Topics in..
.
Chemical lnstrumentatian Edited by GALEN W. EWING, Setan Hall University, SO. Orange, N. J. 07079
I
These articles are intended to serve the readers of THIS JOURNAL by calling attention to new developments i n the themy, design, or availability of chemical laboratory instrumentation, or by presenting useful insights a n d ezplanations of topics that are of practical importance to those who use, or teach the use of, modern instrumentation and instrumental techniques. The editor invites correspondence from prospective contributors.
LXXII. Recent Developments in Dr. Veening was horn in 1931 in The Netherlands. He lived in Instrumentation for Liquid ~ h r o m a t o g r a ~ h ~ 'Velp, Surinam for eleven years and came
Hans Veenina. D e ~ a r t m e n of t Chemistry, Buckneil University,
Since the last review on liquid chromatography (LC) in this series ( I ) , there has been an enormous increase in the amount of published work in this rapidly evolving field. A great deal of effort has gone into improved column technology (21, packings (3, 4), chemically handed phases (51, selectivity in LC (6, and many applications of LC to various chemical and biochemical problems. Basic aspects of modern'high performance LC have also been covered in several books and reviews (816). There have also been many noteworthy new developments in LC instrumentation: versatile LC units supplied with sophisticated gradient devices, improved high pressure pumps, and more versatile detectors are now available. It is primarily the latter aspect, i.e., instrumentation, which this report will emphasize. Some of the recent developments covered here include new gradient elution systems, improved high pressure pump, new detection systems which have been reported recently, unique mixed stream concepts utilized in "reaction detection" systems, specially designed liquid chromatographs for the separation of biochemical mixtures, and the latest commercially available LC units.
n,
GRADIENT ELUTION SYSTEMS Gradient elution or solvent programming is a technique used in LC whereby the composition of the moving phase is changed with time or elution volume. -
~
*The use of specific names of manufacturers and descriptions of their instrumentation does not imply endorsement, nor does the omission of any commercially available products imply an unsatisfactory appraisal. Descriptions of commercial instruments are listed al~habeticallvaccording to the name of the manufacture;,
(When the solvent composition is kept constant throughout a chramatographic run, the mode of operation is known as isoeratic elution.) Gradient elution, whether continuous or stepwise, can provide powerful selectivity effects and improved resolution in LC since the partition coefficients are strongly influenced by the nature of the eluent used. In a way, the technique is comparable to temperature
A number of devices have been developed for generating gradients. One of the most widely used is the versatile ninechamber Varigrad (17). This is a device, however, which requires excessive operator time in preparing the gradient prior to analysis. Recently, several gradient devices have been developed which can generate a variety of linear, exponential, and step-wise gradient profiles. Byme, Schmidt and Johnson have developed a gradient generator which consists of a time-proportioning electromechanical system whereby liquids from two reservoirs are mixed automatically by two electronically controlled proportioning valves (18). The valves are alternately cycled by electronic ramp generators to allow a prescribed amount of each liquid to flow into the miring chamber. The system controls gradient shapes, total gradient times and the initial and final gradient concentrations without equipment changes or calculations. A single pump is used. An automated two-chamber gradient device has been developed hy Chilcote, Scott, and Pitt (19). This unit has been mathematically designed to duplicate simply and repradueihly the performance of mare complicated devices. This gradient generator utilizes two wedge-shaped containers for liquids A and B as shown in Figure 1. The two eluents flaw simulta-
to the U S . in 1944. He obtained the B.A. in Chemistry from Hope College, Michigan and the M.S. and Ph.D. degrees in Analytical Chemistry fram Purdue University in 1955 and 1959. In 1958 he joined the faculty of Bucknell University where he is now Professor of Chemistry. In 1966-67 he was awarded a National Science Foundation Faculty Fellowship for a year of study and research in chromatography a t the University of Amsterdam, Holland, where he was associated with Professor J. F. K. Huher. During 1972-73 he was the recipient of a National Institutes of Health Special Research Fellowship far studying high resolution analysis of physiological fluids by high pressure ion exchange chromatography a t the Oak Ridge National Laboratory in association with Dr. Charles D. Scott. His research interests include high speed liquid chromatography of organometallic compounds, the aoolication of LC methods to clinieal problems, and gas chromatography. His work in LC has been supported by N.S.F. and P.R.F. In 1970 he served as Chairman of the Susquehanna Valley Section of the American Chemical Society. Dr. Veening's earlier review on "LC Detectors" was published in this calumn in 1970.
