Chemistry: analytical and immunological testing – Including chromatography
Reexamination Certificate
1996-10-29
2001-02-13
Eyler, Yvonne (Department: 1646)
Chemistry: analytical and immunological testing
Including chromatography
C422S082050, C210S656000, C250S576000
Reexamination Certificate
active
06187595
ABSTRACT:
The present invention is in the field of analytical methods and equipment. The invention relates to a method of detecting polymers in a solution of the polymer in a solvent.
Polymers can be analysed, qualitatively and quantitatively, using liquid chromatography techniques. The polymers can be separated e.g. on the basis of their molecular weight or size, charge or solubility. The polymers thus separated must subsequently be detected. In HPLC (High Performance Liquid Chromatography) detection is performed using flow-through detectors. The most common detectors are based on the absorption or emission of Ultraviolet (UV) or visible light (VIS) or the emission of fluorescent light.
A disadvantage of UV/VIS detectors for the detection of polymers is that they cannot detect polymers that do not absorb in the UV/VIS frequency range (about 190-800 nm). Also, UV/VIS absorbing solvents cannot be used with these detectors, since they drastically lower the sensitivity of the detection.
Other types of detectors that can be used for assaying polymers include moving belt detectors, flame ionisation detectors (FID) and evaporative light scattering detectors (ELSD). The major disadvantage of these types of detectors is that they are destructive to the sample. Refractive index detection is also frequently used, but it suffers from a low sensitivity and is not applicable with gradient elution.
U.S. Pat. No. 4,983,528 describes a method for determining the amount of unsaturation in an unsaturated elastomeric polymer by subjecting a solution sample of the polymer to gel permeation chromatography and measuring the absorption of UV radiation of 220 nm by the eluted sample. This method does not allow a determination of the amount of polymer which is independent on the degree of unsaturation of the polymer.
U.S. Pat. No. 5,129,723 discloses a method for deriving the molecular weight and other polymer parameters by injecting and mixing a suspension of the polymer into a HPLC tubing and measuring the scattering by a laser-irradiated volume of the suspension. This method is not suitable for determining the amount of polymer, nor for the separation and assaying of polymer.
The most common type of separation and detection of polymers used until now is gel permeation chromatography, combined with detection based on change of refractive index of the eluted sample. However, this method suffers from a poor resolution (inherent to gel permeation chromatography), and a low sensitivity (inherent to refractive index detection).
The object of the present invention is to provide a method and a device for detecting polymers in liquid chromatography techniques in a non-destructive way, without restrictions on the type of polymer or on the solvent to be used.
The method according to the invention for quantitatively detecting a polymer in a solution of the polymer in a solvent, is characterised by carrying out the steps of (a) adding to the solution a non-solvent for said polymer in a sufficient amount to make the resulting liquid turbid and (b) measuring the turbidity of the resulting liquid.
With the method of the present invention, the polymer solution is transformed into a polymer suspension. UV/VIS and fluorescence detectors can detect any kind of polymer in such a suspension, regardless of the type of solvent. Thus the present method has the following important advantages:
=universal applicability: no limitations on polymers, even nonabsorbing polymers such as polydimethylsiloxane can be measured, and even strongly UV-absorbing solvents such as benzene can be used;
=high sensitivity: UV/VIS and fluorescence detectors can detect turbidity with high efficiency;
=high resolution (selectivity): addition of different amounts and/or of different non-solvents allows separation of the polymers to be very finely tuned.
The types of polymers that can be assayed using the detecting system according to the present invention include e.g. polyethylene, polypropylene, poly(vinyl chloride), poly(vinyl acetate), polystyrene, poly(methyl methacrylate), poly(vinyl acetate), polydimethylsiloxane, polyols, which are all non UV/VIS-absorbing polymers, polyamides, polyesters, polycarbonates, polyurethanes, copolymers such as butadienestyrene copolymers, ABS, block copolymers, terpolymers, biopolymers such as polysaccharides, polypeptides etc.
In the present specification, a solvent is understood to be a liquid wherein the polymer to be assayed is essentially soluble.
Suitable solvents for the relatively apolar polymers include e.g. tetrahydrofuran, dioxane, other cyclic or acyclic ethers, dichloromethane, chloroform, other haloalkanes, dimethylformamide, aromatic hydrocarbons such as benzene or toluene, cyclohexane, and mixtures thereof. Suitable solvents for the relatively polar polymers include e.g. water, methanol, ethanol, acetonitrile, and mixtures thereof. The appropriate choice of solvent can be made by the skilled person on the basis of the type of polymer present in the test sample.
A non-solvent according to the invention as a liquid wherein the polymer to be assayed is essentially insoluble, and which, when added to a solution of the polymer, causes the polymer to become undissolved. The non-solvent to be used should be miscible with the solvent of the polymer solution. The appropriate choice of non-solvent can be made by the skilled person on the basis of the type of polymer present in the test sample and of the solvent used.
Suitable examples of non-solvents that can be used in combination with solvents such as tetrahydrofuran, dioxane, dichloromethane, chloroform, dimethylformamide or cyclohexane, include water, methanol, acetonitrile, hexane and isooctane. Suitable examples of non-solvents that can be used in combination with solvents such as water, methanol or acetonitrile include tetrahydrofuran, dioxane and dimethylformamide.
The non-solvent is added to the polymer solution e.g. by means of a HPLC pump. The solution thereby turns into a cloudy, turbid suspension. If necessary for preventing adhesion of the polymer suspension on the walls of the liquid lines, a detergent, in particular a nonionic detergent may be added to the non-solvent. The non-solvent is added in an amount which is sufficient to insolubilise the polymer to be assayed. By adding only a low amount of non-solvent the detecting system can detect polymers selectively. Only one or a few types of polymers become suspended and detectable, while the other polymers remain dissolved and are not detected. A distinction can thus be made, both according to the different chemical nature of the polymers, and according to their molecular weight.
It is sometimes advantageous to cool the polymer-containing solution before adding the non-solvent. Such cooling will result in a reduced solubility of one or more of the polymers and thus in an enhanced turbidity. This enhanced turbidity allows a more selective detection and/or a reduced consumption of non-solvent. The polymer-containing solution is preferably cooled to below 0° C., in particular to about −10° C.
Preferably, both tire polymer solution and the non-solvent are used in a continuous flow, such as in a liquid chromatography system. The turbidity of the suspension resulting from addition of non-solvent to the polymer solution is preferably measured using a UV/VIS detector or a fluorescence detector. A UV/VIS detector measures the light transmitted through the turbid suspension at wavelengths of e.g. 190-600 nm. A fluorescence detector measures the light emitted by the suspension at a 90° angle at wavelengths of e.g. 200-700 nm. Typical settings for fluorescence are an excitation at 350 nm and an emission at 360 nm.
The invention also relates to a detection device for detecting a polymer in a polymer-containing solution, comprising a line provided with a pump for supplying polymer-containing solution, a line provided with a pump for supplying non-solvent, a mixing chamber connected to said lines for mixing the non-solvent with the polymer-containing solution, a line connected to said mix
Basi Nirmal S.
Eyler Yvonne
Janiuk Anthony J.
Waters Investments Limited
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