Abstract:
The invention relates to a novel device for determining the physical and chemical stability of substances and formulations by means of samples. Said device is provided with a vibration spectrometer, a container ( 1 ) for storing the samples in controlled conditions, a robot ( 10 ) for transporting the samples between the vibration spectrometer ( 12 ) and the container, and a computer ( 13 ) for controlling the processes and for automatically storing and evaluating the spectra of the samples received by the vibration spectrometer.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a device and a method for determining the physical and chemical stability of substances and formulations on the basis of spectral data which, with the aid of suitable vibration spectrometers (middle-infrared, near-infrared, Raman spectrometers), may be recorded non-destructively completely automatically in short time intervals (minutes, hours, days) from substances and formulations stored under controlled conditions (temperature and/or ambient humidity and/or light). 
   BACKGROUND OF THE INVENTION 
   Typically, physical and chemical stabilities of substances and formulations are determined in such a way that the substances and formulations are stored in controlled storage conditions for a long period of time. At the beginning of the storage period and time intervals (several weeks, months, years) during the storage, samples are taken from the stored substances and formulations, which are subsequently assayed in a laboratory using physical and chemical analyses (chromatographic, electrophoretic, wet-chemical, and physical methods). These methods have various disadvantages:
         The performance of the classical physical and chemical analyses typically requires a large outlay in time since, for example, complex sample preparations are necessary for chromatographic and electrophoretic analyses.   To perform chromatographic analyses, it is typically necessary for reference material having a known content of the substances to be assayed to be present.   The material taken from the stored substances and formulations for the analyses may no longer be used for further storage, since the samples are destroyed in most cases in the classical physical and chemical analyses.   Because of the great complexity, the analyses may only be performed at long time intervals. In comparison to the present invention, it takes significantly longer to obtain conclusions about the stability of the stored substances and formulations from the experimental data.       

   For example, a device for determining types of adsorbates, in which an infrared spectrometer disperses a beam of radiation from a catalyst which a gas is subjected to for analysis in order to adsorb adsorbates thereon, is known from DE-A-197 44061. The spectrometer outputs spectral data, corresponding to a wave number of the beam of the radiation, to a computer which has reference data stored. The computer standardizes the spectral data and the reference data and then calculates a product of the standardized spectral data and the reference data. A function of the product in relation to the wave number is then differentiated in order to obtain a differential function. Then, a specific wave number is determined for which the differential function is equal to zero, so that the shared peak of the spectral data and the reference data at the specified wave number is determined precisely. 
   It is therefore an object of the present invention to provide a device and a method which confirm information about the physical and chemical stability of substances and formulations rapidly, without destruction to the substances and formulations. 
   SUMMARY OF THE INVENTION 
   The present invention provides a device for measuring the physical and chemical stability of samples of substances and formulations, which comprises a vibration spectrometer, a container for storing samples under controlled conditions, a transport robot for transporting the samples between the vibration spectrometer and the container, and a computer for controlling the sequence of sample movements, and for automatic storage and analysis of the spectra recorded by the spectrometer. 
   The present invention also provides a method for measuring the physical and chemical storage stability of substances and formulations. Vibrations spectra of samples of substances and formulations are recorded by the vibration spectrometer at regular time intervals. Each individual vibration spectrum of a sample is next indexed using a sample number, the storage conditions, and measurement time. The recorded and indexed vibration spectra are then stored in a computer as raw data. As soon as the number of stored spectra exceeds a predetermined threshold value, the raw data of each individual sample is analyzed by way of statistical data anaylsis. 

   
     BRIEF DESCRIPTIONS OF THE DRAWINGS 
     Further advantages and embodiments of the present invention are explained in the following description with reference to the attached drawings, wherein: 
       FIG. 1  shows a schematic illustration of a measurement device of the present invention; 
       FIG. 2  shows a flowchart of the analysis preformed by the device of  FIG. 1 ; 
       FIG. 3  shows a scatter diagram of main components of the device of  FIG. 1 ; 
       FIG. 4  shows a diagram of the main components of  FIG. 3 , weighted with the coefficients of the regression calculation; 
       FIG. 5  shows a diagram illustrating the alteration from the scores; 
       FIG. 6  shows a front view of a sample container having an evaporation device; 
       FIG. 6A  shows a hermetically sealed sample container; and 
       FIG. 7  shows a sample vessel having multiple depressions and an evaporation device for multiple sample containers. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a schematic of a transport robot  10 , commonly known in chemical laboratories, which may be moved back and forth between a storage container  11  and a spectrometer  12  by means of a computer  13 . Samples of substance and formulations are transported by the transport robot  10  in a sample vessel (not shown) from the storage container  11  to the spectrometer  12 , where the spectra are recorded. Subsequently, the robot  10  transports the samples back to the storage container  11 . The movement sequences are programmed in the computer  13  so that the measurements are performed under the same measurement conditions (temperature, incident light, relative humidity). 
   To perform physical and chemical stability studies, in the method described here, vibration spectra from a sample of the substance or formulation stored in defined storage conditions are recorded automatically under identical measurement conditions using the spectrometer  12  in regular time intervals (minutes, hours, days). Middle-infrared, near-infrared, and Raman spectroscopy are vibration spectroscopy methods suitable for these studies. The recorded spectra of each sample are stored in the computer  13  as raw data, each spectrum being provided with the sample number, the storage conditions, and the time of the measurement using an index. The analysis of the raw data is performed through statistical data analysis. It begins for each sample automatically as soon as the number of spectra stored on the computer  13  is sufficient for a reasonable analysis and is recalculated as soon as new spectra of the sample are recorded. The current results of the analysis may be accessed at any time. 
