Apparatus for liquid chromatography

• US 4,772,388 A
• Filed: 09/07/1982
• Issued: 09/20/1988
• Est. Priority Date: 09/09/1981
• Status: Expired due to Term

• Current Assignee: Isco, Inc. (Teledyne Technologies Incorporated)
• Original Assignee: Isco, Inc. (Teledyne Technologies Incorporated)
• Inventors: Allington, Robert W.
• Primary Examiner(s): Therkorn, Ernest G.
• Application Number:
  US06/415,471
• Time in Patent Office: 2,205 Days
• Field of Search: 210/659, 210/741, 210/101, 210/143, 210/635, 210/198.2, 210/137, 210/138, 210/103, 210/105, 73/61.1 C, 422/70
• US Class Current: 210/198.2
• CPC Class Codes: G01N 2030/326 pumps
• CPC Class Codes: G01N 30/32 of pressure or speed G01N30/36 takes precedence

Abstract

To stabilize flow rate in a single-stroke, syringe-type high pressure pump to a constant value after turn-on, a control system increases the pump speed until equilibrium conditions are reached and then pumps at the preset rate. In one embodiment, the control system senses the maximum rate of change of pressure, detects a pressure when the rate of change is two-thirds of the maximum, increases the pump rate until the pressure is three times that at the value of the detected pressure and begins pumping at the preset constant flow rate.

In other embodiments: (1) a pumping system is operated at a flow rate ten times the preset flow rate and, when the time derivative of the pressure has dropped to nine tenths of its maximum, the pump motor speed is reduced to the preset flow rate; (2) the outflow of the column is measured under no load conditions at the desired flow rate and when a column is connected, the pumping speed is increased until the same outflow results before reducing the pumping rate, and (3) the system is operated in a constant pressure mode to a point at which the pressure is estimated to provide the desired flow rate, the flow rate measured, and if the flow rate is not the preset one, a new pressure measurement is set and the procedure repeated.

Claims

1. Apparatus for rapidly bringing a chromatographic means to equilibrium pressure comprising:

pumping system means;

means for setting a pumping speed for pumping fluid from the pumping system means into said chromatographic means at a predetermined rate of flow;

means for measuring, after start up of the pumping system means and before equilibrium pressure is reached and at a time of a low value of pressure of said fluid, the pressure of said fluid being transferred from the pumping system means to the chromatographic means;

means for estimating the equilibrium pressure from said measurements of said pressure made at a low value pressure;

means for increasing the rate of flow of fluid from the pumping system means under the control of at least said measured pressure until said pressure reaches said estimated equilibrium pressure;

said means for estimating including means for taking the time derivative of said measured pressure at first and second times and means for multiplying a value equal to substantially the pressure of the fluid being transferred between the pumping system and the chromatographic system at the second point in time by a factor which is the ratio of the value of the time derivative at the second point in time subtracted from the time derivative at the first point in time divided into the time derivative at the first point in time; and

means for reducing said rate of flow from the pumping system means to said predetermined rate of flow after said pressure reaches equilibrium.

2. Apparatus according to claim 1 in which the means for estimating the equilibrium pressure includes:

means for storing the potential representing the maximum time rate of change of pressure;

means for obtaining a predetermined fraction of said stored potential representing the maximum time rate of change;

means for comparing a potential representing the instantaneous slope with said predetermined fraction of said stored potential representing the maximum time rate of change;

means for generating a potential representing the instantaneous pressure;

means for storing a potential representing a reference pressure when said potential representing said instantaneous slope equals said predetermined fraction;

means for increasing the speed of pumping when said instantaneous slope is equal to said predetermined fraction; and

means for returning said pumping speed to its preset value when said stored reference potential is the same fraction of the potential representing said instantaneous pressure as said predetermined fraction.

3. Apparatus according to claim 2 in which the means for reducing the rate of flow includes:

means for measuring the pressure at which said fluid is transferred between said pumping system and said chromatographic column;

means for obtaining the time derivative of said pressure; and

means for reducing said pumping rate after said time derivative has fallen from said maximum value to a relatively small value.

