Note: Descriptions are shown in the official language in which they were submitted.
~A~IKGROUNI:) 0~ Y'IIE INVENY'70N
.~i e 1 d o f l he Lnven tion
The present invention relates to -the determination of
the ionic strengtll or specific gravity of a test sample.
~ore particularly it relates to a composition, test device
and method for determining the ionic strength or specific
gravity of an aq~leous test sample.
I)eseription of the Prior Art
The determination of the specific gravity of a liquid
has application in numerous arts. Thus, such unrelated
disciplines as brewing, urinalysis, water purification,
preparation of drinking water aboard a ship at sea, etc. all
involve the measurement of specific gravity. Needless to
say, a quick, facile method for determining this property
would greatly enhance the state of many scientific arts,
including any technology where rapid, accurate determination
of specific gravity would be beneficial. Thus, for example,
if a medical laboratory technician could accurately measure
the specific gravity of a urine sample in a matter of seconds,
not only would the rapid results aid the physician in diag-
nosis, but also laboratory efficiency would increase to a
degree where many more analyses could be performed than were
heretofore possible.
Althougll the present invention lends itself to a vast
range of applications, for purposes of clarity this dis-
cussion will be couched largely in terms of the determina-
tion of the ionic strength or specific gravity of urine.
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'75
~pplications to other disciplines will become apparent from
an understanding of how this invention relates to urin-
alysis.
Ihe determinatioll of urine speciEic gravity is of
considerable value in the understandillg and clinical manage-
ment of electrolytc disturbances. Hence, complete urinalysis
should, and usually does, include a specific gravity deter-
mination. Generally, such a determination would include the
measurement of specific gravity directly with a suitable
device, but equally useful is the measurement of some
related property, such as osmolality or ionic strength,
which can then be referred back to corresponding specific
gravity values.
Specific gravity is a dimensionless term and relates,
in the case of a solution, to the ratio of the weight of a
certain volume of the solution to that of an equal volume of
water at the same temperature. For solutions such as urine,
the specific gravity is a function of the number, density,
ionic charge, and weight of the various species of dissolved
solutes.
Prior art methods for determining specific gravity
utilize hydrometers, urinometers, pycnometers, gravimeters
and the like. ~lthough these prior art procedures are
satisfactorily sensitive in most cases, they all involve
fragile, bulky instruments which must be constantly cleaned,
maintained, and calibrated in order to continuously assure
their reliability. In addition, there are many inconveniences
associated with the mechanics of using these instruments.
Tllere may be a difficulty in reading the miniscus. Froth or
bubbles on the liquid surface may interfere with the reading.
There is a tendellcy for urinometers to adhere to the sides
of the vessel conta-illing the liquid sample. In the case of
urine, the sanl~)le (luclntity is frequelltly inadequate for
accommodating one of the arorementioned devices.
A recent brcak-tllrough in which all of the above disad-
vantages have been virtually eliminated, and which affords
rapid osmolality (ergo, specific gravity) determination, is
disclosed in U.S. Patent No. 4,015,462, filed by Greyson et
al. on January 8, 1976 and assigned to the present assignee.
This patent describes an inven-tion in which a carrier matrix
is incorporated with osmotically fragile microcapsules, the
walls of which are composed of a semi-permeable membrane
material. Encapsulated inside the walls is a solution
containing a coloring substance. ~hen the capsules are in
contact with a solution having a lower osmolality than that
within the capsules, an osmotic gradient occurs across the
capsule walls in the direction of the lower osmolality,
thereby increasing the hydrostatic pressure within the
capsules, thus causing them to swell and, ultimately, to
rupture, releasing their colored contents. The amount of
color formed from this phenomenon is a function of the
specific gravity of the solution.
It can be seen from the foregoing that besides the
numerous devices which measure specific gravity directly,
it is also possible to measure specific gravity using an
indirect means such as the osmolality of a solution.
Yet another way of estimating specific gravity without
measuring it directly involves a determination which is
-- 4
proportiollal to the ionic strengt}~ of a solution. Such an
approach is util;zed by the present invention. It is well
known that the speciic gravity of an aqueous system is
greatl~ afEected by the prcsence oE charged species. Thus,
in the case of iOlliC solutions, it is possible to closely
approximate tllc speciEic gravity of the respective solutions
via measurements proportional to their ionic strengths and
referring those measurements to a precalibrated reference
system.
