US3870466A - Method and apparatus for automatic titration - Google Patents

Method and apparatus for automatic titration Download PDF

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Publication number
US3870466A
US3870466A US323971A US32397173A US3870466A US 3870466 A US3870466 A US 3870466A US 323971 A US323971 A US 323971A US 32397173 A US32397173 A US 32397173A US 3870466 A US3870466 A US 3870466A
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value
measurement parameter
electrical measurement
specimen
time
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Werner Rellstab
Hans Steiner
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Mettler Toledo GmbH Germany
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Mettler Instrumente AG
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Assigned to METTLER-TOLEDO AG (METTLER-TOLEDO SA) (METTLER-TOLEDO LTD), IM LANGACHER GREIFENSEE, SWITZERLAND reassignment METTLER-TOLEDO AG (METTLER-TOLEDO SA) (METTLER-TOLEDO LTD), IM LANGACHER GREIFENSEE, SWITZERLAND CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). NOVEMBER 24, 1989 Assignors: METTLER INSTRUMENTE AG
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
    • G01N31/16—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using titration
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T436/00—Chemistry: analytical and immunological testing
    • Y10T436/11—Automated chemical analysis
    • Y10T436/115831—Condition or time responsive
    • Y10T436/116664—Condition or time responsive with automated titrator

Definitions

  • ABSTRACT A method of, and apparatus for, automatic titration of a specimen to be tested, wherein means which causes a reaction with the specimen to be tested, such as a titrating agent or electrical charges for producing a reagent, is discontinuously supplied in individual amounts to the specimen. The variation in time in the value of a measurement parameter characterizing the condition of the specimen is determined. The respective next individual amount of said means is only supplied after the variation in time in the value of the measurement parameter has fallen below a predetermined value.
  • the present invention relates to a new and improved method for automatic titration, such as volumetric potentiometric titration, and also concerns a new and improved construction of apparatus for carrying out the aforesaid method.
  • the compensation voltage compensates for the variation in potential caused by an addition of titrating agent, and automatically causes printing of the respective potential and a further addition of agent when the first coincidence occurs between the electrode potential and the compensation voltage (the latter being generated by a motor-driven potentiometer).
  • Another and more specific object of the present invention relates to an improved method of, and apparatus for, carrying out automatic titration of a specimen or sample wherein the points on the titration curve can be ascertained with a degree of precision which is suffrcient for practical purposes and which is considerably better than the previously proposed techniques and equipment for deriving same.
  • Still a further object of this invention relates to animproved method for automatic titration which can be employed for virtually any titration problems, but especially in redox reactions (a reaction which generally occurs slowly), for titration operations in non-aqueous medium, and in titration operations without a known end point potential, or witha known end point potential which, however, can only be reproducedwith difficulty.
  • Yet a further significant object of the present invention relates to an improved method of, and apparatus for, carrying out automatic titration operations in which there can be obtained both the pattern or course of the titration curve in graphically portrayed form and the numerical values which permit evaluation of the titration by calculation.
  • a still further object of the invention relates to an improved titration method which allows for carrying out measurements with electrodes having unstable potentials in which it is only necessary to ascertain relative changes in potential within the respective titration operation: and such factor plays a part, for instance, in many ion-sensitive electrodes.
  • the method aspects of this development for automatic titration contemplate discontinuously supplying to the specimen to be tested, in individual amounts, constituent which causes a reaction with such specimen, then the next individual amount of such constituent is-supplied only after the variation with time in the value of a measurement parameter characterizing the condition of the specimen has dropped below a predetermined value.
  • the constituent which is discontinuously supplied in individual amounts to the specimen can be a titrating agent or electrical charges for producing a reagent.
  • a reaction vessel having one or more measuring sensing means, means for supplying titrating agent or electrical charges, a measuring amplifier for amplification of the value of the measurement parameter, means for forming the first differential in time of the measurement parameter, means for controlling the supply of titrating agent or electrical charges, said control means being provided with means for comparing the variation in time in the value of the measurement parameter with predetermined value, and means for imparting a supply command to the supply means after the aforesaid variation falls below such predetermined value.
  • FIG. 1 is a schematic block circuit diagram of an exemplary embodiment of apparatus for the performance of the method of this development:
  • FIG. 2 is a front view of a portion of the apparatus depicted in FIG. 1:
  • FIG. 3 is a block circuit diagram of a portion of the apparatus: I
  • FIG. 4 shows in graphic form a time plan depicting the course of the most important functions:
  • FIG. 5 illustrates a titration curve
  • FIG. 6 illustrates a curve depicting the variation of the potential after the delivery of an individual amount of titrating agent.
  • FIG. 1 The schematically shown arrangement of FIG. 1 was used to carry out the titration operation.
  • a titration vessel 10 contained the specimen to be tested.
  • An electrode measuring chain 11 dipped into the solution which was continuously and uniformly mixed by a conventional stirrer (not shown) the electrode measuring chain 11 serving to measure the momentary potential which was dependent on the condition in the solution.
  • a burette l2 supplied the titrating agent or reagent.
  • a burette drive 13 besides a stepping motor and a variable-frequency pulse transmitter, also included a pulse counter for indicating the volume of titrating agent used (a pulse-controlled piston burette with a stepping motor drive was used, as described in principle, for example, in US. Pat. No. 3,319,840 to which reference may be readily made).
  • a measuring amplifier 14 serves for amplification of the electrode potential and for differentiation thereof as a function of time.
  • a digital indicator l5 enables the particular electrode potential to be conveniently read-off, and a recorder 16 serves to record the titration curve.