..
neously fram the respective chamhers into a common mixer. The cross-sectional area a t the top of the dilute eluent chamber (1) is large compared with that of the concentrated eluent chamber (2); however, the cross-sectional area a t the bottom of chamber 1 is small compared to that of chamber 2. Thus if chamber 1 is filled with A and chamber 2 with B, the concentration of A in the eluent will he large a t the start of the chromatographic run and (Continued on poge A4301
Volume 50. Number 9. September 1973
/
A429
Chemical Instrumentation small a t the end. Chamber shape determines the gradient profile. This device was used successfully for the gradient separation of carbohydrates (as their borate complexes) in hady fluids using the Carbohydrate Analyzer developed a t Oak Ridge (20).
Chromatec Gradient Elution Accessories The Model 60W accessory eonsists of a 2 liter reservoir, a storing chamber, a mixing chamber, and a series of valves, and can he used with a single pump. It delivers linear gradient profiles whose slopes can he varied. The accessory is shown in Figure 2. The Chramatec Model 8000 is a 2-pump gradient device which can generate a wide range of solvent programs by mixing two carrier components a t various rates. The extra pumping system also provides for multiple isocratic column operation, however, in gradient elution its main function is to pump the "B" liquid into a mixing reservoir. The Chromatec Model 8000 is shown in Figure 3.
Chromatronix Model 744 Solvent Programmer
F~gure 1 Alltomated two~chamber gradient device. Reprnted from ( 1 9 ) . w t h permission of the Jooroal of Chromalography.
A430
/
Journal of Chemical Education
This is a digital electronic controller for generating a wide variety of elution programs. It is used with two Model 740 pumps, each of which pumps one solvent of a binary mixture. The output from the pumps is combined and mixed so that the total flaw rate is the sum of the two rates and the composition is the ratio of the two rates. The programmer can also he used for flow programming with a single pump. This system is unique in that it has the capability of generating continuous, unlimited-volume gradients without detector noise. Concave, convex, and linear gradients. flow rates and initial and final times
Figure 2. Chromatec Model 6000 Gradient Elution Accessory.
can all be independently selected. The unit is shown in Figure 4.
DuPont Gradient Elution Accessory This gradient generator produces a eontrolled mobile phase composition from two liquids contained in separate solvent reservoirs; i t utilizes the principle described previously (18). The accessory is an automatic, electromechanical instrument far the generation of linear or curved gradients and can provide a programming rate of 1-10% per minute. Total time can he set from 10-100 minutes +5% an a 0-100% gradient. The unit can be incorporated into the DuPont 830 LC. (Continued onpageA432)
Chemical Instrumentation -
lnstrumentation Specialties Company (ISCO) Dialagrad
~
Hewlett-Packard Gradient Elution System As part of the Hewlett-Paekard lOl0B liquid chromatograph, both flow programming and gradient elution accessories are available. Automatic programming of flow or solvent composition is accomplished via a digital programmer. The program consists of 16 linear steps, each consisting of a flow value and a time increment. These values are entered through a keyboard and stored. A huilt-in processor then calculates the required changes as a function af time and controls the process during a run. A schematic of the gradient system is shown in Figure 5.
T h e ISCO Dialagrad achieves linear, curved or stepped gradients by differential pumping with two pumpheads specifically designed for accurate gradient formation with a solid state electronic digital programmer. Eighteen calibrated flow rates are set with positive stop switches. Three models (380, 382 and 384) are available. The Model 380 delivers gradients to 3200 ml/h at 50 psi; the 382 is capable of flow rates from 1 to 640 ml/h a t 200 psi; the 384 will farm gradients u p to 2000 psi with flow rates to 160 ml/h. The Model 384 is suitable for small bore, high pressure columns; all gradients are formed under pressure. The ISCO Model 382 Dialagrad is shown in Figure 6.