The term lliOlliC strength" refers to the mathematical
relationship between the number of different kinds of ionic
species in a particular solution and their respective charges.
Thus, ionic strength ~ is represented mathematically by the
formula
~ cizi
in which c is the molal concentration of a particular ionic
species and z the absolute value of its charge. The sum
is taken over all the different kinds of ions in solution.
U.S. Patent No. 3,449,080 discusses measur~ng dissolved
sodium or chloride ions. This reference is directed to a
test device for determining the concentrations of these ions
in body sweat. Briefly, there is disclosed in this patent
the use of ion exchange resins together with a pH indicator.
Using this device, the presence of sodium or chloride ions
is said to be determined through a color change in the ion
exchange resin caused by the pH indicator. Whereas this
reEerence purports to disclose a way of measuring ionic
strength, it was found by the present inventors that such
teachings, as set forth in the examples, were inapplicable
to the measurement of specific gravity.
Both the osmolality approach and the ionic strength
approach to indirec-tly determining specific gravity could
conceivably be affected insofar as accuracy is concerned by
the presence of non-ionic species. Acc:ordingly, U.S~ Patent
No. 4,108,727, issued August 22, 1978, is directed to a method
for removing this potential source of inaccuracy, and discloses
a device in which the speclfic gravity-sensitive system contains
an ionizing agent capable of converting the non-ionic solute to
ionized species.
To summarize the present state of the art as it might
pertain to the present invention, many methods are known for
the measurement of specific gravity, both direct and indirect.
Direct measurement includes utilizing devices which are fragile,
bulky and expensive, and which must be constantly cleaned,
maintained and calibrated. Of the indirect methods, the measure-
ment of the colligative solution property known as osmolality
can provide an accurate correlation to specific-gravity. The
present invention utilizes a different perspective, the
relationship between specific gravity and the ionic strength
of a solution, and provides a device, composition and method
for taking advantage of this relationship. U.S. Patent No.
3,449,080 describes a method of gauging the concentration of
sodium and/or chloride ions in body sweat. This reference
utilizes the affinity of weakly acidic or weakly basic ion
exchange resins for the unknown ions, and the color changing
capacity of known pH indicators. None of the prior art known
to the present inventors at the time of filing of the instant
application teaches or suggests the invention presently dis-
closed and claimed~
SUM~ IRY OF 'I'llE INVE~'I'ION
Bricfly, the prcsent inventioll rc-~lates to a tes-t compo-
sition, device, and method for determining the specific
gravity of an aqueous test sample. I`he composition com-
prises a weakly acidic or weakly basic polyelectrolytepolymer, whic}l has bcen at least par-tially neutralized, and
an indicator substance capable of producing a detectable
response to ion exchange between the polyelectrolyte and the
test sample. The device of the present invention comprises
a carrier matrix incorporated with the composition. The
method of the present invention comprises contacting a test
sample with the device or compostion and observing a detect-
able response such as a color change.
BRIEF DESCRIPTIO~I OF THE DRA~ CS
Figures 1-8 are graphic portrayals of (a) the responses
of three polyelectrolytes to test samples having varying
specific gravities, and (b) the titration or partial neutrali-
zation of these polymers. Thus Figures 1, 2 and 3 are
titration curves for a copolymer of methyl vinyl ether and
maleic anhydride, poly(acrylic acid), and poly(vinylamine)
respectively. Figures 4, 5 and 6 depict the performances of
these polyelectrolytes in determining urine specific gravities
after varying degrees of partial neutralization of the
polymer pendant group. Figure 7 shows similar performance
of poly(vinylamine) in aqueous salt solutions of varying
concentrations. Finally, Figure 8 shows the performance of
a preferred device.
DEYIA TLED DESCRIPY'ION OE T~E INVENTl ON
The presently claimed composition comprises, as one
ingredient, a weakly acidic or weakly basic polyelectrolyte.
Numerous examples of such polymers are known in the art,
their common characteristics centering about the degree o-E
dissociation oE the ionic pendant groups when the polymer is
suhjected to an aqueous enviromnent. Most polyelectrolytes
are soluble or partially soluble in water, and are readily
ionizable, depending on the ionic nature of (a) the aqueous
system and (b) the ionizable species on the polymer chain.
