Monitoring method for polyacrylic acids in aqueous systems

A quantitative method useful for field monitoring low concentrations of water soluble, polyacrylic acids in aqueous systems containing polyacrylic acids and other soluble ionic materials, such as ionic salts and phosphonates, is provided. The method involves adjusting the pH of the aqueous system to suppress the ionization of the polyacrylic acids followed by selective adsorption and concentration of the polyacrylic acids on a suitable adsorbent. Concentrated polyacrylic acids are then desorbed from the adsorbent and the concentration of the polyacrylic acids in the aqueous system is determined by conventional techniques.

BACKGROUND OF THE INVENTION 
This invention relates to a simple, quantitative method for isolating and 
concentrating water soluble, polyacrylic acids from dilute aqueous systems 
containing polyacrylic acids and the other soluble ionic materials. More 
particularly, the invention relates to a method for selectively adsorbing 
and concentrating low concentrations of ionization suppressed polyacrylic 
acid, polymethacrylic acid, mixtures and copolymers thereof (hereinafter 
defined as polyacrylic acids) from aqueous systems containing these 
polyelectrolytes and other soluble ionic materials, such as ionic salts 
and phosphonates. These soluble ionic materials typically interfere with 
the ability of conventional techniques to monitor the concentration of the 
polyacrylic acids in aqueous systems. 
Water soluble polyacrylic acid, polymethacrylic acid, polymaleic acid, and 
copolymers formed from at least 50 weight percent of acrylic, methacrylic, 
or maleic acid and less than 50 weight percent of another copolymerizable 
monomer and mixtures thereof, referred to hereinafter generally as 
polyacrylic acids, are used commercially as scale inhibitors and 
dispersants in such aqueous systems as cooling towers, boilers, oil field 
production facilities, sea water evaporators, and detergents. These 
polymers interact with scale forming, inorganic salts formed by the 
reaction of hardness ions, such a calcium and magnesium, with anions such 
as carbonate, phosphate and sulfate. The polyacrylic acids function by 
interfering with the growth of the crystals of these salts 
(antiprecipitation), or by introducing a repulsive surface charge to the 
crystals retarding their agglomerating, settling and depositing on 
surfaces (dispersion), or by interfering with the structure of the crystal 
itself making the scale more easily fracturable and dispersable (crystal 
modification). In addition, these polymers are also useful for dispersing 
other suspended particulate matter, such as clay, in aqueous systems. Rohm 
and Haas Company's ACRYSOL.RTM. LMW polymers of polyacrylic acids and 
their corresponding sodium salts, having weight average molecular weights 
ranging from about 1,000 to about 4,500, are known to be effective scale 
inhibitors in aqueous system to inhibit common hardness ion salts. In 
addition, U.S. patent application Ser. No. 485,560 also relates to water 
soluble, low molecular weight copolymers of acrylic acid and methacrylic 
acid which are useful for scale inhibition in aqueous systems. Further, 
U.S. patent application Ser. No. 485,559 relates to a method of dispersing 
inorganic materials in aqueous systems using low molecular weight 
copolymers of acrylic acid and hydrophobic comonomers. 
Other organic compounds, such as organophosphates and organophosphonates, 
are also commonly used as scale inhibitors in aqueous systems. One such 
group of organic phosphonate scale inhibitors are manufactured and sold by 
Monsanto Chemical Company under the trademark Dequest.RTM.. In addition, 
other ionic compounds, such as inorganic phosphates, may also be used in 
these aqueous systems to assist in retarding the corrosion of metal 
surfaces. 
Presently there is no simple, fast, reproducible, and sensitive, low cost 
method for selectively determining the concentration of polyacrylic acids 
in aqueous systems containing other soluble ionic materials such as 
hardness ions and phosphonates. The presence of these soluble ionic 
materials in the aqueous system interferes with the ability of 
conventional methods to measure small concentrations of polyacrylic acids, 
on the order of about 5 ppm or less, in such aqueous systems. One such 
technique in which soluble ionic salts interfere with the determination of 
the concentration of polyacrylic acids involves precipitation with 
bivalent copper, filtration, redissolution of the precipitate, and assay 
of unreacted bivalent copper (U.S. Pat. No. 3,516,795). 
A suitable method for determining the concentration of polyacrylic acids in 
aqueous systems containing soluble ionic materials must be fast, simple, 
and capable of yielding reproducible results. It must avoid the use of 
toxic or hazardous chemicals, must be able to completely isolate 
polyacrylic acids from organic phosphonates, must be able to concentrate 
polyacrylic acids from the aqueous system to gain sensitivity, and must be 
capable of eliminating possible interference in the measurement caused by 
corrosion inhibitors, inorganic salts, colored impurities, and 
interspersed oil droplets. 
