ANALYTICAL CHEMISTRY
9 638 'I'able I .
I r o n (:ontent of Test Samples Before and After
.,
Grinding Sample Filter paper
Operator A
Iron. P.P.hf.a Unground Ground sample semple
i:?,74
7 7 : 7!)
amined. Table I records the analytical results obtained with some samples. Iron determinations weve carried out spectrophotometrically, using cupferron ( 1 ). Recent publications ( 2 , G )have pointed out that contamination of field samples with aerial dust can mask real differences in the iron content of plant samples. Some early tests here disclosed that aerial dust could also give rise to iron contamination of plant materials during grinding in the type of mill discussed above. Such contamination accounted for several variable results in duplicate grindings on different days. Because of the high speed of rotation, a large volume of air is d r a m through the mill during the grinding of a sample, and the aerial dust is apparently effectively retained by the bed of finely ground material. It was necessary to house the mill in a room remote from soil dust and other contamination-e.g., from workshop machines-. where reproducibly good values were always obtained for replicate grindings. The increase in iron content during grinding of 5gram portions of filter paper was consistently less than 4 p.p.m. over a period of several weeks, with t,hree different operators using the mill. The results in Table I show that no serious contamination with iron occurs during grinding in this mill. Ai spectrographic investigation of the resin constituents has revealed that copper, manganese, cobalt, zinc, and molybdenum occur only a t levels of a few parts per million or less, all lower than iron. I t seems safe to assume, therefore, that only negligible contamination with these metals occurs during grinding of plant samples. During the routine grinding of several hundred small samples from pot cultures there has been no visible wear of the chromeplated beater. This has been frequently checked by grinding filter paper samples of known iron content. If necessary, the beater cross could be simply replaced. However, as the result of experience gained with the nonelectrostatic resin compounded from high quality carbon black and Araldite resin, it is now considered feasible to fabricate a beater cross from this material, arid so eliminate metals from the byorking surfaces of the mill. This would avoid the iir:cessit>, lor I'requent checking of the vtlroine plate for ~ v e a r .
Filter Paper Support for Mounting and Assay of Radioactive Precipitates Ben Bloom, National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, Bethesda, Md.
HE advantages of using filter paper as both a quantitative and Tdisposable supporting material in the preparation of radio:tctive precipitates for assay are readily appreciated. Filter paper systems a t present available, however, generally suffer from thtb necessity of transferring an unsupported paper and precipitates rinit from the funnel-plunger assembly to the counting assembly, \\ith frequent separation of paper and precipitate. The use of vmbroidery-type rings to support the filter paper provides a simple means of avoiding such separation. The funnel section and plunger section (see figure) are modifications, as indicated, of similar pieces (Item E-8B, Catalog D, available from Tracerlab, 130 High St., Boston 10, Mass.). The outer and inner rings were turned from stainless steel tubing 1 inch in outside diameter, with a '/]e-inch w-all. The outer ring is 1 inch in outside diameter, with a 0.025-inch wall, and 0.2-inch height: the inner ring is 0.935 inch in outside diameter, with a 0.030-inch wall, and 6/16-inchheight (determined by the allowable height vithin the counting chamber).
'-4 \1 I
FILTER PAPER $I,!'
UTER RING
LITERATURE CITED
The filter paper assembly is prepared by clamping a circle of paper betn-een the inner and outer rings, just as embroidery cloth is held between embroidery rings. The filter paper assembly is placed over the plunger section, which has been inserted into a one-hole stopper set in a suction flask. The plunger section thus conveys the vacuum onto the filter paper. The funnel section is then set in place over the filter paper assembly and, by means of springs, the ears attached to the funnel are secured to the suction flask. This effects, as noted in the figure, the clamping of the paper between the funnel and plunger sections. After filtration of the precipitate and drying by appropriate means (infrared lamp and suction are used on barium carbonate mounts), the filter paper assembly, as a unit, is ready for assay. Separation of the rings, when disposal of precipitate and paper is desired, is facilitated by forcing a wedge-shaped fork between the outer ring and the lip which is left on the base of the inner ring.
( 1 ) Beckwith, 11. S., Chemistry & I n d u s t r y 1954, 663. (2) Jacobson, L., Plant Physiol. 20, 233 (1945). (3) Kretschriier, -4.E.. Randolph. J W,, A s ~ L . CHEX. 26, 1862 (1954). (4) Xeal, W. lI.,Becker, K. B.. J . A g r . Research 47, 249 (1933). (5) Wallihan. E. F.. A m . J . Rot. 42, 101 (1955).
The desrribed support has proved extremely satisfactory during the course of 2 years' use in the preparation of barium carbonate mounts (filtered from an alcohol suspension). Others have found it applicable to the assay of calcium oxalate (water-acetone suspension) and uric acid (water suspension).
ACKNO W LEDGRI E S T
Grateful acknowledgment is made to the B.A.L.M. Paint Co., Port Adelaide, for the supply of pure carbon black, and to C. S. Piper, Division of Soils, C.S.I.R.O., for valuable criticism and itdvice. R. 11. McKenzie carried out the spectrographic examination of the Araldite resin constituents and F. R. Pedler and LV. C. Underwood gave most careful technical assistance. The work described in this paper was carried out as part of the research program of the Division of Soils, C.S.I.R.O. a t the Soils Division, Adelaide, South Australia.