   The execution of the automatic data analysis occurs according to the method indicated in the scheme in  FIG. 2 . At the start  20 , the measurement is initiated by the computer  13 . The first step  21  includes producing a data set which includes all spectra S of a sample at specific storage conditions, according to which a vector S is produced from the spectra entered in the computer  13 . In step  22 , a data transformation S→S′ is then performed, by subtracting a baseline from each spectrum in the vector S, for example. The analysis begins with the spectra of the data transformation of all spectra in the data set which contain a baseline correction or a vector standardization, for example. The second analysis step  23  includes the analysis of the main components or similar transformations of all transformed spectra S′ of a sample. The scatter diagram  24  of the main components may be graphed from this. With the aid of at least one of the calculated main components and the time of the measurement of each spectrum, the systematic temporal change of the spectra is subsequently determined with the aid of a regression calculation  25  of the main components in accordance with the formula t=B*HK+e, t being the vector from the storage time, B being the vector having the regression coefficients, HK being the matrix having the main components, and e being the vector having the experimental errors. The spectral representation  26  of the sums of the main components HK weighted with the regression coefficients then results therefrom. The results obtained from the regression calculation allow qualitative and quantitative statements about the physical and chemical stability of the sample. The projections or scores may be calculated (step  27 ) from the main component regressions  25 , from which the scores may be graphed as a function of the storage time (step  28 ). After the calculation of the scores, the method is ended at step  29  and the measurements are continued on the next sample. 
   In  FIG. 3 , the various main components  1 .HK,  2 .HK,  3 .HK, and  4 .HK are represented in the form of a scatter diagram in each case. These allow conclusions about the number of independent processes occurring during the storage of the sample. In this case, the individual spectra are represented in the diagrams as points which are connected in temporal sequence using a line. Particulars may be inferred from the book “Statische Datenanalyse-Eine Einfuhrung fur Naturwissenschaftler [Statistical Data Analysis—an Introduction for Physical Scientists]” by Werner A. Stahel, Vieweg 1995, about the main components on pp. 307 and 308, about scatter diagrams in chapter 3.1, particularly pp. 34 to 36, and about the matrix of scatter diagrams in chapter 3.6, pp. 48 to 51. 
   A diagram of the sum of the main components (or process factors) weighted with the coefficients of the regression calculation is shown in  FIG. 4 . The wavelength λ is plotted on the x-axis, the y-axis is dimensionless and shows the intensity changes. At a wavelength of approximately 1450 nm, there is a significant decrease of the intensity, from which a decrease of the concentration of the vibration oscillations of the associated molecule, and therefore reduced storability, may be concluded. The main components weighted with the coefficients of the regression calculation thus show the base vector for the temporal drift of the spectra and have the same physical units as these. The process factor allows conclusions to identify the materials participating in the physical and chemical alteration processes. 
   The associated scores are obtained through mathematical projection of the transformed spectra onto the calculated process factor. The scores are shown in the temporal sequence in  FIG. 5 . Together with the time t of the measurement of the spectra, they allow conclusions about the kinetics of the physical or chemical alteration processes. In connection with the Lambert-Beer law, the extent of the alteration (e.g., the chemical degradation) may be established quantitatively from the scores, if the process may be uniquely assigned to a substance present in the sample from the associated loadings. 
   A sample vessel  30  having a cover  32  tightly sealed by seals  31  is shown in  FIG. 6 . An overflow Channel  33  is provided in the cover  32 , which is connected on two diametrically opposite sides to hoses (not shown here) via connections  34 . Using this sample vessel, the samples may be vaporized in a controlled way. For this purpose, the sample vessel  30  is sealed using the cover  32  after pouring in the sample liquid and the hoses are connected. The overflow channel  33  then has a protective gas flow over it in a regulated and/or constant gas flow during the storage and/or the evaporation of the solvent. The measurements of the vibration spectra then occur in the sample vessel  30 . In addition, the sample vessel  30  may also be sealed hermetically using a suitable seal  36  (see  FIG. 6   a ), which includes a mechanical closure  37  (e.g., stopper or twist closure) and an artificial resin layer  38 , poured over it and cured, which hermetically seals the closure  37 . 
   A further embodiment of a sample vessel  40  is illustrated in  FIG. 7 , which includes a microtest plate  41  having multiple depressions  42  and an evaporation device  43 . The evaporation device  43  is provided with multiple cover-like caps  44  and an overflow channel  46  having connections  47 . Such a microtest plate  41  is preferably made of quartz glass and is described, for example, in the catalog 66/97-1 of HELLMA GmbH &amp; Co. D-79371 Mullheim, on page 155. The microtest plate  41  is sealed line by line with the evaporation device  43 , acting as a cover. The overflow channel  46  subsequently has a protective gas flow over it at a regulated and/or constant gas flow during the storage and/or the evaporation of the solvent, which flows via hoses (not shown in the figures) connected to the connections  47 . The measurement of the vibration spectra (NIR, Raman) occurs in the particular depression from below and/or, after the complete evaporation of the solvent and the removal of the evaporation device  43 , from top to bottom in the transmission mode, or using an infrared and/or Raman microscope.