Thus a polyelectrolyte is branded weakly or strongly
acidic or basic depending on its ionic behavior. Generally,
a polyelectrolyte which nearly completely ionizes when
contacted with water, such as poly(vinylsulfuric acid) and
lS poly(styrene sulfonic acid), are considered strong poly-
electrolytes. Weak polyelectrolytes Oll the other hand,
contain weakly acidic or basic ionizable groups. The charge
density along the molecular chain of these polymers can be
varied by varying the degree of neutralization. Examples of
weakly acidic or weakly basic polyelectrolytes which find
particular applicability to the present invention are poly-
(acrylic acid)~ poly(maleic acid), maleic acid/methylvinyl
ether copolymer~ poly(methacrylic acid), styrene-maleic acid
copolymer, poly(4-vinylpyridine), and others.
lhe composition of the present invention includes
weakly basic and weakly acidic polyelectrolytes, but more
particularly it includes those which have been partially
neutralized At least some of the functional groups of the
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polymer, be they weakly acidic (e.g., COOII) or weakly basic,
are first partially titrated with a base or acid, respec-
tively, prior to incorporating the polyelectrolyte into the
test composition. Typically, aqueous solutions of titrant
are employed, and basic titrants include solu~ions of NaOII,
KOII, Na2CO3, poly(etllyleneimine), tris(hydroxymethylamine)
methane and others known to chemists reasonably skilled in
the art. Surprisingly, such partial titration or neutrali-
zation has been found to be necessary in order to enable
significant differentiation between specific gravity levels
in test solutions.
Preferably, the polymer is neutralized to at least
about 50%, i.e., at least about half of the ionizable groups
are neutralized. An ideal neutralization range, and that
presently found most preferred in the present invention, is
from about 75 to about 95% neutralization, 90% having thus
far been found to be optimum in providing the largest sepa-
ration in p~l change or other detectable response with
respect to specific gravity or ionic strength.
The polyelectrolyte selected for use in the present
invention must, as stated supra, be partially neutralized.
This is accomplished by titration of the polymer with
suitable acid or base as desired, or by any other means
which achieves the desired result of partial neutralization.
Thus, Figure 1 constitutes the titration curve of Gantrez
S-97, a maleic anhydride/methylvinylether copolymer marketed
by General Aniline and Film Corporation, with sodium hydroxide
in aqueous solution. Figure 2 shows similar data for
poly(acrylic acid), and Figure 3 poly(vinylamine).
Another element of the composition is an indicator
means responsive to ion exchange. It can take on such
diverse forms as a pH meter, a pH indicator, and other means
determinable by a person having reasonable skill in the art.
Tilus a pll meter can be used with a standard pH electrode (in
solution systems) or with a surface pH electrode ~where the
composition is incorporated with a carrier matrix). The pH
meter response can then be observed over various ionic
strength valucs and a reference system can be established,
a particular change in pH corresponding to a particular test
sample ionic strength.
Alternatively, known pH-sensitive chromogenic reagent
compounds can be employed, and these can provide a change in
or appearance of color, observable by the person performing
the measurement, which is indicative of the ionic strength
or specific gravity of the system being tested. If a
chromogen is used, a reference color system can be estab-
lished beforehand, so that a quick visual comparison of the
composition and the reference system provides the sought
after results. Examples of chromogens suitable for use in
the present invention are bromothymol blue, alizarin, brom-
cresol purple, phenol red and neutral red; bromo~hymol blue
having been found to be especially suitable.
The present invention includes a device in which a
carrier matrix is incorporated with the presently disclosed
test composition to provide a tool for obtaining rapid,
reliable estimations of solution specific gravities. The
carrier matrix is usually, but not necessarily, a porous
substance such as filter paper. Other art-recognized forms
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;2'7~
of carrier matrix materials are felt, porous ceramic strips,
and woven or matted glass fibers (lJ.S. Patcnt No. 3,846,247).
Also suggested are the use of wood~ cloth, sponge material
and argillaceous substances (U.S. I'atent No. 3,552,928).
All such carrier matrix materials are feasible for use in
the present invention, as are others. It has been found
that filter paper is especially suitable.