Such a simple, fast, reproducible, and sensitive, low cost method for 
determining the concentration of polyacrylic acids in aqueous systems 
containing other soluble ionic materials is desired by operators of 
cooling towers, boilers, and other systems which use polyacrylic acids as 
scale inhibitors or dispersants. Such a monitoring method would allow 
operators to make economical decisions in the field concerning the timing 
and need for additional polyacrylic acids. 
It is therefore an object of the present invention to provide a solution to 
the problem of monitoring the concentration of polyacrylic acids in 
aqueous systems by providing a simple, fast, reproducible, and sensitive, 
low cost method for selectively adsorbing and concentrating polyacrylic 
acids from aqueous systems containing other soluble ionic materials so 
that the concentration of the polyacrylic acids in the aqueous system can 
be determined. 
It is also an object of the present invention to provide a method for 
quantitatively monitoring the concentration of polyacrylic acids in 
aqueous systems containing polyacrylic acids and other soluble ionic 
materials. 
It is a further object of the invention to provide a method for determining 
the concentration of both polyacrylic acids and organic phosphonates in 
aqueous systems containing such compounds. 
SUMMARY OF THE INVENTION 
I have found that the above objectives can be realized by a novel method 
for selectively adsorbing and concentrating low levels of water soluble, 
polyacrylic acids from aqueous systems containing polyacrylic acids and 
other soluble ionic materials by suppressing the formation of polyacrylic 
acid ions followed by selectively adsorbing the ionization suppressed 
polyacrylic acids using an effective adsorbent medium, and desorbing the 
concentrated, adsorbed polyacrylic acids, free of interfering ionic 
impurities, for subsequent quantitative determination. 
This method is fast, simple, reproducible, safe accurate, low in cost, and 
especially useful at a field location for routine monitoring operations. 
DETAILED DESCRIPTION OF THE INVENTION 
The method of this invention is directed to the quantitative determination 
of low levels of water soluble, polyacrylic acid, polymethacrylic acid, 
polymaleic acid, and copolymers formed from at least 50 weight percent of 
acrylic, methacrylic or maleic acid and less than 50 weight percent of 
other copolymrizable comonomers and mixtures thereof. Suitable comonomers 
include acrylamide, lower alkyl acrylates, lower alkyl methacrylates, 
hydroxy alkyl acrylates, and hydroxy alkyl methacrylates where the alkyl 
group contains from 1 to about 4 carbon atoms, and the like. These 
copolymers, in their acid form, are soluble in aqueous systems containing 
such polymers and other soluble ionic materials. The polyacrylic acids may 
have a weight average molecular weight ranging from about 1,000 to about 
60,000. Higher molecular weight polyacrylic acids are also suitable in 
this invention as long as they are water soluble. The polyacrylic acids 
may be prepared using any conventional synthesis route including, but not 
limited to, the methods described in U.S. Pat. Nos. 4,314,004; 4,301,266; 
and 3,646,099 for preparing low molecular weight polyacrylic acids. 
Accordingly, the polymer chain of the polyacrylic acids may be terminated 
with any suitable chain terminating moiety, such as isopropanol, 
3-mercaptopropionic acid, sodium bisulfite, and the like, without 
affecting the method of the present invention. 
The method of this invention requires three basic steps: (1) the 
suppression of ions of the polyacrylic acids in the aqueous system; (2) 
adsorption and concentration of the ionization suppressed polyacrylic 
acids onto an effective adsorbent; and (3) desorption of the adsorbed 
polyacrylic acids from the adsorbent utilizing a small volume of an 
effective displacement medium which is compatible with subsequent 
conventional assay methods for quantitatively measuring the concentration 
of the polyacrylic acids. 
Prior to the ionization suppression step, it may be desirable to filter a 
sample of the aqueous solution containing the polyacrylic acids and other 
soluble ionic materials. This filtration step is useful for removing 
particulates and/or suspended oil droplets which may be present in the 
sample and, which if not removed, would contaminate the adsorbent reducing 
its effectiveness and ability to be re-used. Any filter media which is 
compatible with the aqueous system sample can be used to remove the 
particulate material. I have found that filters having a pore size of 
about 5.0 micrometers in diameter are preferred for this application. 
Filters having much smaller pore diameters have been found to clog too 
rapidly and may not, therefore, be capable of handling a sufficient sample 
volume. The most preferred filter has been found to be a Gelman 
Associates, Acrodisc.RTM. 5.0 micrometer, disposable filter assembly 
attached to a syringe fitted with a plunger. This filter assembly has been 
found to be very convenient to handle and the syringe attachment allows 
for rapid filtration of the sample. 
If oil droplets are dispersed in the sample, they may be removed by first 
passing the sample through standard filter paper, such as 12.5 cm Whatman 
No. 41 ashless, folded in a cone, and supported in a funnel. More 
preferably, I have found that glass wool packed into the bottom portion of 
the syringe above the attached Acrodisc.RTM. filter is excellent for 
complete removal of oil droplets from the sample. 
After the particulates and/or oil droplets have been removed from the 
sample, the polyacrylic acids in the sample are ionization suppressed. 
This ionization suppression step is critical in preparing the polyacrylic 
acids for subsequent selective adsorption and concentration. Polyacrylic 
acids are ionization suppressed by the addition of a suitable quantity of 
an acid such as hydrochloric, nitric, or sulfuric acid. While nitric acid 
has been found to be the most preferred acid, sulfuric acid may be 
preferred in certain instances due to safety considerations. Polyacrylic 
acids are sufficiently ionization suppressed when the pH of the sample has 
been reduced to less than about 3.5. At pH of about 1 or lower, however, 
other ions in the sample, such as the organic phosphonates, will also 
become neutralized. Further, at below about pH 2 the cartridge may begin 
to degrade. The neutralization of the other soluble ions in the sample is 
not desired since, if they were so neutralized, the adsorption step would 
not be selective for the adsorption of polyacrylic acids. Therefore, the 
pH of the sample should be adjusted to from about 3.0 to about 2.0 and 
preferably to about 2.5. If the pH of the sample is unintentionally 
lowered below about 2, then back correction of the pH may be made by the 
addition of a suitable amount of a base such as sodium hydroxide. The pH 
adjustment may be accomplished by standard titration and the pH tested by 
pH indicator paper, by the use of a standard pH meter, or other suitable 
techniques. After the polyacrylic acids in the sample have been ionization 
suppressed by pH adjustment, the sample is ready for selective adsorption. 
Selective adsorption and concentration of the ionization suppressed, 
polyacrylic acids is accomplished by passing a suitable volume of the 
sample through a non-polar, adsorbent. The adsorbent must have the 
capability and capacity to selectively and completely adsorb, and thereby 
concentrate, small concentrations of ionization suppressed polyacrylic 
acids while allowing the adsorbed materials to be easily desorbed 
therefrom by the use of a small quantity of a non-interfering, 
displacement fluid. The adsorbents which have been found to be suitable 
for the method of this invention include non-polar, bonded phase, silica 
gels, and certain organic polymeric resins. The silica gel type adsorbents 
include octadecylsilane bonded to silica gel such as Sep-Pak.RTM. C-18, 
manufactured by Waters Associates, Baker-10 octadecyl, manufactured by J. 
T. Baker Company and Bond Elut.RTM. C.sub.18 .RTM. manufactured by 
Analytichem International. Silica gel coated with octylsilane is also a 
suitable adsorbent for the process of the invention. The organic polymeric 
resins which can also be used in this invention include rigid, 
macroreticular styrene-divinylbenzene copolymer resins having adsorptive 
properties similar to the above packings, such as PRP-1.RTM. manufactured 
by Hamilton Company. The preferred adsorbent for use in the invention is 
the Sep-Pak.RTM. C.sub.18 cartridge. The adsorbents may be packed into a 
column but are preferably used in the form of small cartridges fitted with 
a syringe. 
Prior to passing the ionization suppressed, polyacrylic acid sample through 
the adsorbent, it is desirable to condition the adsorbent as by properly 
wetting the adsorbent. This conditioning may be conducted by treating the 
adsorbent with methanol followed by a water rinse, the water being at 
about the same pH as the ionization suppressed, polyacrylic acid sample. 
The ionization suppressed polyacrylic acid sample is then passed through 
the adsorbent. The best technique for conducting the adsorption is by 
attaching the top of the adsorbent cartridge to the fitting of a three-way 
syringe valve connected to a 50 cc Luer-Lock syringe. The sample is then 
fed downflow through the syringe, through the valve and through the 
adsorbent cartridge. 
The top of the syringe may be fitted with a plunger to force the sample 
through the adsorbent at a rapid rate of about 25 milliliters per minute. 
Subatmospheric pressure (vacuum) can also be applied to the syringe to 
force the sample through the adsorbent. The water, hardness ions, 
phosphates, and phosphonates are not adsorbed and exit the adsorbent as 
effluent. This effluent may be collected, as it leaves the adsorbent, for 
subsequent phosphonate analysis. 
The adsorbed, ionization suppressed, polyacrylic acids are therefore 
selectively concentrated on the adsorbent. The volume of the sample passed 
through the adsorbent is recorded so that the concentration of the 
polyacrylic acids in the aqueous system sample can be determined. By 
increasing the volume of the sample fed to the adsorbent, the sensitivity 
of the concentration measurement of the polyacrylic acids in the sample 
will be increased. 
