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experimental errors, but rather that copper is underdetermined in all cases. We noticed that the color of the Cu(1)Ferrozine complex fades on long exposure. This suggests that the complex is unstable. I t is known that in aqueous solutions of many low molecular weight copper(1) compounds, univalent copper is almost instantaneously oxidized into copper(I1) by molecular oxygen (9). This means that many copper(1) complexes will have a limited stability in the presence of oxygen. This can explain our observation t h a t the color of the Cu(1)-Ferrozine complex fades on long exposure and the fact that copper cannot be determined quantitatively by the use of ferrozine. The precision of such determinations for Cu(1) is improved by the addition of sodium sulfite as shown by the results in Table IV. There is, however, a possibility that this method may be used to determine copper quantitatively if oxygen is completely excluded.
A Figure 1. Absorbance of a solution containing copper(1) and iron(I1) salts after treatment with Ferrozine
LITERATURE CITED ( I ) L. L. Stookey, Anal. Chem., 42, 779 (1970). (2) S. K . Kundra, M. Katyal, and R. P. Singh, Anal. Chem., 46, 1605 (1974). 131 C. R. Gibbs. Anal. Cbem.. 48. 1197 (1976). (4j B. Jaselskk and S.J . Nelepathy, Anal. Chem., 44, 379 (1972). (5) A. Atari and B. Jaselskis, Anal. Chem., 44, 1515 (1972). (6) R. Osterberg, Coord. Cbem. Rev., 12, 309 (1974). (7) R. L. Nagel, G. Bemski, and P. Pincus, Arch. Biochem. Biophys., 137, 428 (1970). (8) B. F. Cameron, Anal. Biochem., 11, 164 (1965). (9) A. Zuberbuhler, Helv. Chim. Acta, 50, 466 (1967).
T a b l e IV. D e t e r m i n a t i o n of C o p p e r in t h e Presence of S o d i u m Sulfite Copper taken, mg/mL
C o p p e r found, mg/mLa
1.39
1.28
1.72 2.11 3.12 4.16
1.61 2.58 3.00 3.91
Alphonso C. I. Anmiem* Gbeminiyi B. Ojo
E a c h of t h e d a t a r e p r e s e n t s t h e average of a t least 5 samples.
Department of Chemistry Cniversity of Ibadan Ibadan, Nigeria
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as iron in inorganic Fe(I1) solutions by this method. All the results show that the amount of copper found is consistently lower than the expected value. The deviations observed show that the results cannot be attributed to random
RECEIVED for review July 27, 1977. Accepted November 17, 1977.
AIDS FOR ANALYTICAL CHEMISTS Positive Pressure Columns for Solvent Cleanup or Chromatography B. P. Semonian, J. A. Lubkowitz,' and L. B. Rogers" Department of Chemistry, University of Georgia, A thens, Georgia 30602
There are many applications, such as solvent and sample purifications, which still utilize the classical gravity-feed columns. However, the use of volatile solvents often generates problems in those (gravity-feed) systems. The most common inconveniences are, first, the formation of gas bubbles in the column bed, which renders the column useless and, second, the loss of mobile phase by evaporation from the solvent reservoir. In addition, the dissolution of water vapor (from the air) a t the column outlet, can contaminate the sample or solvent. T o minimize those problems, a closed system was devised in which the high partial pressure of the solvent provided a protective gas blanket. T h e columns were based on the principle of an addition funnel ( I ) , and with the aid of a simple mercury pressure valve, the problem of gas bubble formation was eliminated when purifying n-pentane over silica gel. The loss of n-pentane Present address, A p a r t a d o 1747, Caracas 101, Venezuela. 0003-2700/78/0350-0532$01 O O / O
through evaporation was substantially reduced and water contamination was essentially eliminated. The pseudo-sealed system utilized the partial pressure of the n-pentane to generate a pressure of approximately 50 Torr greater than the ambient pressure. The pressure served several functions. It served to collapse any bubbles already present in the column. At the same time. the positive pressure also kept air from leaking around the sides of the stopcock which often generates additional bubbles in the column packing through evaporation. Since the system was a pseudo-closed one, the liquid vaporized to the point of establishing its characteristic partial pressure. After this pressure had been achieved, further losses due to evaporation were eliminated. This system could also be used to exclude atmospheric gases by employing a purge gas.
