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Spectroscopic analysis methods

A technology of spectrum and spectral value, applied in the field of spectroscopic instruments, can solve problems that are difficult to explain, unstable main components, etc.

Active Publication Date: 2009-07-01
RENISHAW PLC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

In this case the model is unstable to the principal components and becomes difficult to interpret

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment I

[0045] Example I: Simulated mixture spectra

[0046] Pure Raman spectra of three pigments added in different ratios ( figure 2 ) to form a matrix of 2500 mixed spectra. The average, minimum and maximum ratios for each pigment spectrum are given in Table I. Spectra 1 and 2 are present in the entire dataset, while Spectrum 3 is only present in 100 spectra to simulate minor components. Random noise with Poissonian statistics is added to the data set to simulate disturbances caused by noise. The spectra used to form the data set were normalized by subtracting the minimum value (minimum value subtraction) and dividing by their intensity sum. This removes the intensity uncertainty from the dataset and facilitates direct comparison with the ALS method.

Embodiment II

[0047] Example II: Drug powder

[0048] The analyzed sample was a powdered mixture containing 1% active pharmaceutical ingredient (API) and 99% excipients including cellulose, lactose and dicalcium phosphate. The surface of the sample is leveled and point-focused spectra are collected from the surface. The map area is 600 μm x 66 μm with a 6 μm step size, giving 1212 collected spectra.

Embodiment III

[0049] Embodiment III: ranitidine tablet

[0050] A commercially available tablet containing 75 mg of ranitidine as API was analyzed. API accounts for approximately 50% of the total tablet mass. Excipients present at the core are microcrystalline cellulose and magnesium stearate. Use a scalpel to cut the tablet horizontally. Line focus maps were collected from an area of ​​1.68 mm x 1.95 mm. With a step size of 6 μm in x and an intrinsic step size of 5.81 μm in y, this gave 94000 collected spectra.

[0051] theory

[0052] For chemometric analysis the hyperspectral image cube expands into a matrix X, so each collected spectrum occupies a row of the data matrix ( figure 1 ). The matrix has dimension I x J, where I is the total number of spectra from the data set and J is the number of variables which are the frequencies at which the intensities were collected. The purpose of curve analysis is to resolve this matrix into physical submatrices C and S:

[0053] X=C·S T +E...

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Abstract

A spectroscopic analysis method in which spectral data of mixtures obtained from a plurality of points on a sample surface are resolved into component spectra and concentrations. A new alternating least squares multivariate curve resolution technique is presented which iteratively resolves the components. The technique starts from an initial estimate that the spectral values of a first component of the sample are all equal (an 'empty model'), and resolves that component. Then successive further components are iteratively resolved, from initial 'empty model' estimates of those components and from previously resolved spectra. In the common case where the main component is present in nearly pure form in the data set, this empty modelling technique results in more accurate resolution of the components. This is due to the ability of the technique to resolve the pure spectra of minor components without modelling concentrations of the main component into them.

Description

technical field [0001] The present invention relates to spectroscopic instruments and methods. It is particularly useful in Raman spectroscopy, although the invention can also be used in other forms of spectroscopy, for example using narrow line photoluminescence, fluorescence, cathodoluminescence or infrared. Background technique [0002] The Raman effect is a phenomenon in which a sample scatters incident light of a given frequency into a spectrum having lines resulting from the interaction of the incident light with the molecules that make up the sample. Different compounds have different characteristic Raman spectra, and thus this effect can be used to analyze the compounds present. [0003] Examples of Raman spectrometers are known from US Patent Nos. 5,442,438 and 5,510,894, which are incorporated herein by reference. The sample is illuminated with monochromatic light from a laser. Typically, the scattered light is then dispersed into a Raman spectrum by a dispersiv...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01J3/44
CPCG01N21/65G01J3/44G01N2201/1293G01N2021/6423
Inventor 乌特·卡佩尔
Owner RENISHAW PLC
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