Figure 3. Chromatec Model 8000 Gradient Elution Accessory (shown with the Chromatec Model LC3100 Liquid Chromatograph).
LKB 11300 Ultrograd Gradient Mixer This instrument can mix simultaneously two or three liquids and it can be used to repeat, automatically, the complete chramatographie processes of equilibration, gradient production and column rinsing. The Ultragrad is a combination of an electronic control unit and a photoelectric scanner. The electronic unit controls either one or two-way valves, which are connected between the solution vessels and the mixing cell. The scanner consists of a combined light heam and photocell which immediately senses any changes in the light-reflecting quality of the area being scanned. T h e scanning is done over a rectangular window in which the gradient profile chart is placed. The photoelectric unit begins scanning from left to right until the run is completed. T h e actual mixing is controlled by signals which are relayed from the scanner. The Ultrograd has been described previously (21) and is shown in Figure I .
Micromeritics Gradient Elution Device Micrameritics' Model 7000 LC does not require two pumps for the gradient elution accessory. T h e 7000 with gradient is q u i p p e d with two sets of pistons, each set controls the flow of one solvent. The
Figure 4. Chramatrooix Model 744 (690) Solvent Programmer.
(Continued onpageA434J A432
/
.... . . .. . ~ .
Journal ot Chemical Educafion
instrumentation h
TS r*umn
woC.mm.r
... %
v'
LL Figure 5. Hewlett-Packard Gradient Elution ~yilem Schematic
flow of solvent from each set is controlled by the amount of hydraulic fluid it receives. The amount of hydraulic fluid delivered in turn is controlled by a distribution valve. The distribution valve is controlled by electronic circuitry. This grsdient device will automatically mix two solvents in any proportion and will automatically program the mixing of these solvents starting from any concentration and finishing a t any higher concentration; linear and exponential solvent curvatures can be generated. During gradient elution or isocratic operation "% strong concentratian" is continually displayed to 0.1% accuracy on a digital panel meter. The gradient can be performed in either the constant flow or constant pressure mode.
Packard Gradient System This gradient device can be included in the Packard Model 8200 liquid chromatograph. A special valve mixes the two solvents in response to pulses from the gradient controller. The valve opens, sequentialling the two solvent channels in a ratio proportional to the required solvent e m position. The percentage change of solvent ratio per unit time is set digitally by thumbwheel switches, and the unit also incorporates a light emitting diode display of the percentage composition of the solvent a t any time.
Perkin-Elmer Gradient Operation Perkin-Elmer supplies two gradient attachments. The inexpensive Model 1240 consists of a synchronous motor driven syringe which delivers solvent A into a cantinuously stirred low-volume degassing reservoir containing solvent B. Convex, linear and concave gradients can be obtained. The Model 1220 employs two sepa-
.
rate pumps which can be charged with different solvents and by means of digital control, the precise blend desired can be dialed into the drive control. To create a convex, linear or concave gradient, one pump begins to pump a t the preselected flow rate while the second is stopped. As the first pump is reduced in speed, the second picks up speed so that the two separate flow rates always add u p to a constant total flow rate. Total time to cornplete the solvent program can be selected from 1 to 1100 minutes. Initial and final isacratic hold periods, digital display of the gradient, and retrace control are also
Pharmacia Gradient Mixer The GM-1 Gradient Mixer is designed primarily for linear gradient elutmn Ion exchange chromatography. It consists of two identical 250 ml reservoirs which are attached an a base plate. One reservoir carries a stirring motor and a blade configuration stirrer as shown in Figure 8. The base plate is fitted with a reservoir connection valve and a needle flow control valve. Materials which come in contact with liquids are polymethylpentene, polypropylene, and fluara rubber. The GM-1 mixer can be used for aqueous solutions of commonly used buffers, organic acids, alkahs, and alcohols. The mixer can be autoclaved without the motor.
