Heavy Metal Contamination from Use of Some Rotary Evaporators Robert M. Zacharius and Samuel Krulick, Eastern Regional Research Laboratory, Philadelphia 1 8, Pa.
tion, a short glass trap was constructcd (Figure 1) and inserted between the evaporator and concentration flask. This trap was found most suitable m here a. Ti'duction in space is required, although larger commercially available round glass condensers can be emplo:,-cd. After some continual use, a blue condensate was observed in the trap, hut the concentrate was devoid of the contaminant. I n the isolation or analysis of milligram quantities of material, the presence of heavy metals may prove serious. I n the preparation of 250 mg. of a dipeptide necessitating the concentration of 0.5N acetic acid solution, an 8.3y0 ash containing an appreciable quantity of copper and nickel oxides was found on analysis. Employment of a glass trap provides a npcessary safeguard during the use of a rotary sealed evaporator wherein solvent comes in contact with the metal parts.
available rotary evapC orators are widely used, particularly for the rapid removal of solvents under OMMERCIALLY
relatively mild conditions. They have been especially valuable in the concentration of biological extracts, where low temperatures are desirable t o avoid destruction or modification of labile constituents. I n the determination of the nonprotein amino nitrogen constituents of plant extracts, it has been necessary to concentrate fractions obtained by ion exchange chromatography on a preparative scale. The concentrates, obtained after evaporation of the solvent (frequently 0.5 to 1.ON acetic acid) on a metal rotary sealed evaporator at 40' C. under reduced pressure, had a definite bluish hue when large fractions necessitated prolonged use of the evaporator. On exposure t o hydrogen sulfide, copper sulfide was precipitated. It was first thought that the copper may have arisen from the ion exchange column through the process of grading the resin particle size on metal (copper-containing) sieves [Edge, El. A., Chemist Analyst 47, 72 (1958) 1. Further investigation demonstrated that amino acid solutions could be contaminated by copper with-
Figure 1
out prior exposure to ion exchange resins. Moreover, nickel has been identified as a contaminant also arising from the Monel metal parts of the evaporator. The contamination is considered to arise from the metal rotary seal of the evaporator, by corrosion and/or abrasion during its operation. The degree of contamination varies with the particular volatile acid, volume concentrated, and the conditions which govern the period of contact of the vapor condensate with the metal rotary seal. To circumvent this metal contamina-
ACKNOWLEDGMENT
The authors acknowledge the assistance of Harry J. John of this laboratory in the design and construction of the glass trap.
Reduction of Cyclo-octatetraene by Controlled-Potential Electrolysis Richard E. Frank and Donald L. McMosters,' Department of Chemistry, University of North Dakota, Grand Forks,
1898, Fritz Haber (4) showed in inInitrobenzene vestigation of the electroreduction of that the cathode potential N
is the governing factor in electrolytic reductions. Through further work by Lassieur (6), Sand (9),Hickling (6), Lingane ( 8 ) , Diehl (a), and others, controlled-potential electrolysis has become a potent tool of research and analysis. Because the decreasing concentration of the substance being electrolytically reduced or oxidized makes frequent voltage readjustments necessary, manual potential control is laborious. With a good potentiostat 100% current efficiency is attained at all times with minimum attention on the part of the operator. Many chemists fail to take advantage of the controlled-cathode or controlled-anode-potential method for preparative or analytical work, because Present address, Department of Chemistry, Beloit College, Beloit', Wis.
a potentiostat is not available or they fear the complexities of the apparatus. One other way to control the potential during an electrolysis is to control the concentration of the substance being electrolyzed. Such a proposition seems self-defeating, because the substance in question is used up by the electrolytic process. It becomes feasible if a solvent is used which dissolves only a limited quantity of the substance a t one time, and that solution is kept saturated by stirring excess substance into it throughout the electrolysis. The present authors used this method for the electroreduction of cyclo-octatetraene with water as the solvent and lithium chloride as the supporting electrolyte. With an efficient stirrer, they kept the solution saturated a t all times, except during the very last few minutes of the electrolysis when all the suspended cyclo-octatetraene had been used up. Consequently, the desired cathode potential could be maintained constant with only infrequent minor adjustments
N. D.
of the cell voltage. The simplicity of the equipment and the carefree operation amply compensated for the somewhat extended reaction time. I n previous work on the electroreduction of cyclo-octatetraene (1, S), solvents or solvent mixtures were used that would completely dissolve the sample of reducible substance. The circuit was the one suggested by Lingane ( 8 ) ,except for a vacuum tube voltmeter in the auxiliary circuit with the saturated calomel electrode, advantageously replacing the galvanometer with the megohm resistor. The reaction vessel consisted of a creased four-necked round-bottomed 2-liter flask with a two-way stopcock outlet in the bottom and a high-speed stirrer in the center neck. A mercury pool, retractable through the bottom outlet into a leveling bulb, served as cathode, and a silver-wire coil inside a cylindrical diaphragm (ceramic filter candle) as anode. Three to five 6-volt automobile batteries in series were the power source, and a 12-ohm rheostat capable VOL. 31, NO. 12, DECEMBER 1959
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