U.S. patent number 3,870,466 [Application Number 05/323,971] was granted by the patent office on 1975-03-11 for method and apparatus for automatic titration.
This patent grant is currently assigned to Mettler Instrumente AG. Invention is credited to Werner Rellstab, Hans Steiner.
United States Patent |
3,870,466 |
Rellstab , et al. |
March 11, 1975 |
METHOD AND APPARATUS FOR AUTOMATIC TITRATION
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.
Inventors: |
Rellstab; Werner (Steg,
CH), Steiner; Hans (Greifensee, CH) |
Assignee: |
Mettler Instrumente AG (Zurich,
CH)
|
Family
ID: |
4211269 |
Appl.
No.: |
05/323,971 |
Filed: |
January 15, 1973 |
Foreign Application Priority Data
Current U.S.
Class: |
436/51; 422/75;
204/405; 205/788.5 |
Current CPC
Class: |
G01N
31/16 (20130101); Y10T 436/116664 (20150115) |
Current International
Class: |
G01N
31/16 (20060101); B01k 003/00 (); G01n
031/16 () |
Field of
Search: |
;23/23R,253R
;204/1T,195T ;324/3C |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Scovronek; Joseph
Attorney, Agent or Firm: Kleeman; Werner W.
Claims
We claim:
1. 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.
2. The method as defined in claim 1, including the step of
discontinuously supplying in individual amounts a titrating agent
serving as said constituent.
3. The method as defined in claim 2, including the step of
discontinuously supplying the titrating agent in equal individual
amounts at least over part of the titration operation.
4. The method as defined in claim 3, further including the step of
adjusting the size of the equal individual amounts of the titrating
agent.
5. The method as defined in claim 1, wherein the preselected range
is adjustable.
6. The method as defined in claim 1, including the step of setting
a predetermined time delay in order to take into account the
response time of the measuring system.
7. The method as defined in claim 2, further including the step of
visually displaying the respective value of the electrical
measurement parameter prior to the commencement of each operation
of supplying each said individual amount of said titrating
agent.
8. The method as defined in claim 7, further including the step of
visually displaying the respective value of the electrical
measurement parameter only after at least one time interval has
passed since the preceding supply of one said individual amount,
the length of said time interval being governed by the maximum
value of the particular variation in time in the value of the
electrical measurement parameter, but not falling below a given
minimum value, and its number being determined by the frequency
with which the variation in time of the value of the electrical
measurement parameter passes through said preselected region.
9. The method as defined in claim 7, further including the step of
automatically preventing display of an electrical measurement
parameter value upon premature termination of the supply of
titrating agent to the specimen.
10. The method as defined in claim 2, further including the step of
registering the respective value of the electrical measurement
parameter prior to the commencement of each operation of supplying
each said individual amount.
11. The method as defined in claim 10, wherein the registration of
the respective value of the electrical measurement parameter occurs
only after at least one time interval has passed since the
preceding supply of one said individual amount, the length of said
time interval being governed by the maximum value of the particular
variation in time in the value of the electrical measurement
parameter, but not falling below a given minimum value, and its
number being determined by the frequency with which the variation
in time of the value of the electrical measurement parameter passes
through said preselected region.
12. The method as defined in claim 10, further including the step
of automatically preventing registration of the electrical
measurement parameter value upon premature termination of the
supply of titrating agent to the specimen.
13. 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 of the 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.
14. The apparatus as defined in claim 13, further including means
for setting said preselected range.
15. The apparatus as defined in claim 13, further including means
for setting the size of the individual amounts of the supply of
titrating agent.
16. The apparatus as defined in claim 13, further including means
for selectively time delaying a response time of the apparatus.
17. The apparatus as defined in claim 13, further including means
for visually displaying a respective value of the electrical
measurement parameter before the beginning of the supply of each
individual amount of titrating agent.
18. 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.
19. The apparatus as defined in claim 17, further including means
for automatically preventing further display of the value of the
electrical measurement parameter when the supply of titrating agent
to the specimen is prematurely terminated.
20. The apparatus as defined in claim 13, further including means
for registering a respective value of the electrical measurement
parameter before the beginning of the supply of each individual
amount of titrating agent.
21. The apparatus as defined in claim 20, 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 registration of the
respective value of the electrical measurement parameter.
22. The apparatus as defined in claim 20, further including means
for automatically preventing further registration of the value of
the electrical measuring parameter when the supply of titrating
agent to the specimen is prematurely terminated.
Description
BACKGROUND OF THE INVENTION
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.