4. Apparatus according to claim 3 in which the means for controlling the pumping rate includes:

means for setting the desired flow rate;

means for obtaining a signal which when operated upon the measured flow rate yields actual flow rate;

means for operating upon the measured flow rate with the calibration signal; and

means for applying the calibrated measured signal to the control means for causing said pump to be controlled in speed until the desired flow rate is reached.

5. Apparatus according to claim 4 in which the means for obtaining a calibration signal includes:

means for applying the outflow from the pumping system to the flow measuring system, whereby a signal is obtained representing the flow rate without loading by the chromatographic column;

means for generating a signal corresponding to a desired flow rate;

means for operating on said preset signal with said measured calibration signal; and

means for adjusting said calibration signal until the operated-upon signal equals the measured signal under no load, whereby the calibration signal is obtained which when operated upon the measured signal under load results in a signal indicating deviations from the desired set signal.

6. Apparatus according to claim 5 in which said means for applying said signal to said motor control circuit includes:

switching circuit means;

said switching circuit means incuding means for determining when said outflow corresponds to said preset outflow;

means for switching to said calibrated measured circuit when said reference circuit differs from said outflow circuit;

said switching circuit means having an output connected to one of the two inputs of the subtractor and to a motor control circuit means for driving a motor;

the other input of said subtractor being electrically connected to a means for deriving an electrical signal representing the rate of outflow of the chromatographic column;

a sample-and-hold circuit;

feedback means including said subtractor and sample-and-hold circuit for generating a signal when said pump is controlled by a signal from said flow rate selector which when operated upon the measured flow rate equals a calibrated factor;

means for storing said calibrated factor and said sample-and-hold circuit;

means for applying the signal stored in said sample-and-hold circuit to an operating circuit for operation upon the measured signal; and

means for applying the measured signal to one input of the subtractor while the signal from the flow rate selector is applied to another input of the subtractor and the output is applied to the motor control circuit to cause the motor to drive the pump at a rate which causes the outflow from the chromatographic column to equal the rate set on said switching circuit.

7. Apparatus according to claim 1 in which said means for increasing the rate of flow includes a means for controlling the rate of advance of a syringe pump.

8. Apparatus according to claim 7 in which said chromatographic means is a high pressure micro-scale chromatographic system and said means for estimating includes a microprocessor.

9. Apparatus according to claim 1 in which the first point in time is determined by measuring the maximum rate of change of pressure with respect to time.

10. Apparatus according to claim 9 in which the value equal to substantially the pressure at the second point in time is approximately the value of the actual pressure at the second time minus a very small pressure which occurs at the first time.

11. Apparatus for rapidly bringing a chromatographic means to equilibrium pressure comprising:

pumping system means;

means for setting a pumping speed for pumping fluid from the pumping system means into said chromatographic means at a predetermined rate of flow;

means for measuring, after start up of the pumping system means and before equilibrium pressure is reached and at a time of a low value of pressure of said fluid, a characteristic of said fluid being transferred from the pumping system means to the chromatographic means related to the pressure of the fluid;

means for increasing the rate of flow of fluid from the pumping system means under the control of at least said measured characteristic until the equilibrium value of pressure is reached;

means for reducing said rate of flow from the pumping system means to said predetermined rate of flow;

said means for measuring including means for measuring the fluid outflow from the chromatographic means and for providing a signal proportional thereto; and

said means for increasing including control means responsive to said means for measuring for controlling the rate at which fluid is pumped to the chromatographic means to cause the outflow to be at a predetermined rate.

12. Apparatus according to claim 11 in which the means for measuring the outflow rate includes:

means for measuring the flow rate from the chromatographic means; and

means for applying a corection factor to the signal from the outflow.

13. Apparatus according to claim 12 in which the means for measuring the outflow includes:

means for counting drops;

means for conditioning electrical signals derived from said drops to form a stable analog signal representing the rate of flow of fluid from the column; and

means for amplifying said signal to provide a calibrated output representative of the flow of fluid from the column.