  • a remote control unit 17 for instance of the type described in Swiss Pat. No. 501,217 was used for starting and for selecting the speed of delivery (pulse or volume per time). Finally, there was provided an increment control unit 118, a coupler l9 and a puncher 20.
  • FIG. 1 A portion of the elements diagrammatically shown in FIG. 1 are arranged above one another in the form of a module system in stackable housings, namely the measuring amplifier 14, the digital indicator 15, the increment control unit 18 and the coupler 19.
  • the burette l2 and the burette drive 13 are constructed in the form of a structural unit.
  • the increment control unit 18 forms an important component of the apparatus according to the invention. Its functions will be described in greater detail hereinafter'with reference to the operation of automatic potentiometric titration with the above example,
  • the stirrer is set into operation in order to thoroughly mix the specimen.
  • the following settings are made at the increment control unit 18: at a rotary switch 21 the time handicap or delay of 1 second for the response time of the measuring system: at a rotary switch 22 the value of the variation in time of the potential 2 mV/min; at a rotary switch 23 the pulse preset or selection, that is to say, selection of the desired number of pulses until the end of the titration operation; and finally, at a multiswitch 24 the number of pulses per increment.
  • the device cuts out after 100 increments.
  • the 10,000 pulses correspond pre cisely to the burette volume of 10 ml; each increment therefore embraces 0.1 ml.
  • the preset pulse counter 34 is designed such that when the preset number of pulses is reached, an increment which may just have been started (for example, as a result of awkward coordination of the number of pulses per increment to the total of pulses), is supplemented to the full number (here 100) of pulses before the end signal is delivered. This prevents an incorrect measurement parameter value owing to the delivery of an incomplete increment.
  • the delivery or infeed speed is set at the remote control unit 17 by controlling the frequency of the pulse transmitter in the burette drive 13, for example 100 pulses (0.1 ml) in 6 seconds.
  • the apparatus is then started by pressing a start button of the remote control unit 17 and cutting in the mains connection of the burette assembly l2, l3 and the amplifier 14.
  • This starting pulse causes operation of a first relay of a relay group 25 which forms a galvanic coupling between external elements (l3, l7) and the increment control unit 18.
  • a logic release 26 is operated which takes over the communication between the relay group 25 and the internal electronic assembly of the increment control unit 18, and the apparatus begins to operate.
  • the condition of operation is signalled by the weak illumination of a lamp 27 on the increment control unit 18.
  • a zero measurement is carried out first of all: the potential as measured by the electrodes 11 is amplified and differentiated in the amplifier 14, the differentiated signal passes the analog amplifier 28 and arrives at the threshold switch 29.
  • the response value of the threshold switch 29 is determined or controlled by the analog amplifier 28 which can be switched by means of a series of parallel connected resistors, that is to say, the differentiated signal is amplified to a greater or lesser degree according to the desired degree of sensitivity (setting at the rotary switch 22). If the amplified differentiated signal drops below the predetermined threshold value, then the timers 30 come into operation and determine the length of the delay before the measurement value output.
  • This delay is composed of an internally variable time interval r and, the adjoining externally set time handicap r r depends on the magnitude of the variation in potential as a function of time, and at most amounts to 10 seconds, the minimum value being 3 seconds (when the limits of the range are reached, +G and G of FIG. 6); I is the time handicap or delay as set at the switch 21, in this case amounts to I second.
  • the differentiated signal still lies within the region between +6 and -G (the range set at the switch 22), it is therefore less than 2 mV/min, then by means of the data transfer 31 there is given the signal for measurement parameter value output.
  • the potential supplied by the amplifier 14 is indicated both in the digital indicator l5 and also transmitted by means of the coupler 19 to the tape puncher or perforator 20. From the beginning of the entry of the differentiated measurement parameter into the region delimited by +6 and G, until transfer of the value of the measurement parameter is concluded, a monitoring lamp 36 (FIG. 2) is illuminated.
  • the coupler 19 has registered or receipted the data there follows the analog-digital reset, at component 32, with subsequent starting order for the first increment supply to the increment pulse counter 33, according to the zero measurement which has now been completed.
  • the increment pulse counter 33 transmits the starting order to the burette drive 13 and at the same time again places into operation the analog evaluation (threshold switch 29) which was interrupted during the analogdigital reset 32.
  • the timers 30 are blocked, in order to avoid premature output of the measurement parameter, for example due to sluggish reaction.
  • the cycle described above for zero measurement is repeated, to wit: tracing the pattern of the potential, falling below the threshold value, passing of the time delay, removal of the value of the measurement parameter, reset, delivery of a fresh increment.
  • the preset pulse counter 34 supplies a signal which cuts-out the apparatus after the last time delay has expired and the value of the measurement parameter has been taken off.
  • the lamp 227 is now brightly illuminated and in this way visually signals that the titration operation has been completed.
  • Irrespective of the preselected termination point or end the titration operation can be interrupted at any time, that is to say, the apparatus can be cut-out by actuating the remote control unit 17.
  • an oscillator 35 assumes the function of again cutting-in the analogdigital reset 32.
  • FIG. 4 illustrates the essential steps of the individual measuring operations in the form of a sequence diagram. The correlation of the individual phases described above will be recognised.
  • FIG. 4 therefore also illustrates a burette empty signal which will occur if for any reason (for example operating error) the preset volume exceeds the amount still contained in the burette; after the remainder of the burette contents has been titrated to the vessel 10, the signal burette empty which is to be delivered by the burette drive 13 and transmitted by way of the preset pulse counter 34 to the data transfer 31, causes the measurement to be immediately interrupted and the apparatus to be cut out, without the started increment producing a measurement parameter value. This not only prevents that an incorrect value of the measurement parameter will be produced, but also ensures that there is no recording of dummy" measurement parameters, which are not preceded by an increment delivery (apart from zero measurement at the beginning of the measurement series).