Technicon Autograd The Autograd consists of a base and motor assembly and 9 interconnecting 150 ml chambers, each provided with a motordriven polyethylene agitator. The chambers are molded of clear acrylic plastic and are recommended for use with aqueous solutions. The chambers are interconnected by individual, spring-loaded, positive action valves. Extra chambers can be added. Provision is also made for purging with an inert gas. This module can supply smooth, uninterrupted, reproducible gradients of pH and/or ionic strength from the various buffers contained in each chamber. The gradient profile will depend on the composition of preselected buffers in the chambers. The Autograd is part of the Teehnicon Amino Acid Analyzer.
Varian Flow and Solvent Programmers Varian offers a linear solvent programmer as well as a multilinear solvent/flow programmer (MLSP) far use with its Model 4200 liquid chromatograph. The solvent-flow programmer is a module
AH-
&--. -
-
.5
\
6,@'
:,, Figure 7 , Figure 6.
A434
/
ISCO Dialagrad.
Journal of Chemical
ducat ion
LKB 11300 Ultragrad.
(Continued onpageA436J
Chemical Instrumentation L
shown in Figure 9.
I
Figure 8.
Pharrnac~aG M ~ Gradient l Mixer.
which directs the pump by programming the eluent flow rate, continuously increasing it during the chromatographic run. This effectively reduces analysis time. T h e MLSP gradient system provides for gradient elution a n d consists of a solvent/flow programmer, a multilinear module and two 5000 psi pumps with their flow control and pressures monitored. Convex, linear and concave gradients or combinations of these can be formed. The rate of change of solvent composition is selected by means of a matrix pin hoard. Regeneration of the
A436
/
Journal of Chemical Education
olution per unit time, hence there is a tendency to use smaller diameter columns, smaller particle diameter packings, and higher column inlet pressures. Such col-
Waters Model 660 Solvent Programmer Both gradient elution and flow programming modes are possible with this unit. The Model 660 Programmer connects with and functions as the central control module with one Waters Model 6000 P u m p for flow programming or two Model 6000 pumps for gradient elution as well as solvent scouting when refining a separation. T h e solvent programming or gradient elution schematic is shown in Figure 10. The combined flows are fed to a mixer and then to the column. T h e Model 660 Solvent Programmer, shown in Figure 11, offers a selection of eleven programs for flow or solvent programming: one linear, two step, four convex, and four concave. Other controls enable selection of starting and ending solvent composition, program duration, and total flow rate. Operating controls include Run, Initial Conditions (reset), Hold, Reverse Flaw, and Stop Flow, Indicator lights key initial and final conditions while meters display percent elapsed program time and composition during the run.
PUMPS Efforts in LC continue to be directed toward higher performance, i.e. higher res-
Figure 9. Varian Multilinear Solvent Program-
mer.
mEconoEm
Figure 10. Waters Solvent Programming and Scouting Schematic. umns require pressures of up to 5000 psi and accordingly there has been a trend tr build oumos with hieher oressure eaoabil. great deal of interest in producing pulse. less and constant flow pumps. Two difierent types of pumps can bt used in LC: constant pressure (direct pres. surization of the mobile phase with ar inert gas) and constant flow. In constant flaw pumps, the flow is held constant anc the pressure is allowed to vary as columr permeability changes. These pumps pas. sess as their main advantage, the fact thal a change in pressure has little effect on 2 chromatographic separation, whereas 2 change in flow affects retention time, reso. lution, and baseline characteristics. Can. stant flow pumps can he further subdivid. ed into "reciprocating" and "single dis. placement" types. In the reciprocatinc pump, pressure changes due to viscositj changes cause leak rates in the check valves and piston packing materials to re. sult in complex flow behavior. For the sin. gle displacement (syringe type) pump, tht flaw is independent of fluid properties. Ex. eellent reviews and discussions of the prin. ciples of solvent delivery systems has beer given by MacDonald (9, 10). A number a: new pumping systems which are availabh or have been reported will he discussed. A novel pumping system involving r continuous gas displacement pump (CDP has been reported by Karger and Berrj (22). The system pressure in this pump i: maintained constant with a gas regulator and a pulsating piston pump supplies tht flow. This flow is split between the mair flowstream and a controlled leak sectior which recycles the excess solvent to a res.
