Absorbance Detector Dynamic Range Extension via Stray Light Correction

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Absorbance detectors in liquid chromatography have a limited dynamic range, struggling to accurately measure both low and high concentrations of analytes due to stray light and non-linearity, which restricts their ability to capture both impurities and active ingredients in pharmaceutical substances within acceptable error ranges.

Innovation Solution

The method involves receiving calibration data to calculate and correct for the contribution of stray light, using equations to transform absorbance data and remove its impact, thereby expanding the dynamic range of absorbance detectors by 1.5 to 2.1 AU, allowing for improved concentration measurement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If absorbance detectors are used to measure analyte concentrations, then detection capability is provided, but the dynamic range is limited to about five orders of magnitude due to stray light and non-linearity

Engineering Contradiction:

Improvedetection capabilityVSAvoiddynamic range

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent applies parameter changes by transforming the absorbance scale from the traditional logarithmic scale to a linear scale through mathematical transformation. This changes the measurement parameter representation, allowing the detector to maintain measurement precision across a broader concentration range while correcting for stray light effects through the transformation equation: A_linear = -log10(10^(-A_log) - 10^(-A_stray))

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If the dynamic range is extended to measure both small and large peaks, then quantitation accuracy for impurities and active ingredients is improved, but stray light causes non-linearity at high absorbance values

Engineering Contradiction:

Improvequantitation accuracyVSAvoidlinearity

Core Design Contradiction:

Measurement precisionVSStability of the object's composition

Solution Approach 1:

The patent converts the harmful effect of stray light into a beneficial correction factor. By modeling stray light as a measurable parameter and applying mathematical transformation, the previously harmful non-linear distortion is converted into a correctable deviation, extending the linear dynamic range from 2 AU to 4 AU while maintaining quantitation accuracy

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent replaces the physical/optical approach to extending dynamic range (which would require complex optical systems) with a mathematical transformation approach. This substitution of mathematical correction for physical modification simplifies the system while achieving the same goal of extended dynamic range and improved linearity

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enhances the dynamic range of absorbance detectors, enabling more accurate quantitation of both small and large peaks, reducing errors and maintaining chromatographic resolution, as demonstrated by the correction of absorbance data and its impact on chromatogram peak broadening.

Implementation Method 1

Absorbance (A), a dimensionless number commonly expressed in absorbance units (AU) for convenience, is calculated from log(I0/I) and displayed as the instrument output. Absorbance is proportional to the product of path length (b) and concentration (c). This relationship between absorbance, path length, and concentration is known as Beer's Law.

Methodology Applied

Scientific EffectBeer's Law: Absorption (EM radiation)

Implementation Method 2

Broad spectrum or bandwidth limited light is directed through a sample, and then measured at the chosen analytical wavelengths by a detector, such as a photodetector.

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS10551362B2Method for extending the dynamic range of absorbance detectors

Publication Date: 2020.02.04 WATERS TECHNOLOGY CORP

AI summary

The invention generally provides methods for improving the dynamic range of an absorbance detector and absorbance detectors having improved dynamic range. In an exemplary embodiment, the method includes receiving calibration data for a plurality of samples, the calibration data comprising an absorbance for a concentration of each of the samples, calculating a contribution of stray light to the calibration data, and correcting subsequent data by removing the contribution of stray light.