  • FIG. 5 A typical curve is portrayed in FIG. 5 in which the delivered volume V is plotted in ml as a function of the potential E. Only a small number of increments are illustrated for the sake of clarity.
  • FIG. 5 clearly shows the step form which is characteristic of the present method and the large jump in potential at the equivalence point P.
  • FIG. 6 diagrammatically shows one form of the course or pattern of the curve ofthe potential E differentiated in time as a function of the time t.
  • the preselected range for the variation in time which range is delimited by +G/G (in the above example: i2 mV/min) is illustrated by a hatched area.
  • the rest of the time 1 is either still 3 seconds (minimum time) when more than 5 seconds has passed since the maximum M or if, for example, only 3 seconds have passed since M the remaining time is 5 seconds.
  • the external time handicap r would thereafter have to expire before the value of the measurement parameter could be removed or taken-off. Since, however, the variation in potential has already moved out of the hatched region in the negative area, before r I has passed, then when the limit G, that is to say, the threshold switch 29, is exceeded, both timers 30 have been reset and the delay began anew. At the minimum M r is about 5 seconds; after about 4 seconds, the limit G is again reached.
  • the method provides equilibrium titration; only when the value of the differential quotient of the value of the measurement parameter versus time is lower than a predetermined value, that is to say, a good approximation to a condition of equilibrium is established in the specimen to be tested, is the next amount of titrating agent supplied (or produced).
  • discontinuous supply is effected, at least over a part of the titration operation, in equal individual amounts, since the supply of equal individual amounts or increments affords the substantial advantage that evaluation by calculation of the individual points on the curve, for example by means of desk computers, is greatly simplified.
  • the size of the respective individual amounts of titrating agent or electrical charges to be supplied is preferably adjustable. It is also of advantage for the predetermined value of the variation in time in the value of the measurement parameter to be adjustable; in this way, it is possible to achieve an approximation according to the particular problem encountered, which is virtually as precise as may be desired to the particular condition of equilibrium.
  • the removal or pick-up of the measurement parameter value is preferably such that, before the commencement of each operation of supplying an individual amount, the respective value of the measurement parameter is indicated and/or registered in an analog and/or digital manner.
  • the volume of titrating agent is indicated by means of a recording pen for example on the abscissa, while the particular potential measured is entered on the ordinate (as shown in FIG. in that case, the paper feed is synchronised in known manner with the supply of titrating agent, for example by a drive by means of two synchronously moving motors.
  • the particularvalue of the measurement parameter is indicated and/or registered'only after at least one time interval has passed since the preceding supply of an individual amount of titrating agent.
  • the length of the time interval depends upon the maximum value of the particular variation in time of the measurement parameter, but without falling below, a given minimum value, and its number being influenced by the frequency with which the variation in time in the value of the measurement parameter passes through the region delimited by the predetermined value.
  • This facet of the method takes account of the fact that in many cases the variation in the measurement parameter must first swing in or oscillate about a value before a condition of equilibrium is established, that is to say, the variation for example experiences a rapid increase, then falls back and assumes a negative value, and so forth. The above mentioned step avoids premature removal or pick-up of the measurement parameter.
  • the response time of the measurement system is taken into account by the selection of the additional time handicap or delay.
  • the titration method described above can adapt its time requirement exactly to the particular condition, that is to say, measurement parameter values of virtually any desired precision are fully automatically produced without requiring an excessive amount of time.
  • the inventive method makes it possible to determine precise values even when the nature of the titration curve is unknown, in other words without empirical date, and so-to-speak to titrate blind.
  • the conventional principle of manual operation is followed: delivery of titrating agent, waiting, reading-off, noting, delivery, and so forth.
  • the method is virtually universal in application and, particularly when operating with uniform increments within each titration operation, it is highly suitable for connection to electronic data processing means, for example for the determination by calculation of the equivalence points in accordance with one of the known methods (for example, the Kolthoff or the Fortuin methods).
  • Another possible use of the method is building up process controls by the connection of suitable elements.
  • the method is suitable not only for carrying out volumetric titration operations, but is likewise applicable to coulometric procedures in which a reagent performing the function of the titrating agent is formed in the specimen by supplying electrical charges, and the number of charges supplied is monitored.
  • a method for the automatic titration of a specimen to be tested comprising the steps of discontinuously supplying in individual amounts to the specimen a constituent which causes a reaction with the specimen, determining the variation in time in the value of an electrical measurement parameter characterizing the condition of the specimen, and supplying a respective next individual amount of said constituent only after the variation in time in the value of said electrical measurement parameter has entered a preselected range.
  • An apparatus for the automatic titration of a specimen to be tested comprising a reaction vessel for the specimen and having at least one measuring sensing means, means for discontinuously supplying individual amounts of a titrating agent to the specimen, a measuring amplifier for amplification ofthe value of an electrical measurement parameter characterizing the condition of the specimen, means for forming the first differential in time of the electrical measurement parameter, means for controlling the supply of titrating agent, said controlling means incorporating means for comparing the variation in time in the value of the electrical measurement parameter with a preselected range, and means imparting a supply command to said supply means after said variation has entered said preselected range.
  • the apparatus as defined in claim 17, further including means for producing at least one variable time interval between the first variation in the value of the electrical measurement parameter falling below the preselected range and the indication of the respective value of the electrical measurement parameter.

