KR20010080977A - Method for the Quantitative Determination of Polyaspartic Acid - Google Patents

Abstract

The present invention relates to a method for quantitative determination of polyaspartic acid (PASP) and derivatives thereof in an aqueous formulation.

Description

Method for quantitative determination of polyaspartic acid {Method for the Quantitative Determination of Polyaspartic Acid}

The present invention relates to a method for quantitative determination of polyaspartic acid (PASP) and derivatives thereof in an aqueous formulation.

The preparation and use of polyaspartic acid (PASP) and its derivatives have long been the subject of many literatures.

Polyaspartic acid (PASP) studied is, for example, the polymers described in EP-A-650 995 and derivatives thereof. As such, salts of polyaspartic acid (PASP) can be used in the analytical method.

The preparation of polyaspartic acids has been described in a number of documents by various modification methods. Here, by way of example, mention may be made of US-A 839,461 (= EP-A 0,256 366), US-A 4,590,260 and US-A 5,288,783.

DE-A 4 221 875 describes the preparation of polyaspartic acids modified by polycondensation and their use as additives for anti-coating agents in the evaporation of detergents, laundry materials, water treatment compositions and sugars.

In particular, according to DE 19 647 293 C1 and DE 19 700 493 A1 polyaspartic acid (PASP) can be used for membrane preparation, surface treatment and process and waste water treatment.

The term "polycarboxylate" means, in addition to the group consisting of polyaspartic acid and derivatives thereof, in general, in particular a group consisting of polyacrylic acid, homopolymers and copolymers thereof and salts thereof. Thus, polyacrylates are generally acrylic acid homopolymers or copolymers based on acrylic acid and maleic acid or based on maleic acid and methyl vinyl ether. They may have acidic, neutral or basic properties.

These two groups of polymers (polyaspartic acid and polyacrylic acid) have anionic properties, but they differ in several respects with respect to physico-chemical properties.

However, no method has been described to date that can monitor the polyaspartic acid content of an aqueous system for practical judgment of the need to add polyaspartic acid to maintain process conditions optimally. On the other hand, the available area of polyaspartic acid, which requires a process involving such an analysis as quality control, continues to increase. For example, polyaspartic acid is used in the automotive industry, water treatment or textiles and leather.

Unlike the analysis of polyaspartic acid, several methods of measurement of the group consisting of polyacrylates have been published in the past.

DE 3842747 A1, for example, describes a method for measuring the concentration of polyacrylates. This method is based on quantitatively determining the polyacrylate content of an aqueous system containing an interference cation by contacting polyacrylic acid complexed with a polyvalent cation with an ion exchange resin to essentially remove the interference cation. The polyacrylic acid content of the aqueous solution is then analyzed by conventional methods. In the conventional method, the determination of the carboxyl content of polyacrylic acid is carried out using the iron thiocyanate method. The iron thiocyanate method is based on the formation of a colorless complex between iron (III) and polyacrylic acid, while the complex formed between iron (III) and thiocyanate ions is red. The color reduction of the iron thiocyanate complex due to the complex formation of iron (III) and polyacrylic acid is directly proportional to the polyacrylic acid concentration. Allow iron (III) to form a colorless complex with polyacrylic acid and then add potassium thiocyanate in aqueous solution to the complex. Thiocyanate ions react with uncomplexed iron (III) ions to form a red iron thiocyanate complex.

Therefore, the correlation between the content of iron (III) and the added thiocyanate ions can be formed by the chromaticity of the resulting solution to obtain the concentration of polyacrylic acid. The chromaticity of the resulting solution expressed by the ratio of transmitted light is a measure of the concentration of polyacrylic acid.

However, this method uses polyaspartic acid because the absorbance curve when titrating iron (III) chloride with potassium thiocyanate without the addition of polyaspartic acid and the curve shape of the initial PASP before addition of iron ions are substantially the same. Cannot be measured.

Method for measuring polyacrylate and its derivatives using polyelectrolyte in aqueous samples [U. Schroeder, D. Horn, K. H. Waβmer, Seifen-Oele-Fett-Wachse 117 (8) (1991) 311-314. This colorimetric endpoint measurement is based on the detectable chromaticity change of a polycation suitable as a titrant, for example ECST or polybrene®. However, in the case of polyaspart it does not show analytical values with the required accuracy and reproducibility.

