for grouped survival times

With parametric cure models, we can express survival parameters (e.g. cured fraction, location and scale parameters) as functions of covariates. These models can measure survival from a specific disease process, either by examining deaths due to the cause under study (cause-specific survival), or by comparing all deaths to those in a matched control population (relative survival). We present a binomial maximum likelihood algorithm to be used for actuarial data, where follow-up times are grouped into specific intervals. Our algorithm provides simultaneous maximum likelihood estimates for all the parameters of a cure model and can be used for cause-specific or relative survival analysis with a variety of survival distributions. Current software does not provide the flexibility of this unified approach.     

A photovoltaic detection system for flow injection and liquid chromatography

A photoionization system has been developed for flow injection and liquid chromatographic applications that employs photovoltaic rather than traditional photoconductive detection. This detection system utilizes an excimer laser at 248 nm (5.0 eV) to achieve one-photon excitation in alcoholic, aqueous, and ionic solutions. The photovoltaic response is reported for a variety of solutes including aliphatic and aromatic amines, aldehydes, ketones, carboxylic acids, and halogenated compounds. The photovoltaic method is characterized with respect to solute concentration and flow rate. The detection limit is 5 × 10(-)(6) M (2.3 ng) for aniline in methanol with a linear dynamic range greater than 2 orders of magnitude, which compares favorably to UV-visible absorbance detection. Photovoltaic detection is demonstrated for a series of substituted anilines and aldehydes separated by reversed-phase liquid chromatography.     

Medium modified nucleon-nucleon cross sections in a nucleus

A simple reliable formalism is presented for obtaining nucleon-nucleon cross sections within a nucleus in nuclear collisions for a given projectile and target nucleus combination at a given energy for use in transport, Monte Carlo and other calculations. The method relies on extraction of these values from experiments and has been tested for absorption experiments to give excellent results.