A Method for the Introduction of Unstable, Solid Metallic Chlorides onto Gas Chromatography Columns C. P. Ellis, Department of Chemistry, The Universily o f Natal, South Africa
, li-ho attempted to sepaK rate t'he( I )pentachloiides of niobium CLLER
and tantalum by introducing them into the gas chromatography column in solution with carbon tetrachloride, found that the temperature of the sample injection unit did not ensure immediate vaporization of the solute, which meant that the material did not enter the column 3s a plug. This resulted in excessive peak broadening. He also commented that the greatest difficulty in this work (chromatography of metal halides) is i,he preparation and introduction of mcasured samples under anhydrous conditions. TT'ork along similar lines in these laboratories confirmed the above observat'ions. Small qwintities of niolium(V) and tantalum( T') chlorides are almost instantaneously converted into the oxychlorides or oxides if thej- are nlloived to come into contact n-ith moist air, and for efficient vaporization, the preheater temperature, must exceed the boiling point. The Fimple apparatus described below n-as designed to overcome these difficulties and was found to operate satisfactorily. r7 1he lirinciple is as follows : The small glass tube labelled H in Figure 1 is partly filled (in a d r j box) with the finely powdered substaiice to be tested. The tube is then stoppered, rT-eighed, and attached to this apparatus by means of a short length of polyethylene tubing. At,tachment should be effected within a nitrogen-filled plastic bag to exclude air and moisture. Thl: carefully dried carrier gas, admitted st G, should be flowing out through thl: tap, I , prior t o and during attachment. The t a p is then closed. Before introduct'ion of a sample into the column, the appsratus must be carefully dried and the carrier gas allowed to fill the c'mtainer, F , b y withdrawing the plungcr, E , beyond the exit tube, D . Both D and G should be connected to phosphorous pentoxide drying tubes, the small crucible, J , should be in the position shown in the figure. and the nickel :,Doon withdrawn to" the point M. T o effect introduction of the sample into the preheater of the chromatonraphy column, both taps are openea, the small spoon, L, is pushed forward over the crucible, J , and through the key of tap, I , into the p m d e r contained in the tube, H . The full spoon is then withdrawn until i t ~ e a c h e s a point immediately above the crucible, J , when
it is reversed by twisting the metal rod nhich supports it, thus spilling its contents into the crucible. Finally the spoon is withdrawn to Jf, both taps are shut, and the crucible is pushed forward into the preheater by means of the handle, B , until i t reaches the column packing. Should additional heating be required, a n electric current may be passed through the element wires which support the crucible. The weight of sample used can be found by detaching the container, H, in an atmosphere of dry nitrogen as described above and then reweighing it. Apparatus. T h e t a p s and '/(-inch i.d. tubing were made of borosilicate glass. When constructing t h e apparatus i t is necessary t o ensure t h a t t h e holes in t h e wide-bore taps are aligned t o allow free passage of t h e nickel rod and spoon. T h e cross piece, H S ,must be connected t o t h e upper half of t h e section A K t o allow t h e spoon t o pass freely just above t h e top of t h e crucible in IIS. The crucible was constructed of the mineral lavite (wonder-stone). The upper portion was bowl-shaped, about 0.32 em. in diameter and 0.16 em. in depth. Below the bowl was a pedestal around which were wrapped tivo turns of fine, electric heating wire. This wire served to support the crucible in addition to heating i t when required. The crucible was baked in a pottery kiln for 12 hours previous to use to remove any volatile impurities which may have been present. The heater element was n elded to two stout nichrome wires, F , each 12 em. in length which, after passing through the cyl-
inder, E , nere connected to copper leads, A , and these in turn were passed through a rvooden plunger, B. The element wires were heated from a 10-volt supply regulated by a rheostat. The cylinder, C, was constructed from Perspex. It had a n outer diameter of about 1.25 em. and was accurately bored to contain a Perspex cylinder, E , 1.0 em. in diameter fitted with two rubber O-rings made to slide readily \vithin the outer tube and to maintain a gas-tight joint. The cylinder was connected to the glass tube by a short length of polyethylene tubing. hrrangements were made for clamping the wooden handle in any desired position. The nickel spoon was trough-shaped, and its approximate dimensions nere: length, 0.3 em.; width, 0.25 cm.; and depth, 0.1 em. An average filling n i t h SbC1, weighed about 0.002 gram. Considerably less powder could, of course, be taken if desired. The nickel (or stainless steel) rod supporting the spoon had a diameter of 0.14 cm. A good air-tight joint was formed simply by forcing the pointed end of the nickel wire through a rubber stopper, N, before inserting this into the tube. (If the wire does not run easily it may be rubbed with a little glycerine.) NOTES
This device keeps unstable, solid substances available for introduction onto the column and avoids the difficulties encountered when each sample has to be sealed in a capillary tube. The device also eliminates the use of a
-' I*
H
0 t
K
Figure 1.
