Safe, Simple Method of Opening Irradiated Silica Ampoules Ray Porritt and Malcolm Thackray, Australian Atomic Energy Commission, Research Establishment, Lucas Heights, Australia
w
PERFORMING irradiations in high-flux nuclesr reactors, it is frequently necessary to seal samples in small silica tubes. Since the tubes and their contents become highly radioactive and often generate appreciable gas pressures, the safe opening of the tubes and the quantitative recovery of their contents often presents a difficult problem. When the contents constitute a single liquid or solid phase, the ampoule can be crushed in a suitatlle metal or plastic beaker using a plastil: rod and annular beaker cover. Hon ever, with semisolid biological samples (blood, butter, etc.), this technique often gives poor recovery and leads to very great difficulties when, as frequently happens, the next step is a per:hloric acid oxidation of the organic r a t t e r . Moreover, the technique is not easily adaptable to remote operatior! from behind a lead shield. While performing :t series of activation analyses on butter and butterfat, we developed a very safe technique which gives quantitzttive recovery of the ampoule contents and can be easily HEN
H
-POLYETHYLENE STOPPER
1 LAB-JACK
w Figure 1. Apparatus irradiated samples
for
opening
operated from behind a 4-inch lead shield. Briefly, the method consists of crushing the ampoule in a vertical piece of flexible plastic tube,
N. S. W.,
The steps are as follow (see Figure I.): Select a piece of clear plastic tubing (PVC or polythene) about 5 inches long and having an i.d. about twice the external diameter of the ampoule to be opened. Place a suitable polythene stopper in the lower end and loosely support the tube vertically in the V of a strong laboratory clamp. Clean the ampoule of all external contamination and drop it into the plastic tube. Move the plastic tube upward until the ampoule is opposite the clamp, and gently tighten the clamp onto the ampoule. Transfer the polyethylene stopper from the bottom of the tube to the top. By means of a laboratory jack, raise a beaker into position around the lower end of the plastic tube. Tighten the screw clamp until the ampoule breaks. Remove the polyethylene stopper, and slacken the clamp so that it only just supports the plastic tube. Rinse through with acetone or other suitable solvent, and boil off the acetone before beginning a perchloric acid oxidation. Although this method uas developed to deal with semisolid biological samples, we now find it the simplest way of opening any active ampoule.
A Partition Sampler for Vapor Analysis by Gas Chromatography Ewan R. Colson, Research and Testing Department, Gas and Fuel Corp. of Victoria, 469 St. Kilda Rd., Melbourne, Victoria, Australia HAVE H.4D TO dequanritatively small amounts of comparatively high-boiling compounds such as naphthalene, in concentrations up t c about 0.45 mg. per liter, and thiophane (tetrahydrothiophene), about 0.03 mg. per liter, present in manufactured gas from various sources. Conventional methods of sampling and gas chromatographic analysis proved unsuitable, probably because of sorption of the compound of interest on the walls and fittings of the glass gas-sampling tubes used for transport of samples from the plant or pipeline to the labora1,ory. It is now believec that a suitable method of sampling gases prior to gas chromatographic antilysis for naphthalene, thiophane, or other compounds has been developed which overcomes sorption difficulties with gas-sample tubes and enables easy transport of samples. Tt-hile the partition sampler described was developed for tiampling directly from process pipelinea, it should offer advantages over the gel adsorbers described by Widmark and Widmark ECEKTLP,
R termine
WE
(1) for their applications-chromatographic analysis of vapors in air, and quantitative collection and reinjection of compounds separated by gas chromatography. EXPERIMENTAL
Procedure. The method comprises drawing a measured volume of the gas through a short metal tube which contains a suitable packing for quantitatively absorbing the compound of interest. The tube is then sealed and transported to the chromatograph. Here the carrier gas is temporarily shut off, and the sample tube is inserted between the carrier-gas supply and the column inlet. The tube is heated rapidly for about 5 seconds to change the equilibrium partition of absorbed substances between packing and vapor space, and the carrier-gas flow is restarted during the heating period. The compound of interest is separated and the peak is measured in the usual way. From a consideration of the principles of chromatography, the sampling method described is quantitative providing the gas-sample volume does not exceed the initial retention volume of
the compound of intcre>t on the packing uerd (at the temperature and flow rate of sampling). Kidmark and Midmark, in their technique for collection and reinjection of fractions from and into a gas chromatograph, have reported an average loss of 1.5% per collection-reinjection cycle for 1+1. samples of substances not irreversibly sorbed by the silica gel packing used. Sample Tube. After unsatisfactory experiences with activated charcoal and alumina, probably because of varying moisture contents, Silicone Oil (Embaphaee, X a y and Baker) on Chromosorb P (30- to 60mesh) has proved a suitable packing for the sampler. However, any stationary phase, liquid and stable over the necessary temperature range (in our case 20' to 150' C.), and any normal chromatographic support should be satisfactory for this purpose. Stainless-steel tubing is particularly suitable for containing the packing as its high resistivity enables fast, direct resistance heating with simple equipment. As an example, for thiophane, samplers of stainless-steel tubing, 4.1mm. i. d., containing 12.5 cm. of 30% Silicone Oil on Chromosorb P have proved suitable. The sample volume is VOL. 35, NO. 8, JULY 1963
1 1 11
limited to 100 ml. for ambient temperatures up to 37" C. The rate of sampling is 50 ml. per minute. The tubing has a wall thickness of 0.74 mm. and is heated by passing a current of about 90 amp. a t 1.3 volts for 5 seconds, whereby a temperature of 150' C. is attained in the center of the packing. This power can be obtained by parallel operation of two soldering-iron transformers with secondary windings intermittently rated (on 6 seconds, off 36 seconds) at 3.3 volts, 30 amp. The above sampler, when used for naphthalene, would pass a gas sample volume about 25 times that for thiophane before slippage of naphthalene would occur. However, the sampling time may be inconveniently long and the sample unnecessarily large for a sensitive detector. Hence a sampler containing less packing could be substituted (or one with a lighter liquid loading), so that a 100-ml. sample volume may be used. =in unnecessarily long partition sampler may quantitatively retain components of lesser retention volume than the component of interest, making unnecessary demands on the column used in the later analytical separation.
to the chromatograph and heated as described before.