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US323971A 1972-02-01 1973-01-15 Method and apparatus for automatic titration Expired - Lifetime US3870466A (en)

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CH147272A CH534877A (de) 1972-02-01 1972-02-01 Verfahren zur automatischen Titration sowie Vorrichtung zur Durchführung des Verfahrens

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JP (1) JPS5424676B2 (sv)
CH (1) CH534877A (sv)
DE (1) DE2300793C2 (sv)
FR (1) FR2163190A5 (sv)
GB (1) GB1381966A (sv)
SE (1) SE388046B (sv)

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4095272A (en) * 1977-01-11 1978-06-13 Phillips Petroleum Company Automatic turbidimetric titration
US4120657A (en) * 1976-04-20 1978-10-17 Egyt Gyogyszervegyeszeti Gyar Process of and equipment for the analysis of liquid samples by titration
US4165218A (en) * 1976-11-04 1979-08-21 Siemens Aktiengesellschaft Monitoring surfactant in electrolyte during metal treatment
US4180440A (en) * 1978-05-15 1979-12-25 Fisher Scientific Company Variable endpoint analyzer
US4302299A (en) * 1977-12-27 1981-11-24 Mitsubishi Kasei Kogyo Kabushiki Kaisha Titration control method
US4554255A (en) * 1982-07-09 1985-11-19 Sanwa Shoji Co., Ltd. Determination of sulfurous acid in liquids and an apparatus therefor
US5104527A (en) * 1988-03-24 1992-04-14 Ashland Oil, Inc. Automatic total reducers monitoring and adjustment system using titration
US5246863A (en) * 1988-08-29 1993-09-21 Harald Dahms Karl Fischer titration techniques
US5291418A (en) * 1991-07-05 1994-03-01 Eastman Kodak Company Adjustment of electric potential by automatic titration
US5518933A (en) * 1989-03-10 1996-05-21 Unitika Ltd. Method of analyzing washings for free acids and ions
EP0892268A1 (en) * 1997-07-18 1999-01-20 ENITECNOLOGIE S.p.a. Method for determining the flocculation of asphaltenes in oil
US6372505B1 (en) * 1998-11-03 2002-04-16 Mehler-Toledo Gmbh Process and apparatus for titrating
US6793387B1 (en) 1999-05-08 2004-09-21 Chata Biosystems, Inc. Apparatus for automatic preparation of a mixture and method

