single ion detection and that, a t most, the sensitivity loss is only 22%.
Table I. Comparison between Dynamic and Static Single Ion Detectiona
CONCLUSIONS The described circuit is successful in eliminating the focus instability problems associated with the Du Pont 21490 Mass Spectrometer and makes it possible for users of this instrument to achieve mass fragmentography capability. The DSID circuit costs approximately $350 in parts (plus the cost of an inexpensive oscilloscope) to manufacture. An additional $100 in parts is needed for the DDID circuit. Furthermore, the circuit can be simply plugged into the scan sweep of the mass spectrometer. No modification of the mass spectrometer, digital processing equipment, or analog-digital interconversion is necessary.
Injection No.
RECEIVEDfor review March 13, 1974. Accepted June 20,
the Journal Series, New Jersey Agricultural Experiment Station, Cook College, Rutgers University-The State University of New Jersey, New Brunswick, N.J. 08903.
1974. This work was supported in part by Regional Project NE-83, United States Department of Agriculture. Paper of
Dynamic
Static
39.5t 39.5 39.5 37.5 40.0 Mean s t d dev a
39.2 0.975
50.5 47.5 33.5 41.0 27.5 s t d dev
40.0 9.57
For 39-ng on-column injections of hexadecane. Expressed as
% scale deflection at recorder = 50 mV, attenuation = 128.
Solubility Product Constants of Some Divalent Metal Ions with Ammonium Pyrrolidine Dithiocarbamate Michel Arnac and Gilles Verboom Universite du Quebec a Rimouski, Depatiement des Sciences Pures. 300 Avenue des Ursulines, Rimouski, P.Q., Canada, G5L 3A 1
It has been demonstrated that a number of heavy metals can be satisfactorily extracted from an aqueous solution into organic solvents like methyl isobutyl ketone (MIBK) with the use of ammonium pyrrolidine dithiocarbamate (APDC) as a chelating agent ( 1 ) . Determination of trace elements in the aquatic ecosystem has become an important area of pollution studies. APDC in MIBK has been widely used for concentration of metals from sea-water for X-ray fluorescence analysis (P),and by atomic absorption workers (3.4 ) . Precipitations were noted on reacting some metals with APDC and the precipitates were extractable into organic solvents ( 5 ) . Only the stability constants of complexes of some divalent metal ions with a variety of N-substituted dithiocarbamic acids have been done recently (6). Further investigations involving APDC were considered desirable for several metals. A careful study of the literature shows a lack of information on the solubility product constants of metal ions with APDC. The experimental conditions on this subject that are found in the literature vary from one author to the other. Used concentrations for the APDC complexing solutions are in the range 1-10%. The objective of the present study is to investigate this field of analytical chemistry. EXPERIMENTAL Polarography (amperometry) was used to determine the stoichiometry of the precipitating reaction. Solubility measurements of equilibrium-saturated systems were made using atomic absorption spectrophotometry. W. Slavin. Af. Absorption Newslett.. 4, 273 (1965). A. W. Morris, Anal. Cbim. Acta, 42, 797 (1968). R . R . Brooks, B. J. Presley, and I. R . Kaplan, Talanta, 14, 809 (1967). P. G. Brewer, D. W. Spencer. and C. L. Smith, Amer. SOC.Test. Mater., Spec. Tech. Pub/., 443, 70 (1969). (5) H. Malissa and E. Schoffman, Mikrocbim. Acta, 1, 167 (1955). (6) R. R . Scharfe, V. S. Sastri, and C. L. Chakrabarti,'AnaL Chem., 45, 413 (1973). (1) (2) (3) (4)
Apparatus. Dc polarograms were recorded using a classical three-electrode technique. The apparatus composed of several Tacussel units has been described in an earlier paper (7). Measurements were done a t constant temperature in a Tacussel waterjacketed cell, Model RM 06. Atomic absorption measurements were carried out on a double-beam Perkin-Elmer Model 306 Atomic Absorption Spectrophotometer equipped with a four-inch single-slot standard burner for use with air-acetylene. Standard Perkin-Elmer Intensitron hollow cathode lamps were used for all elements. The outputs of the instrument were recorded with a Perkin-Elmer Model 56 recorder. The spectrophotometer is capable of producing readings integrated over three and ten seconds, either on the digital or on the laboratory recorder. Electrodes. All potentials were measured with reference to the saturated calomel electrode. The auxiliary electrode was a bright platinum foil of large area. The capillary tube used in this work was described previously (7). Reagents. All reagents used were of analytical grade purity, without further purification. Commercially obtained reagents (Fisher Certified or J. T. Baker Analyzed Reagent) were employed as the nitrate salts. The pyrrolidinecarbodithioic acid (J. T. Baker) was used as the ammonium salt (APDC). Standard solutions for atomic absorption calibration curves were bought from Harleco. Doubly distilled mercury which has been tested for impurities was utilized throughout the polarographic studies. Before preparing solutions, water was primarily deionized, distilled in borosilicate glass, then deionized again, and finally fed at low flow rate through a mixed-bed ion exchange column. Average specific conductance of ohm-' cm-' a t the purified water was between 0.4 and 1.2 X 25 "C. Procedure. Polarography. Fifty milliliters of aqueous solutions containing m grams of a nitrate salt [Cu(N03)24H20; Pb(NO:
