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ANALYTICAL CHEMISTRY, VOL. 50, NO, 8, JULY 1978
would be futile to check the validity of Equation 4 from the value of the y intercept of the straight line of unit slope that was obtained experimentally. The unexpected pH dependence that was found in the region, 8.5 < pH C 9,5, cannot be explained unless further work is carried out with a single reagent rather than the commercial extractants which are invariably mixtures of organic reagents. A plot of log D VI. pH for the extraction of Cu2+is included in Figure 1 for the purpose of comparison with the corresponding plot for the extraction of Ni2+. In the region, L O C pH C 3.5, the slope of the log D vs. pH plot for Cu2+is 0.7 and in the region 5. C pH C 6.5, the slope is 3.1. In addition to these two regions in which the p H dependence resembles that of the Ni2+ extraction, there is an intermediate region, 3.5 < pH C 5., in which the pH seems to have little effect on the extraction of Cu2+. The complexity of the extraction system is such that no simple explanation can be given for the behavior of Cu2+.
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ACKNOWLEDGMENT The authors gratefully acknowledge the gift of nodule samples from the Hawaii Institute of Geophysics.
LITERATURE CITED (1) E,Meyer-Qalow, K. H. Schwarz, and V. Boln, "Interocean'73,Dusseldorl", C. Kruppa, Ed., Hamburg, Seehafen-Verlag Erlk Blumenfeld, 1073,Vol. 1, p 458. (2) P. H. Cardwell, Mln. Congr. J . , 59 (11),38 (1973). (3) G.Hubred, Mlnerals Scl. fng., 7, 71 (1675). (4) U S . Patent, pendlng (filed by Unlverslty Patents Inc.), (5) B, Bernas, Anal. Chem., 40, 1682 (1066), ( 6 ) A. W. Ashbrook, Coord. Chem. Rev., 16, 285 (1075). (7) P. J. Belles, C. Hanson, and M. A. Hughes, Chem. Eng. (Aug. 30),88 (1076).
RECEIVED for review December 5, 1977. Accepted April 21, 1978. The authors are grateful to the Department of Planning and Economic Development in the State of Hawaii and to the College Sea Grant Program a t the University of Hawaii (04-6-158-44114) for financial support.
Detection, Identification and Structural Investigation of Biologically Important Compounds by Secondary Ion Mass Spectrometry Alfred Bennlnghoven" and W. K. Slchtermann Physikalisches Instltut der Universltaet Muenster, Schlossplatz 7, 4400 Muenster, Federal Republic of Germany
Secondary Ion mass spectrometry (SIMS) has been applled to the lnvestlgation of biologically important organic compounds. The positive and negative secondary Ion spectra of about 40 compounds, e.g., amlno acids, peptldes, drugs, etc., have been recorded by low primary ion dose denslty (statlc) SIMS. From virtually ail compounds, highly intenslve "parent-ilke" secondary ions of the general composition (M 4- H)' or ( M H)- and characteristlcaliy large fragment ions correlated wlth functional groups are emitted. The technique especially allows the detection, identification, and structural Investigation of nonvolatlle and thermally instable compounds. The experimentally determined values of the absolute secondary ion ylelds (number of secondary lonshumber of primary ions) are in the 0.1 range.
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The detection, identification, and structural determination of organic compounds, very often available only in extremely small total quantities, is an important analytical problem in general organic chemistry, biochemistry, medicine, environmental control, etc. A wide variety of organic materials is of interest in these fields, e.g., amino acids, peptides, drugs, vitamins, pharmaceuticals, herbicides, and pesticides. Mass spectrometry plays an important role in analytical chemistry because of its high sensitivity and the kind of information provided. Very often mass spectrometry is applied in combination with separation procedures, as for example in GC-MS (gas chromatograph-mass spectrometer) coupling. Virtually there exist four ionization techniques widely applied in organic mass spectrometry: electron impact ionization (EI),chemical ionization (CI), field ionization (FI), 0003-2700/78/0350-1 l8O$Ol .OO/O
and field desorption (FD) (1). All these techniques require evaporation of the sample material, with the exception of field desorption. From this, serious problems result for nonvolatile or thermally instable material. Applying electron impact ionization, an additional serious limitation is the fragmentation process during ionization, providing very often uninterpretable spectra. For chemical ionization and field ionization, this fragmentation can almost be avoided in many cases. But evaporation of the sample material is still required. So far, only field desorption can handle nonvolatile material, giving, in addition, simple molecular spectra. Some problems in FD, however, result from the delicate sample preparation. Plasma desorption mass spectrometry (PDMS) (2) represents another approach to the analysis of the nonvolatile organic compounds. This technique, however, is not yet widely applied, because of some experimental problems. The main postulates for an ionization technique applicable to large organic molecules, as for example to many biologically important compounds, can be summarized as follows: (1)High absolute sensitivity (