Figure 11. Waters Model 660 Solvent Programmer. (Continued onpogeA441)
Volume 50, Number 9, September 7973
/
A437
Chemical Instrumentation p
~
~
-
~
ervair. The CDP controls pressure to f0.5%. The advantages of the classical gas displacement pump, i.e., no pulsations, inexpensive construction and a n equivalent detector noise level, are realized with this system. An increasing number of commercially available high pressure pumps are now marketed by several companies. These generally fall into the two categories of "reciprocating" and "single displacement."
Beckman Accu-Flow Pump Beckman Instruments offers the Aceuflow pump as part of its amino acid analyzer. It is a reciprocating, positive displacement pump. The single speed model can he adjusted from 3 t o 160 ml/h; a two
speed version extends the available range to 625 ml/h. Flow rate accuracy is *0.1 ml/h in 24 hours under a back pressure of 2 to 150 psi.
Chromatec Models 5000 and 3000 Pumps Chromatee offers a high pressure Model 5W0, and a low cost, moderate pressure Model 30W pump. The Model 5000 (part of the Model LC-2200) goes to 6000 psi and is a pneumatically driven, pulse-free, single displacement unit. An external air supply connected to the accessory drives the pump. The liquid chamber volume is 70 ml, the refill rate is 50 ml/sec, and maximum flow is 100 ml/min. The Model 3W0 is a reciprocating constant displacement pump which oomes in two versions, one with a maximum pressure capability of 1000, and the other 2000 psi. The pump incorporates a short stroke, wide diameter unbreakable plunger. Both frequency and length of stroke can he varied. High frequency operation eliminates the need far a pulse damper. The maximum flow is 10 ml/min. The Chromatec Model 3000 pump was shown previously as part of the gradient system in Figure 3.
Figure 13.
Chrornatronix Model 740 Pump.
ired volume, yet is pulseless. The Model 740 is a motor-driven dual reciprocating piston, precision metering pump. The 180" phase difference and special cam shape result in a steady flow, interspersed by minor fluctuations due to compliance of the chambers and solvent. These fluctuations are eliminated by a flow-feedback system: a flow-through transducer in the pump outlet line continually measures the flow rate (not pressure) and sends the information to the control module where it is compared with the flow rate setting. Any fluctuations create an error signal which changes the motor speed accordingly. The "closed loop" system is illustrated diagramatically in Figure 12. The Model 740 pump, shown phatagraphically in Figure 13, is rated for 7000 psi a t 0-4 ml/min and 1500 psi a t 4-20 ml/min.
DuPont Pump Chromatronix Model 740 Metering Pump ~~
Figure 12. Schematic.
Chromatronix
Flow-Feedback
. . .
T.. h.. i. s is i svstem n .e ~- a new 7000 osi ~ u m ~ " available for the G o m a t r o n i x Series 3500 LC units. The unique feature of this pump is that it produces metered flow of unlim~~~
As part of the DuPont Model 830 liquid chromatograph, a pneumatic, single displacement pump is featured. The 830 pump works on a pneumatic amplifier as shown in Figure 14. Air or ni(Continued on page A442j
Volume 50.Number 9 . September 1973
/
A441
Chemical Instrumentation
10."
Figure 14. DuPont Model 830 Pneumatic Pumping System (shown as part of a complete LC).
trogen a t 0-100 psi is delivered to a hydraulic piston of much smaller surface area: the pressure amplification is 45:l. The pump draws a continuous supply of liquid from an integral large volume reservoir and delivers 70 ml before refilling. The working pressure ranges from 100 to 3000 psi with a flow rate range which is continuously adjustable up t o greater than 100 ml/min. In the DuPont Model 840 liquid chromatograph, a pressurized 450 ml coil pumping system is available. The coil design minimizes gas diffusion into the mobile phase, and can be pressurized to 1500 psi from a nitrogen cylinder. Six or seven hours of uninterrupted operation from a single coil filling (at 1 ml/min) are thus possible.