Furthermore, turbidimeter and potentiometer methods for the measurement of complexing agents are known (Ullmann's encyclopedia of industrial chemistry, volum A 10, p. 98, 5th edition, 1987). Furthermore, in some cases, PASPs can be included in the group of complexing agents in a broad sense because the complex formation constants of some transition metals to polyaspartic acid are high.

All methods of determination of polyacrylates known from the prior art have a common feature that they are not suitable for differentiation to polyaspartic acid and its derivatives and salts since PASPs are also always measured.

Since the aqueous solution of polyaspartic acid has different physicochemical properties compared to polyacrylates due to the considerably different surface structure, the obvious results of achieving reproducible and accurate measurement of PASP content by originally known titration methods are obtained from the methods discussed so far. It is obvious that it cannot be obtained. Such other surface structures are always produced by individually linked monomers, corresponding to an α, β-linkage of 30 to 70 from a statistical point of view. However, the binding capacity of metal ions to the polyaspartic acid polymer is mainly affected by the different end group patterns, the α / β ratio at the molecular level, and the spatial orientation of the polymer. Simple 1: 1 correlations or complex correlations of saturation of anions to cations are only limited in effectiveness. The goal is to find conditions under which apparent correlations are statistically valid.

Since no direct and convenient method for measuring polyaspartic acid has ever been disclosed in the prior art, the qualitative and quantitative measurement of polyaspartic acid or additional components is usually indirect and in some cases very complex methods, for example It is performed by NMR and FT-IR spectroscopy, mass spectroscopy, HPLC, GC and elemental analysis. Measurements by elemental analysis function reliably only in practically ideal single component systems, ie in aqueous PASP solutions.

It is an object of the present invention to develop a method for monitoring the polyaspartic acid content of an aqueous system, for example, so that it is possible to simply and reliably investigate the amount of polyaspartic acid added to an industrial process. This analytical method should be sensitive enough to reliably measure low polyaspartic acids.

In industrial use, for example in the automotive industry, construction, water treatment, mining or cosmetic applications, so that the content of polyaspartic acid and many additional components such as polyacrylates and salts and derivatives thereof can be determined reliably and completely. In-process analysis is required. Further components are also considered to mean in particular anionic, nonionic or cationic components or water miscible or water soluble substances, for example organic solvents.

Another object of the present invention is to reproducibly measure the content of polyaspartic acid (PASP) in an aqueous formulation in the presence of additional components by a suitable method. A method that makes this distinction reliable, i.e. a method which is sensitive enough to take into account mutual influences and to measure reproducibly even low contents of PASP, has not been disclosed until now.

Another aim is to define physical parameters to the extent that reliable analysis is possible in industrial processes.

The object of the present invention is achieved by measuring the content of polyaspartic acid by turbidity titration with transition metal salts under certain limiting conditions and overcoming the above disadvantages.

The invention is characterized in that the measurement is carried out by turbidity titration with a transition metal salt, preferably a cation salt selected from Cr (III), Fe (II), Fe (III), Cu (II) and Cd (II). And a method for the quantitative determination of polyaspartic acid in an aqueous formulation.

Surprisingly, turbidity titrations with transition metal salts can successfully determine the content of polyaspartic acid in aqueous formulations with high accuracy.

In turbidity titration, the consumption of standard solutions (eg FeCl ₃ solution) is measured in the vessel. The calibration curve may show a correlation between the consumption of standard solutions and the time required for this purpose.

The content of the PASP standard sample may be used for reference purposes. The content is usually measured by elemental analysis. If the content is known, the standard sample can be diluted sufficiently and a calibration curve created for a series of dilution concentrations. The content of each sample is known, i.e., given a constant addition rate, only a measurement of the time past the equivalence point is needed.

For example, when FeCl ₃ − is added to an aqueous solution of PASP at pH = 8, FeCl ₃ immediately precipitates in the solution to form turbidity. A competition reaction occurs between Fe (OH) ₃ formation and complex (Fe polyaspartate) formation. After Fe (III) is removed by excess polyaspartic acid (sodium salt), the turbidity of the solution increases very slowly due to Fe (OH) ₃ while Fe polyaspartate is formed. The equivalence point is reached when all polyaspartic acid (sodium salt) binds to Fe (III) and Fe (OH) ₃ precipitates out of the way. The equivalence point is determined by, for example, the maximum value of the first derivative of the permeability curve.

