Table I. Recovery of 3-14C-hydroxymethylglutaricAcid and Contamination from Sample to Sample No. of dpm samadded” plesb 11,855 11,855 5,960 5,960 617 617 10,300
1
1 1 1 1 1 7
dPm recovered
Blank spot, dpmC
11,920 36 11,800 31 5,750 36 . 6,000 43 20 620 615 25 10,250f 83 (std. dev.) 28.5 f 4.3 (std. dev.)
a Averages of duplicate samples. The series of single determinations was done in one sequence in the order listed. A blank spot was collected following each radioactive spot.
Figure 1. Zone collector assembled with a counting vial
of radioactive spots even if the compound adsorbed in them cannot be easily or completely eluted from the stationary phase. Conditions for scintillation counting of a wide range of 14C and 3H labeled compounds in the presence of solid supports were established by McKenzie and Gholson ( 4 ) . T o illustrate the general usefulness of the device, results are presented on the collection and counting of 3-14C-hydroxymethylglutaric acid adsorbed on silica gel, a case where quantitative elution is not feasible. EXPERIMENTAL Description. The “vacuum cleaner” principle is employed. The device consists of a screw cap for a scintillation vial, machined in Teflon, into which two glass tubes are inserted with a tight fit. One tube ends in a fritted glass disk and is connected to the vacuum line. The other (5-mm 0.d.) is bent and fitted with a piece of polyethylene tubing for collection (Figure 1).The outlet tube was prepared from a 10-mm i.d. chromatography column with a coarse fritted disk, by elongating the end with 7-mm 0.d. tubing followed by cutting and grinding the column down to the plane of the filter. Usually light tapping is sufficient to dislodge the silica gel accumulated on the filter during the collection of a sample, after disconnecting the vacuum. Slight pressure from a rubber bulb may be necessary occasionally. Procedure. 3-14C-3-hydroxy-3-methylglutaric acid (New England Nuclear) was spotted on commercial silica gel G plates, layer thickness 0.25 mm, without fluorescent indicator (Brinkmann Instruments). The acid cannot be quantitatively eluted from silica gel with either
acetone, ethanol, or aqueous ammonia. Hydroxymethyglutarate in a TLC spot can be efficiently counted by suspending the silica gel in gelled Aquasol (New England Nuclear).
RESULTS A N D DISCUSSION The collection efficiency and the degree of cross-contamination between samples were tested. Areas containing a decreasing amount of radioactivity were collected in sequence following each spot with a blank area of the same size. Table I shows quantitative recoveries of l*C-hydroxymethylglutarate samples over a 20-fold decrease in radioactivity. Cross-contamination between samples is low even under the extreme changes in the level of radioactivity employed to test the system. The collection device can be used over a wide range of zone and sample sizes which makes i t useful in preparative as well as analytical thin-layer chromatography. In the case of a preparative separation the zone can be extracted in the vial, aided by stirring and heating if necessary. LITERATURE CITED (1) B. Goidrick and J. Hirsch, J. Lipid Res., 4, 482 (1963). (2) F. J. Ritter and G. M. Meyer, Nature, 193, 941 (1962). (3) 0. Sudilovsky and P. H.Hinderaker, Anal. Biochem., 45, 5 2 5 (1972). (4) R. M. McKenzie and R . K. Ghoison, Anal. Biochem., 54, 17 (1973).
RECEIVEDfor review September 10, 1976. Accepted November 30,1976. This work was supported by operating grant MA-4770 of the Medical Research Council of Canada.
