R EDL Temperature
Controlled System #I
EDL Temperature C o n t r o l l e d System +2
Figure 1. Block diagram of optical system containing power divider for thermostated electrodeless discharge lamps in atomic fluores-
cence spectrometry
Table 1. Detection L i m i t s of Several E l e m e n t s in A t o m i c Fluorescence Flame (Air/H2) S p e c t r o m e t r y Using Electrodeless Discharge L a m p s Operated w i t h T w o “A” A n t e n n a s Joined ‘viaTwo-Port Power Divider EDL Wavelength, temperature, Element
Ag Cd
Cr cu Hg Mg Ni Pb Sb Sn Te T1 Zn
nm
“CQ
328.1 228.8 357.9 324.8 253.7 285.2 232 .O 405.7 231.1 303.4 214.3 377.6 213.8
580 420 475 430 50 470 65 255 150 110
Detection limits, en/ml This study
0.0008 0,001 0.01
0.002 0.01
0.00005 0.07 0.03 0.01
0.5
Best reported (Reference)
0.0001 (6) 0.000001 (6) 0.005 (7)
0.0005 (8) 0.02 (2) 0.00015 (9) 0.003 (10) 0.02 ( 2 1 ) 0.05 (12) 0 . 1 (13)
410
0.07
0.006 (14)
310
0.002 0.005
0.008 (6) 0.00004 (15)
400
a All EDLs except for Hg and P b were operated at 120-W microwave power or 60 W per E D L because of use of the power divider. The Hg and Ph EDLs were operated at SO W or 40 W per EDL.
each element (or compound) present in a lamp is largely uninfluenced by the presence of other elements (2). The T l and the multielement Cd/Zn/Se EDL were operated simultaneously with the power divider; switching the two lamps in the thermostated systems resulted in similar atomic fluorescence signals for a solution containing 1 Fg/ml of each element (signals within 8% for Cd, Zn. and T1 resulted for the two orientations). The P b and Hg EDL were operated simultaneously a t 40-W incident microwave power under both thermostated and nonthermostated conditions. Without thermostating, because of the low radiant output from the P b EDL, there was no observable AF signal, while for a 100 Fg/ml solution of Hg, without thermostating, there was a decrease of 10x in AF signal. There were not any noticeable problems or difficulties associated with using two thermostated EDLs with the power divider and a single microwave generator. The most obvious advantage with the use of thermostated EDL,s is the ease with which maximum spectral output from a n EDL can be obtained cia variation of the EDL temperature. Future work is planned for the use of a multiport power divider and a 800-W microwave power supply for the simultaneous use of several thermostated EDLs. Received for review August 22, 1973, Accepted Novenlber 19, 1973. The research was supported by AF-AFOSR1880-701.
High Pressure Gradient Chamber for Liquid Chromatography E. H. Pfadenhauer, T. N e wport
E. Lynes, and T. V. Updyke
Pharmaceuticais Internationai, lnc.. 7590 Monrovia Bouievard. Ne wport Beach. Calif. 92660
Gradient elution is a useful technique in many applications of chromatography, and is especially important to high pressure liquid chromatography where speed and resolution of analysis are major factors in justifying the expense of the necessary equipment. In our work, we were interested in doing rapid, high resolution determinations of oxypunnes in blood plasma, and wished to explore the possibility of using gradient elution in high pressure liquid chromatography. In cases where the gradient can be made up at atmospheric pressure, the problem is trivial. However. if a screw-driven syringe type high pressure pump is used, the gradient must necessarily be made a t high pressures.
Commercial gradient accessories include a second high pressure pump (Sester-Faust 1200, Varian Aerograph 4200) or a complex arrangement of 5 high pressure valves, a holding coil. and a mixing chamber (DuPont 820). The device described here suffers from the limitation of being able t o deliver only a single convex gradient shape which is not usually the most desirable chromatographically, but is considerably less expensive than a second pump. entailing approximately only one-tenth the cost. The DuPont arrangement is not available as a separate unit. As seen in Figures l a and l b , the gradient device consists of a removable mixing chamber. and a cap through which is drilled a n inlet from the high pressure pump and A N A L Y T I C A L CHEMISTRY, VOL. 46, NO. 4 , APRIL 1974
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MILLILITErlS
Figure la. Assembled and disassembled views of the gradient
chamber
0s ELLANT
Figure 2. Gradient shapes calculated for chamber size of 5, 10, and 30 ml with a column dead volume of 7 ml Circled points are of t h e observed gradient for a lo-ml chamber Volume asdi '' ' "
'
Top: Assembled as viewed from the underside. Bottom: (lower left to
right) Retainer; mixing chamber with "0' ring: cap
Figure 1b. Cutaway schematic of assembled gradienf chamber
a n outflow to the column. Stainless steel, type 303, was used throughout for corrosion resistance and relatively easy machineahility. Tube fittings were 316 stainless steel and were purchased from Parker-Hannifin Company. "0" rings (Parker Seal Company) were selected for solvent resistance. Polysulfide was found to be an excellent material for "0' rings, showing stability against diethylether, alcohols, water, and dilute acetic acid. Unfortunately, polysulfide is a rather soft material and not resistant to mechanical abrasion. Teflon-covered silicone "0" rings would give a wider range of chemical resistance if desired. The overall seal design gave excellent performance, and ether was held under 5000 psi with no apparent leakage. The size of the holes in the outlet part of the cap, as well
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46. NO. 4, APRIL 1974
as tllr LuvL115 cyIIII~LIIyIID, uLlyulu vr DlllLlll as possible to minimize dead volume. In actual operation, the chamber is filled with the starting eluant, and a solvent of higher elution power is pumped in a t high pressure a t the desired flow rate. Mixing is accomplished with a small Teflon-coated magnetic stirring bar placed in the bottom of the chamber. Most stainless steels are nonmagnetic and there is no difficulty with the stirring operation. During routine use of the system, retention times of compounds after repetitive injections were found to remain stable, indicating satisfactory mixing in the chamber. The actual size of the chamber is dictated by the shape of the gradient desired. A larger chamber will give a less steep gradient and vice versa. The size illustrated here has a 10-ml capacity, and the theoretically calculated and actual gradient delivered by the device are illustrated in Figure 2. The observed points were obtained by using a solvent in the high pressure pump of higher UV ahsorhance than the initial eluant in the gradient chamber, and monitoring W absorhance of a column effluent. The device has also been found useful in ''slurry packing" small diameter packing materials into columns. With this method, the packing material is added to a carrier solvent in the desired slurry consistency and then poured into the mixing chamber. The empty column is attached to the outlet of the cap, the magnetic stirrer turned on, and the slurry pumped through a t high pressure.
ACKNOWLEDGMENT. The authors wish io acknowledge the help of R. F. Updyke of Engineering Specialists, Canoga Park, Calif., in the design of this instrument. Received for review August 6 , 1973. Accepted October 3,
