standards was determined by several methods in several different laboratories. The results of the measurements are presented in Table I ; they give a good idea of the sensitivity of the system and the reproducibility of measurements a t various levels of oxygen content. The column titled “Rel. std. dev.” represents the relative standard deviation of the normalized gamma ray counts; this quantity was calculated from 10 measurements which were made on each sample. The column titled “Total rel. std. dev.” represents the relative standard deviation of the measured relative oxygen content of each sample; this was calculated from the usual rules of error accumulation.
Some aspects of Table I merit special mention. Sample Be-7 weighed 1.44145 grams; thus, 11 p.p.m. of oxygen represents a weight of only 16 kg. of oxygen. Since beryllium is a lowdensity metal, 11 p.p.m. of oxygen in the same size sample of another metal could correspond to considerably more oxygen and a proportionally higher count rate. The standard deviation of 11 p.p.m. of oxygen would decrease then as the density of the sample increased. Conversely, considerably smaller relative oxygen contents could be measured with the same standard deviation with higher density metals.
ACKNOWLEDGMENT
The authors are grateful to Charles D. Houston, Wright-Patterson A.F.B., Ohio, for the beryllium samples and titanium standards which were used in this work.
LITERATURE CITED
(1) Anders, 0. U., Briden, D. W., ANAL. CHEM.36, 287 (1964). (2) Bame, S. J., Haddad, Eugene, Perry, J. E., Smith, K. R., Rev. 81%.Instr. 29, 652 (1958). (3) Mott, W. E., Orange, J. M., ANAL. CHEM.37, 1338 (1965). (4) Steel, E. L., Meinke, W. W., Ihid., 34, 185 (1962).
Pulseless High-pressure Pump for liquid Chromatography R. E. Jentoft and T. H. GOUW, Chevron Research Co., Richmond, Calif.
1“
HIGH-PRESSURE liquid chromatography, the eluting solvent is generally pumped into the column by a reciprocating piston or bellows pump. Pulses generated by this pump can often be discerned by t’he detector. Besides introducing difficulties in the interpretation of the detector output, pulses also have a detrimental effect on the separating efficiency of the column. A major portion of these pulses can be eliminated by the use of surge tankse.g, , spring-loaded bellows connected to tees in the line between the pump and the column inlet. But even careful design n-ill not remove all pulses from the flow pattern and rather complicated and/or large surge tanks, with concurrent large holdup of material, are necessary to reduce the level of the flow variations to a negligible level. I n addition, damage to this pump and surge system is feasible if the outlet line is accitlentally blocked. TT’itl.1 the pump described here, high pressures up to 1000 p.s.i. can be generated at the outlet of the pump. I n comparison, many of the commercially available pumps are incapable of opei,ating above 100-1i.s.i. pressure. Delivery into the chromatographic s>.stem can be carried out without any discernible pulses for any length of time and any amount of solvent. Accidental blocking of the outlet line does not damage the pump a t all. Construction is simplei, than reciprocating plunger pumps of equivalent rating.
cury as the displacing agent prevents the dissolution of the air in the solvent. The outlet of the pump is on the top of Vessel A . For operation up to 250 p.s.i., a dual back-reference flow controller with integral micrometering valves (Millaflow No. 9986 220) is mounted between this outlet and the inlet of the chromatographic column. Because these type flow controllers are currently not available for higher pressure ratings, a fine metering valve is used for work at higher pressures. The pressure-reducing valve in the air line is adjusted to yield a pressure about one and one-half to two times the desired inlet pressure to the column, but not less than 100 p.s.i. to minimize the effect of the variations in the mercury levels. Prior to introduction into the pump, the solvent in the external reservoir is heated by a n infrared lamp. This degases the liquid sufficiently to
prevent air from coming out of solution in the column and creating artifacts in the chromatogram. At the normal mode of operation, neither of the threeway solenoid valves is energized. The air pressure, which is now connected to B , is transmitted through the mercury to the solvent in A . There is vacuum on D, and C is being refilled from the external solvent reservoir. Mercury rises in A as solvent is delivered to the chromatographic column. As soon as the mercury in Vessel A comes in contact with the upper electrode, the solenoids are energized. B is now connected to atmospheric pressure or to a regulated pressure somewhat lower than the operating air pressure in D. The latter is the desired mode of operation a t high pressures. The air pressure, which is now on D, refills A from C and, a t the same time, keeps up the uninterrupted delivery of the solvent at the External RSe22r Check Valves
T Relay
-Gravity Type Check Valves
DESCRIPTION AND OPERATION OF PUMP
Pressure Reducing
h schematic drawing of the unit is given in Figure 1. Four %inch by 8-inch stainless steel reservoii s, constructed from pipe nipples, are half-filled with m m u r y , the displacing agent. High pressure air is used as the source of operating pressure. The use of mer-
N.C.
To Atmosphere c_jt 1 3-Way Solenoid Valves
Figure 1.
4
ommon N.C.,
@ @
Pulseless high pressure pump VOL. 38, NO. 7, JUNE 1966
949
P is for upper m e r c u r y contact Q i s for lower m e r c u r y contact
I
S i s connected to m e r c u r y
1wkn
Min. Neon Panel Lamp W i t h Side Opened Ciarex T m
-Relay Line - Live
Figure 2.