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS50126292U (sv) * 1974-03-30 1975-10-16
JPS5913699B2 (ja) * 1977-01-12 1984-03-31 三井金属鉱業株式会社 亜鉛溶解液に溶存する鉄イオン濃度の測定装置
US4283201A (en) * 1979-11-02 1981-08-11 Phillips Petroleum Company Method and apparatus suitable for repeated, accurate chemical analyses
JPH02107070U (sv) * 1988-12-30 1990-08-24
DE59308722D1 (de) * 1993-04-07 1998-08-06 Metrohm Ges Mit Beschraenkter Kombinierte Titriervorrichtung

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2740694A (en) * 1952-11-07 1956-04-03 Harold A Frediani Method and apparatus for control of titrations and other phenomena
US2834654A (en) * 1954-02-01 1958-05-13 Murayama Makio Method and apparatus for automatic amperometric titration
US2950178A (en) * 1957-10-09 1960-08-23 Geigy Ag J R Apparatus for automatic titration
US3305468A (en) * 1962-12-12 1967-02-21 Velsicol Chemical Corp Automatic titration apparatus

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2740694A (en) * 1952-11-07 1956-04-03 Harold A Frediani Method and apparatus for control of titrations and other phenomena
US2834654A (en) * 1954-02-01 1958-05-13 Murayama Makio Method and apparatus for automatic amperometric titration
US2950178A (en) * 1957-10-09 1960-08-23 Geigy Ag J R Apparatus for automatic titration
US3305468A (en) * 1962-12-12 1967-02-21 Velsicol Chemical Corp Automatic titration apparatus

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4120657A (en) * 1976-04-20 1978-10-17 Egyt Gyogyszervegyeszeti Gyar Process of and equipment for the analysis of liquid samples by titration
US4165218A (en) * 1976-11-04 1979-08-21 Siemens Aktiengesellschaft Monitoring surfactant in electrolyte during metal treatment
US4095272A (en) * 1977-01-11 1978-06-13 Phillips Petroleum Company Automatic turbidimetric titration
US4302299A (en) * 1977-12-27 1981-11-24 Mitsubishi Kasei Kogyo Kabushiki Kaisha Titration control method
US4180440A (en) * 1978-05-15 1979-12-25 Fisher Scientific Company Variable endpoint analyzer
US4554255A (en) * 1982-07-09 1985-11-19 Sanwa Shoji Co., Ltd. Determination of sulfurous acid in liquids and an apparatus therefor
US5104527A (en) * 1988-03-24 1992-04-14 Ashland Oil, Inc. Automatic total reducers monitoring and adjustment system using titration
US5246863A (en) * 1988-08-29 1993-09-21 Harald Dahms Karl Fischer titration techniques
US5518933A (en) * 1989-03-10 1996-05-21 Unitika Ltd. Method of analyzing washings for free acids and ions
US5291418A (en) * 1991-07-05 1994-03-01 Eastman Kodak Company Adjustment of electric potential by automatic titration
EP0892268A1 (en) * 1997-07-18 1999-01-20 ENITECNOLOGIE S.p.a. Method for determining the flocculation of asphaltenes in oil
US6372505B1 (en) * 1998-11-03 2002-04-16 Mehler-Toledo Gmbh Process and apparatus for titrating
US6793387B1 (en) 1999-05-08 2004-09-21 Chata Biosystems, Inc. Apparatus for automatic preparation of a mixture and method

Also Published As

Publication number Publication date
JPS4885193A (sv) 1973-11-12
JPS5424676B2 (sv) 1979-08-22
CH534877A (de) 1973-03-15
SE388046B (sv) 1976-09-20
GB1381966A (en) 1975-01-29
FR2163190A5 (sv) 1973-07-20
DE2300793A1 (de) 1973-08-09
DE2300793C2 (de) 1984-03-15

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