The adsorbed, ionization suppressed, polyacrylic acids are then desorbed 
from the adsorbent by the use of a suitable displacement fluid which 
completely displaces adsorbed polyacrylic acids and does not interfere 
with the ability of the adsorbent to be reused. A suitable displacement 
fluid is an aqueous solution of 0.1 normal sodium hydroxide. When the 
displacement fluid is to be added to the syringe, the valve should be 
closed to the cartridge and the plunger removed. When the valve is not 
attached, the adsorbent cartridge should first be removed to prevent 
disturbance of the adsorbent. The three-way Luer-Lock valve, which is 
preferably used in the practice of this invention, allows for variety of 
operations. One position of the valve is closed to the cartridge and the 
air. When the valve effluent pathway is positioned in the direction of 
liquid flow through the syringe, the liquid passes directly through the 
cartridge. This position is used during conditioning, adsorption, and 
desorption. When the valve effluent pathway is positioned in a direction 
perpendicular to flow through the syringe, the syringe effluent pathway is 
to air. This position allows for the removal of the syringe plunger 
without disturbing or removing the cartridge. This valve position also 
allows for drawing a reagent up into the syringe for subsequent passage 
through the cartridge without removal of the plunger. When the three-way 
valve is not connected to the syringe, the cartridge must be removed 
before the syringe plunger is pulled back to allow for the addition of 
additional fluid. After the plunger is removed, the cartridge may then be 
replaced and the displacement fluid is pushed through the adsorbent with 
the reinserted plunger. 
Methanol, sodium hydroxide solution, or other suitable displacement fluids 
may be used to desorb the adsorbed polyacrylic acids. Desorbing the 
polyacrylic acids using methanol is preferred since the adsorbent is also 
being conditioned for subsequent adsorption. If a sodium hydroxide 
solution is used as the displacement fluid, the adsorbent should be 
re-conditioned prior to subsequent adsorption. 
The desorbed polyacrylic acid solution is collected for subsequent assay. A 
number of conventional methods are available to measure the concentration 
of polyacrylic acids in a concentrated solution of the displacement fluid 
in the absence of other soluble ionic materials. The concentration of the 
polyacrylic acids in the aqueous system may then be calculated based on 
the concentration of the desorbed polyacrylic acids in the known volume of 
displacement fluid and the initial volume of the aqueous system sample. 
The following are some of the conventional assay methods which can be used 
to measure the concentration of the desorbed polyacrylic acids in the 
displacement fluid. 
One method is based on the formation of an insoluble complex between 
polyacrylic acids and a cationic surfactant, followed by the determination 
of resulting turbidity by absorbance measurements and a calculation of the 
concentration from a calibration curve. The cationic surfactant is 
preferably a 0.06 percent solution of diisobutylphenoxyethoxyethyl 
dimethyl benzyl ammonium chloride monohydrate, such as Hyamine 1622.RTM. 
manufactured by Rohm and Haas Company, in deionized water. A citrate 
buffer of 3% solution of trisodium citrate dihydrate in deionized water is 
first pipetted into the polyacrylic acid solution followed by the cationic 
surfactant solution. The solutions are allowed to stand undisturbed for 
about 30 minutes and the absorbance is measured with a spectrophotometer 
at 800 nanometers. The absorbance of a polyacrylic acid solution without 
complexing agents is used as a control. The concentration of the 
polyacrylic acids in the sample is then calculated using a calibration 
curve. 
Another method for determining the concentration of polyacrylic acids in 
water, in the absence of other soluble ionic impurities, is a colorimetric 
technique utilizing calcium carbonate and a solution of methylene blue. 
The polyacrylic acid solution is passed through a column of analytical 
grade calcium carbonate. The adsorption column containing the calcium 
carbonate can be a funnel fitted with a medium porosity fritted disk, such 
as Corning Inc. Number 36060. After the polyacrylic acid solution is 
adsorbed onto the calcium carbonate column, a solution of methylene blue, 
in distilled or deionized water, is passed through the column. The amount 
of methylene blue adsorbed by the polyacrylic acids is determined by 
eluting the column with water and measuring the optical absorbance at 660 
nanometers, as compared to standard solutions and blanks, using a suitable 
spectrophotometer or filter photometer with a red filter. 
Another method for determining the concentration of polyacrylic acids in 
aqueous solutions utilizes an aqueous solution of mercurous acetate 
buffered with one normal acetic acid and the use of a blue dye, such as 1% 
diphenyl carbazone. The polyacrylic acid solution containing a specified 
amount of the mercurous acetate buffer solution is heated to 85.degree. C. 
for 20 minutes to form a precipitate. The precipitate is filtered 
immediately with a suitable filter paper. The precipitate is washed with 
water to remove soluble materials. The blue dye is then added to the 
filter paper, washed with about 50 ml water, and the color of the filter 
paper is visually compared to standard colored papers. The dye is also 
added to the filtrate to determine if any polyacrylic acids were not 
precipitated. 
