Nonaqueous sedimentation field flow fractionation

Abstract

spectrometer and data system to determine tracer enrichment with high precision over a period of several hours, these samples were analyzed every hour for 5 h. Results show that the 42Ca and ^Ca isotopes were enriched by 6.7 ± 0.2% and 3.3 ± 0.2%. CONCLUSIONSThese results demonstrate that isotopic abundances of calcium in urine can be determined by FARMS with high precision (CV < 0.2%). The primary factor limiting the precision is related to the surface structure of the sample, which causes changes in the isotope effect of the particle desorption process. Analysis of other factors, such as ion statistics, electron multiplier gain, probe tip configuration, instrument stability, and the data system, suggest that isotopic abundance measurements with CV less than 0.1% can likely be made once better methods for loading the sample are developed. Despite the small uncertainty which results from the changing isotope effect occurring during particle desorp-tion, the present level of performance is adequate for quantifying stable isotopic tracers of calcium used in clinical investigations. The fact that such measurements can be made with a conventional mass spectrometer which is routinely used for a variety of other measurements, such as high mass FAB analyses, exact mass measurements, and El and Cl, is most significant. It is also notable that only very minimal sample preparation is required.

Field-flow fractionation

“…As in other elution chromatographic systems, resolution increases with the square root of the channel length, and under otherwise identical conditions, the FFFractionation system will show somewhat higher resolution than the SF3. Currently neither system is suitable for extended operation in nonaqueous carriers, However, two units of the FFFractionation type have been successfully operated in ethanol (16,17), Both systems are under microprocessor control, which allows the operator to select operational parameters such as field strength with or without a programmed decay. The Du Pont unit limits its programming options to exponential field decays of the type shown in Figure 7 (18), whereas the FFFractionation system offers a somewhat broader array of functional forms for its field programming.…”

Field-Flow Fractionation

“…Currently neither system is suitable for extended operation in nonaqueous carriers. However, two units of the FFFractionation type have been successfully operated in ethanol (16,17).…”

Separation of particles in nonaqueous suspensions by thermal-electrical field-flow fractionation

“…Such investigations have encouraged the use of a standard GC/MS transfer line on the mass spectrometer (designed primarily as a pressure drop from atmosphere to vacuum) as a short (1-m) capillary GC column for separation of atmospheric components. Further, the enhanced sensitivity capabilities of the ion trap mass spectrometer (Finnigan-MAT) (15,16), to detect sample quantities on the order of 100 fg (17) in both full-scan MS and MS/MS modes, allow for direct sample introduction without preconcentration.…”