In a preferred embodiment, filter paper is wetted with
a solution or suspension of a partially neutralized poly-
electrolyte in water or other suitable vehicle easily
determinable by routine laboratory experiments and then
dried. The polyelectrolyte-bearing filter paper is subse-
quently wetted with a solution of the desired indicator
means (such as bromothymol blue) in methanol or other
suitable solvent such as ethanol, N,N-dimethylformamide,
dimethylsulfoxide, and subsequently dried. Alternatively, a
one-dip method can be used whereby the polyelectrolyte and
indicator means are simultaneously present in the initial
solution or suspension.
The dried, reagent-bearing carrier matrix can be
mounted on a backing material if desired. The test device,
in a preferred embodiment, thus comprises a filter paper
carrier matrix~ incorporated with a partially neutralized
polyelectrolyte and indicator means as described supra, the
matrix being affixed to one side to an elongated piece of
transparent polystyrene film. The matrix is secured to one
end of the film by any suitable means, such as double faced
adhesive tape (Double Stick~ available from 3M Company), the
other end of the polystyrene film serving as a handle. In
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~ 5
use, such a device is held by the free end of the poly-
styrene film backing material and the matrix end is immersed
into the test sample (e.g., urine) and quickly removed. Any
color format;on or other .letectable response is observed
after a precLetermined time and compared with a reference
standard corresponding to responses to known solution ionic
strengths or specific gravities.
The particular reference standard employed depends on
whether the composition is used by itself or incorporated
with a carrier matrix, as well as on the particular indi-
cator means. Thus if the partially neutralized polyelec-
trolyte is added directly to the test sample, and the
indicator means is a pH meter, a reference standard can be
devised by adding a standard weight of polyelectrolyte to a
standard volume of a solution of known ionic strength. The
pH change before and after polyelectrolyte addition is
recorded using the pH meter. This procedure is followed for
a series of solutions having varied known ionic strengths.
To determine the ionic strength of an unknown test sample,
the same procedure is followed and the pH change compared
with those for the known solutions.
Where a test device comprising a carrier matrix con-
taining partially neutralized polyelectrolyte and a chromogen
is employed, a reference standard can comprise a series of
color blocks depicting the color developed by the carrier
matrix after a predetermined time in response to solutions
of known ionic strengths. When testing an unknown sample,
the carrier matrix of a test device is immersed in the
sample, removed, and observed for the appearance of or
change in color after the predetermined time. Any color
response is then compared with the reference standard color
blocks to ascertain the ionic strength or specific gravity
of the sample.
The following ixamples are provided to further teach
how to make and use the present invention. Thus, preferred
embodiments are described and analyzed. The Examples are
meant to be illustrative only, and are in no way intended as
limiting the scope of the invention described and claimed
herein.
A. THE COMPOSITION
ExampZe I - PartiaZ NeutraZization of MaZei~ Anhydride/
MethyZvinyZet~er ~opoZymer
This experiment was performed to study the partial
neutralization of a polyelectrolyte (Gantrez~ S-97 marketed
by General Aniline and Film Corporation), and its effect on
a composition for measuring solution specific gravity.
A modular automatic titrator was assembled for the
titration of various polyelectrolytes for study pertinent to
the present invention. The titrator consisted of an auto-
matic pipetter, Model No. 25000, from Micromedic Systems,
Inc. This instrument is capable of dispensing a constant
volume of titrant per unit time into the polymer solution to
be titrated. The rate of addition of titrant (ergo, the
rate of polyelectrolyte neutralization), was controlled
through the selection of pipette volume, the fraction of
pipette volume dispensed, and the concentration of titrant.
Changes in pll during titration were detected using a standard
pH electrode and an Orion Model 701 digital pH meter.
'75
The output of the pH meter ~as fed into a ~lewlett-rackard
~lodel 17500A ten inch strip chart recorder, the scale of
which had been calibrated such that one inch corresponded to
a change of one pH unit. Hence, the recorder provided a
continuous monitor of p~ changes with respect to time (ergo
with respect to volu~e of titrant added~.
