The field of clinical chemistry is concerned with the detection and
quantification of various substances in body fluids. Included among those substances
which can be determined are cholesterol and glucose, urea, as well as cations
such as calcium and potassium which are found in various body fluids such as urine
One of the most frequently used analytical devices in clinical chemistry
is the test strip which is contacted with the body fluid to be tested. Various
reagents incorporated into the test strip react with the analyte to be determined
in the body fluid to provide a detectable signal which is typically a change in
color. These color changes are measured either visually or, where greater accuracy
is required, spectrophotometrically. The detected signal is correlated to a standard
to thereby give a value for the amount of analyte in the sample.
Clinical analysis of the type described above, especially when automated
systems are used, must necessarily be extremely accurate to ensure that the measurement
taken is valid. Control reagents are used to verify this accuracy by determining
that the device is giving the correct response.
A control reagent is a specimen or solution which is analyzed solely
for quality control purposes and is not used for calibration. A suitable control
reagent should be stable and available in aliquots or vials so that it can be
analyzed periodically over a long time. There should be little or no aliquot-to-aliquot
or vial-to-vial variation so that differences between repeated measurements can
be attributed to the analytical method alone.
Modified human serum known in the art as "control serum" is one type
of control material. One of the requisites of a control material is stability.
Control materials based upon serum, however, are inherently unstable due to the
various components contained therein. In addition, sera will vary from source to
source thereby rendering unpredictable the reproducibility of the results of using
control serum from different lots. Control reagents, with which the present invention
is concerned, are control materials which are not based on, and do not contain,
serum of any type.
United States Patent 3,920,580 discloses that control reagents for
glucose determinations can be prepared without any serum or components thereof
by incorporating an antidiffusing agent into a glucose/water solution. The antidiffusing
agents disclosed in this patent include polyvinylpyrrolidone, polyvinyl alcohol,
polyethylene glycol, dextran and bovine serum albumin.
United States Patent 5,028,542 discloses a glucose control reagent
comprising a predetermined amount of glucose, water and polystyrenesulfonate or
a soluble salt thereof.
These prior art control reagents are somewhat limited in that their
stability, compatibility with the tetrazolium salt indicators used in certain test
strips, and surface tension are all lower than that of serum. We have discovered
a particular class of polymers for use in these control reagents which enhance
the solubility of tetrazolium salt indicators and thereby improve the performance
of the control reagent.
Summary of the Invention
The present invention is a serum free control reagent for the determination
of a pre-selected analyte which comprises an aqueous solution of the analyte together
with a polymerized quaternary salt of di- or mono- allyl, di- or tri- alkyl ammonium
characterized by the formulae:
or copolymers thereof. In the foregoing formulae, R is straight or
branched chain alkyl of 1 to 4 carbon atoms, n is a number of at least 9 representing
the degree of polymerization and ϑ represents a counteranion.
Optionally, the formulation also contains a buffer, a colorant and
Description of the Invention
The basic formulation of the cationic quaternary ammonium polymer
and water is used as a base to which analytes such as glucose, BUN, sodium, protein
and uric acid are added to prepare aqueous controls for diagnostic test systems.
The formulation is suitable for the control of the accuracy and precision
of methods of determination using automatic analyzers by using a control reagent
containing the analyte to be determined in a known and precisely fixed concentration.
Many aqueous controls contain polymers such as polyvinylpylpyrrolidone,
and polyvinylalcohol in their formulation. The present invention involves the use
of a synthetic, water soluble polymer of the type previously described in a stabilized
buffer system for use in aqueous diagnostic controls. This control system is especially
useful in conjunction with dry reagent strip assays in which a redox indicator,
particularly a tetrazolium salt, and a reagent system, which upon rehydration
will elicit a detectable response in the indicator upon exposure to a pre-selected
analyte, are uniformly dispersed in a matrix material. The cationic polymer is
useful as a thickening agent to reduce the migration of reagents in the reaction
layer (via chromatography) to provide more uniform color in the reacted reagent
pad and control assay kinetics by the rate of reaction (diffusion) since the rate
of wetting affects the final result. The surface active properties of the polymerized
quaternary ammonium compounds of the present invention e.g. poly(diallylmethyl
ammonium)-chloride (PDDA) and its analogs are distinguished from PVP and PVA in
that the polymers of the present invention help with the wetting of dry reagent
pads thereby limiting the need for the addition of other surfactants to the formulation.
While polystyrene sulphonate is known to possess surface active properties, it
differs from the polymers used in the present system in that it is negatively
charged while PDDA and its analogs are positively charged.
In preparing the present reagent system, the polymer is dissolved
in water (preferably distilled) up to a level to provide a solution with the desired
viscosity and wetting properties. Typically, this will involve a concentration
of from 0.5 to 5.0 weight % (preferably 0.2 to 2.0%) depending on the particular
polymerized quaternary ammonium compound selected and the polymer's molecular
weight. These polymers are prepared by polymerizing allyl or diallyl quaternary
ammonium salts in which the valence bonds of the nitrogen not occupied by an allyl
group are occupied by straight or branched chain alkyl groups of 1-4 carbon atoms.
These salts and the polymers obtained by their polymerization typically have a
halide, e.g. chloride or bromide, as the counteranion but may be combined with
other counteranions such as acetate or sulfonate. Poly(diallyldimethyl ammonium)
chloride, PDDA, is the polymer of choice for use in the present invention and
can be obtained from Polysciences, Inc. The degree of polymerization of these polymers,
i.e. the value of n in the above formula, is typically from about 800 to 2300
with a degree of polymerization of from about 1100 to 1900 being preferred.