14. Apparatus according to claim 13 in which said means for providing a calibration signal includes an analog multiplier having a first input adapted to receive said flow rate signal and a second input adapted to receive a calibration signal.

15. Apparatus according to claim 14 in which the means for increasing rate of flow includes:

means for setting a predetermined flow rate;

means for obtaining a calibration signal which when operated upon by the flow rate measured under no load yields desired flow rate;

means for operating upon the measured flow rate under load with the calibration signal; and

means for applying the calibrated measured signal to the pumping system for causing said rate of flow to be controlled until the desired flow rate is reached.

16. Apparatus according to claim 15 in which the means for obtaining a calibration signal includes:

means for applying the outflow from the pumping system to the flow measuring system, whereby a signal is obtained representing the flow rate without loading by the chromatographic column;

means for generating a signal corresponding to a desired flow rate;

means for operating on said preset signal with said measured calibration signal; and

means for adjusting said calibration signal until the operated-upon signal equals the measured signal under no load, whereby the calibration signal is obtained which when operated upon the measured signal under load results in a signal indicating deviations from the desired set signal.

17. Apparatus according to claim 16 in which said means for increasing the rate of flow includes:

motor control circuit means;

means for applying said signal to said motor control circuit means;

said means for applying includes a switching circuit;

said switching circuit means including means for determining when said outflow corresponds to said preset outflow; and

means for switching to said calibrated measured circuit when said reference circuit differs from said outflow circuit.

18. Apparatus according to claim 16 in which the means for increasing the rate of flow includes:

a subtractor;

flow rate adjusting means for generating a potential proportional to a preset rate;

said flow rate selector means having an output connected to one of the two inputs of the subtractor and to a motor control circuit means for driving a motor;

the other input of said subtractor being electrically connected to a means for deriving an electrical signal representing the rate of outflow of the chromatographic column;

a sample-and-hold circuit;

feedback means including said subtractor and sample-and-hold circuit for generating a signal when said pump is controlled by a signal from said flow rate selector which when operated upon the measured rate selector which when operated upon the measured flow rate equals a calibrated factor;

means for storing said calibrated factor and said sample-and-hold circuit;

means for applying the signal stored in said sample-and-hold circuit to an operating circuit for operation upon the measured signal;

means for applying the measured signal to one input of the subtractor while the signal from the flow rate selector is applied to another input of the subtractor and the output is applied to the motor control circuit to cause the motor to drive the pump at a rate which causes the outflow from the chromatographic column to equal the rate set on said flow rate selector means.

19. Apparatus according to claim 11 in which said means for increasing the rate of flow includes a means for controlling the rate of advance of a syringe pump.

20. Apparatus according to claim 19 in which said chromatographic means is a high pressure micro-scale chromatographic system.

21. Apparatus for rapidly bringing a chromatographic means to equilibrium pressure comprising:

pumping system means;

means for setting a pumping speed for pumping fluid form the pumping system means into said chromatographic means at a predetermined rate of flow;

means for measuring, after start up of the pumping system means and before equilibrium pressure is reached and at a time of a low value of pressure of said fluid, a characteristic of said fluid being transferred from the pumping system means to the chromatographic means related to the pressure of the fluid;

means for increasing the rate of flow of fluid form the pumping system means under the control of at least said measured characteristic until the equilibrium value of the pressure is reached;

means for reducing said rate of flow from the pumping system means to said predetermined rate of flow;

said means for inreasing the rate of flow including a means for controlling the rate of advance of a syringe pump;

said chromatographic means being a high pressure micro-scale chromatographic system;

means for measuring a characteristic of the chromatograph that is inversely related to said pressure; and

means for setting up a proportion between the measured pressure and the range of said dynamic characteristic, whereby any other pressure may be calculated.

22. Apparatus according to claim 21 in which said means for measuring a characteristic includes a means for obtaining the time derivative of said pressure.

23. Apparatus according to claim 22 in which the means for setting up a proportion includes means for measuring the pressure at a point and setting up a proportion between the time derivative of the pressure at that point and the range between the maximum and substantial zero values of the time derivative as related to the measured point of pressure and another value.

