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M F Burke

Publications and source records attributed to M F Burke.

13 recordsLinked to original sources
PubMed2001

Development of a generic method to the solid-phase extraction of acidic compounds from complex matrices.

A mixed-mode solid-phase extraction procedure was developed for the isolation and purification of acidic compounds from complex biological matrices. Urine samples were spiked with several acidic drugs and diluted in ammonium acetate buffer. Isolute HAX columns (a mixed-mode phase consisting of both hydrophobic and ion-exchange ligands) were conditioned with methanol and ammonium acetate prior to sample loading. Once the samples were loaded, the cartridges were rinsed sequentially with ammonium acetate and a 50:50 ratio of methanol and deionized water. The analytes were eluted with an 80:20 ratio of methanol and acetic acid. The eluates were evaporated to dryness and reconstituted to a final volume with a 98:2:0.1 ratio of deionized water, acetonitrile, and trifluoroacetic acid. Samples were analyzed by high-performance liquid chromatography. The absolute recoveries for most of the tested acidic drugs exceeded 80% at an original concentration of 1 microg/mL. Hydrophobic and ion-exchange sorbents were also investigated separately; however, the retention of the analytes suffered during sample application as well as the purity of the eluted extract. Results on anion-exchange columns show that the correct choice of counter-ion is extremely important to the retention of acidic analytes. The highest absolute recoveries were obtained when acetate was the counter-anion on the ion-exchange sorbent.

Carboxylic Acids↗
PubMed1997

The determination of ice composition with instruments on cometary landers.

The determination of the composition of materials that make up comets is essential in trying to understand the origin of these primitive objects. The ices especially could be made in several different astrophysical settings including the solar nebula, protosatellite nebulae of the giant planets, and giant molecular clouds that predate the formation of the solar system. Each of these environments makes different ices with different composition. In order to understand the origin of comets, one needs to determine the composition of each of the ice phases. For example, it is of interest to know that comets contain carbon monoxide, CO, but it is much more important to know how much of it is a pure solid phase, is trapped in clathrate hydrates, or is adsorbed on amorphous water ice. In addition, knowledge of the isotopic composition of the constituents will help determine the process that formed the compounds. Finally, it is important to understand the bulk elemental composition of the nucleus. When these data are compared with solar abundances, they put strong constraints on the macro-scale processes that formed the comet. A differential scanning calorimeter (DSC) and an evolved gas analyzer (EGA) will make the necessary association between molecular constituents and their host phases. This combination of instruments takes a small (tens of mg) sample of the comet and slowly heats it in a sealed oven. As the temperature is raised, the DSC precisely measures the heat required, and delivers the gases to the EGA. Changes in the heat required to raise the temperature at a controlled rate are used to identify phase transitions, e.g., crystallization of amorphous ice or melting of hexagonal ice, and the EGA correlates the gases released with the phase transition. The EGA consists of two mass spectrometers run in tandem. The first mass spectrometer is a magnetic-sector ion-momentum analyzer (MAG), and the second is an electrostatic time-of-flight analyzer (TOF). The TOF acts as a detector for the MAG and serves to resolve ambiguities between fragments of similar mass such as CO and N2. Because most of the compounds of interest for the volatile ices are simple, a gas chromatograph is not needed and thus more integration time is available to determine isotopic ratios. A gamma-ray spectrometer (GRS) will determine the elemental abundances of the bulk cometary material by determining the flux of gamma rays produced from the interaction of the cometary material with cosmic ray produced neutrons. Because the gamma rays can penetrate a distance of several tens of centimeters a large volume of material is analyzed. The measured composition is, therefore, much more likely to be representative of the bulk comet than a very small sample that might have lost some of its volatiles. Making these measurements on a lander offers substantial advantages over trying to address similar objectives from an orbiter. For example, an orbiter instrument can determine the presence and isotopic composition of CO in the cometary coma, but only a lander can determine the phase(s) in which the CO is located and separately determine the isotopic composition of each reservoir of CO. The bulk composition of the nucleus might be constrained from separate orbiter analyses of dust and gas in the coma, but the result will be very model dependent, as the ratio of gas to dust in the comet will vary and will not necessarily be equal to the bulk value.

Ammonia↗
PubMed1996

Inorganic mercury chloride-induced apoptosis in the cultured porcine renal cell line LLC-PK1.