Hewlett-Packard Pumping System (Orlita pump) The Hewlett-Packard Model IOlOB Hupe+Busch series liquid chromatograph utilizes the Orlita dual-piston diaphragm pump, which is well known for its aeeuracy and reliability. Its design is shown in Figure 15. The solvent is in contact only with stainless steel. A working piston and a floating piston oppose each other in a n oil chamber, which is separated from the solvent chamber by a stainless steel membrane. The working piston operates a t a constant stroke of 15 mm a t 100 strokes per minute. If the stroke of the opposing piston is the same as that of the working piston, they move in harmony, and no pressure is developed. Delivery rate of the pump is adjusted by limiting the travel of the opposing piston to some fraction (O100%) of the working piston. Maximum pressure capability is 4875 psi (325 atm) and the maximum flow rate is 600 rnl/h. An in-line pulsatinn damping device reduces pressure pulses to a negligible value.
~umo housiw
%went
pinon rat
Figure 15. Hewlett-Packard (Orlita) Dual-Piston Diaphragm Pump Schematic.
utilize a Teflon diaphragm and a stainless steel and Teflon piston respectively. Flow rates for the three ISCO pumping systems are 1.5 to 2500 ml/h a t 0 psi; 1 to 500 ml/h a t 0 psi; and 0.8 to 200 ml/h a t 2000 psi respectively. The Model 314 pump is shown in Figure 16.
JEOL Pump A "buffer pump" is included as part of the JEOL JLC-6AH Amino Acid Analyzer. This pump delivers continuous flow by means of two plungers, driven by precisian-machined cams which perform alternate strokes for suction and delivery. The flaw rate can be varied in 10 steps by changing gears from 0.51 to 2.17 ml/min with an accuracy of +I% a t 10 kg/cmZ. Normal operating pressure for the pump is 30 kg/cm2 with a maximum possible pressure of 40 kg/cm2. Overpressure protection is provided. The JEOL pump is shown in Figure 17.
ISCO Precision Metering Pumps Three single displacement pumps are provided by ISCO, the Models 310, 312 and 314. The output pressures for these systems are 50, 200 and 2000 psi respectively. In the Model 312 (general purpose) the piston pump head is constructed of Kel-F, Teflon, and glass. The Teflon piston is driven by a linear cam having a quick return, so that about 80% of the cycle is used for discharge. Variable flow is accomplished by varying the rotation speed of the cam. The Models 310 and 314 A442
/
Journal of Chemicai Education
Figure 16.
ISCO Model 314 Metering Pump.
(Continued on page A444J
Figure 18. Figure 17.
Milton Roy Milroyal D Pump
JEOL Pump.
Lapp Microflo Pulsafeeder Metering Pumps Lapp Process Equipment supplies the Microflow Pulsafeeder pump which is a combination plunger-diaphragm pump. A plunger reciprocates a t an established stroke length, displacing an exact volume of petroleum oil. By means of this oil, the plunger hydraulically moves a diaphragm alternately forward and backward. The displacement from this diaphragm movement, in turn, takes in the moving liquid through a suction check valve on the suction stroke and discharges a like amount of liquid through t h e discharge eheck valve on the discharge stroke. Pulsafeeder pumps have maximum flaw rate eapacities from 123 to 6500 ml/h a t pressures of 300 to 3000 psi depending on piston diameter and motor power. These pumps can be used a t flows as low as 5% of their maximum rating.
Micromeritics Hydraulic Pump Mieromerities provides a pumping system which is unique in that it delivers pulseless flow without a pulse damper, can operate from an unlimited reservoir, requires only one pump for gradient elution and can operate in the constant flow or constant pressure mode. This 6000 psi pump consists of dual, hydraulically controlled reciprocating pistons. Oil is distributed by the system to each of the pistons which are 180' out of phase. While one ist ton is delivering solvent, the other is prepressurizing. Hydraulic fluid is put into motion by a high quality gear pump which delivers a fixed volume of hydraulic fluid to the control system for every revolution it turns. The gear pump, in turn, is set into motion by a constant speed motor which is controlled by a tachometer feedback circuit. During the time af piston switch over, special compensating circuits are used to eliminate flow rate irregularities due t o seal expansion, compression of liquids, closing oi check valves, and expansion af tubing.