24. Apparatus according to claim 23 in which said means for establishing the ratio includes a means for establishing the ratio with the equilibrium pressure of said chromatographic system.

25. Apparatus according to claim 24 in which said chromatographic means is a high pressure microscale chromatographic system.

26. Apparatus according to claim 25 in which the means for controlling the speed of the pump in a constant pressure mode includes:

a comparator;

means for deriving a signal representing the speed of the pump;

means for deriving a signal representing the difference between the pump head pressure and the set value of pressure;

said means for obtaining a signal representing the pump speed and said means for obtaining a signal representing the difference between the pump head pressure and the set pressure being attached to different ones of the inputs of said comparator; and

the output of said comparator being electrically connected to a means for controlling the speed of the motor, whereby the speed of the motor is raised to said set pressure in said constant pressure mode.

27. Apparatus according to claim 25 in which the means for developing a signal representing the difference between the set pressure and the head pressure includes:

comparator means having first and second inputs;

the first input of said comparator being electrically connected to said means for measuring the head pressure of said pump.

28. Apparatus according to claim 27 in which said means for increasing the rate of flow includes a means for controlling the rate of advance of a syringe pump.

29. Apparatus for rapidly bringing a chromatographic means to equilibrium pressure comprising:

pumping system means;

means for setting a pumping speed for pumping fluid from the pumping system means into said chromatographic means at a predetermined rate of flow;

means for measuring, after start up of the pumping system means and before equilibrium pressure is reached and at a time of a low value of pressure of said fluid, a characteristic of said fluid being transferred from the pumping system means to the chromatographic means related to the pressure of the fluid;

means for increasing the rate of flow of fluid from the pumping system means under the control of at least said measured characteristic until the equilibrium value of pressure is reached;

means for reducing said rate of flow from the pumping system means to said predetermined rate of flow;

said means for measuring includes means for measuring the pressure of the fluid being transferred between said pumping system means and said chromatographic means at a low value;

said means for increasing the pressure including means for increasing the speed of the pump in a constant pressure mode, a comparator, means for deriving a signal representing the speed of the pump, means for deriving a signal representing the difference between the pump head pressure and a predetermined pressure, means for obtaining a signal representing the pump speed, said means for obtaining a signal representing the difference between the pump head pressure and the set pressure being attached to different ones of the inputs of said comparator and the output of said comparator being electrically connected to a means for controlling the speed of the motor, whereby the speed of the motor is raised to said set pressure in said constant pressure mode.

30. Apparatus according to claim 29 in which the means for developing a signal representing the difference between the set pressure and head pressure includes:

a pressure comparator having first and second inputs;

the first input of said comparator being electrically connected to said means for measuring the head pressure of said pump;

said second input of said comparator being electrically connected to the means for developing a signal representing the setting of said pressure;

a sample and hold circuit; and

the output of said comparator being electrically connected to a sample-and-hold circuit.

31. Apparatus according to claim 30 including means for changing from a constant mode to a constant flow mode;

said means for changing from a constant pressure mode to a constant flow mode includes means for applying a strobe potential to said sample-and-hold circuit in said constant pressure mode, whereby said sample-and-hold circuit applies a signal representing the difference between the measured pressure and the predetermined pressure to said speed comparator and for applying a second potential to said sample-and-hold circuit whereby said sample-and-hold circuit applies a constant potential to said speed comparator.

32. Apparatus according to claim 31 including:

means for determining when equilibrium has been reached;

the means for determining when equilibrium has been reached including means for detecting a substantially zero slope in the pressure-time characteristic, means for determining when the difference between the measured pressure and the set pressure is approximately zero and gate means for applying an output signal when the slope of the pressure-time curve and the difference between the measured pressure and set pressure are each approximately zero.