A still further method for measuring the concentration of the desorbed 
polyacrylic acids is an iron-thiocyanate colorimetric method described in 
Chemistry and Technological Waters, U. Glukhova, P. A. Perov, Kiev 
(Russia), 3(3), p 236-237 (1981). This method is based on the formation of 
a colorless complex between iron (III) and polyacrylic acids while a 
complex formed between iron (III) and thiocyanate ions is red. Therefore, 
a decrease in the color of iron-thiocyanate complex, upon complexing of 
iron with polyacrylic acids, is directly proportional to the polyacrylic 
acid concentration. The reaction involved between iron III (Fe.sup.+3) and 
polyacrylic acids (PAA) is as follows: 
EQU xFe.sup.+3 +y(PAA).fwdarw.Fe.sub.x (PAA).sub.y 
After the iron (III) has been allowed to complex with the polyacrylic acids 
to form the colorless Fe.sub.x (PAA).sub.y complex, potassium thiocyanate 
is added as an aqueous solution to the Fe.sub.x (PAA).sub.y complex. The 
thiocyanate (SCN-) ions will react with non-complexed iron (III) ions to 
form the red iron-thiocyanate complex according to the reaction: 
EQU Fe.sup.+3 +nSCN-.fwdarw.Fe(SCN).sub.n -.sup.(3-n) 
where n=1, 2 or 3. Therefore, the color of the resulting solution can be 
correlated with the quantity of iron (III) and thiocyanate ion added to 
arrive at the concentration of the polyacrylic acids. The color of the 
resulting solution, in terms of the percentage of light transmitted 
therethrough, is an accurate measure of the polyacrylic acid 
concentration. This assay method is especially suitable for use with the 
method of the invention because it is fast, sensitive, and because sulfate 
ions, introduced during ion suppression when using sulfuric acid, do not 
interfere with the procedure. The sensitivity of the method is a function 
of the molecular weight of the polyacrylic acids and increases with 
increasing polyacrylic acid molecular weight. Therefore, the molecular 
weight of the polyacrylic acids that have previously been added to the 
aqueous system should be recorded prior to relying on the accuracy of the 
results of this method for polyacrylic acids having other molecular 
weights. 
The method of the present invention is also useful for simultaneously 
measuring the concentration of organic phosphonates in aqueous systems. 
The phosphonates, which are not adsorbed with the polyacrylic acids, may 
be collected and assayed using conventional techniques. One such assay 
method utilizes thorium (IV) nitrate to form a stable colorless complex 
with organic phosphonates. After the organic phosphonates are complexed, 
xylenol orange may be used as an indicator. The xylenol orange complexes 
with the noncomplexed thorium (IV) forming a bright pink color. This 
complex-colorimetric titration is specific for organophosphonates. 
Polyacrylic acids and/or other soluble ionic materials do not interfere 
with the technique.

The following examples are intended to illustrate, and not to limit, the 
invention. 
EXAMPLES 1-6 
"Five or ten parts per million of radiotagged C.sub.14 Acrysol.RTM. LMW-20X 
polyacrylic acid and 10 parts per million of Dequest.RTM. 2010 organic 
phosphonate were added to each of six samples of oil well production 
water." The source of the water and the concentration of the polyacrylic 
acid is illustrated in Table I. 
Sixty milliliters of each of the samples were separately passed through a 
50 milliliter disposable syringe. In the case of a sample contaning oil 
droplets, Sample 6, the syringe was packed with 15 milliliters of glass 
wool. All the syringes were fitted with a Gelman Associates Acrodisc.RTM. 
5.0 micrometer disposable filter assembly. The flow rate of the sample 
through the syringe was about 50 mL/min. The filtered aqueous samples were 
then pH adjusted to about pH 2.5 to suppress polyacrylic acid ion 
formation with 2N nitric acid. 
An adsorbent cartridge of Sep-Pak.RTM. C.sub.18 was conditioned for use by 
attaching it to a three-way syringe valve mounted on a 50 cc. Luer-Lock 
syringe. About 10 milliliters of methanol was passed through the cartridge 
at a rate of about 25 mL/min followed by about 25 milliliters of water, 
adjusted to a pH of about 2.5, at a flow rate of about 25 mL/min. 50 mL 
each of the ionization suppressed, filtered polyacrylic acid containing 
samples was separately passed through a conditioned adsorbent cartridge. 
The plunger at the top of the syringe provided for a flow rate of the 
sample through the cartridge of about 25 mL/min. The non-absorbed effluent 
was collected in a beaker. Following the adsorption and concentration 
step, the polyacrylic acid was desorbed from the cartridge by the use of 
10 mL of 0.1 normal sodium hydroxide displacement fluid at a rate of about 
10 mL/min. The desorbed and concentrated (five times) polyacrylic acid was 
collected in a beaker. 
The collected polyacrylic acid effluent was pH adjusted to 2.5 with nitric 
acid. One half milliliter of ferric chloride solution, prepared from 1.00 
gram FeCl.sub.3.6H.sub.2 O plus 2.5 ml concentrated nitric acid in 1 liter 
deionized water, was added to the pH adjusted polyacrylic acid effluent. 