The other essential ingredient is, of course, the analyte of interest.
The following discussion is directed to glucose as the analyte of interest with
the understanding that it is equally applicable to other analytes.
The glucose used is typically D-glucose of a high grade so that an
accurate quantity will be included in the control solution. D-glucose and dextrose
are regarded as equivalent materials for use in this invention and may be substituted
one for the other. Although the amount of glucose in the solution is not critical
within its solubility limits, the control solution will typically contain from
about 1-1,000 mg% (mg/100 ml solution). Within this range, control reagents can
be prepared containing glucose within the normal range (80 to 120 mg/dL) and the
pathological range (250 to 500 mg/dL).
It is beneficial to include a preservative in the control reagent
to prevent microbial growth therein. Suitable preservatives include benzoic acid,
sodium benzoate, dichlorophene, hexachlorophene, sorbic acid, phosphoric acid
and esters of p-hydroxybenzoic acid. A preferred preservative is Dowicil 200, whose
active ingredient is [cis-1-(3-chloroalkyl)-3,5,7-triaza-1-azoniadamantane chloride]
(95%) and which contains hexamethylenetetramine hydrochloride (5%) (w/v) as residual
starting material, due to its ability to maintain antimicrobial activity at a neutral
pH as opposed to benzoate which is not an effective preservative at pH 7.5. Typical
concentrations of the preservative in the formulation are from 0.1 to 0.5% by
The control reagent is preferably buffered to a pH of about 7.5 since
this is close to the physiological pH of blood. Since the type of reagent pad under
consideration is designed for use with blood, the control solution should mimic
blood as closely as possible with respect to physical properties, one of which
is pH. Suitable buffers include HEPPS (N-2-hydroxyethylpiperazine-N'-3-propanesulfonic
acid); MOPS [3-(N-Morpholino)propanesulfonic acid] and HEPES [4-(2-hydroxyethyl)-1-piperazine
ethane sulfonic acid]. HEPES is particularly suitable due to its ability to buffer
solutions to pH 7.5.
Further adjuvants may be added to the control solution to impact
a particular color or physical appearance. A red blood color which is desirable
in this sort of formulation to assist the user in applying the control solution
to the correct area of the reagent strip may be obtained by incorporating a red,
water insoluble like dye into the formulation. Red dye #40 works well for this
purpose. This is significant because it is difficult to see whether the drop is
correctly applied to the application site when the solution is colorless.
The present invention is further illustrated by the following example.
Aqueous glucose control reagents were formulated as follows:
37.4 g/L (1.5 M) HEPES 0.5 sodium salt
0.4 g/L FD&C Red Dye #40
Glucose at 30, 100, 300, 450 and 600 mg/dL.
One reagent contained 60 g/L of poly(diallyldimethyl ammonium)chloride and the
other contained no polymer. Each of the control reagent was tested on a technique
independent dry reagent glucose format using human plasma as a control with the
reactivity (in terms of K/S values) being determined at 60 seconds after application
of the control reagent and the plasma containing the indicated glucose concentrations.
The results of this experiment using the polymer free control reagent
are set out in Fig. 1 with the results obtained using the PDDA containing control
reagent being graphically illustrated in Fig. 2. These figures demonstrate that
the reactivity of the control reagent containing the polymer of the present invention
is much closer to that of plasma than is that of the control reagent without the
A serum free control reagent formulation for determination of a pre-selected
analyte which comprises an aqueous solution of a predetermined amount of the analyte
together with a polymerized quaternary salt of di- or mono- allyl, di- or tri-
alkyl ammonium characterized by the formulae:
or copolymers thereof wherein R is straight or branched chain alkyl of 1 to 4 carbon
atoms, n is a number of at least 9 and -O represents a counteranion.
The control reagent of Claim 1 wherein the quaternary salt is a salt of the
poly(diallylmethyl ammonium) cation.
The control reagent of Claim 2 wherein the anion is chloride, bromide, acetate
The control reagent of Claim 3 wherein the anion is chloride.
The control reagent formulation of Claim 1 wherein the polymerized quaternary
salt is present in a concentration of from 0.5 to 5.0 weight percent of the control
The control reagent formulation of Claim 5 wherein the polymerized quaternary
salt is present in a concentration of from 0.2 to 2.0 weight percent.
The control reagent of Claim 1 wherein the analyte is glucose, BUN, sodium,
protein or uric acid.
The control reagent of Claim 1 wherein the analyte is glucose and is present
in either the normal range of 80 to 120 mg/dL or the pathological range of 250
to 500 mg/dL.
The control reagent of Claim 1 which contains a buffer capable of buffering
the reagent to a pH of about 7.5.
A serum free control reagent formulation for the determination of glucose which
comprises glucose in a predetermined amount together with from 0.5 to 5.0 weight
percent of the reagent formulation of poly(diallylmethyl ammonium)chloride having
a degree of polymerization of from 800 to 2300, 4-(2-hydroxyethyl)-1-piperazine
ethane sulfonic acid to buffer the formulation to a pH of about 7.5 and from 0.1
to 0.5 weight percent of cis-1-(3-chloroalkyl)-3,5,7-triaza-1-azoniadamantane
chloride as preservative.