Method and apparatus for end point detection in potentiometric titration

Claim 2

The method of claim 2, wherein said electrical signals are digital representations of the quantity of titrant delivered, said digital signals being accumulated to provide a continuous record of the quantity of titrant added to said sample.

Claim 3

The method of claim 3, further including the step of halting said titration when said first derivative returns to said preset value.

Claim 4

The method of claim 4, wherein the measurement of titrant added to said sample further includes: accumulating all of the said digital signals generated before said first derivative reaches said preset value; and accumulating one-half of the said digital signals thereafter generated.

Claim 5

The method of claim 5, further including the step of displaying a value represented by said accumulated digital signals to obtain the volume of titrant added to said sample to reach the said end point.

Claim 6

The method of claim 6, wherein the step of displaYing a value includes the steps of summing the digital signals accumulated before said preset first derivative value is reached with the digital signals thereafter accumulated, the value of said sum representing the total volume of titrant added to reach said end point.

Claim 8

The method of claim 8, further including selecting said predetermined value sufficiently near the maximum value of said first derivative that said derivative is substantially symmetrical about said maximum value above said predetermined value.

Claim 9

The method of claim 9, wherein the said second rate of accumulation of said electrical signals is one-half the said first rate of accumulation.

Claim 10

The method of claim 10, further including the step of halting said titration when said first derivative returns to said predetermined value, and thereafter obtaining directly from the accumulated electrical signals the amount of titrant added to reach the end point of said titration.

Claim 12

The method of claim 12, further including supplying said titrant to said sample at a first rate until a predetermined quantity has been dispensed, and thereafter supplying titrant at a second rate.

Claim 13

The method of claim 13, further including the step of reading the accumulated pulse count to provide a direct indication of the volume of titrant added to said sample to reach said end point.

Claim 14

The method of claim 14, including the step of selecting said predetermined threshold value sufficiently near the maximum value of said first derivative that said derivative is substantially symmetrical about said maximum value and above said threshold.

Claim 16

In a potentiometric titrator for determining the equivalence point of a sample, apparatus for providing a direct and accurate measure of the volume of titrant added to said sample in reaching said equivalence point, comprising: a sample cell for receiving a sample to be titrated; means for supplying titrant to said sample cell; means for generating electrical signals corresponding to the volume of titrant supplied; means for measuring the electrical potential of said sample and producing an output corresponding to the first derivative of said potential; means for storing all of said electrical signals until said first derivative reaches a predetermined value and for thereafter storing only a predetermined portion of said electrical signals; and means responsive to said first derivative output for halting said titration when said first derivative returns to said predetermined value.

Claim 17

The apparatus of claim 17, further including means responsive to said first derivative output for producing a threshold signal when said output reaches said predetermined value, said means for storing electrical signals responding to the occurrence of said threshold signal to store only said predetermined portion of said electrical signals.

Claim 18

The apparatus of claim 18, further including means for reading out the total value of said stored electrical signals to obtain the total volume of titrant supplied to reach said equivalence point.

Claim 19

The apparatus of claim 18, wherein said means for reading includes display means.

Claim 20

The apparatus of claim 17, wherein said means for generating electrical signals includes pulse means for producing at least one pulse per unit volume of titrant delivered.

Claim 21

The apparatus of claim 21, wherein said means for storing electrical signals comprises counter means for counting said pulses.

Claim 22

The apparatus of claim 22, wherein said means for storing electrical signals includes gate means responsive to said first derivative output, said gate means operating in a full count mode to deliver all of said pulses to said counter means until said first derivative reaches said predetermined value, said gate means thereafter operating in a half-count mode to deliver only alternate pulses to said counter means.

Claim 23

The apparatus of claim 23, wherein said gate means includes means responsive to said first derivative output for producing a threshold signal when said output reaches said predetermined value, and a count gate responsive to said threshold signal, said threshold signal shifting said count gate from a full count mode to a half-count mode.

Claim 24

The apparatus of claim 24, further including readout means for obtaining a direct indication of the accumulated count in said counter, and thus of the total volume of titrant added to said sample.

Claim 25

The apparatus of claim 17, wherein said means for supplying titrant includes burette means for delivering metered quantities of titrant to said cell, and electric motor means for driving said burette at a controlled speed.

Claim 26

The apparatus of claim 26, wherein said means for generating electric signals comprises means responsive to the operation of said burette to generate at least one electrical pulse for each unit volume of titrant delivered by said burette.