Wiring diagram of relay
adjusted pressure to the chromatographic system. As soon as the mercury in A drops below the lower electrode, the solenoids are de-energized, and the pump assumes operation at the normal mode. Spring-loaded check valves in the solvent lines ensure the correct direction of flow. Gravity-type check valves above the cylinders prevent mercury from getting out but pass solvents in both directions. We have found it necessary to introduce a n impedance to flow between the output lines and the solvent reservoirs, among others, to prevent these check valves from slamming shut during the change between the cycles. Microporous disks of Kel-F have been found satisfactory for this purpose. Figure 1 shows the locations of these disks. The electrodes in A are 0.047-inch
stainless steel rods which are mounted through a modified Conax packing gland assembly which is sealed a t the base with epoxy cement. T o provide for the cycling between the two mercury levels in A , we have modified a commercially available "Solid State Relay," obtained from Scientific Kit Co., so the relay can be locked up. This alteration is required because the initial electrical contact, which starts the refilling of A , is broken as soon as the refilling operation is initiated. The wiring diagram is given in Figure 2. As the solvent in C should account for both the filling of A and the delivery to the chromatographic column during the time of filling, the displacement in this vessel should be larger than the amount displaced in A between the two electrodes. For the stated dimensions, flows u p to 100 ml. per minute have
been attained. For larger capacities, C and D should be larger than indicated. No major problems should be encountered during scaling up. The output pressure will vary with the heights of the mercury levels. To keep this variation negligible in relation to the output pressure, increase in size should preferably be found in increasing the reservoir diameter instead of the length. The limit is reached when the pressure rating of the vessel falls below the desired operating pressure. The 2-inch stainless steel nipples are rated at 3000 p.s.i. All the Swagelok connections used throughout the pump and the thick-walled l/r-inch stainless steel tubing have ratings far in excess of this number. The maximum operating pressure is determined by the accessory equipment-Le., the solenoids and the flow controller. Commercially available items are rated up to 250-500 p.s.i.; and to go to higher pressures, specially constructed equipment may be necessary. It is, however, not difficult to achieve operating pressures up to 1000 p.s.i. I n comparison, a piston pump with the equivalent rating would have to be much heavier in construction. Operation of the pump has been carried out a t pressures up to 1000 p s i and flow rates up to 100 ml. per minute with no discernible changes in output flow or output pressure during the different cycles of the pump. ACKNOWLEDGMENT
The authors are indebted to J. F. Johnson for helpful discussions and to W. C. Eaton for assembling and testing this pump during initial development stages.
The Purity, Properties, and Analytical Determination of 4-sec-Butyl-2-(ac-methylbenzyl)phenol 8. Z. Egan and W.
D. Arnold,
Oak Ridge National Laboratory, Oak Ridge, Tenn.
COMPOUND 4-sec-butyl-2- (aT z t h y 1 b e n z y l ) p h e n o l (BAMBP) has been used as a reagent in the analytical determination of cesium and rubidium (18), in process applications for the extraction of cesium from reactor waste solutions ( 2 , 11, 16, 17) , and for the recovery of cesium and rubidium from ore leach liquors ( I ) . These applications require that the purity and properties of the reagent be known, and that a reliable method be available for the determination of its concentration in solution. This paper is concerned with the identification of impurities occurring in largescale (10 to 50 lb.) preparations of BAMBP, the estimation by distillation and gas-liquid chromatography of the concentrations of the impurities, the determination of some of the chemical and physical properties of BAMBP, the development of a spectrophotometric method for accurately measuring the
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ANALYTICAL CHEMISTRY
concentration of BAMBP in various diluents, and a comparison of this method with an existing potentiometric method. DISTILLATION O F BAMBP A N D IDENTIFICATION O F IMPURITIES
An Aerograph Autoprep Model A-700 gas chromatograph was used to obtain chromatograms of 1M solutions of BAMBP in benzene or in diisopropylbenzene. The 1/4-inch X 20-foot copper column was packed with 60/80 mesh Chromosorb, treated with hexamethyldisilazane, and then with 20% silicone SE 30 rubber. Column temperature was programmed from 140" to 245' C. Helium flow rate was 65 ml./minute a t 50 p.s.i. The similarity of the chromatograms of different batches of BAMBP indicated that the same impurities occurred, but in different amounts, in the batches tested. A chromatogram of the most impure batch of BAMBP is
shown in Figure la. The different batches contained 2-401, of impurities more volatile than B.4MBP and 2 4 % of impurities less volatile than BAMBP. Samples of BAMBP were fractionated by distillation a t reduced pressure in a Podbielniak distillation apparatus, equipped with a 1- X 36-inch column, packed with Heli-Grid packing. I n two separate runs, a colorless B h h I B P product was collected a t 186" f 1" C. (6 mm. of Hg) and 207" i 2" C. (15 mm. of Hg). Distillation was discontinued during collection of the BAhlBP product, leaving unrecovered BARIBP and any higher boiling impurities in the still pot residue. Comparison of the chromatograms of commercial BAMBP and the distilled product shows that distillation removed most of the impurities (Figure 1). The purity of the distilled product was estimated to be greater than 98% BAMBP. During the synthesis of BARIBP,