Portable Field Water Sample Filtration Unit Alvin J. Hebert* and Gardener G. Young Lawrence Berkeley Laboratory, University of California, Berkeley, Calif. 94 720
The need for a lightweight back-packable filtration unit that could easily be cleaned without cross-contamination a t the part-per-billion level while allowing rapid filtration of boiling hot and sometimes muddy water has given rise to the unit shown in Figure 1. Filtrations are performed by pouring the solution into the funnel or by placing a piece of Tygon tubing down a well or spring and drawing the water up and through the filter. Boiling water has been drawn up old geothermal well pipes as high as 5 meters in this manner. Filtration usually takes less than 1 or 2 min per 500-mL bottle when the water is not too muddy. During the filtration process, it is important that 672
ANALYTICAL CHEMISTRY, VOL. 49, NO. 4, APRIL 1977
bubbles not be allowed in the input line, otherwise the unit will cease functioning properly until it is reopened and a new filter inserted. The first few hundred mL filtered are discarded. The filtered samples are essentially free of bacteria and particulates, and in most cases may be stored for months or more without algae growth occurring. Field and laboratory tests show no changes in carbonic acid or in bicarbonate ion concentrations when filtrations are performed a t approximately 113 atmosphere of vecuum even though the p H value may range from 3.2 to 9.4. The unit is designed to accept a standard Millipore acetate filter (variety HAWP-142,0.45-~m,142-mm plain white filter
Figure 1. Portable field water filtration unit
Flgure 3. Typical nipple connector and Teflon plate with mating recess. The aluminum backing plates shown in Figure 1 hold the connectors in place
Cross section of nipple hub
O-ring groo
Filter
ves
Partial section
Flgure 2. Groove and hole pattern for Teflon bottom plate in filter
unit. The cross section view of the nipple hub is enlarged by X 2 relative to the 16.5-cm diameter disk
sheet). The filter is laid over the leaf-channel filter support plate and large black Viton O-ring, shown in Figure 1.Additional filter support, that could be a source of cross-contamination, is unnecessary. The 125-mm diameter by 2-mm deep recess in the upper Teflon disk allows even distribution of the incoming fluid. Both Teflon plates are backed by 164-mm diameter by 12.7-mm thick aluminum plates. The hand vacuum pump is manufactured by the Nalgene Labware Division of Nalge Sybron Corporation. The legs on the unit are easily removed for backpacking. The ends of the tie-down bolts are expanded so that the brass butterfly nuts will not fall off. T h e aluminum tubing sleeve, shown in Figure 1on one of the 500-mL Nalgene bottles, guards against bottle collapse when filtering very hot water. The snap-in nipples for line connections to the lid for the sample bottles were machined from nylon. The regular sample bottle lids are replaced after filtration and taped to guard against loosening during transport. Total unit weight without lines or bottles is 3.5 kg.
Figure 2 shows the machined groove pattern of the lower Teflon plate. These grooves are “round-bottomed” to facilitate cleaning. A Tygon line is connected to the reverse side of each Teflon plate via a small nylon nipple and Viton O-ring to ensure vacuum integrity. The eight central holes shown in Figure 2 lead to a nylon nipple connector which fits into a mating recess on the reverse side, as shown in Figure 3. Two filtration units have been built as described and used extensively in geochemical studies of the north-central Nevada desert (1-4).The units were found to be rugged and reliable.
LITERATURE CITED H. R. Bowman, A. J. Hebert, H. Woilenberg, and F. Asaro, “A Detailed Chemical and Radioactive Study of Geothermal Waters and Associated Rock Formations with Environmental Implications”, presented at the University of Missouri-Columbia, Conference on Nuclear Methods in Environmental Research, July 29, 1974 H. R. Bowman, A. J. Hebert, H. Woiienberg, and F. Asaro, ”Trace Minor and Major Elements In Geothermal Waters and Associated Rock Formations (North Central Neveda)”, presented at the Second United Nations Symposium on the Development and Use of Geothermal Resources, San Francisco, Calif., May 1975. A. J. Hebert and H. R. Bowman, “Nondispersive Soft X-Ray Fluorescence Analyses of Rocks and Waters”, in the proceedings of the Second United Nations Symposium on the Development and Use of Geothermal Resources, San Francisco, Calif., May 1975. H. A. Woiienberg, “Sampling Hot Springs for Hot Radioactlve and Trace Elements”, presented at the US. Environmental Protection Agency Workshop on Sampling Geothermal Effluents, Las Vegas, Nev., October 20-21, 1975.
RECEIVEDfor review October 18,1976. Accepted December 9,1976. This work was done with support from the U S . Energy Research and Development Administration.
ANALYTICAL CHEMISTRY, VOL. 49, NO. 4, APRIL 1977
673
