well established 70-eV electron impact fragmentation patterns of organic compounds or the performance of the quadrupole GC/MS system. The detection limits attained This technique made the method applicable to the analysis of relatively clean surface or drinking water. using conventional data acquisition were 1-50 ppm which makes the technique compatible with the concentrations of ACKNOWLEDGMENT organic compounds found in domestic sewage and other waste effluent water samples. Greater sensitivity, to about 50 ppb, was attained with real time data acquisition from subsets of the ions used in conventional mass spectrometry.We thank Tom Bellar of this Laboratory for the original suggestion to analyze tap water for chloroform. Sedimentation field-flow fractionation (SFFF), one member of the field-flow fractionation (FFF) class of techniques, is described and Its potential advantages and disadvantages for macromolecular and particle separatlons are discussed. Theoretical equations for retentlon and plate height are given along with an analysis of possible disturbances caused by relaxation effects, polydispersity, secondary flow, and sample size effects. The conclusions are tested experimentally using polystyrene latex particles having diameters from 907A to 4808A. Measured retention parameters are in excellent agreement with theory but a considerable discrepancy exists in piate height results. This is traced to a possible sample overloading effect. Particle fractionation is illustrated and the further potential of the method is discussed.

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expected in an optimal system. Most importantly, the rotational velocity and the field strength must be increased to gain any significant advances. The degree to which performance might be enhanced is shown below.Under conditions of high retention, Equation 13 can be substituted into Equation 14 to yield the potential plate height H = 24h'~~(~)/D (33) With the aid of Equation 10 this expression becomes where the zone velocity in the column, R ( u ) has been written simply as u. If now Equation 8 is used to eliminate X2, we haveIf diffusion coefficient D is replaced by the Stokes-Einstein value, D = kT/3agd, where 7 is the coefficient of viscosity, we get 432If H is written as Cv, then the nonequilibrium coefficient C not only reflects the level of H achievable, but, more importantly, C can be shown to equal the minimum time in which a theoretical plate can be generated. We have 432 k T y c = -This equation shows that the efficacy of SFFF can be improved by manipulating a number of variables, including viscosity, temperature, and density. The method will, in theory, work much better with large particles than small, as reflected in the fifth power dependence on particle diameter d. However there are practical limits to this gain which will become apparent as d approaches either layer thickness 1 or surface-roughness dimensions in magnitude.Equation 37 shows that C for a given particle is inversely proportional to the square of the sedimentation field strength, G. The dependence on rotational velocity is therefore inverse fourth power. In the present study the maximum G was about 500g. If ultracentrifuges, with field strengths up to 300 times greater than this, were adapted to SFFF, C values could in theory be reduced by (300)2 = 90,000. While such gains would not be totally applicable to particles in the size range used here because of the previously mentioned restrictions on size, the above factor would be applicable to much smaller particles and to macromolecules, thus making their separation convenient also.Particle size analysis is significant in many fields of environmental control and industrial operation. The present method is promising in such analyses by virtue of its predictable dependence on simple mass and density parameters and its potential for further improvements in fractionating power. This paper describes the development of two programming systems for sedimentation field-flow fractionation (SFFF): programmed field strength SFFF and programmed solvent density SFFF. The necessity for developing programming systems in SFFF is discussed, and both general and specific theories of programming are developed. A centrifugal SFFF system was adapted to programming by the controlled variation of rotation speed and solvent density. Polystyrene latex beads with diameters from 1756 to 3117A were fractionated by this device. Agreement between theoretical and experimental retention times was within about 5%, showing that the essential features of the technique are well characterized.Sedimentation field-flow fra...

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