EXPERIMENTAL Apparatus. A diagram of the system is shown in Figure 1. All unions used were 24/40 ground glass unions. The column was c\ 1978 American Chemical Society
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mercury pool. Once the pressure had been set to a desired value. no other adjustments were necessary. Procedure. The silica gel was first dried overnight at 170 "C. It was then slowly poured into the column which had previously been filled with n-pentane. The top reservoir was then attached and also filled with n-pentane. The routine operation of the column consisted of four steps: (a) Filling the reservoir, (h) cleaning the receiver of vapor by blowing filtered house air into it, (c) clamping the receiver to the hottom of the column, and (d) adjusting the flow rate of liquid to a desired level. Once those steps had been taken, the column required no further maintenance.
RESULTS AND DISCUSSION IVe have repeatedly used this technique for cleaning u p technical grade n-pentane. The advantages of this system are. first. that slow flow rates can be used without vaporization losses of the n-pentane becoming a problem. We have used up to 12 h to pass 2 L of n-pentane without appreciable loss. Second, more efficient columns were maintained since bed-disrupting bubbles were prevented from forming. Third, safety was increased because an increase in ambient teniperature could not generate either higher coiumn pressures or noticeable amounts of gaseous n-pentane. (Nevertheless. this system was operated in a good fume hood!) Fourth. the pseudo-closed system eliminated the access of water vapor to the outlet of the column. Finally, accidental degradation of the column material by water adsorption was reduced. Even in cases where the column was accidently allowed to run dry and to remain in that condition for several hours, there was no evidence that atmospheric water had penetrated the system to an extent that deactivated or seriously impaired the operation of the column. Obviously, this type of technique could also be used to exclude atmospheric gases if ian appropriate purge gas were employed. The system was ideal for solvent cleanup, and it can be readily adapted to fraction collection by incorporating several containers inside the receiver flask. In this mode of operation, one would (most probably) use the optional ballast tank.
Figure 1. Column with upper and lower (2-L) reservoirs
60 cm X 2.54 cm (o.d.1and 2.24 cm (i.d.). The sintered-glass frit was of medium porosity. The top joint of the reservoir was fitted with a tubing-adapter. A latex rubber tube was used to connect the reservoir tubing adapter, through a glass "T", to the venting arm that followed the column. The third port of the "T" was connected by latex tubing to a 4-mm o.d. glass tube which had been inserted through a two-hole rubber stopper and into the mercury reservoir. (An optional ballast tank could be placed as a branch at any convenient location along the latex tubing.) Thr pressure was regulated by the mercury reservoir, and it was adjusted by raising or lowering the height of the glass tube in the
LITERATURE C!ITED (11 "Separatory funnels,addition, pressure equalizing." Item No. 5237-H 10, A r t h u r H. Thomas Co. Catalog, 1976.
RECXIVEI) for review August 5, 1977. Accepted November 14, 1977. This work was supported by the U.S. Energy Research and Development Administration through Contract No. E(38 -1)--854.
Preparation of Wet Fish Reference Material from Shark Meat Yukiko Dokiya, Masashi Taguchi,' Shozo Toda, * and Keiichiro Fuwa2 Department of Agricultural Chemistry, Faculty of Agriculture, The University of Tokyo, Bunkyoku, Tokyo, Japan, 1 13
Standard reference materials or certified reference materials for metal analysis of biological or environmental samples have recently attracted the attention of analytical chemists who deal with those "soft" materials. Since H. J. M. Bowen ( I ) prepared his Kale Powder in the early 1960's, several trials for preparing such materials have been performed, including grass samples by J. B. Jones (21, Orchard Leaves and Bovine
Liver by NBS research groups ( 3 , 3 ) ,Cd-rice by N. Yamagata ( 5 ) and Oyster Powder by R.Fukai ( 6 ) . Among these works, those of NBS research groups are considered t o be the most systematic and comprehensive. An unprecedented demand for Orchard Leaves and Bovine Liver is currently reported by J. P. Cali (7). T h e authors, in a cooperative study with h'BS research groups, have performed some researches for new biological reference materials, and the work includes the preparation of Tea Leaves and Pepper Bush samples (8). No standard reference materials of fish meat have been successfully
IPresent address, Department of Fisheries, Faculty of Agriculture, The University of Tokyo, Bunkyoku, Tokyo, Japan, 113. Present address, Department of Chemistry, Faculty of Science. The University of Tokyo, Bunkyoku, Tokyo, Japan, 113. 0003-2700/78/0350-0533$01.00/0
C
1978 American Chemical Society