This apparatus was used to titrate and observe the
effects of partial neutralization on'IGantrez S-97" a weakly
acidic polyelectrolyte. A solution of~Gantrez~was prepared
comprising 20 grams of the polyelectrolyte per liter of
deionized water. Three 100 milliliter (ml) aliquots of this
solution were placed in 250 ml bea~ers. One aliquot was
made 0.lN and another l.ON with NaCl. No salt was added to
the remaining aliquot. By titrating each of these poly-
electolyte solutions with l.ON NaOH in a 50 ml. pipette ata rate of 9.0 ml. titrant per hour, and recording pH change
VerSus volume of titrant, it was possible to study the
titration characteristics of ~'Gantrezq as well as the effects
of partial neutralization on its ability to differentiate
varying ionic strengths.
The titration data obtained in this experiment is
plotted graphically in Figure 1. Curve A represents the
titration of the polyelectrolyte solution to which no salt
was added, curve B represents titration of the polyelec-
trolyte solution made 0.1N in NaCl, and curve C representsthe titration of the polyelectrolyte solution containing
NaCl at l.ON concentration. The clear separation which
occurs between curves A, B and C in Figure 1 is indicative
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.,"~ ,"~,
~ 5
of the effect of ionic stren~th on the apparent pK of the
polymer. Thus, by observing the clegrees of separation
between the titration curves i.e. 5 of pH values for a given
amount of titrant, one can estimate maximization with
respect to determining different levels of specific gravity.
For example, greater separation is observed in the regions
between pH 5 and pH 10 than at other stages of polymer
neutralization. The curves in Figure 1 indicate that
optimum separation occurs with a degree of polymer neutrali
zation from about 70% to 95% or more (i.e., addition of
about 6.0 to 9.0 ml. titrant). Not only is this information
useful in gauging the effectiveness of the polymer in
aqueous systems, but it also helps towards determining
optimum neutralization of the polyelectrolyte for incor-
poration with a carrier matrix as will be seen in ExampleIV, infra.
The percent neutralization of a given polyelectrolyte
can be calculated from titration data such as that presented
graphically in Figure 1 by curve A (the titrat;on of the
polyelectrolyte, here'l~antrez S-97~ with no added salt).
Percent neutralization of the polymer is calculated for a
given pH of titrated polymer solution by finding the solution
pH on the vertical axis, extending a horizontal line from
the vertical axis to curve A, and extending a vertical line
from that point on curve A to the horizontal axis (i.e., ml.
of l.ON NaOH). The volume of titrant (corresponding to the
intersection of the vertical line and the horizontal axis)
divided by the titrant volume at the end point of titration,
multiplied by 100 yields a close approximation of the per-
cent of polyelectrolyte neutralization. Titration end point
is indicated by vertical linearity of curve A at the far
right, and can be expressed in terms of the volume of
titrant added.
Thus, forJ~Gantrez S-97,' the end point shown in Figure 1
is very close to 9.0 (about 8.6) ml of l.ON NaOH titrant.
Titration of thel'Gantrez~fsolution in deionized water to a pH
of about 7.5 corresponds to a volume of about 6.0 ml titrant.
Since the end point is about 8.6 ml of titrant, percent
neutralization is calculated by
6.0 ml. (titrant) x 100 = 70 (percent
~.6 ml. (titrant at end point) neutralized)
E.~ampZe II - PartiaZ NeutraZization of PoZy(acryZic aci~J
This experiment was performed to study the partial
neutralization of poly(acrylic acid) and the effects of such
neutralization on the usefulness of this polyelectrolyte in
determining solution specific gravity. The modular auto-
matic titrator, pH meter and electrode described in Example
I were employed, as was the procedure.
A solution of the poly~acrylic acid), a weakly acidic
polyelectrolyte obtained from Aldrich Chemical Co. (Cata-
logue No. 19,205-8), was prepared by dissolving 20 grams of
polymer in one liter of deionized water. Aliquots of 100
milliliters each of this solution were placed in 250 ml
beakers. One of the aliquots was made 0.lN and another l.ON
in NaCl. No salt was added to the third aliquot. Each of
these solutions was then titrated with 10.ON NaOH in a
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,~ .
'75
50 ml. pipette at a rate of 3.0 ml. titrant per hour. The
results are reported in ligure 2 in wllich curve A represents
tlle polyelectro]y~e solution containing no salt, curve B the
solution made 0.lN in NaCl, ancl curve C the solution made
l.ON in NaCl.
