Report
cessfully employed for selenium samples. These methods require t h a t the sample be dried before combustion, a n d care should be t a k e n t h a t volatile elements are not lost in the drying step. Freeze d r y ing under v a c u u m is commonly employed. A relatively new method of oxidation which should prove to be very useful for the preparation of organic and biological samples for trace metal analysis is the low temperat u r e ashing technique developed b y Gleit and coworkers (25-27). A radiofrcqucncy dicharge is used to produce activated oxygen radicals which are very reactive and will a t t a c k organic m a t t e r a t low temperatures. Temperatures of less t h a n 100 °C can be maintained, and hence volatility and diffusion losses are small. Introduction of elements from the container and the atmosphere is reduced as well as are retention losses. Biological tissues, graphite, filter paper, and ion exchange resin have been oxidized b y this method. R a t e s of one gram per hour can be achieved. Radiotracer studies demonstrated t h a t seventeen representative elements can be q u a n t i t a t i v e l y recovered after complete oxidation of organic substrate. Selenium-75, for example, was recovered from alfalfa with 99 percent efficiency, being found entirely in the sample boat and none in a cold t r a p . A commercial model of this instrument is available. T h e design has been significantly altered from Gleit's original a p p a r a t u s and t h e oxidation efficiency is considerably reduced. Consequently, ashing times are quite long, up to several days. T h e idea of a method of this t y p e is attractive and with commercial improvement of the a p p a r a t u s it will probably find wide application. Preconcentration
Often, it is necessary to separate the element of interest from the sample matrix in order t o eliminate interferences, or to concentrate t h e element to obtain a better sensitivity. These two steps can conveniently be combined in m a n y cases. One of the simplest and most effective ways of accomplishing this is
Yearsahead of its time! The Orion system for pH, ion activity or potentiometric data accumulation. Interested?
digital pH/mv meter model 801 • 4-digit data display with automatic decimal polarity sign. • Binary-coded decimal output for card or recorder or computer interfacing. • ±0.001 pH to 13.999 pH in 0.001 increments • —999.9 to +999.9 mv in 0.1 increments and
point, out-of-range input and tape, printer, magnetic data and with ±0.001 repeatability. with ±0.1 repeatability.
digital printer system model 851 • Prints exact readings to four significant figures. • Eliminates interpolation and extrapolation errors . . . requires no zero or range adjustments. • Prints sample numbers from 0 to 999 automatically, manually or by elapsed time mode. • Provides accuracy of better than 0.05 seconds. manual electrode switch model 605 • Measures up to six samples with one pH meter. • Measures up to six ions in one sample. • Eliminates "crosstalk" by complete isolation of electrode positions. • Can be used with any other pH meter and all Orion specific ion meters. For complete information on this unique analytical system or any of the individual components, write . . . W. H. Curtin & Company, P. O. Box 1546, Houston, Texas 77001.
W . H. C U R T I N &
COMPANY
SCIENTIFIC A P P A R A T U S · CHEMICALS · LABORATORY FURNITURE H O U S T O N · T U L S A · LOS A N G E L E S · N E W O R L E A N S · A T L A N T A · S A N FRANCISCO D A L L A S « J A C K S O N V I L L E * W A S H I N G T O N « W A Y N E , N. J . · M E X I C O C I T Y " M O N T E R R E Y G E O R G E T. W A L K E R S CO. DIVISION · M I N N E A P O L I S , M I N N E S O T A
Circle No. 68 on Readers' Service Card VOL. 4 1 , NO. 1, JANUARY 1969
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