In addition, the method allows for highly accurate determination of polyaspartic acid in the presence of additional components, ie in the case of mutual influence.

In many cases, the possible effects of the additional components can be minimized so that they can be reliably measured even in the complex mixture of the aqueous formulation.

Therefore, the present method can effectively and quickly measure the content of PASP, thus providing a very inexpensive alternative to the elemental analysis method using less complicated instruments and less time consuming.

The average molecular weight (M) of the polyaspartic acid which can be measured by the method of the present invention may vary within a wide range, and it is more preferable to use polyaspartic acid having a molecular weight of 500 to 100,000 g / mol. However, polyaspartic acid having a molecular weight of 1000 to 50,000 g / mol is particularly preferred, and a molecular weight of 1000 to 30,000 g / mol is particularly preferred. The molecular weight distribution can be determined by gel permeation chromatography (GPC) using 0.9% aqueous sodium chloride solution as an eluent on a Shodex OH-Pack column (Merck). Assays can be best performed using, for example, pure polyaspartic acid from Sigma, whose molecular weight is determined by an absolute measurement method, such as Low Angle Scattering (LALLS).

Transition metal salts, in particular cations of the first transition element, complex aminocarboxylic acids are known. Likewise, it is known that polyaspartic acids optionally form stable complexes with cations of transition metals and alkaline earth metals.

For the purposes of the invention, for example Al (III), Cr (III), Fe (II), Fe (III), Cu (II), Cd (II), Pb (II), Pb (IV), Sn (IV) Cations can be used to complex with PASP, respectively. Fe (II) and Fe (III) cations are preferred. Fe (III) ions are particularly preferably used.

PASP measurement by turbidity titration can be performed, for example, in the range pH = 3 to pH = 12. The titration may preferably be carried out in a pH range of pH = 5 to pH = 9. Particularly advantageously, the titration can be carried out in a pH range of pH = 7 to pH = 9. The pH must be kept constant during turbidity titration. This can be accomplished using a variety of methods, for example burettes, pH electrodes, indicators or buffers. For example, a borex or dihydrogen phosphate based buffer may be used. In addition, other buffer systems may be used.

In order to minimize the mutual influence between the various components, the properties of polyaspartic acid are decomposed at elevated temperatures in acidic media. Degradation occurs mainly within the pH range of pH 0-7, temperature range of 10 ° C to 200 ° C. The polyaspartic acid preferably decomposes in a pH range of pH = 0 to pH = 4, in the temperature range of 40 ° C to 200 ° C. Particular preference is given to a pH range of pH = 0 to pH = 2, a temperature range of 140 ° C. to 160 ° C. It is preferable to select a pressure range of 1 bar to 10 bar. It is of course also possible to choose higher pressures. If necessary, the decomposition can also be carried out under the influence of microwaves or under pressure.

Thus, decomposition by ultrasonic waves or shock waves is preferable.

All components are titrated with transition metal salts, preferably iron salts, followed by specific degradation of the polyaspartic acid by selection of suitable parameters (temperature or pH) or by a combination of these parameters, followed by titration of the additional components, followed by aqueous formulation. By forming a difference within the polyaspartic acid content to determine the content of the polyaspartic acid it is possible to continuously minimize or exclude the mutual influence of the additional components. Where appropriate, sensitivity can be increased by evaporation of the PASP sodium salt solution.

The measuring device for performing the turbidity titration according to the present invention may preferably be composed of a constant temperature reaction vessel with a magnetic stirrer. It is also possible to use containers with other types of motors. Here, it is always advantageous to use a constant temperature vessel. The measuring device also consists of an automatic device for metering a cationic solution and an automatic device to ensure a constant pH range. It is also possible to use other devices and / or methods for this purpose, for example buffers, pH electrodes and other acid / base additives with or without burettes, indicators and combinations of the devices and / or methods. . The resulting turbidity is recorded by optical and / or turbidity measurement, for example with a photometer, and then transferred to an evaluation system, for example a plotter, data analysis or a recording device using a computer.