The data depicted by Figure 2 illustrates that the
greatest separation Wit}l respect to ionic strength (i.e.,
between curves A, B and C) occurs from about 50% to about
95% or greater neutralization of the polymer (i.e., addition
of about 1.5 to about 3.0 ml. titrant). Thus, for example,
where the polymer has been titrated over a 40 minute period
(with 2.0 milliliters of 10N NaOE-I), one can see marked
separation of the resultant pH depending upon the ionic
strength of the solution. Curve C which corresponds to l.ON
NaCl provides a resultant pH value of about 5.25, curve B
corresponding to 0.lN NaCl yields a pEI value of about 5.S,
and curve A, which corresponds to zero concentration of
NaCl, yields a pH value of about 6.25. Thus, the ionic
strength or specific gravity of a particular solution can be
approximated by using these values and interpolating between
them.
ExampZe III - Partie~ Neutra~izetion of PoZy~viny~a~ine,'
This experiment was performed to study the partial
neutralization of a weakly basic polyelectrolyte, poly-
(vinylamine) obtained from Dynapol, Inc., and the effects ofsuch neutralization on the usefulness of this polyelectro-
lyte in determining specific gravity. The modular automatic
titrator, pH meter and electrode described in Example I were
employed, as well as the procedure.
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A solution of poly(vinylamine) in its hydrochloride
salt form (completely neutralized) having a molecular weight
of about 60,000 was prepared having a polymer concentration
of 20.0 grams per liter of deionized water. Three aliquots
of 100 milliliters each of this solution were placed in 250
ml beakers. One of the aliquots was made 0.5N and another
3.ON in NaCl. No salt was added to the remaining aliquot.
Each of these solutions was then titrated with l.ON NaOH
using a 50 milliliter pipette at a rate of 9.0 ml titrant
per hour. The results are depicted in Figure 3 in which
curve A represents titration of the polyelectrolyte solution
to which no salt was added, curve B the solution made 0 SN
in NaCl and curve C titration of the solution made 3.ON in
NaCl.
The data in Figure 3 shows that little response occurs
with respect to ionic strength when the polymer is com-
pletely in the amine or non-neutralized form (pH 10, 35
minutes), whereas excellent separation occurs at lower
degrees of titration, i.e. where neutralization of the
polymer is more extensive. Hence, the ability of poly-
(vinylamine) to differentiate different ionic strength
levels varies inversely with the amount of titrant, SUC]I
that at the onset of the titration (in excess of 95~ neutrali-
zation) excellent separation is produced, whereas at zero
neutralization (addition of about 5.3 ml. titrant), no
separation occurs.
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~ . THE ~5~ DEVICE
E~ampZe IV - Performance of ~Zeic Anhydride/MethyZvin~ether
CopoZymer in a Carrier ~atrix
The solution employed in Examyle I~ (20 grams of~'Gantrez
S-97"per liter of deionized water) was further studied to
observe its behavior in measuring urine specific gravity
when incorporated with a carrier matrix.
A test device sensitive to ionic strength or specific
gravity was prepared by incorporating the solution of Gantrez
S-97 into filt~r paper and then drying. Several test de-
vices were prepared in order to study the performance of the
polyelectrolyte at various degrees of neutralization. Thus,
aliquots of the~l~antrez S-97~solution were neutralized to
different extents by titration with NaOH. Strips of filter
paper obtained from Eaton and Dikeman ~No. 204) were respec-
tively immersed in these partially titrated aliquots and
subsequently dried. Impregnated dried strips made from each
of the aliquots were then respectively dipped into urines
having different known specific gravities and into dei-onized
water, and the pH thereof was measured. A p~ meter having a
flat surface electrode obtained from Markson Science, Inc;
(No. 1207 BactiMedia combination pH/reference electrode) was
used for these measurements. The values of QpH, i.e., the
difference in the pH of identical strips dipped respectively
into deionized water and urine of known specific gravity,
are tabulated below.
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~ .
pH of Polyelectrolyte ~pH Values Produced by Urines
Solution Aliquots of Indicated Specific Gravities
Sp.Gr. Sp.Gr. Sp.Gr.