Calibration, The partition sampler offers a neat way of introducing calibration samples into the chromatograph. It obviates the necessity of using an accurately known liquid volume of 1 pl. or less for calibration of sensitive ionization detectors. Although large dilutions of the sample component in a solvent may be required, the sampler can eliminate the solvent peak from calibration runs. An accurate dilution of the calibration substance is made in a pure solvent, so that a reasonable volume (10 or 20 pl.) of this calibration mixture will give a peak area approximating that of the samples. The solvent is chosen so that its vapor will break through the partition sampler (at room temperature) during the passage of a volume of air which is insufficient to elute the vapor of the calibration solute. To avoid possible evaporation losses, a slow current of air is also drawn through the sampler while the liquid is being injected into one end from a microsyringe. Then the partition sampler containing the calibration solute alone (and possible solvent impurities) is connected
CONCLUSIONS
The partition sampler provides an effective means of sampling naphthalene, thiophane, or other vapors in gases. The use of the partition absorber instead of the silica gel adsorber of Widmark and Widmark should overcome their reported difficulties with water vapor, and should prevent decomposition of lower alcohols, esters, ethers, and ketones which is caused by heating these substances on the gel. ACKNOWLEDGMENT
The author acknowledges the advice and assistance of G. M. Brown and other colleagues, and thanks the management of the Gas and Fuel Corp. of Victoria for permission to publish this paper. LITERATURE CITED
(1)
Widmark, K., Widmark, G., A c h
Chem. Scand. 16, 575, (1962).
A Convenient Mass Reference Plate for Use in Spark Source Mass Spectrometry F. Neil Hodgson, Monsanto Research Corp., Dayton, Ohio Michel Desjardins, University of Cincinnati, Cincinnati, Ohio William L. Baun, Aeronautical Systems Division, Wright-Patterson Air Force Base, Ohio
frequently encountered in spark source mass spectrometry is the accurate assignment of mass numbers to the lines observed on the photographic plate. Though mass reference plates which may be compared to the unknown plate are now available ( I ) , setting the magnetic field to duplicate exactly the dispersion of the reference plate masses is tedious and can be accomplished only after some experimentation. Additionally, reference plates are available for only a limited number of mass ranges. Therefore, it may be necessary to sacrifice needed resolution for the convenience of having a ready-made mass reference plate. A method of making a mass reference plate, which is sufficiently accurate for most line identscation, has been developed as a result of spark source studies performed on polynuclear aromatic hydrocarbons (6). This type of compound, when introduced into the spark, gives lines representing masses up to the molecular weight. Using coronene, CZJIl2, for example, an exposure of approximately 10-9 coulomb yields lines a t almost every mass unit up to mass 300. Since these lines arise, largely, from CI2 (mass 12.000) and H1 SE PRoBLEii
1 1 12
ANALYTICAL CHEMISTRY
(mass 1.00%) combinations, the lines are arrayed a t nominally whole mass number intervals. Lines a t masses much greater than the molecular weight of the compound can be obtained by increasing the exposure. For example, the spectrum of anthracene recorded a t IOp9 coulombs exposure showed lines up to the molecular weight, but the spectrum of anthracene, recorded at a coulomb exposure 20-fold greater, showed ions of masses up to the anthracene dimer. These additional lines can be used as mass references also. PROCEDURE
The technique for making the reference plate is quite simple. Electrodes, formed of high purity aluminum, are hollowed out and packed with a polynuclear aromatic hydrocarbon. Saphthalene is not satisfactory for this purpose because of its high vapor pressure, but anthracene, or any hydrocarbon of three or more fused rings, may be used. Exposures are made on a suitable photographic emulsion, using these electrodes to produce the spark. Either Ilford Q2 plates or Kodak SWR plates are satisfactory. After the plate is processed according to the recom-
mended procedure and dried, it may be placed on a viewing box and every 5th or 10th mass number labeled with a soft lead pencil or a crow quill pen. The strongest lines will be in the low mass region and three outstanding lines will be recognized as due to carbon a t mass 12 and to aluminum a t masses 27 (Al+)and 13.5 Csing these lines as guides, the other mass lines can be identified with little difficulty. The great advantage of this approach
t o the identification of mass lines is its flexibility. A reference plate may be made to cover any mass range. The reference scale may be made as the last exposure of the plate on which the lines to be identified occur. Additionally, instrumental irregularities, which might cause a mismatch with a fixed mass reference, will be compensated, because the same instrument and conditions can he used for making the reference plate as for running the samples. LITERATURE CITED
(1) Consolidated Electrodynamics Corp., Pasadena, Calif., 21-110 News Letter, Vol. 1, N o . 1, Jan. 10, 1963: (2) Hodgson, F. N., Desjardins, Michel, Baun, W. L., J . Phys. Chem. 67, 1250 (1963).
