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Implementation of chemometric techniques in chromatographic data station softwarePowerPoint Presentation

Implementation of chemometric techniques in chromatographic data station software

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### Implementation of chemometric techniques in chromatographic data station software

Yuri Kalambet, Ampersand Ltd., Moscow, Russia

www.ampersand.ru

Data processing data station software

- Noise level estimation
- Noise filtration and/or data bunching
- Peak search
- Peak quantification (area, height, asymmetry, etc.)
- Table of components (qualitative analysis)
- Calibration graph (quantitative analysis)
- Peak shape analysis and deconvolution
- Periodic noise filtration
- Multichannel (spectral) data analysis

Noise data station software

- High-frequency noise estimation using the whole time series data set
- Noise filtration could cause questions from GLP rules
- Bunching never causes questions from GLP, but can significantly reduce observed noise
- Noise is taken into account while:
- peak detection;
- approximation quality evaluation
- multichannel/spectral analysis

Peak Quantification data station software

- Baseline Y position using weighted Savitsky-Goley approximation with evaluation of approximation quality
- Primary peak parameters using adaptive polynomial approximation, where parameters of polynomial depend on target peak width and asymmetry
- Criterion for algorithm selection: Peak parameters should be resistant to bunching operation

Noise definition data station software

- 1st derivative point DOES NOT belong to “noise pool of points” if both of the neighboring derivative points have the same sign
- 1st derivative point DOES NOTbelong to “noise pool of points” if its absolute value is outside 5 sigma of absolute values distribution (iterative procedure)

Calibration data station software

Predictive relationship between input and detector response

- Input: calibration samples – concentrations of components
- Output: peak area or height
- Prediction: Predict unknown input looking at response

ESTD Calibration data station software

- Response (Area or Height) versus Quantity
- Quantity is provided without error - false
- Response is measured with random normally distributed error – sometimes true

Calibration Curve data station software

- Axes: Q – Quantity (NOT Concentration), R – Response (Area or Height)
- Independent variable: Typically Q, sometimes R
- Calibration curve: polynomial interpolation
- Prediction: either solution of polynomial equation (independent Q) or value of polynomial (independent R) – we denote either of them W(R)

Quantification data station softwareAbsolute Concentration

- Quantity of injected substance
Qx = W(Rx)

- Concentration of initial sample
Cx = Qx/V = W(Rx)/(Vinj*A/D)

- Vinj – injection volume
- A – amount
- D – dilution

ISTD Targets data station software

Reason Axis

- Sample-size variations Q
- Effect of sample preparations Q
- Instrument drift R
All reasons are acting always together

ISTD tricks data station software

- Add component with known concentration to sample
- Add component with known concentration to calibration samples
Usually it’s done together, but who told that you can’t do it separately?

ISTD with ESTD calibration = Relative Concentration data station software

- Accounts for systematic error due to sample-size error and sample losses while preparation.
- Assumption: volume is unknown and is calculated using known concentration of the internal standard
V = Qxistd/Cxistd = Wistd(Rxistd)/Cxistd,

- Qxistd is calculated using calibration curve of Internal standard from Rxistd, Cxistd – declared concentration of standard in sample
- Relative Concentration
C = Qx/V = Cxistd×Wx(Rx)/ Wistd(Rxistd)

“Universal” ISTD Calibration data station software

- If calibration is nonlinear, we must measure this nonlinearity, i.e. we MUST know ESTD calibration curve of the Internal Standard component
- In the case we learned this curve somehow, we can use this curve to change positions of calibration points of other components using the same trick as was used while calculating Relative Concentration:
Qn = Cn×V = Cn×Wistd(Ristd)/Cistd

- So, for Internal Standard predefined curve is in use, all other components get curves constructed conditionally, condition being known calibration curve of the Internal Standard component

Pro et Contra data station software

Advantages:

- Only one type of axes
- Calibration curves are suitable for calculation of both Absolute and Relative concentrations
Disadvantages:

- ESTD Calibration curve of Internal Standard is required

Q data station softwaren = Cn×V = Cn×Wistd(Ristd)/Cistd

- Multiplication of Q axis of Internal Standard to any number will multiply Q coordinates of all corrected points of all components to the same number, hence causing “affinity” change of all calibration curves. Calibration curve will change, absolute concentration also, but not Relative Concentration
C = Cxistd×Wx(Rx)/ Wistd(Rxistd)

- If all calibration dependencies are linear through origin Q = K×R, it is possible to select multiplication factor so, that Kistd = 1 and we will get relative response factors for all other components.

