ANALYTICAL CHEMISTRY, VOL. 51, NO.
large molecules into the CI ion source without using any separation column. In this case, testing solutes of interest are first dissolved in an appropriate solvent which becomes a good reagent gas for CI, and then an aliquot of the solution is introduced into the coaxial capillary by a constant flow of the same solvent from a micro-feeder pump of the LC. With this technique, it was possible to take fairly stable CI mass spectra of polyethyleneglycols u p to m / e = 600, and many of the free amino acids, oligopeptides, a n d steroids (9). Further investigation along these lines is under way.
ACKNOWLEDGMENT T h e authors are indebted to T. Watanabe for his skillful glass-blowing of the newly designed nebulizer.
LITERATURE CITED (1) R P W Scott, C G. Scott, M Munroe, and J Hess, Jr , J Chromafogr , 99,395 (1974)
1, JANUARY 1979
169
(2) P. R. Jones and S . K. Yang, Aria/. Chem., 47, 1000 (1975) (3) W. H. McFadden. H. L. Schwartz, and S . Evans. J Chromatogr., 122,
389 (1976). (4) E. C. Homing, D. I. Carioll, I . Dzidic. K. D. Haegele, M. G. Homing, and R . N. Stillwell, J , Chromatogr. So., 12, 725 (1974). (5) P. Arpino, M. A. Baldwin, and F. W. McLatferty. B/omed. Mass Specfrom..
1. 80 (1974). (6) P. J. Arpino. B. G. Dawkins, and F. W. McLafferty, J . Chromatogr. S o . . 12, 574 (1974). (7) F. W. McLafferty, R . Knutti, R . Venkatarayhavan. P. J. Arpino, and €3. G. Dawkins, Anal. Chem., 47, 1503 (1975). (8) T. Takeuchi. Y. Hirata, and Y. Okumura, Anal. Chem., 50,659 (1978). (9)Y. Hirata, T. Takeuchi, and S. Tsuge, Org. Mass Spectrom., in press. (lo) D.Ishii, K. Asai, K. Hibi, T. Jonokuchi, arid M. Nagaya, J . Chromatogr., 144, 157 (1977).
RECEIVED for review August 2, 1978 Accepted October 10, 1978.
Double-Reservoir Rotoevaporation Vessel for Residue Analysis Thomas W. May* and David
L. Stalling
Columbia National Fisheries Research
Laboratory,
Route
# I,
Columbia, Missouri 6520 1
Advances in chromatographic techniques and instrumentation during the past several years have increased the accuracy, sensitivity, specificity, and efficiency of residue analysis. T h e automation of gel permeation chromatography ( G P C ) for lipid-residue separation ( I ) has significantly increased the number of lipid extracts that can be cleaned up and processed. There has been little improvement, however, in reducing the number of manual transfers involved in processing a sample through extraction and cleanup procedures. Standard techniques for sample preparation include several steps: extraction, lipid removal, and fractionation by sequential adsorption chromatography. Each step involves removal or concentration of large volumes of solvent (2, 3). Solvent removal and quantitative transfer of the residues are time-consuming and limit the number of samples that can be prepared for gas chromatographic analysis within a given period. T o use the advantages of rotoevaporation (rapid evaporation under vacuum with little heat) over other methods of organic solvent concentration (e.g.,Kuderna-Danish), we designed a double-reservoir rotoevaporation vessel for collection, concentration, and final volume calibration of column eluates (Figure 1). Solvents eluted from our automated GPC
Organic Residue Analysis
7 --
L
Column Aasorption
Pesticides
24/40 f JOI N < [ H
-
250 M L
--RESERVOIR-
UPPER
'LOWER
!I I; 100 M L
VOLUMETRIC
RESERVOIR Figure 1. Double-reservoir rotoevaporation vessel This drlicle not subJect to U S Copyright
I I
L
I -.
-
-
I
i - .~. .A__ I Gas Cnrorndtoyraphlc _ _i_ .
L ~
Analysis
3
___.
Figure 2. Flow scheme of laboratory procedure. A * designates the steps where a quantitative transfer is eliminated by the use of a double-reservoir rotoevaporation vessel
system and adsorption chrorilatography d u r n n s are collected directly in the double-reservoir vessels and rijtoevuporatrd t o a small volunie in the lower reservoir, The ves~elwalls art? then riiised with a suitable solvent until the vi)lume reaches Published 1978 by the Amer,Lan Chenilial Society
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). T h e 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 a n off-vertical position. T h e opening between the upper and lower reservoir is approximately 15-mm i d . , and a meniscus mark is located a t this narrow constriction. T h e 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). T h e 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.