The sample was allowed to sit for 5 minutes. Following this time, one 
milliliter of potassium thiocyanate solution, prepared from 9.6 grams KSCN 
in 50 mL deionized water, was added followed by the addition of 8.5 mL of 
pH 2.5 water. About 10 mL of this complexed solution containing the 
polyacrylic acid, iron chloride and potassium thiocyanate is removed and 
the intensity of the color was measured using a Hach colorimeter (model DR 
100) and compared against a calibrated color standard of polyacrylic acid. 
The concentration of the polyacrylic acid in the initial sample was then 
calculated based on the volume of the sample and the dilutions. This 
procedure was followed for all samples. 
In addition, the effluent from the adsorption and concentration step was 
also assayed using the thorium nitrate/xylenol orange method for the 
concentration of organic phosphonate in the aqueous sample. The results of 
these assays are presented in Table I and compared with a C.sub.14 
scintillation analysis conducted on the desorbed polyacrylic acid 
solution. 
TABLE I.sup.2 
__________________________________________________________________________ 
Polyacrylic Acid 
Concentration 
Concentration 
Thorium 
of Acrysol 
Measurement 
Nitrate 
LMW 20X .RTM. C.sub.14 
C.sub.14 
Fe/SCN 
Organic 
Radiotagged) 
Count 
Test Phosphonate 
Sample 
Water Type 
ppm 1,4 ppm ppm ppm 
__________________________________________________________________________ 
1 South Delta 
5 4.4 3.2 10 
Offshore La. 
2 Marathon Oil 
5 4.2 4.2 10 
Co., Tensleep 
Field, Oregon 
Basin, 
Cody, WY 
3 Conroe Field 
10 7.7 8.2 10 
E. Texas 
4 Duncan, OK 
10 7.8 8.4 10 
5 Texaco 5 4.0 4.2 10 
W. Texas 
6 Long Beach, 
5 3.9 4.2 (3) 
CA 10 9.2 8.2 
10 8.2 10.0 
7 Tap Water 
7 6.0 8.0 10 
3.5 3.1 3.4 10 
__________________________________________________________________________ 
.sup.1 Acrysol LMW20X is a polyacrylic acid having a weight average 
molecular weight of about 2000. 
.sup.2 All samples were charged with 10 ppm Dequest .RTM. 2010 organic 
phosphonate. This compound has the structural formula: 
##STR1## 
.sup.3 Could not be detected due to yellow color of sample. 
.sup.4 C.sub.14 radiotagged samples found to contain 12% radioimpurity 
The test shows that the concentration of polyacrylic acids in the sample 
was determined within +20% accuracy using a five-fold concentration. At a 
five-fold concentration, a concentration as low as about 1 ppm can be 
detected when a five-fold concentration is used. Accordingly, the method 
of the invention is sufficiently accurate for the determination of the 
concentration of polyacrylic acids in aqueous systems containing other 
soluble ionic materials for use as a monitoring method at a field 
location. If the sample and adsorbent volumes are increased and more 
polyacrylic acids are adsorbed and concentrated on the adsorbent, the 
sensitivity of the method increases. Further, since the volume of the 
sample and the adsorption system can be increased in scale, the 
concentration of very small concentrations of polyacrylic acids on the 
order of as low as 0.1 ppm can be determined. 
EXAMPLE 7 
This example demonstrates that other soluble ionic compounds in aqueous 
systems do not interfere with the adsorption/concentration method of this 
invention. Ten parts per million of zinc sulfate was added to Sample 7 of 
example 1 containing 10 ppm of radiotagged Acrysol.RTM. LMW-20X. The 
procedure of example 1 was repeated and the concentration of the Acrysol 
LMW-20X was determined by the method of the invention. The radiotagged 
scintillation method used for comparison purposes measured 7.0 ppm 
polyacrylic acids in the sample prior to adsorption. The method of the 
invention determined the presence of 7.6 ppm polyacrylic acids in the 
sample. Accordingly, the concentration of polyacrylic acids measured 
according to the method of the invention is not disturbed by the presence 
of other soluble ionic impurities such as zinc or sulfate ions. 
EXAMPLE 8 
This example was similar to example 7 except that 25 ppm sodium 
lignosulfonate, dispersant, was added to Sample 7 containing 5 ppm 
radiotagged Acrysol.RTM. LMW-20X. The polyacrylic acid count (via 
scintillation) prior to the test was 4.1 ppm. The concentration of 
polyacrylic acids determined by the procedure of example 1 was 5 ppm. 
Therefore, the presence of dispersants, such as sodium lignosulfonate, in 
aqueous systems does not interfere with the polyacrylic acid concentration 
determination. 
