Apparatus for investigating fast chemical reactions by optical detection

• US 4,074,939 A
• Filed: 05/13/1976
• Issued: 02/21/1978
• Est. Priority Date: 12/19/1973
• Status: Expired due to Term

• Current Assignee: Max-Planck-Gesellschaft Zur Foerderung Der Wissenschaften e.V. (Max-Planck-Gesellschaft zur Frderung der Wissenschaften e)
• Original Assignee: Max-Planck-Gesellschaft Zur Foerderung Der Wissenschaften e.V. (Max-Planck-Gesellschaft zur Frderung der Wissenschaften e)
• Inventors: Rabl, Carl-Roland
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Rosenberger, R. A.
• Application Number:
  US05/686,023
• Time in Patent Office: 649 Days
• Field of Search: 356/103, 356/104, 356/204, 356/206, 356/208, 356/244, 356/246, 250/573, 250/574, 250/575
• US Class Current: 356/435
• CPC Class Codes: G01N 2021/0389 Windows
• CPC Class Codes: G01N 2021/0392 Nonplanar windows
• CPC Class Codes: G01N 2021/1738 Optionally different kinds of measurements; Method being valid for different kinds of measurement
• CPC Class Codes: G01N 2021/6491 Measuring fluorescence and transmission; Correcting inner filter effect
• CPC Class Codes: G01N 21/0303 Optical path conditioning in cuvettes, e.g. windows; adapted optical elements or systems; path modifying or adjustment G01N21/031 - G01N21/15 take precedence
• CPC Class Codes: G01N 21/0332 with temperature control control of temperature G05D23/00; cryostats F17C3/08
• CPC Class Codes: G01N 21/272 for following a reaction, e.g. for determining photometrically a reaction rate (photometric cinetic analysis)
• CPC Class Codes: G01N 21/59 Transmissivity G01N21/25 takes precedence
• CPC Class Codes: G01N 21/6445 Measuring fluorescence polarisation
• CPC Class Codes: G01N 21/645 Specially adapted constructive features of fluorimeters
• CPC Class Codes: G01N 2201/1226 Relaxation methods, e.g. temperature jump, field jump
• CPC Class Codes: G01N 2201/127 Calibration; base line adjustment; drift compensation

Abstract

An apparatus for investigating the course of fast chemical reactions in lid chemical systems, using optical detection and an external perturbation, especially by the temperature-jump method. The optical part of the apparatus comprises first and second light paths conveying a probing light beam and a sense light beam, respectively, and an optical lens system of extremely high aperture for measurements of absorption, fluorescence, and fluorescence polarization. The opto-electronic detection system comprises individual photodetector heads and a signal processing unit wherein special circuits for electronic division, zero-correction, large aperture error correction, and signal coupling eliminate disturbing signal components, reduce inherent errors of electronic signal processing, and simplify operation of the apparatus.

Claims

1. An apparatus for investigating the course of fast chemical reactions by optical detection, said reactions being initiated in chemical system by an external perturbation, said apparatus comprising a sample cell forming a chamber for holding a liquid sample of said chemical system, means performing said perturbation, monochromatic illumination means, at least one light path transversing said sample cell, and opto-electronic detection means including at least two photodetectors operatively connected to a signal processing unit, the improvement wherein said signal processing unit comprises input amplifiers and means for adjusting and balancing of normalized signals, a first main amplifier performing a subtraction of said normalized signals and a second main amplifier performing a summation of said normalized signals, further comprising a divider circuit wherein said first main amplifier is connected to the numerator input and said second main amplifier is connected to the denominator input of said divider, said first main amplifier having at least two selectable gain factors one of which gives a numerator-denominator gain ratio of the order of one and the other one being considerably larger, said unit also comprising means for selecting one output of said main amplifiers and said divider circuit, said selected output being connected to a zero-correction circuit which is electronically controlled by said perturbating means, the output of said zero-correction circuit being connected to signal averaging and recording means.