Claim 27

The apparatus of claim 27, wherein said burette is operated by a rotary, motor-driven shaft, and said pulse generating means comprises photoeleCtric means reponsive to the rotation of said shaft for producing a plurality of pulses for each rotation of said shaft.

Claim 28

The apparatus of claim 27, further including control means for said electric motor means for selectively driving said burette at one of two speeds.

Claim 29

The apparatus of claim 27, wherein said means for storing said electrical signals comprises counter means for receiving said generated electrical pulses and for accumulating a count corresponding to the number of pulses received.

Claim 30

The apparatus of claim 30, wherein said means for storing said electrical signals further comprises count gate means having a full count mode and a half-count mode, said count gate shifting from one mode to the other when said first derivative reaches said predetermined value.

Claim 31

The apparatus of claim 31, further including readout means for displaying the count accumulated in said counter and to display the volume of titrant added to said sample.

Claim 32

The apparatus of claim 17, wherein said means for measuring the electrical potential of said samples includes electrode means for immersion in said sample, said electrodes producing a potential difference which is a measure of the pH of said sample, and circuit means connected to said electrodes for producing the first derivative of said electrode potential difference.

Claim 33

The apparatus of claim 33, further including trigger means responsive to a predetermined value of said first derivative, said trigger means producing an output threshold signal as long as said first derivative exceeds said predetermined value.

Claim 34

The apparatus of claim 34, wherein said means for storing said electrical signals includes count gate means responsive to said threshold signal, said count gate means operating in a full count mode to store all of said electrical signals in the absence of said threshold signal and operating in a half-count mode to store only alternate ones of said electrical signals in the presence of said threshold signal.

Claim 35

The apparatus of claim 35, wherein said means for generating electric signals comprises burette means for delivering metered quantities of titrant to said cell, and means responsive to the operation of said burette to generate at least one electrical count pulse for each unit volume of titrant delivered by said burette.

Claim 36

The apparatus of claim 36, wherein said means for generating electric signals further comprises second trigger means for supplying said electrical count pulses to said count gate means.

Claim 37

The apparatus of claim 37, wherein said means for storing said electrical signals comprises counter means responsive to count pulses passed by said count gate, said count gate being operative in its full count mode to pass all of said count pulses to said counter means, and being operative in its half-count mode to pass alternate ones of said count pulses.

Claim 38

In a potentiometric titrator for automatically determining the volume of titrant added to a sample to reach the end point of a titration; a sample cell for receiving a sample to be titrated; burette means for delivering metered quantities of titrant to said cell, and electric motor means for driving said burette; motor control logic circuit means for regulating the speed of said electric motor means; means responsive to the operation of said burette to generate at lease one count pulse for each unit volume of titrant delivered by said burette; counter means for receiving said count pulses and for accumulating a count corresponding to the number of pulses received; count gate means interposed between said means for generating count pulses and said counter means, said count gate having a full count mode wherein all of said generated count pulses are passed to said counter means and having a half-count mode wherein only one-half of said generated count pulses are passed to said counter means; means for measuring the potential of said sample during titration thereof, and ciRcuit means for producing the first derivative of said potential; means responsive to a predetermined value of said first derivative to produce a threshold signal; and circuit means for applying said threshold signal to said count gate to shift said count gate from a full count mode to a half-count mode and for holding said count gate in the half-count mode as long as the value of said first derivative exceeds said predetermined value.

Claim 39

The apparatus of claim 39, wherein said motor control logic circuit means includes a delivery selector network responsive to said counter means, said delivery selector network producing an initial delivery signal upon delivery of a predetermined volume of titrant to said sample, said motor control circuit being responsive to said initial delivery signal to change the speed of said electric motor means, whereby an initial quantity of titrant can be added to said sample at a different rate than the rate at which the remainder of titrant is added.

Claim 40

The apparatus of claim 40, further including inhibit circuit means for inhibiting the production of said threshold signal, said delivery selector network including means for producing a permit signal subsequent to said initial delivery signal and upon delivery of an additional predetermined volume of titrant, said permit signal disabling said inhibit circuit means.

Claim 41

The apparatus of claim 41, wherein said motor means includes a high speed motor and a low speed motor, and wherein said motor control logic circuit means includes switching means for selectively energizing said motors, said switching means initially energizing said high speed motor and being responsive to said initial delivery signal to de-energize said high speed motor and energize said low speed motor.

Claim 42

The apparatus of claim 42, further including means responsive to the termination of said threshold signal for disabling said count gate and for de-energizing said electric motor means.

Claim 43

The apparatus of claim 43, further including means for reading out the total count accumulated in said counter means to obtain the total volume of titrant delivered to said sample to reach said end point.