tical. At a zero capacity setting on the micrometer control, no plunger reciprocating motion is produced. At a 100% setting, the stroke control inclines the polar crank 18" resulting in a full one-inch travel of the plunger and a maximum flow. During reciprocation, fluid is alternately drawn in and discharged from the liquid end. During these cycles, the plunger action seats and unseats double ball check valves on the suction and discharge ends. Flow rate can be set continuously from 0 to 100% on a micrometer adjustment contml. Plunger sizes of YB or 1/1 inch are available depending on maximum flow rates desired (1800 or 7150 ml/h). The maximum pressure available is 1000 psi. Also available is a 3000 psi Milroyal D pump of the same basic design and operating characteristics. This pump has a maximum rate capacity of 123 ml/h a t SO00 psi. Milton Roy also offers its familiar instrument Minipump capable of flow rates from 16 to 460 ml/h a t 1000 psi. A new Minipump capable of 3000 psi has reportedly become available recently.
Perkin-Elmer Pump Systems The reciprocating, positive displacement pump provided for the P.E. Model 1240 liquid chromatograph delivers flow rates from 0.7 to 7.47 ml/min and pressures up to 1000 psi. A damping system effectively removes pump pulsations. For the Model 1220 liquid chromatograph, a positive displacement digitally controlled constant delivery pump is provided. Flow rates are continuously variable from 0.05 to 6.0 ml/ min and reproducible to +0.1% a t a pressure rating of 7000 psi.
Varian Pumps A low pressure pump for the Varian Series 4000 liquid chromatograph, and a high
Milton Roy Pumps Milton Roy has a number of well known pumping systems which are availahle for high pressure LC. The new Milroyal D pump operates by use of a unique patented polar crank drive mechanism as shown in Figure 18. The gear system reduces and transmits rotary motion from the motor to the polar crank assembly which rotates in a plane adjustable up t o 18" from the verA444
1 Journal of Chemicai Education
Figure lea. Wailace and Tiernan Piston-Diaphragm Pump.
displacement and lack of off-line dampers of any type. Uniform, pulseless flow is provided by combining the output from each of the two positive displacement chambers. The piston displacement profiles which make this possible are shown in Figure 19. The forward motion of the n is tan begins . a t A. In this reeion the s h e increases. resultine- in ~~~~a corresponding gain in flaw rate. In region B, slope and flow rates are constant with all the flow provided by a single piston. The chamber of the other delivery head fills during this interval. In Section C, the piston slows dawn and the other piston begins its forward movement (Section A ) with the net result of a constant combined solvent delivery rate. The Waters Model 6000 Pump, shown in Figure 20, is provided with a unique internal feedback control system. Motor speed is controlled by a variable frequency oscillator, stable over the range of 47 t o 63 cycles. Power sufficient to maintain a constant motor speed is supplied only on a demand basis avoiding heat generation from excess power input. If pressure builds, a solvent compressibility eompen&tion factor is applied to the speed control. This modifies the motor speed as necessary to maintain actual solvent delivery exactly as selected on the flow rate setting. ~
Figure 19. W a t e r s Model 6000 P u m p Piston D i s o l a c e m e n t Profiles.
pressure pump for the 4100/4200 series are available. The low pressure pump is a constant pressure, gas driven, pulseless flow system capable of 1000 psi. The Series 4100 pump is a single displacement, 5000 psi syringe piston made of stainless steel and PTFE. A pressure monitor shuts off the pump when 5000 psi is exceeded. Two ranges of flow rates are available and are continuously adjustable from 0 to 20 ml/h and from 0 to 200 ml/h. Flow rate accuracv and reoeatabilitv are +I% and *0.1% of full range. Emptylfill rate is less than 4 min for a 250 ml volume.
Wallace and Tiernan PistonDiaphragm Pump This pump is the one which is used in the Pye LCM2 liquid chromatograph. The unit, shown in Fig. 18a, delivers 0 to 0.621 I/h (continuously variable) and is capable of 4000 psi. A diaphragm is hydraulically operated through a fluid displaced by a plunger. Pressure in the hydraulic system is controlled by a relief valve (top) and the quantity of fluid by a snifter valve (bottom).
Waters Model 6000 Pump ' h e ncu M'attr. \ l ~ d e I 6001. S , d \ e n t Dehrery system is n roniranl flow PLI-Cless pump cmplming s palr