HgCl2 is known to be a renal toxin, but its mechanisms of toxicity are not well understood. The cell line LLC-PK1 was used as a model for renal proximal tubule cells, and the effects of different concentrations of HgCl2 were studied. Apoptosis in response to 35 microM HgCl2 was confirmed by observation of morphological features characteristic of apoptotic cells as well as cleavage of chromosomal DNA into fragments of multiples of 200 base pairs. Ten percent of LLC-PK1 cells in a monolayer underwent apoptosis. These cells detached from the culture flask before apoptosis. Measurement of transepithelial resistance (TER) was used as a functional assay of junctional complex integrity in a novel approach to characterize preapoptotic events in this cell line. Monolayers of LLC-PK1 cells that contained apoptotic cells showed a transient decrease in TER followed by a recovery of TER to the initial levels. The decrease in TER was accompanied by a loss of hemicysts within the monolayer. These data indicate a temporary loss of junctional complexes within the monolayer during apoptosis. One hundred micromolar HgCl2 caused all cells to become necrotic within 3 hr. HgCl2 (10 microM) caused some changes in cell morphology, but no cell death.

Animals↗
PubMed1995

Conservative therapy of breast cancer in Queensland.

PURPOSE: Primary radiation therapy following breast-conserving surgery has been an accepted alternative to mastectomy in Europe and North America for many years. In Australia, however, the history of breast conservation for early invasive breast cancer is much shorter. The purpose of this study was to evaluate the results of breast conservation in a state-wide Australian radiotherapy service. METHODS AND MATERIALS: Between January 1982 and December 1989, 512 patients were treated with primary radiation therapy after breast conserving surgery. This analysis is based on a review of these patients, all of whom had Stage I or II breast cancer. RESULTS: With a median follow-up of 50 months, the 5-year actuarial rate of overall survival was 84% and disease-free survival was 80%. There have been 22 isolated local recurrences in the breast. The time to an isolated breast recurrence ranged from 12 to 83 months (median, 26 months). The 5-year actuarial rate of an isolated breast recurrence was 4%. The recurrence rate was higher for patients with involved margins (15% vs. 2%, p < 0.01). Local recurrence was also more likely in the presence of extensive ductal carcinoma in situ (DCIS), as opposed to no extensive DCIS (10% vs. 2%, p < 0.01). CONCLUSION: These results affirm that primary radiation therapy after breast conserving surgery in Queensland, has been given with a low rate of local recurrence, comparable to that obtained in other centers.

Actuarial Analysis↗
PubMed1990

Changing patterns in the presentation of breast cancer over 25 years.

The clinical stage at presentation of 280 women with histologically proven breast cancer is reviewed over a 25 year time span from 1962 to 1987. The data from 240 unscreened patients, including 87 women from the period 1962 to 1963, 103 women from 1981 to 1982, and 50 women from 1986 to 1987 demonstrate a chronologically based improvement in the stage of disease at presentation over the 25 years. Specifically, over that period, there was a fall in the mean tumour diameter, a reduction in the proportion of patients with involved axillary nodes, and a greater percentage of patients with Stages I and II disease. A reduction in the symptomatic period was also noted over this time, and a direct relationship was found between the duration of symptoms and tumour size, nodal status and overall stage of disease. A subsequent comparison with the staging data from 40 women with breast cancer detected at a breast screening clinic (1985-87) shows that significant further advances in the earlier diagnosis of breast cancer can be achieved. Mammographic breast screening centres represent the best-known means of early breast cancer detection, and thus may hold the key to reducing breast cancer mortality.

Adult↗
PubMed1979

The separation of peptide hormone diastereoisomers by reverse phase high pressure liquid chromatography. Factors affecting separation of oxytocin and its diastereoisomers--structural implications.

Experimental conditions and parameters involved in high performance liquid chromatography (HPLC) separations of the peptide hormone oxytocin and seven of its diastereoisomers, namely [1-hemi-D-cystine]-, [2-D-tyrosine]-, [4-D-glutamine]-, [5-D-asparagine]-, [6-hemi-D-cystine-], [7-D-proline]-, and [8-D-leucine]-oxytocin, on reverse phase columns were investigated. The effects of solvent, pH, and salt concentration were studied. Using the solvent systems 10% tetrahydrofuran-ammonium acetate buffer or 18% acetonitrile-ammonium acetate buffer and the muBondapak C18 support, oxytocin was separated from each of its diastereoisomers under all conditions studied, but the order of elution of diastereoisomers was highly dependent on solvent and to a lesser extent on pH. Separations of the hormone and its diastereoisomers on reverse phase HPLC and on classical partition chromatography on Sephadex G-25 were compared. The results are discussed in terms of the interactions of the solute with the reverse phase column and the solvent system. Implications of these findings in terms of the different solution conformations of the peptides are discussed.

Amino Acid Sequence↗
PubMed1977

Forceps delivery.

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Extraction, Obstetrical↗