1.030 1.015 1.005
_
4.75 0.20 0.29 0.32
6.0 1.04 0.91 0.54
7.0 1.70 1.44 0.65
8.0 2.41 2.06 1.04
9.25 3.24 2.29 1.09
9.75 3.52 2.66 1.65
The data in the above table has been plotted in Figure
4, wherein the three curves represent values of ~pH produced
by urines having the indicated specific gravity values when
tested with strips made from aliquots of different degrees
of neutralization. It can be seen from ~igure 4 that the
degree of separation of the curves increases markedly as the
degree of neutralization of the polyelectrolyte, i.e., the
pH, increases. Thus, the more partial neutralization of the
~IGantrez"polyelectrolyte, the greater the ability to differ-
entiate between specific gravity levels in urine.
ExampZe V - Performance o~ PoZy(acryZic acidJ in a Carrier
Matrix
The polyelectrolyte employed in Example II (20 grams of
poly(acrylic acid) per liter of deionized water) was further
studied to observe its behavior in measuring urine specific
gravity when incorporated with a carrier matrix.
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'75
Test devices were prepared and tested as in Example IV,
except that poly(acrylic acid) was substituted for"Gantrez
S-97./ A solution of 20 grams of poly(acrylic acid) per
liter of deionized water was prepared. Aliquots of this
solution were titrated with lON sodium hydroxide until the
pH levels stated in the table below were achieved. Strips
of filter paper obtained from Eaton and ~ikeman (No. 204)
were respectively dipped into these aliquots and dried.
They were then respectively dipped into urines of different
known specific gravity and into deionized water and the pff
thereof was measured. The values of QpH were determined as
in Example IV and are tabulated below. A pH meter having a
flat surface electrode obtained from Markson Science, Inc.
(No. 1207 BactiMedia combinatian pH/reference electrode) was
used for these measurements.
pH of Polyelectrolyte QpH Values Produced by Urines
Solution Aliquots of Indicated Specific Gravities
Sp.Gr. Sp.Gr. Sp.Gr.
1.005 1.015 1.030
4.0 0.11 0.05 0.00
5.0 0.5 0.64 0.70
6.0 0.56 0.88 1.09
7.0 0.76 1.29 1.68
7.5 0.91 1.40 1.98
8.0 1.15 1073 2.29
8.25 1.10 1.82 2.10
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~ ~!~ - .
~7~
'75
The data in the above table is plotted in Figure 5,
which, like Figure 4, shows that the degree of separation of
the curves therein increases markedly as the degree of
neutralization, i.e., the pH, of the polyelectrolyte increases.
E~ampZe VI - Performance of Po~y(vinyZamine) in a Carrier
~atrix
The polyelectrolyte employed in Example III was further
studied to observe its behavior in measuring various urine
specific gravities when incorporated with a carrier matrix.
Test devices were prepared and tested as in Examples IV
and V except that poly(vinylamine) was substituted for
"Gantrez S-97 and poly(acrylic acid), respectively. A
solution was prepared comprising 20 grams of poly(vinylamine)
(obtained from Dynapol, Inc., 60,000 M.W., see Dawson, et
al.J J.A.C.S. 98, 5996, 1976) per liter of deionized water.
The polyelectolyte used was in the hydrochloride form and
thus was in the completely neutralized state. Aliquots of
this solution were respectively titrated with l.ON NaOH to
produce the solution pH levels stated in the table below.
Strips of filter paper obtained from Eaton and Dikeman (No.
204) were respectively dipped into these aliquots and dried.
They were then respectively dipped into different known
specific gravity urines and into deionized water and the pH
thereof was measured using the flat surface electrode
described in Examples IV and V. The values of apH were then
determined as in Examples IV and V and are tabulated below.
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7S
pH of Polyelectroylte ~pl-l Values Produced by Urines
Solution Aliquots of Indicated Specific Gravities
Sp.Gr. Sp.Gr. Sp.Gr.
1.005 1.015 1.030
2.8 1.05 1.60 1.78
3.0 1.06 1.64 1.92
3.5 .89 1.11 1.29
4.0 .89 1.17 1.21
6.0 +.06 -.10 -.33
8.0 -0.71 -.99 -1.70
10.0 -1.45 -1.47 -2.24
11.0 -1.80 -2.50 -2.81
12.0 -2.Z4 -2.57 -3.07
The graph of this data, Figure 6, portrays useful
separation when the polyelectrolyte is partially neutralized
to below about pH 5. Thus the curve for urine having a
specific gravity of 1.005 results in a much smaller change
in pH than for urine at a specific gravity of 1.030. The
urine having a specific gravity of 1.015 resulted in inter-
mediate ~pH values as expected.
