Deactivation of Capillary Injectors Bernard M. Mitzner and George Hild Polak’s Frutal Works, l n c . ( A Wholly Owned Subsidiary of Hercules l n c . ) , Middletown, N. Y . 10940
The gas chromatographic decomposition of heat sensitive materials is a common phenomenon in the perfume and flavor industry. The presence of trace materials, as acids, facilitates the decomposition and isomerization process, and this subject has been discussed previously ( I ) . The analysis of a wide variety of essentials oils, natural products, and perfume, exposes the injectors to acids directly, as well as to chlorinated compounds which may form acids. The injectors of commercial capillary gas chromatographs, because of the incorporation of a splitter, have an unusually large surface area-to-sample size ratio. The presence of a decomposition “site” is thus very critical. It has been our experience that when such sites are formed (usually after prolonged usage), washing with the usual aqueous materials as well as organic solvents are of no avail. Heat labile materials such as linalyl acetate tend to readily break down even after prolonged washing procedures. We have developed a procedure that has eliminated this problem. We wash the injector with methylene chloride and acetone. We then coat the injector by passing 20 cm3 of a 10% Se-30 solution in methylene chloride through it (at room temperature), then allowing it to evaporate. The injector is then allowed to heat up. The coating has proved to be effective for a period of over 16 months with no evidence of linalyl acetate suffering any decomposition or isomerization. Table I indicates the observed analysis, before and after treatment, if lina-
Table I. Analysis of Linalyl Acetate a n d Linalool as Observed before the Injector of a PerkinE l m e r Model 990 Was Treated, after T r e a t m e n t , and Sixteen M o n t h s L a t e r A. Linalyl Acetate
Linalyl Acetate
Terpenes
Neryl and generyl acetate
1) After decomposition
23
48
29
100 100
... ...
...
Linalool
l’erpenes
became obvious 2) After coating 3) 1 6 months after coating €3. Linalool
1) After decomposition
became obvious 2) After coating 3) 16 months after coating
...
82
18
100 100
...
, . .
...
...
...
lyl acetate and linalool, which are prime examples of heat labile compounds. During the 16-month period, the injector was constantly maintained a t a temperature of 240 “C. This procedure was successfully carried out with injectors that became “active” of both Perkin Elmer Models 226 and 990. We can surmise that the active sites have been covered by the coating, thus leaving an inert surface. Received for review January 28, 1974. Accepted March 25, 1974.
(1) B. M. Mitzner, Anal. Chern., 36, 242 (1964)
Two-Chamber Furnace for Flameless Atomic Absorption Spectrometry D. A. Church, T. Hadeishi, L. Leong, R. D. McLaughlin, and B. D. Zak Lawrence Berkeley Laboratory. University of Ca/,forn/a. Berkeley. &/if. 94 720
In order to successfully measure trace element concentrations by an atomic absorption (AA) technique, the sample must be reproducibly vaporized and dissociated so that the element of interest can absorb the incident resonance light. Flameless AA measurements are often carried out by placing the sample in a carbon tube. through which the light beam passes. The carbon tube, when heated, serves as a furnace ( I ) to vaporize and dissociate the sample. With such a furnace, it is generally necessary t o carry out drying or ashing steps prior to atomizing the sample, in order to obtain meaningful results. If the sample element to be measured is volatile, or exists in volatile compounds, as do mercury, arsenic, and selenium, these drying and ashing steps may well lead to loss of this element before the actual measurement. ‘(1) 6. V. L’Vov, “Atomic Absorption Spectrochemical Analysis, ’ translated by J. H. Dixon.’Adam Hilger Ltd. (London), 1970, p 213.
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As a means of circumventing these procedures, we describe a furnace consisting of two heated chambers, which does not suffer from the deficiencies mentioned above. The sample is introduced into the first (combustion) chamber in a holder, along with a stream of carrier gas (Figure 1). Rapid conductive and radiative heating of the sample holder vaporizes the sample. An oxidizing carrier gas not only assists with the combustion of‘ the sample. reducing smoke and other interferences, but also carries the dissociated constituents reproducibly into the light beam. Following the short residence time in the windowless absorption tube, the sample vapor is vented to the surrounding atmosphere. We have tested such a furnace as a component of the Isotope-shift Zeeman-effect Atomic Absorption (IZAA) spectrometer (2-4) applied to the (2) T. Hadeishi and R . D. McLaughiin, Science. 174, 404 (1971).
AUGUST 1974