33. Apparatus according to claim 32 in which the means for determining when equilibrium has been reached includes:

gating means for applying a first output signal upon receiving a zero difference signal from said zero difference signal means and a zero slope signal from said zero slope detector and a second signal at other times, said first signal being electrically connected to a switch;

said switch providing a first signal upon receiving the signal from said gating means;

means electrically connected to said switching means for providing a signal thereto when the pressure is said pump moves from a value substantially zero to a greater value;

the output from said switch means being connected to an analog gate; and

means for applying a signal to the input of said analog gate representing the speed of the pump motor, whereby, said speed of said output motor is provided to the output of said analog gate when said transitory period is over.

34. Apparatus according to claim 33 further including a means for indicating the constant flow rate as a set equilibrium constant pressure when the chromatograph is operating in the constant pressure mode.

35. Apparatus according to claim 34 in which said means for increasing the rate of flow includes a means for controlling the rate of advance of a syringe pump.

36. Apparatus according to claim 34 in which said chromatographic means is a high pressure microscale chromatographic system.

37. Apparatus for rapidly bringing a chromatographic means to equilibrium pressure comprising:

pumping system means;

means for setting a pumping speed for pumping fluid from the pumping system means into said chromatographic means at a predetermined rate of flow;

means for measuring, after start up of the pumping system means and before equilibrium pressure is reached and at a time of a low value of pressure of said fluid, a characteristic of said fluid being transferred from the pumping system means to the chromatographic means related to the pressure of the fluid;

means for increasing the rate of flow of fluid from the pumping system means under the control of at least said measured characteristic until the equilibrium value of pressure is reached;

means for reducing said rate of flow from the pumping system means to said predetermined rate of flow;

said means for measuring includes means for measuring the pressure of the fluid being transferred between said pumping system means and said chromatographic means at a low value;

said means for measuring including means for taking the derivative of the head pressure with respect to time, means for setting predetermined pressure, means for comparing the predetermined pressure with the head pressure to obtain a signal indicating the difference between the two, means for detecting when the time derivative of the pressure with respect to time and the difference signal are both substantially zero, whereby the end of the transitory period is indicated and means for detecting when the head pressure of the pump is near zero and increasing rapidly, whereby the starting point of the transitory period is detected.

38. Apparatus for providing a chromatogram having equal units of flow rate as the abscissae during a constant pressure chromatographic run comprising:

a pumping system for solvent;

chromatographic column means for receiving solvent from the pumping system and eluting constituents of a sample;

means for detecting said constituents of said sample as they are eluted from the column system;

means for recording the detected components of said sample detected by said means for detecting;

means for measuring the rate of flow of said fluid; and

means responsive to the means for measuring for controlling the means for recording so that the abscissae of the chromatogram is related to the rate of flow of said fluid.

39. Apparatus according to claim 38 in which said means for controlling includes a means for changing the speed of said means for recording to be proportional to the rate of flow of said fluid from the column outlet.

40. Apparatus for making a constant-pressure chromatogram in which the time abscissae is corrected so as to correspond to constant units of flow rate per unit time, comprising:

means for measuring the flow rate during operation of the chromatograph;

a chart recorder;

said chart recorder being adapted to hold a paper for the making of a chromatogram

means for driving the chart recorder; and

means for causing the chart recorder to be driven at a speed directly proportional to the rate of flow of fluid through the chromatograph.

41. Apparatus according to claim 40 in which the means for measuring the rate of flow of fluid includes a means for measuring the pump motor speed and deriving an electrical signal proportional thereto.

42. Apparatus according to claim 41 in which the means for measuring the pump motor speed includes the means for detecting the transitory period of the chromatograph and for gating the signal proportional to the pump motor speed to the means for driving the strip chart recorder only when the chromatograph is outside of the transitory period.

43. Apparatus for predicting the pressure in a chromatographic system having a pumping system and a solvent receiving system comprising:

means for measuring, after start up of the pumping system but before the pressure reaches a constant value, the pressure at which the pumping system supplies liquid to the solvent receiving system;

means for measuring a characteristic of the chromatograph that is inversely related to said pressure; and

means for setting up a proportion between the measured pressure and the range of said dynamic characteristic, whereby any other pressure may be calculated.

44. Apparatus according to claim 43 in which said means for measuring a characteristic includes a means for obtaining the time derivative of said pressure.