Apparatus for introduction of solid samples onto gas chromatography columns VOL. 35, NO. 9, AUGUST 1963
1327
solvent nhich, in addition to increasing the bulk of a sample, may lead to undesirable side reactions or contamination. As a result of the heat provided by the preheater, augmented by direct heating of the crucible itself, the sample is very rapidly volatilized and, therefore, more likely to enter the column as a plug than would otherwise be the case. Manipulation of the spoon can be readily achieved with a little practice and the average size of the sample judged fairly accurately. As described above, the actual amount introduced
into the column can be ascertained by weighing; however, because of the possibility of adherence of particles to the interior of the spoon, the weighings are not very accurate. The method is, however, suitable for qualitative or preparative work. The dryness of the apparatus may be tested with niobium pentachloride, which turns from yellow to white if the least trace of moisture is present. The apparatus is inexpensive, easy to construct, and may be readily cleaned. As designed, the sample port is intended for attachment to a horizontal column.
A device for introducing a dilute solution of a volatile solvent onto gas chromatography columns, which aho makes use of a small mounted spoon. has recently been described by Renshaw and Brian ( 2 ) . LITERATURE CITED
(1) Keller, R . H., J . Chromatog. 5, 225 ( 1961). (2) Renshaw, -4.) Brian, L. A . , Ibid., 8,
343 (1962).
A Research Fellowship, awarded by the South African Atomic Energy Board, enabled this work to be undertaken.
Fractionation of Fine Particle-Sized Ion Exchange Resins Basil Vassiliou and Robert Kunin, Rohm & Haas Co., Philadelphia, Pa.
T
THE
A CG-120
PRESEKT
time, Amberlite
(Mallinckrodt Chemical Works, Cat. No. 3339) is employed extensively for the purpose of obtaining the necessary 20- to 40-microns cut required by the Spackman, Stein, and Moore (2) procedure for the automatic analysis of amino acids. Although the procedure is widely used, difficulty has been experienced in obtaining the required particle-sized resin in quantity. Since the screening of such small particles is practically impossible, a n elutriation process was developed which is essentially a modification of the method devised by Hamilton (1). The procedure has the advantage of eliminating much of the time previously required and offers the possibility for obtaining different particle sized fractions simultaneously. By using a combination of two separatory funnels with different maximum diameters in series, one can employ the Hamilton procedure and obtain the desired cut in a single step. The design of the apparatus is given in Figure 1. The calculation of the input flow rate was made by using Stoke's law
VBtcke
Input flow rate (cc./minute)
Figure 1. Diagram of elutriation apparatus used for fractionation of resin
case in which the particles n-ith diameter greater than 40 microns are to be retained in the loner vessel. In this study, the loiver vessel had a maximum radius of 7.65 em.
rR2max
X
Vltake
where R,,, refers to the maximum radius of the separatory funnel. The input flow rate was first calculated for the ANALYTICAL CHEMISTRY
(2
2(1.27 - 1.0) X x 10-312 x 980 x 60 9 x 0.00s94
-
= * R 2 x VStokea 3.14 X (7.65)2 X 1.573 = 289.9 = 290 cc./minute
=
9 X 0.00894 0.395 cm./niinute
Tr
EXPERIMENTAL W O R K
T-tnput
and the relation
2 X (1.27 - 1.0) X (1 X 10-s)2 X 980 X 60 -
I
1 . 5 2 cm./minute
V : settling velocity a: radius of particle d l : density of particle d0: density of medium 7: viscosity of medium g: gravitational constant
=
and
v8toke =
where
1328
fraction of 20 to 40 microns a t the above flow rate was calculated as follows:
A.R. 400- to 600-Mesh
I n other n-ords, a t a flow rate of 290 cc. per minute, particles greater than 40 microns will be retained in the lower vessel and those smaller in size will pass up into the upper vessel. The greatest diameter of the upper vessel required to retain a desired particle size
Using the above data, the apparatus described in Figure 1 was constructed. At a point just above the stopcock of the lower vessel, a sintered-glass plate (coarse porosity) was inserted for the purpose of supporting the resin and to reduce the axial streaming. This made it possible, for all practical purposes, to assume a linear uniform velocity, Vup. The apparatus was clamped vertically and the input was connected with a source of deionized water. A flow meter was used to measure the flow rate. The output was filtered (medium-porosity filter paper) to separate the outflow fine (less than 20 microns) resin which enabled one to recycle the water. A centrifuge pump was used to recycle all the water in the system. The desired flon- of 290 cc. per minute M-as arranged by adjusting the capacity of the pump. The resin [Amberlite CG-120 A.R. 400- to GOO-mesh (Rlallinckrodt)] was pretreated by suspending the material in water to hydrate the resin and breakup any clumps that were present. For each run, a sample of 350 cc. of resin was loaded into the lower vessel and water was passed upflow a t the calculated flow rate. After 90 minutes, the effluent water of both vessels was clear and the run vias terminated.