EXAMPLE 9 
Acrylic Acid/Ethyl Acrylate Copolymer 
A radiotagged sample of a low molecular weight (about 3000 weight average 
molecular weight) copolymer formed from about 95 weight percent acrylic 
acid and about 5 weight percent ethyl acrylate with the addition of 10 ppm 
Dequest 2010 was prepared and tested using the same procedure as described 
for Examples 1-6. The sample contained 8.1 ppm of the copolymer. It was 
concentrated five-fold and desorbed using sodium hydroxide. The 
colorimeter measured as concentration of 37.8 ppm versus the actual 
concentration of 40.5 ppm indicating that the method is sensitive for 
measuring the concentration of acrylic acid copolymers in aqueous systems. 
EXAMPLES 10-17 
Screening Tests 
The following examples were performed to determine the utility of the 
method of the invention, as described in Examples 1-6, for measuring the 
concentration of other polyacrylic acids. Radiotagged samples of all the 
following polyacrylic acids were not available and, accordingly, a before 
and after adsorption/colorimetric test method (iron-thiocyanate) was 
utilized. An aqueous sample containing a known concentration (10 ppm 
unless otherwise indicated) of a polyacrylic acid to be measured was 
prepared, ionization suppressed by adjusting the pH to pH 2.5, 
concentrated five times using a C.sub.18 packing, and desorbed with sodium 
hydroxide. A control sample of sodium hydroxide containing the polyacrylic 
acid, at the same concentration as would be achieved upon 100 percent 
adsorption and desorption of the sample to be tested after a five fold 
concentration, was also prepared. Both samples were subjected to an 
iron-thiocyanate colorimetric test and the percent transmittance of each 
was recorded and compared. Differences in the percent transmittance 
achieved between the adsorbed sample and the control was due to 
breakthrough and/or incomplete desorption. 
Examples 10 and 11 evaluated whether the method was applicable for other 
commercial, low molecular weight polyacrylic acid homopolymers. Example 10 
utilized Goodrite K-752.RTM. polyacrylic acid, chain terminated using 
isopropanol, and Example 11 was of (20 ppm) Colloid 211.RTM. polyacrylic 
acid, chain terminated with 3-mercaptopropionic acid. Example 10 resulted 
in a 40% transmittance while the control yielded 32% transmittance 
indicating the utility of the method and good agreement using the 
screening test despite some breakthrough or incomplete desorption. Example 
11 showed a 30% transmittance while the control averaged 32% 
transmittance, also evidencing good agreement. 
Example 12 evaluated a higher molecular weight polyacrylic acid, Rohm and 
Haas Company's Acrysol.RTM. A-1, having a weight average molecular weight 
of about 60,000. The sample recorded a 28% transmittance while the control 
read 40% transmittance, indicating that the test method was applicable 
despite a greater degree of breakthrough. 
Example 13 was of a polymethacrylic acid product, (Mw about 5000), Rohm and 
Haas Company Tamol 960.RTM.. Instead of a 10 ppm concentration, the sample 
contained 120 ppm and was concentrated five times. The control contained 
600 ppm. The samle resulted in a 52% transmittance in very close agreement 
with the control (56%) transmittance. 
Example 14 was of a polyacrylic acid copolymer, formed from about 70 
percent acrylic acid and about 30 percent methacrylic acid, having the 
weight average molecular weight of about 3400. 100 percent agreement (36% 
transmittance) between the sample (10 ppm with five fold concentration) 
and the control was found. 
Example 15 was of another polyacrylic acid copolymer, formed from about 65 
percent acrylic acid and about 35 percent hydroxypropyl acrylate, having a 
weight average molecular weight of about 3000. The percent transmittances 
of the sample (30%) and the control (34%) were in close agreement. 
Example 16 was of another polyacrylic acid copolymer formed from about 92 
percent acrylic acid and about 8 percent acrylamide having a weight 
average molecular weight of about 2300. Using a 10 ppm concentration 
sample with five fold concentration the percent transmittance of the 
sample was 44% and the control 42%. 
The samples of Examples 15 and 16 were prepared with 10 ppm of the Dequest 
2010. The Dequest 2010 was collected as adsorption effluent and the 
concentration of the phosphonate was tested using the thorium nitrate test 
described in Examples 1-6. Full accountability (10 ppm) of the phosphonate 
was found, indicating that the method of the invention is applicable for 
isolating and measuring the concentration of soluble ionic impurities in 
aqueous systems, as well as separating and measuring the concentration of 
polyacrylic acids. 
Example 17 was of a polymaleic acid having a weight average molecular 
weight of about 1000 and a solids content of 50.8 percent by weight 
manufactured by Ciba-Geigy Corporation under the trademark Belgard.RTM.. A 
sample containing 200 ppm polymaleic acid and 20 ppm Dequest.RTM.2010 and 
a control sample containing 1000 ppm of the polymaleic acid were prepared 
and evaluated using the screening test method. The adsorbed sample 
resulted in a 49% transmittance and the control measured 46% 
transmittance. 
