170
ANALYTICAL CHEMISTRY, VOL. 51, NO. 1, JANUARY 1979
Figure 3. Vessel the authors
5.s
support
rack. Construction details are available from
the calibrated meniscus mark. An aliquot is withdrawn by transfer pipet for later cleanup and gas chromatographic analysis. Two sizes of the vessel were developed (Figure 1). The larger size consists of a 250-mL round-bottomed flask (24/40 standard taper joint) with a volumetrically calibrated 10-mL spherical reservoir (fl70 tolerance) attached to the bottom-center, enabling the vessel's contents to be rotoevaporated a t an off-vertical position. The opening between the upper and lower reservoir is approximately 15-mm i d . , and a meniscus mark is located a t this narrow constriction. The smaller vessel is identical. except that it incorporates a 100-mL round-bottomed flask and a 5-mL spherical reservoir attachment. T h e vessels were constructed from heavy-wall Pyrex Brand Glass (Corning) or KG-33 glass (Kimble). The cleanup procedure for fish extracts used by the Columbia National Fisheries Research Laboratory ( 2 ) provides
an example of how the double-reservoir vessel can save time and reduce error and laboratory contamination. Before the vessels were developed, eluants from extraction or cleanup columns were collected in open vessels, and the resulting large volume was evaporated to a small quantity (2 mL) with a water bath or hot plate. This concentrated sample was transferred to a volumetrically calibrated test tube by repeated rinsings with solvent. Although such liquid transfers are not difficult, they increase the potential for contamination and error, and require considerable time. Incorporation of the double-reservoir rotoevaporation vessels into our residue method (Figure 2) eliminates six quantitative transfer steps for each sample analyzed. Although glass or plastic beakers suffice as readily available vessel supports, we constructed a Plexiglas carrying rack (Figure 3) that accommodates 25 vessels and facilitates their safe transport in the laboratory. The dimensions are tailored to allow for placement of the rack beneath collection tubes of the automated gel permeation chromatography equipment. %'e designed a multihead rotoevaporation unit of Teflon and stainless steel construction, which minimizes backcontamination from the unit. If the double-reservoir vessels are used with commercially available rotoevaporation systems, the back-contamination should be assessed. and the use of evaporation traps may be necessary.
LITERATURE CITED R. C. Tindle and D. L. Stalling, Anal. Chem.. 44, 1768 (1972). "Handbook of Procedures for Pesticide Residue Analysis", U.S. Dept. of Interior, Fish and Wildlife Service, Technical Paper No. 65, August 1972. "Manual of Analytical Methods for the Analysis of Pesticide Residues in Human and Environmental Samples", U S. Environmental Protection Agency, Environmental Toxicology Division, December 1974.
RECEIVEDfor review August 17,1978. Accepted October 12. 1978. Reference to trade names does not imply Government endorsement of commercial products.
CORRECTION Microsampling Nebulizer Technique for Premixed Flame Atomic Spectrometry In this article by R. C. Fry and M. B. Denton, Anal. Chcm., 50, 1719 (1978),the captions for Figures 2 and 3 are correct,
but the figures themselves have been reversed. On page 1720, line eight under precision, Z mL should read 21 mL. In the caption for Figure 4,the caption should include: (i) 0.2 ppm Fe microsampling replicates in acid. analysis succeeds.