Example

Example Equipment of Experimental Apparatus

The measuring device consists of a constant temperature reaction vessel of about 120 ml volume equipped with a magnetic stirrer driven by a Metrohm® magnetic stirrer drive. Metrom® Tritrino 719S is used for pH adjustment. Weighing is performed with Metrom® Dosimat 665. The resulting turbidity data was recorded on a Metrom® 662 photometer using a Delphin® box and transferred to a computer for evaluation with an MS-DOS Excel program.

Example 1

To determine the content of polyaspartic acid in aqueous solution, the assay curve was first created from a series of dilutions of polyaspartic acid of known concentration. Weighing time was plotted in ordinate and the percentage content of PASP was plotted in abscissa (FIG. 1). For example, the standard polyaspartic acid selected was a polyaspartic acid solution having a molecular weight of about 3000. The content of the sample was determined to be 42.8 wt% using elemental analysis. Table 1 shows the measurement results of the turbidity titration using iron (III) chloride. The solution was stabilized between pH = 7.9 and pH = 8.1 using Borex solution and the measurements were recorded at 20 ° C. 1 shows the measured values graphically.

Μl used 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 PASP% concentration 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 First measurement [minutes] 3.25 5.00 7.25 8.75 10.75 12.50 14.50 18.00 19.00 21.25 22.50 23.50 2nd measurement [min] 3.00 4.75 6.50 8.75 10.75 12.50 14.50 16.50 18.25 21.00 22.50 25.50 Average [minutes] 3.13 4.88 6.88 8.75 10.75 12.50 14.50 17.25 18.63 21.13 22.50 24.50

Using this standard curve, additional samples E7 and E12, whose contents were known by elemental analysis, were measured by comparison with the turbidity titration with iron (III) chloride. Table 2 compares the values measured by elemental analysis with the values.

Sample number Turbidity Titration with FeCl ₃ Elemental analysis E7 40.2% 40.3% E9 39.1% 38.6% D10 40.5% 40.8% D012 42.4% 42.4%

Example 2

The corresponding calibration curve of sample E0013 is shown as described in Example 1. Ten additional samples were analyzed with each measurement using the calibration curve. The results of this test are shown in Table 3.

Sample number Turbidity Titration with FeCl ₃ Elemental analysis E4 36.7% 37.5% E6 36.2% 37.6% E7 40.1% 40.3% E9 39.1% 38.6% E19B 41.4% 39.7% E24 40.6% 41.5% D3 37.5% 37.1% D10 39.6% 39.6% D12 41.7% 40.8% D13 43.3% 43.7%

To demonstrate the method, sample E7 was measured several times. To obtain the results as shown in Table 4.

[%] Primary measurement 40.3 Secondary measurement 40.0 3rd measurement 40.0 4th measurement 39.5 5th measurement 39.7 6th measurement 40.0 7th measurement 39.2 8th measurement 39.7 Arithmetic mean 39.8 Standard Deviation ± 0.4

Example 3

In order to confirm the mutual influence between the various components, polyacrylates and surfactants were investigated in an aqueous formulation containing polyaspartic acid. The properties of polyaspartic acid that degrade under each influence of temperature and / or pH, or under appropriate combinations of the above parameters were used. The degradation product formed was no longer detected by the turbidity titration according to the invention.

Table 5 below shows the titration results before and after decomposition of polyaspartic acid for some examples.

Decomposition measurement time [min] Measurement time after decomposition [min] Sokalan CP 10 (registered trademark) (1% concentration) * 7.0 7.0 Socalan CP 10 (registered trademark) (1% concentration) * + PASP (1% concentration) 15.6 7.1 Dodecylbenzenesulfonate sodium salt 1.6 1.5 Dodecylbenzenesulfonate sodium salt + PASP (1% concentration) 10.2 1.5 100 ppm Mersolat® (100%) ** 0.6 0.6 100 ppm Mersolette® (100%) ** + PASF (1% concentration) 9.2 0.6 Blank sample (the number of Leverkusen main building) 0.8 0.7 * Sodium polyacrylic acid salt of 4000 g / mol (manufacturer: BASF) ** C ₁₅ alkanesulfonate (manufacturer: Bayer AG)

In Table 5, polyaspartic acid was successfully distinguished for additional components and the time units expected before completion of titration were maintained with high accuracy.