2. Apparatus according to claim 1 having a first light path monochromaticly probing said sample and a second light path for conveying optical radiation derived from said sample, wherein said two photodetectors are arranged in said second light path at opposite sides of said sample cell, further comprising polarizing analyzers between said sample cell and said photodetectors, said photodetectors giving signals which are essentially proportional to the emission light vector perpendicular and parallel to the axis of said first light path, respectively, said photodetectors being connected to two input amplifiers of said signal processing unit the outputs of which give said normalized signals, wherein the input of said first main amplifier receives also a proportion of the sum of said normalized signals via a calibrated potentiometer, said proportion being subtracted from the difference of said normalized signals.

3. Apparatus according to claim 2 wherein the aperture angle of said sample cell in said second light path is considerably larger than in said first light path, said signal processing unit further comprising a calibrated attenuator network at the input of said second main amplifier, said network modifying the balance of said normalized signals in order to correct for the large aperture error of the degree of polarization.

4. Apparatus according to claim 2 wherein the aperture angle of said sample cell in said second light path is considerably larger than in said first light path and said input amplifiers have negative feedback networks, said networks having switch contacts at the amplifier outputs providing an independent and an interconnected operational mode, said interconnected mode correcting said normalized signals for the larger aperture error of the degree of polarization.

5. Apparatus according to claim 1 having a first light path monochromaticly probing said sample and a second light path for conveying optical radiation derived from said sample, further comprising at least three photodetectors and a reference beam divider in said first light path prior to said sample cell, one photodetector receiving optical radiation via said beam divider in order to give a reference signal, a second photodetector receiving optical radiation transmitted through said sample cell in order to give a transmission signal, and at least one photodetector in said second light path in order to give an emission signal, said signal processing unit including at least three input amplifiers which give said normalized signals, wherein said first main amplifier subtracts from the normalized emission signal a proportion of the sum of the normalized reference signal and the normalized transmission signal, said second main amplifier giving a signal which is proportional to said sum of said signals, the outputs of said main amplifiers being connected to said divider in order to correct for the inner filter effect.

6. Apparatus according to claim 1 having one photodetector optically coupled to a beam divider between said illumination means and said sample cell, said photodetector giving a reference signal to one input amplifier of said signal processing unit, said input amplifier having a variable lowpass filter for selectively reducing the optical noise of said reference signal.

7. Apparatus according to claim 6, wherein said input amplifiers except said reference input amplifier have adjustable input offsets and offset selector switches, said offsets subtracting stray light signals in reference to said reference signal, and dark current signals in reference to a constant voltage.

8. Apparatus according to claim 1, further comprising differential analog meters connected to the outputs of said input amplifiers and controlling said normalized signals in reference to a comparison voltage, further comprising a meter and a meter selector switch for measuring the static signal values at the inputs and the outputs of said input amplifiers and at the outputs of said main amplifiers and of said divider circuit, also comprising a threshold detector disconnecting said divider circuit in periods wherein the denominator voltage becomes a small value.

9. In an apparatus for investigating the course of fast chemical reactions by optical detection, said reactions being initiated in a chemical system by an external perturbation, said apparatus comprising a sample cell holding a liquid sample of said chemical system, means performing said perturbation, monochromatic illumination means, a reference beam divider, at least one light path transversing said sample cell, and optical detection and signal processing means, said means comprising:

at least two photodetectors operatively connected to signal input amplifiers, means for adjusting and balancing of normalized signal, at least one main amplifier for arithmetic combination of said signals by subtraction, further comprising a zero-correction circuit for processing the arithmetically combined signal, said zero-correction circuit including a trigger circuit triggered by said perturbation means the improvement wherein said trigger has an undelayed and a delayed operational mode, said delayed mode providing a series of selectable delay times, said zero-correction circuit further including differentiating means followed by a high-impedance buffer amplifier the output of which is connected to signal averaging and recording means, said differentiating means comprising a low-leakage capacitor and a semiconductor switch gated by said trigger, being in its low resistance on-state prior to said perturbation and during the selected delay time, and being in its high-resistance off-state hereafter, further comprising a selector switch changing the value of said capacitor and the on-state settling time constant of said differentiating means together with the operational mode and the delay time of said trigger, providing a large settling time constant in said undelayed mode and a settling time constant shorter than, but increasing with said delay time in said delayed mode, said trigger also providing a gate signal controlling said signal recording means.