45. Apparatus according to claim 44 in which the means for setting up a proportion includes the means for measuring the pressure at a point and setting up a proportion between the time derivative of the pressure at that point and the range between the maximum and substantial zero values of the time derivative as related to the measured point of pressure and another value.

46. Apparatus according to claim 45 in which said means for establishing the ratio includes a means for establishing the ratio with the equilibrium pressure of said chromatographic system.

47. Apparatus for controlling a chromatograph comprising:

chromatographic means;

pumping system means for applying solvent to the chromatographic means;

means for injecting samples into the chromatographic means, whereby the solvent will elute constituents of the samples;

means for measuring the fluid outflow from the chromatographic means for providing a signal proportional thereto; and

control means responsive to said signal for controlling the rate at which solvent is applied to the chromatographic column to cause the outflow to be at a predetermined rate.

48. Apparatus according to claim 47 in which the means for measuring the outflow rate includes:

means for measuring the flow rate from the chromatographic means; and

means for applying a correction factor to the signal from the outflow.

49. Apparatus according to claim 48 in which the means for measuring the outflow includes:

means for counting drops;

means for conditioning electrical signals derived from said drops to form a stable analog signal representing the rate of flow of fluid from the column; and

means for amplifying said signal to provide a calibrated output representative of the flow of fluid from the column.

50. Apparatus according to claim 49 in which said means for providing a calibration signal includes an analog multiplier having a first input adapted to receive said flow rate signal and a second input adapted to receive a calibration signal.

51. Apparatus according to claim 50 in which the means for increasing the rate of flow includes:

means for setting a predetermined flow rate;

means for obtaining calibration signal which when operated upon the analog signal obtained under no load operation of the chromatograph, yields the predetermined flow rate signal;

means for operating upon the analog flow rate with the calibration signal under load; and

means for applying the calibrated measured signal to the pumping system for causing said rate of flow to be controlled until the desired flow rate is reached.

52. Apparatus according to claim 51 in which the means for obtaining a calibration signal includes:

means for applying the outflow from the pumping system to the flow measuring system, whereby a signal is obtained representing the flow rate without loading by the chromatographic column;

means for generating a signal corresponding to a desired flow rate;

means for operating on said preset signal with said measured calibration signal; and

means for adjusting said calibration signal until the operated-upon signals equals the measured signal under no load, whereby the calibration signal is obtained which when operated upon the measured signal under load results in a signal indicating deviations from the desired set signal.

53. Apparatus according to claim 52 in which said means for increasing the rate of flow includes:

motor control circuit means;

means for applying said signal to said motor control circuit means;

said means for applying includes a switching circuit means;

said switching circuit means including means for determining when said outflow corresponds to said preset outflow; and

means for switching to said calibrated measured circuit when said reference circuit differs from said outflow circuit.

54. Apparatus according to claim 53 in which the means for increasing the rate of flow includes:

a subtractor;

flow rate adjusting means for generating a potential proportional to a preset rate;

said flow rate selector means having an output connected to one of the two inputs of the subtractor and to a motor control circuit means for driving a motor;

the other input of said subtractor being electrically connected to a means for deriving an electrical signal representing the rate of outflow of the chromatographic column;

a sample-and-hold circuit;

feedback means including said subtractor and sample-and-hold circuit for generating a signal when said pump is controlled by a signal from said flow rate selector which when operated upon the measured flow rate equals a calibrated factor;

means for storing said calibrated factor and said sample-and-hold circuit;

means for applying the signal stored in said sample-and-hold circuit to an operating circuit for operation upon the measured signal; and

means for applying the measured signal to one input of the subtractor while the signal from the flow rate selector is applied to another input of the subtractor and the output is applied to the motor control circuit to cause the motor to drive the pump at a rate which causes the outflow from the chromatographic column to equal the rate set on said flow rate selector means.

55. Apparatus according to claim 54 in which said means for increasing the rate of flow includes a means for controlling the rate of advance of a syringe pump.

56. Apparatus according to claim 55 in which said chromatographic means is a high pressure microscale chromatographic system.