General description of the examples

2.000 g of the test aqueous solution was placed in a 50 ml volumetric flask. 1000 μl of this was placed in a constant temperature (20 ° C.) reaction vessel and diluted with 90 ml of distilled water. Furthermore, 5.5 ml of 0.05 m Borex solution and 4.5 ml of 0.1 m hydrochloric acid in water were added. The pH was maintained at pH = 7.99 to pH = 8.01 using Metrom® Titrino 719 S. The measurement was started while injecting 0.05 mol of FeCl ₃ solution. Measurements made with a Metrom® 662 photometer were recorded by a Delfin® box and evaluated by computer (MS-DOS Excel). The measured time was multiplied by the slope calculated from the calibration curve and the dilution factor 25 incorporated to give the final results in weight percent.

Decomposition of the polyaspartic acid was typically carried out over 20 minutes at 148 ° C. after addition of 5 ml of 1 n HCl using a unit heater (Thermostat LT1W, Dr. Range).

Example 4

Determination of the content of PASP in the range of 1 ppm to 10 ppm

reagent

Ferric chloride (III) (p.A. Riedel-deHaen) solution, 0.005 M

Solution 1: 0.005 m Borex solution consisting of 12.37 g of H ₃ BO ₃ (pA Merck) and 100 ml of 1n NaOH (Kraft GmBH) per liter

Solution 2: HCl (Kraft GmbH) 0.1 m

HCl (Kraft GmbH) 1 m

Distilled water

Way

90.0 g of aqueous polyaspartic acid with a content of 1 ppm to 10 ppm are placed in the reaction vessel. 1, 5.5 mL of solution and 2, 4.5 mL of solution are added. The pH is maintained at 7.99 to 8.01. The measurement is started while injecting 0.05 mol of FeCl ₃ solution at a rate of 0.5 ml / min. The measurements by the Metrom® photometer are recorded by means of a Delfin® box and evaluated by computer (MS-DOS Excel). The measured time is multiplied by the slope calculated from the calibration curve and divided by 0.9 (90 ml of starting material diluted to 100 ml by solutions 1 and 2).

Ppm of PASP 0 One 2 3 4 5 7.5 10 Hours [minutes] 1.5 3.0 5.5 7.5 9.0 10.5 15.5 20.0

Claims (12)

Determination of polyaspartic acid in aqueous formulations by turbidity titration with transition metal salts, preferably cation salts selected from Cr (III), Fe (II), Fe (III), Cu (II) and Cd (II) Characterized in that the method for quantitative determination of polyaspartic acid in an aqueous formulation. Process according to claim 1, characterized in that the turbidity titration is carried out using an iron (III) salt or an iron (II) salt, preferably a salt of iron (III). Method according to claim 1 or 2, characterized in that it is measured in the pH range of pH = 3 to pH = 12, preferably pH = 5 to pH = 9, particularly preferably pH = 7 to pH = 9. . The method of claim 3, wherein the pH is maintained substantially constant upon measurement. 5. The method according to claim 4, wherein the pH is kept constant at the time of measurement using a buffer system, preferably Borex buffer or monohydrogen phosphate buffer. The method of claim 5, wherein the measurement is performed under substantially isothermal conditions. The method according to claim 6, characterized in that polyaspartic acid having a content of 1 ppm or less is measured in the presence of additional components, if necessary, for example after concentration of the sample under reduced pressure (<10 ⁵ Pa). The method according to any one of claims 1 to 8, wherein after the first measurement of the sample by turbidity titration, the polyaspartic acid in the second sample is specifically pyrolyzed in the pH range of pH = 0 to pH = 7, and then pH = By adversely affecting the turbidity titration of aqueous formulations by measuring the content of additional components by turbidity titration at 3 to pH = 12, preferably pH = 5 to pH = 9, particularly preferably pH = 7 to pH = 9. Measuring the content of polyaspartic acid in the presence of a known or possibly unknown other component. 9. The process according to claim 8, wherein the decomposition is preferably carried out in the presence of ultrasonic waves or microwaves or with a unit heater. A temperature range of 40 ° C. to 200 ° C. and a pH range of pH = 0 to pH = 4, particularly preferably a temperature range of 140 ° C. to 160 ° C. and a pH of 0 to pH = 2. Disintegrating at pH The method according to claim 10, wherein the titration is carried out manually, semi-automatically or online fully automatically. 12. The method of claim 11, wherein the content determination is carried out in a fine range or approximately quantitatively below a measurement limit of 1 ppm polyaspartic acid (PASP).