Methods of automatic titration have long been known in the art and
are used successfully particularly for neutralization and
precipitation reactions in aqueous solution. Generally, automatic
titration does not cause serious difficulties in the case of
reactions which take place rapidly, with the course of the
titration curve being known (for example electrode potential
plotted as a function of the volume of added titrating agent).
This is not the case, however, as regards a number of other
titration problems, particularly redox titrations which generally
occur slowly, titration operations in non-aqueous solution, and
titration operations without a precisely known end point. There
have been many attempts to automate titration in these cases, but
the methods previously proposed in this regard are still not
entirely satisfactory. Thus, for example, some potentiometric
titration methods have been proposed (Swiss Pat. No. 363,508:
Chemische Rundschau No. 35 -1969, , pages 639- 640) in which a
compensation voltage is added to the varying potential of the
electrodes. 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).
Now with the above indicated technique of adding compensation
voltages, it is possible only within limits to achieve precise
titration curves or the points corresponding thereto. This is so
because the follower potentiometers for adjusting the compensation
voltage operate only in one direction during one titration, so that
compensation can be effected only in the direction of increasing
potential (or in the direction of decreasing potential
respectively). This presupposes a titration curve in which the
gradient does not change in sign, and while this is always correct
in theory in the case of potentiometric titrations, it is by far
not always the case in practice.
In particular, however, the reason for one shortcoming of the
above-mentioned method lies in the operating principle. Each
particular point on the curve is determined when the applied
compensation voltage has reached the value of the electrode
potential at that moment. Further changes in the latter, which
occur after such coincidence has been established, remain unheeded,
so that in many cases the points on the curve substantially differ
from the respective "true" points.
SUMMARY OF THE INVENTION
Hence, it is a primary object of the present invention to provide
an improved method of, and apparatus for, automatically titrating a
sample in a manner not associated with the aforementioned
limitations and drawbacks of the prior art proposals.
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 sufficient 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 an improved
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 with a known end point potential which,
however, can only be reproduced with 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.
Now in order to implement these and still further objects of the
invention, which will become more readily apparent as the
description proceeds, the method aspects of this development for
automatic titration, considered in their broader aspects,
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.
Not only is the invention concerned with the aforemenioned method
aspects but also relates to an improved construction of apparatus
for the performance of the aforesaid method, which comprises 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.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and objects other than
those set forth above, will become apparent when consideration is
given to the following detailed description thereof. Such
description makes reference to the annexed drawings wherein:
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:
FIG. 4 shows in graphic form a time plan depicting the course of
the most important functions:
FIG. 5 illustrates a titration curve: and
FIG. 6 illustrates a curve depicting the variation of the potential
after the delivery of an individual amount of titrating agent.
DETAILED DESCRIPTION OF THE INVENTION
A typical redox reaction was selected for the purpose of the
present description, and specifically the volumetric titration of
bivalent iron with permanganate according to the following
equation:
5 Fe.sup.+.sup.+ + MnO.sub.4.sup.- + 8
H.sup.+.fwdarw..sup.+.fwdarw.Mn.sup.+.sup.+ 5 Fe.sup.+.sup.+.sup.+
+ 4 H.sub.2 O
0.01 n KMnO.sub.4 solution was titrated in increments each of 0.1
ml into an original solution comprising 5.241 g of approximately
0.01 n FeSO.sub.4 solution. As was found from evaluation of the
measured electrode potentials, the equivalence point was reached
after the addition of 4.9 ml of titrating solution. A
Pt/AgAgCl-electrode in 3 m KCl solution was used as the measuring
chain.
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 12 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 U.S. 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 15 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 18, a coupler
19 and a puncher 20.
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 12 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, and while referring to FIGS. 2 and 3. After the specimen
to be tested has been introduced into the titration vessel 10 and
the burette 12 has been filled with titrating agent (the electronic
pulse(=volume) counter now being set to zero), 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. This permits a setting between 10 and 990,
and in the embodiment illustrated was set at 100; this means that
with a pulse preset of 10 .times. 10.sup.3 = 10,000, the device
cuts out after 100 increments. In the present embodiment the 10,000
pulses correspond precisely 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 12, 13 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 (13, 17) and the
increment control unit 18. After a second relay of the group 25 has
received the signal "ready" from the burette drive 13, then 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 t.sub.int and, the adjoining externally set time handicap
t.sub.ext ; t.sub.int 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); t.sub.ext is the time handicap or
delay as set at the switch 21, in this case amounts to 1
second.