10. Apparatus according to claim 9, further comprising at least one series-connected resistor with said capacitor and said semi-conductor switch, wherein one arm of said semiconductor switch is grounded and the other arm is also coupled to a gate signal inverter via a small capacitor.

11. Apparatus according to claim 9, wherein said zero-correction circuit provides also another delayed operational mode wherein said settling time constant is very large as compared to the selected delay time, said capacitor being large and series-connected with a resistor which is at least one order of magnitude larger than the on-state resistance of said semiconductor switch.

12. Apparatus according to claim 9, wherein said trigger circuit produces in its delayed mode an undelayed and a delayed gate signal, said zero-correction circuit comprising first and second differentiating means, and first and second buffer amplifier, said first and second differentiating means being gated in successive operation for simultaneous undelayed and delayed processing of the same differential signal following said perturbation, having large and short settling time constant, respectively, said short settling time constant being selected together with the applied delay time, said zero-correction circuit further including means for storing and measuring the signal shift which occurs between the outputs of said first and second buffer amplifier after said delay time.

13. Apparatus according to claim 12, wherein said storing means comprise a semiconductor switch gated to its low-resistance on-state during the time interval of measurement, a series-connected capacitor, and a double-throw switch for switching said capacitor into the feedback loop of one of said buffer amplifiers.

14. In an apparatus for investigating the course of fast chemical reactions by optical detection, said reactions being initiated in a chemical system by an external perturbation, said apparatus comprising a sample cell holding a liquid sample of said chemical system, means performing said perturbation, monchromatic illumination means, a reference beam divider, at least one light path transversing said sample cell, and optical detection means including at least two photodetectors operatively connected to a signal processing unit, said unit comprising adjustable input amplifiers for setting of normalized signals and at least one main amplifier for arithmetic combination of said normalized signals, said unit further comprising a zero-correction circuit for processing the arithmetically combined signal, said zero-correction circuit including a trigger circuit triggered by said perturbation means, wherein said trigger has an undelayed and a delayed operational mode, said delayed mode providing a series of selectable delay times, said zero-correction circuit further including differentiating means followed by a high-impedance buffer amplifier the output of which is connected to signal averaging means, said differentiating means comprising a low-leakage capacitor and a semiconductor switch gated by said trigger, being in its low-resistance on-stage prior to said perturbation and during the selected delay time, and being in its high-resistance off-state thereafter, further comprising a selector switch changing the value of said capacitor and the on-state settling time constant of said differentiating means together with the operational mode and the delay time of said trigger, providing a large settling time constant in said undelayed mode and a settling time constant shorter than, but increasing with said delay time in said delayed mode, said trigger also providing an oscilloscope unblanking signal.

15. Apparatus according to claim 14, further comprising at least one series-connected resistor with said capacitor and said semiconductor switch, wherein one arm of said semiconductor switch is grounded and the other arm is also coupled to a gate signal inverter via a small capacitor.

16. Apparatus according to claim 14, wherein said zero-correction circuit provides also another delayed operational mode wherein said settling time constant is very large as compared to the selected delay time, said capacitor being large and series-connected with a resistor which is at least one order of magnitude larger than the on-state resistance of said semiconductor switch.

17. Apparatus according to claim 14, wherein said trigger circuit produces in its delayed mode an undelayed and a delayed gate signal, said zero-correction circuit comprising first and second differentiating means, and first and second buffer amplifier, said first and second differentiating means being gated in successive operation for simultaneous undelayed and delayed processing of the same differential signal following said perturbation, having large and short settling time constant, respectively, said short settling time constant being selected together with the applied delay time, said zero-correction circuit further including means for storing and measuring the signal shift which occurs between the outputs of said first and second buffer amplifier after said delay time.

18. Apparatus according to claim 17, wherein said storing means comprise a semiconductor switch gated to its low-resistance on-state during the time interval of measurement, a series-connected capacitor, and a double throw switch for switching said capacitor into the feedback loop of said second buffer amplifier.