57. Apparatus for detecting the transitory period of a chromatograph having a pumping system, and a chromatographic column system comprising:

means for measuring the head pressure of the pumping system;

means for taking the derivative of the head pressure with respect to time;

means for setting a desired pressure;

means for comparing the desired pressure with the head pressure to obtain a signal indicating the difference between the two;

means for detecting when the time derivative of the pressure with respect to time and the difference signal are both substantially zero, whereby the end of the transitory period is indicated; and

means for detecting when the head pressure of the pump is near zero and increasing rapidly, whereby the starting point of the transitory period is detected.

58. Apparatus for predicting the pressure at equilibrium in a chromatographic system having a pumping system and a fluid receiving system comprising:

means for measuring the pressure at start up of the pumping system in the fluid being transferred from the pumping system to the fluid receiving system;

means for taking the time derivative of said measured pressure; and

means for multiplying the pressure of the fluid being transferred between the pumping system and the chromatographic system by a factor which is the ratio of the value of the time derivative at the same point in time subtracted from the maximum time derivative divided by the maximum time derivative.

59. Apparatus according to claim 58 in which the means for estimating the equilibrium pressure includes:

means for storing the potential representing the maximum time rate of change of pressure;

means for obtaining a predetermined fraction of said potential;

means for comparing a potential representing the instantaneous slope with said stored value;

means for storing a potential representing the instantaneous pressure when said potential representing said slope equals said stored value of potential representing a fraction of said maximum;

means for increasing the speed of pumping when said instantaneous slope is equal to said predetermined value of said maximum slope; and

means for returning said pumping speed to its preset value when said potential representing said instantaneous pressure is the same fraction of said stored potential representing said instantaneous potential as said fraction of slope at the predicting point.

60. Apparatus according to claim 59 in which the means for reducing the rate of flow includes:

means for measuring the pressure at which said fluid is transferred between said pumping system and said chromatographic column;

means for obtaining the time derivative of said pressure; and

means for reducing said pumping rate after said time derivative has fallen from said maximum value to a relatively small value.

61. Apparatus according to claim 60 in which the means for controlling the pumping rate includes;

means for setting the desired flow rate;

means for obtaining a signal which when operated upon the measured flow rate yields actual flow rate;

means for operating upon the measured flow rate with the calibration signal; and

means for applying the calibrated measured signal to the control means for causing said pump to be controlled in speed until the desired flow rate is reached.

62. Apparatus according to claim 61 in which the means for obtaining a calibration signal includes:

means for applying the outflow from the pumping system to the flow measuring system, whereby a signal is obtained representing the flow rate without loading by the chromatographic column;

means for generating a signal corresponding to a desired flow rate;

means for operating on said preset signal with said measured calibration signal; and

means for adjusting said calibration signal until the operated-upon signal equals the measured signal under no load, whereby the calibration signal is obtained which when operated upon the measured signal under load results in a signal indicating deviations from the desired set signal.

63. Apparatus according to claim 62 in which said means for applying said signal to said motor control circuit includes a switching circuit;

said switching circuit including means for determining when said outflow corresponds to said preset outflow; and

means for switching to said calibrated measured circuit when said reference circuit differs from said outflow circuit.

64. Apparatus according to claim 63 in which said means for increasing the rate of flow includes a means for controlling the rate of advance of a syringe pump.

65. Apparatus according to claim 64 in which said chromatogaphic means is a high pressure microscale chromatographic system.

66. Apparatus for reducing the transitory time of a chromatograph including at least a pumping system means and a column means comprising:

means for measuring the outflow of fluid from the column means;

means for operating said chromatograph selected one of pump means for a constant flow rate or constant pressure operation from said column means while the speed of said pumping system means varies at the start of a chromatographic run;

indicator means for indicating the pressure;

means for rapidly increasing the pressure of said chromatograph to a predetermined pressure;

means for determining when said chromatograph has reached a stable substantially constant pressure; and

means for operating said pumping during a chromatographic run after said pressure has become substantially constant at a constant rate.