The results of the screening tests (Examples 10-17) establish that the 
method of the invention is applicable to polyacrylic acid homopolymers of 
a wide molecular weight range, polymethacrylic acid homopolymers, 
polymaleic acid polymers, polyacrylic/methacrylic acid copolymers, 
polyacrylic/lower alkyl acrylate copolymers, polyacrylic/acrylamide 
copolymers, and polyacrylic/hydroxy alkyl acrylate copolymers. 
Accordingly, as long as polyacrylic acid is present in the polymer, 
copolymer, or a mixture thereof, at a concentration of about 50 weight 
percent or more, the method of this invention is useful for adsorbing, 
concentrating, and separating the polyacrylic acids from an aqueous 
solution for subsequent determination of the concentration of the 
polyacrylic acids in the sample. Losses of polyacrylic acids on the 
adsorbent or breakthrough resulting from the method can be corrected by 
calibrating the test results by first running a screening test as 
described in these examples with controls containing known concentrations 
of the polyacrylic acids. 
ANTIPRECIPITATION TEST 
Example 18 illustrates that the method of the invention is useful for 
measuring the concentration of polyacrylic acid in aqueous systems 
containing polyacrylic acid and common hardness ions. Polyacrylic acids in 
effluent water, such as oil well production effluent, may possess little 
residual antiprecipitation activity after the polyacrylic acids have 
interacted with inorganic salts and clay present in the aqueous system. A 
two-stage, laboratory, antiprecipitation test was conducted to simulate 
field conditions and to demonstrate the utility of the method of the 
invention under such conditions. Acrysol LMW-20X polyacrylic acid was 
exposed to a supersaturated calcium carbonate solution. The 
antiprecipitation activity of the polyacrylic acid was measured and the 
concentration of the polyacrylic acid, which had not interacted with the 
hardness ions, was measured using the method of the invention as described 
in the previous screening tests. 
Two stock solutions A and B were prepared. 
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Stock Solution A Stock Solution B 
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2.10 g/L CaCl.sub.2 
0.85 g/L Na.sub.2 CO.sub.3 
2.04 g/L KCl 2.04 g/L KCl 
4.97 g/L MgCl.sub.2.6H.sub.2 O 
4.97 g/L MgCl.sub.2.6H.sub.2 O 
76.68 g/L NaCl 76.68 g/L NaCl 
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To an eight ounce jar was added 100 mL of Stock Solution A followed by the 
addition of 0, 6 or 10 mL of pH 8, 0.1 weight percent Acrysol LMW-20X 
solution to form an initial polyacrylic acid concentration of 0, 30 ppm 
and 50 ppm, respectively. One hundred milliliters of Stock Solution B was 
then added to each jar. Each jar was then sealed and placed in a 
70.degree. C. shaking water bath for 16 hours. Each sample was then 
removed from the water bath, cooled for one hour, and filtered through a 
0.45 micrometer Millipore filter to remove precipitate and associated 
polyacrylic acid. A portion of each filtrate was then analyzed for 
residual calcium ions by a standard EDTA titration technique and for 
residual polyacrylic acid concentration using the method of the invention. 
This was accomplished by first establishing a calibration curve of the 
percent transmittance versus the concentration of the polyacrylic acid 
using control samples of known polyacrylic acid concentration. The actual 
concentration of the polyacrylic acid in the filtrate was then determined 
by measuring the percent transmittance of the polyacrylic acid in the 
filtrate as obtained by the method of the invention, as described in the 
screening test examples, followed by utilizing the calibration curve. 
The percent antiprecipitation or antiprecipitation activity was calculated 
as follows: 
##EQU1## 
The second step of the test involved adding 1 mL of 10.5 g/L Na.sub.2 
CO.sub.3 to 100 mL of each of the remaining, unanalyzed filtrates of the 
first step. The jars were then sealed, shaken in a 70.degree. C. water 
bath for 16 hours, removed from the bath, cooled for one hour, filtered 
through 0.45 micrometer Millipore filter and analyzed as described above 
for percent antiprecipitation and residual polyacrylic acid ion 
concentration. 
The results of these two step, antiprecipitation tests are presented in 
Table II. The results clearly demonstrate that the method of the invention 
provides a useful correlation between the concentration of residual 
polyacrylic acid in an aqueous system and the antiprecipitation activity 
achieved as a function of the initial concentration of polyacrylic acid 
added to the aqueous sample. 
TABLE II 
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ANTIPRECIPITATION TEST 
Initial Polyacrylic Residual Polyacrylic 
Acid Concentration 
Antiprecipitation 
Acid Concentration 
(ppm) Percent (ppm) 
______________________________________ 
After First Precipitation 
0 60 -- 
30 95 8.4 
50 97 14.0 
After Second Precipitation 
0 55 -- 
30 75 4.0 
50 98 8.5 
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