If after the entire delay time has passed the differentiated signal
still lies within the region between +G 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 15 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 + G and - G, until transfer
of the value of the measurement parameter is concluded, a
monitoring lamp 36 (FIG. 2) is illuminated. Then, after 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 analog-digital reset 32. During the course of the
increment delivery the timers 30 are blocked, in order to avoid
premature output of the measurement parameter, for example due to
sluggish reaction.
After the increment infeed or delivery is concluded, 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.
If, after the preselected number of pulses, the measurement series
has reached the end, then 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 27 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.
In another mode of operation of the apparatus where there is no
punching of the measurement parameter values or no receipting by
the coupler, an oscillator 35 assumes the function of again
cutting-in the analog-digital 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.
Experience has shown that it can occur that a titration operation
is started although, for example, the amount of titrating agent
present in the burette is no longer sufficient to conclude the
titration operation. In order to take this and similar operating
errors into account the invention contemplates that unintentional
termination of the supply of titrating agent (or electrical
charges) to the specimen automatically ensures that the particular
value of the measurement parameter is no longer digitally indicated
and/or registered. In this way measurement values which are not
produced, for example, after the correct addition of titrating
agent, cannot be used to calculate the particular parameter being
sought.
The lowermost broken line 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).
The function of graphic recording of the measurement parameter
values is performed by the recorder 16 connected to the measurement
amplifier 14 and the burette drive 13 (it can also be connected to
the increment control unit 18, instead of to the measurement
amplifier 14, as generally shown in FIG. 1 by a broken line). 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 of the 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: .+-.2
mV/min) is illustrated by a hatched area. There will be recognized
the point E.sub.1 of the beginning of an increment delivery,
followed by a rapid rise in the potential change up to the positive
maximum M.sub.1, to which corresponds an internal time delay
t.sub.int of about 8 seconds. This is followed by a rapid potential
reversal, until the region at B.sub.1 is reached for the first
time. Here the rest of the time t.sub.int is either still 3 seconds
(minimum time) when more than 5 seconds has passed since the
maximum M.sub.1, or if, for example, only 3 seconds have passed
since M.sub.1, the remaining time is 5 seconds. The external time
handicap t.sub.ext 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 t.sub.int + t.sub.ext
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.sub.2, t.sub.int is about 5
seconds; after about 4 seconds, the limit -G is again reached. The
variation in potential, which is now significantly slowed, is still
in the region with (.+-.) 2 mV/min after the passing of t.sub.int +
t.sub.ext = 3 s (minimum value) + 1 s = 4 s, and the value of the
measurement parameter is now removed and, after analog-digital
reset which requires about 0.5 second, a new increment is delivered
at E.sub.2 and thus a new cycle begins.
Because of the dependency of t.sub.int upon the maximum variation
in potential there is taken into account the fact that rapid and
large variations frequently occur in the specimen which change the
sign. There is thus the danger that with an insufficient time
reserve a measurement parameter would be registered, although the
variation again subsequently leaves the set range +G/-G; therefore
an incorrect measurement parameter would be recorded.
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).
The mode of operation of the self-controlling method according to
the invention was described above with reference to a volumetric
potentiometric titration operation, which gives a potentiometric
indication of the course of the reaction, but in principal other
methods of indication also can be used, for example,
conductometric, voltametric, amperometric, photometric or
thermometric titration operations can be performed with the present
method. As the particular characteristic measurement parameter
(conductivity, current strength, transmission, temperature, etc.)
is usually converted into an electrical voltage for reasons of
measuring technique, the term measurement parameter generally used
in connection with the method described above also always signifies
an electric voltage corresponding thereto.
It is preferred for the discontinuous supply to be 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.
So that the method can be adapted to the circumstances of different
titration operations, 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.
It will be noted that 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. In the case of analog
registration 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. 5);
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.
It is also preferred for the particular value of the measurement
parameter to be 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.
According to the nature of the employed measurement sensing means
and the mixing in the titration vessel it can occur that a certain
time passes, after the addition of the titrating agent, before a
variation in the value of the measurement parameter can be
measured. This is particularly the case for electrodes with a
certain response inertia. Thus, in order to be able to also take
these factors into account, 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).
It is obvious that instead of the potentials, as in the above
described example, p.sub.H - or any other suitable p.sub.x - values
can be determined.
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.
While there is shown and described present preferred embodiments of
the invention, it is to be distinctly understood that the invention
is not limited thereto but may be otherwise variously embodied and
practiced within the scope of the following claims.
Accordingly,
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