This effect is even more dramatically demonstrated whenthe poly(vinylamine) test devices are respectively dipped
into aqueous salt solutions of different ionic strengths and
into deionized water and the pH thereof measured to provide
~pH values. Thus strips prepared as above were tested with
various concentrations of sodium chloride in deionized
water. Specifically these salt solution concentrations were
0.5, 1.5 and 3.ON in NaCl. The data obtained in this
- 23 -
experiment is tabulated below and plotted in Figure 7.
Curves A, B and C correspond to salt solutions of 3.0, 1.5
and 0.5N in NaCl, respectively.
pl-l of Polyelectrolyte ~pH Values Produced by Salt
Solution Aliquots Solutions of Indicated Normalities
0.5N NaCl 1.5N NaCl 3.0N NaCl
2.8 .60 .63 .93
3.0 1.04 1.37 1.46
3.5 .88 .99 1.23
4.0 1.00 1.32 1.61
6.0 .90 .93 1.03
8.0 .64 .64 .68
10.0 .61 .64 .60
11.0 -.01 -.03 -.10
12.0 -.09 -.22 -.29
Referring to Figure 7, at pH 10 where the polyelec-
trolye is essentially unprotonated and uncharged, the effect
of varying salt concentration is virtually non-existent.
Partial neutralization of the polymer, however, effects a
steadily increasing divergence of performance in response to
ionic strength, as evidenced by the increasing difference
between the respective plots reflecting widely divergent ~pH
response to differing ionic strengths.
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E~ampZe VII - ~e~t D~vice Prepared Vsing Ma~eic finhydride/
~e~hyZvi~yZether Copo~ym~r and Bromothymo~ B~ue
The test composition of Example I was employed in a
carrier matrix together with bromothymol blue, a known pH
indicator, to study the characteristics of the presènt
invention with respect to visual determination of specific
gravity.
A solution was prepared containing 20 grams of Gantrez
S-97/per liter of deionized water. An aliquot of this
solution was titrated with NaOH until the resultant solution
pH was 8.0 as measured with the pH meter and electrod~
described in Example I. A strip of filter paper (Eaton
Dikeman No. 204) was immersed in the partially titrated
(neutralized) aliquot and subsequently dried. The dried
polymer-bearing strip was then immersed in a methanol solu-
tion of bromothymol blue at a concentration of 1.2 grams per
liter. After drying, the filter paper strip was mounted on
a clear plastic backing material (Trycite* obtained from Dow
Chemical Co.) using double faced adhesive tape ~bouble
Stick" obtained from 3M Company). The resultant test devices
each comprised a strip of~Trycite"measuring about 3.5 in. by
0.2 in., one end of which bore a square of the impregnated
filter paper measuring 0.2 in. on a side. The rest of the
'ITrycite"served as a handle.
The sensitivity of these test devices to specific
gravity was studied by ~esting with three different specific
gravity urine samples and with water. A device was immersed
in the particular test solution and quickly removed After
- 25 -
* Trade Mark for axially orientated polystyrene film
._:f~.. ~
,t.. ...
,~'. . j
~ 5
60 seconds the device was examined in reflectance spectro-
photometer which scans and measures the intensity of reflected
light from the test device over the visible spectral regions
every half a second.
S The data obtained at 60 seconds is plotted in Figure 8
and shows marked scparation enabling easy and accurate
specific gravity differentiation between water (specific
gravity l.000) and urines at specific gravity levels of
1.005, 1.015 and 1.030. Visual color differentiation was
equally easy, the device exhibiting a blue color with water,
blue-green with urine at specific gravity 1.005, green at
1.015 and yellow at 1.030.
This example demonstrates the relationship between
partial polyelectrolyte neutralization and specific gravity
or ionic strength determination. The'GantTez"solution from
which the device was made had a pH of about 8. Referring to
curve A of Figure 1, this pH corresponds to about 6.8 ml of
titrant. Using the calculation described in Example I, this
corresponds to about 79% neutralization. The remarkabie
differentiation between specific gravity levels realized in
the foregoing experiment is attributable to this relatively
high degree of polyelectrolyte neutralization.
- 26 -
.~
-- .,
