. (1997). Study on the retention behaviour of low-molar-mass polystyrenes and polyesters in reversed-phase liquid chromatography by evaluation of thermodynamic parameters. Journal of Chromatography, A, 790(1-2), 101-116. DOI: 10.1016/S0021-9673(97)00739-5 General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. AbstractPolymers can be characterized under sorption conditions, to obtain information on molar mass and chemical composition. In order to get a better understanding of their retention behaviour under such conditions, the evaluation of thermodynamic parameters obtained from van't Hoff analyses on low-molar-mass polystyrenes (PS) and polyesters (PE) in various THF-water mixtures on a C column is described in this study. Linear van't Hoff behaviour was observed in almost all 18 cases. Negative values for both DH and DS were found for both PS and PE oligomers, which increase with increasing %THF. For DS this is explained from multi-site attachment effects. For PS, the non-linear relations between DH and DS, and degree of polymerization ( p) could be properly described by the Stockmayer-Fixman equation. Although less clear, similar trends were found for PE. For PS, evidence for penetration effects of oligomer chains into the bonded chains was obtained. Martin plots for both PS and PE were shown to be non-linear in all investigated eluent compositions. The extent of non-linearity is suggested to depend on the conformation of a polymer in solution. No distinct enthalpy-entropycompensation temperature (EECT) independent of p was found for PS, thus confirming the findings of an earlier study in which no exact molar mass independence was found under critical conditions. Further evaluation of EECT for PS oligomers revealed a retention mechanism independent of the binary eluent composition. This indicates that conclusions from this study can also be used for a qualitative understanding of sorption mechanisms in the gradient elution mode. Finally, for PS it was shown that DG equals zero under critical conditions, thus confirming theoretical predictions. © 1997 Elsevier Science B. V.

SWANTON, ELLEN M. (Brooks Hospital, Brookline, Mass.), WILLIAM A. CURBY, AND HOWARD E. LIND. Experiences with the Coulter Counter in bacteriology. Appl. Microbiol. 10:480-485. 1962-Viable and killed suspensions of Staphylococcus aureus SM, Escherichia coli, and Serratia marcescens, as well as polystyrene spheres, 0.81 and 2.85 A in diameter, were counted electronically with a model A Coulter Counter. Simultaneous counts by standard bacteriological methods and microscopy were done for purposes of control and comparison with the data from the Coulter Counter. Results indicated: (i) electrical characteristics of different bacterial populations are different; (ii) electronic counts were consistent for species used; (iii) live S. aureus exhibits a denser pattern of thick bright pulses on the cathode-ray tube than does live E. coli; (iv) killed bacteria resemble inert particles in pulse pattern; and (v) some viable bacteria do not react independently of current flow, as do inert particles and killed bacteria. The object of this study was to determine the reliability as well as the limitations of an electronic counting system, the Coulter Counter, in enumerating bacteria in suspension in a fluid medium. Previous studies by Kubitschek (1958) and Lark and Lark (1960) cited the utility of the Coulter Counter in measuring the volumes of bacterial cells and volume ratios of bacterial populations and mixtures of bacteria and spores. As yet, reports with data on actual numbers of bacteria in a given population have not appeared in the literature. (During the completion of this study, such a work was published: Toennies, G., L. Iszard, N. B. Rogers, and G. D. Shockman. 1961. Cell multiplication studied with an electronic counter. J. Bacteriol. 82:857-866.) The assembled Coulter Counter includes an aspirator pump, a mercury manometer stand with aperture tube and microscope, and a unit containing the electronic components: the pulse-amplifying system, the oscilloscope, and the decade counter. Particles suspended in a 0.900% solution of sodium chloride (equivalent conductance, 97.5 mhos/cm at 22 C) are counted and sized while flowing through an aperture immersed in the sus-1 Presented before the Laboratory Section of the American Public Health Association on Wednesday November 15, 1961, at Detroit, Mich.

No abstract

SUMMARYSeveral micro-organisms of similar initial size ( 0 . 2 5~~) were used to study the intra-species and inter-genus variations in the electronic counting cliaracteristics and population distribution as functions of culture age. A. Coulter Counter Model A was used to count populations of Staphylococcus aureus SM, Escherichia coli (Sias), an E. coli variant, E . freundik (8454), and an E. freundii variant. Initial inocula into brain heart infusion broth were from agar slopes. Cultures were incubated at 37" for various growth periods from 4 to 24 hr.; centrifuged at 1500 g for 25 min, and the deposit resuspended in 0.9 :h (w/v) NaCl twice, then resuspended in 10 ml. saline, diluted 1/104, shaken, and counted in the Coulter counter a t maximum gain on aperture current settings (a.c.s.) 4, 5 and 6 with threshold settings from 5 to 100. Population distributions were made with a phase-contrast microscope in a Petroff-Hauser counting chamber. The numbers of aggregates containing 1, 2, 3, 4 and > 4 organisms were recorded as percentage of total populations. Counts were established for all bacterial populations tested as well as for the 0 . 8 1 ,~ diameter latex sphere counting standard. With a technique based on the addition of random variables, true bacterial population counts could be formulated. Some of the actively dividing populations displayed characteristic sensitivities which [were dependent in part on the aperture current setting. It is concluded that intra-species as well as inter-genus variations exist. These variations are the result of factors such as: the given organism, its age, distribution and growth rate at the time of count, dilution and counting media, aperture diameter and magnitude of the current field in the electronic counting system.

Viable and killed suspensions of Staphylococcus aureus SM, Escherichia coli , and Serratia marcescens , as well as polystyrene spheres, 0.81 and 2.85 μ in diameter, were counted electronically with a model A Coulter Counter. Simultaneous counts by standard bacteriological methods and microscopy were done for purposes of control and comparison with the data from the Coulter Counter. Results indicated: (i) electrical characteristics of different bacterial populations are different; (ii) electronic counts were consistent for species used; (iii) live S. aureus exhibits a denser pattern of thick bright pulses on the cathode-ray tube than does live E. coli ; (iv) killed bacteria resemble inert particles in pulse pattern; and (v) some viable bacteria do not react independently of current flow, as do inert particles and killed bacteria.