“Classic” ISTD data station software

- Calibration dependence in coordinates Response Ratio vs. Concentration ratio
- Calibration curve: polynomial, typically straight line through origin
- Prediction: from Response Ratio predict Concentration Ratio
- Peculiarities: no calibration curve for Internal Standard component

Example of “Classic” ISTD failure data station software

ESTD/”Universal” ISTD Calibration data station software

“Classic” ISTD calibration curve data station software

Device Drift data station software

- Drift model: R = K×F(Q)
- Drift can be compensated completely, if exists such k, that
K×F(Q)=F(k×Q)

- Particular case: linear through origin calibration; K = k

Example data station software

Conclusions data station software

- ISTD is split in two parts: ISTD quantification (Relative Concentration) and ISTD Calibration. Parts can be applied separately
- Relative Concentration is applicable for both ESTD and “Universal” ISTD calibrations
- Full “Universal” ISTD calibration can be used for both ESTD and ISTD calculations
- Simplified “Universal” ISTD calibration can be used in the case of linear through origin calibrations instead of “Classic” ISTD calibration including imitation of user interface
- Full “Universal” ISTD solution still works where “Classic” already fails, i.e. it allows to get into account wide concentration range of Internal Standard in the case of nonlinear calibrations

Difficulties data station software

- User mind. The more users are used to “Classic” ISTD method, the more difficult it is to change their minds. Typical argument: -“Old approach works. We typically use linear through origin calibrations. Why should we change the way how we work?”.

Peak deconvolution by shape data station software

Peak shape

- Gaussian
- Exponentially modified Gaussian
- Corresponds to reference peak
Tuning, specific to chromatography

- Peak width
- individual for every peak;
- the same for all peaks
- proportional to retention time
- asymmetry of the same sign (2)
Optimization criterion

- quadratic(sum of squares of residuals)
- weighted quadratic (weight = response)

Gaussian peak shape analysis data station software

Gaussian peak shape analysis data station software

Gaussian peak shape analysis data station software

EMG peak shape analysis data station software

Problems: product of zero to infinity for some range of parameters

Solution:

or “standard” Gaussian function, depending on parameter values

Fourier-domain periodic noise filtration data station software

- Median filter in Fourier space

Periodic noise filtration – mains frequency data station software

Periodic noise filtration data station software– pump pulsations

Multichannel chromatogram questions data station software

- Which channel is better?
- How to detect peaks?
- How to identify peaks?
- How to access substance purity?

Multichannel chromatogram answers data station software

- Calculated channels
- Using weighted PCR: Noise-normalized detector response space for spectra comparison
- Measure of difference for spectra: angle
- “Local” spectrum quality: angle with neighbors
- Factor analysis with missing (overloaded) points allowed
- Qualitative and quantitative spectra comparison

Weighted PCA data station software

- Channel weighting
- Point weighting

Calculated channels Summary. data station software

Types of Calculated channels:

- Total
- Average
- Difference
- Integral
- Derivative - up to 3-rd order
- Angle
- «Response/Time» channel
- Spectral ratio channel

Spectral chromatogram with angle profile. data station software

Best purity spectrum advantage data station software

Step 2 data station software:

Performing recognition.

Step 3 data station software:

Conflicts resolving.

Step 4 data station software:

View and print report.

Calculated channels in data station software“Chrom&Spec”. Summary.

Types of Calculated channels:

- Total
- Average
- Difference
- Integral
- Derivative - up to 3-rd order
- Angle
- «Response/Time» channel
- Spectral ratio channel

Main spectral window. data station software

3D data station softwaremulti-channel chromatogram view.

2 data station softwareD multi-channel chromatogram view.

Factor analysis example. data station software

Picture shows the “sum of s/n” channel of multi-channel chromatogram.

Usual peak-detection procedure failed to resolve peaks.

What about factor analysis?

Factor analysis. Step 1. data station software

Software makes PCR of the region selected and suggests number of components in the analyzed region (Rank).

Overlapping only 2 peaks means that software does not look for overlapping of 1st and 3rd components, only 1st and 2nd and then 2nd and 3rd.

Factor analysis. Step 2 data station software

On the left panel we can choose any channel to view peak deconvolution results.

Rotation is selected using “local purity” attribute, resulting in “Pure component” approach

Factor analysis. Step 3 data station software

The resolved peaks are displayed together with the original channel.

The chromatogram with additional newly generated channels can be saved into separate file. Each generated channel represents the detector response, corresponded to particular component.

When user finishes the wizard, the original peak is split in the proportions, corresponding to component’s fractions.

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