The peak impurity check is a 3D-UV feature in OpenLab CDS allowing you to verify if the peaks can be considered as pure (no impurity underneath), or impure if there is any impurity across the peak absorbing at the defined UV wavelengths.
A sensitivity percentage is used to adjust the spectra purity threshold towards the considered instrument or application. The result is highly dependent on noise, column, solvent, matrix etc. Therefore, the returned match factor must always be reviewed by a chemist.
To check for UV impurities:
Run a pure standard that contains the compounds of interest.
Depending on the type of samples and your application, you may choose to spike a blank with the pure standard compounds.
Do an impurity check calculation for that standard.
Compared to ChemStation, there is a simplified set of parameters. You only need to adapt the sensitivity (globally or per compound) so that the peaks of interest are shown as pure. The sensitivity basically shifts the threshold curve up or down.
Adapt the sensitivity, and check the purity ratio curve in the Peak Details window.
Use this processing method to analyze your samples.
| Be aware that a UV impurity check has its limits and always needs to be evaluated by a chemist. |
Any spectra functionality has dependencies with the instrument accuracy as well as the chromatographic application and its way to process the data. Here are examples of influencing parameters when computing a UV peak purity:
Signal-to-noise is a generic parameter that is influenced by many system variables. As a generic observation, the lower the signal-to-noise, the higher the contribution of the noise. The peak purity considerates and retrieves the noise from the peak start and end. However, with a low signal-to-noise (for example, lower than the limit of detection), the calculation of the noise is difficult and will lead to fluctuating peak purity results. An opposite effect can be observed working at too high concentration reaching the detector upper range limit. In this case, the absorbance of the components will fluctuate, and the peak purity will not be accurate.
Instrument health and maintenance: Pump accuracy, solvent degasser, injector carryover, column bleed and detector linearity are factors that influence spectral analysis.
Solvent cutoff and quality: Every solvent manufacturer delivers the UV specifications of the solvent batch purchased. This solvent cutoff needs to be considered in the wavelength bandwidth taken for the spectra purity calculation, especially when working with a solvent gradient.
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Parameter | Default recommended values |
Comments |
|---|---|---|
Sensitivity | 50 % for conventional, routinely maintained, or new instrument after instrument checkout 75 % for state-of-the art chromatography | Decrease the default value by 10 to 20% for each of the following point not fulfilled:
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Wavelength Bandwidth | According to solvent cutoff (L0 + 5 nm) According to compound spectral absorptions (if known) | For example, paracetamol in acetonitrile/water: 205-300 nm |