Concentration Measurement with Ultrabroad Dynamic Range Using Few-Step Variable Optical-Path-Length Slope Method

Concentration measurement has important applications in many fields, including pollution assessment in environmental science and drug dosage calculation in biomedical research. In the conventional methods, concentration is determined by measuring absorbance along a fixed long optical path. However, it is not suitable for high-concentration measurement. Herein, we have proposed a few-step variable optical-path-length slope method (fs-VOSM) for ultrabroad dynamic-range concentration measurement. As a proof of the method, we devised an fs-VOSM system in which a reference path is included to enhance the accuracy and repeatability. The measurement is conducted at 5 positions along ultrashort optical path (0-20 μm) for 800 ms. In the measurement of potassium dichromate solution concentration, the fs-VOSM system exhibits a wide dynamic range from 0.879 to 70.726 g/L with coefficient of variation (CV < 1.4%) and high accuracy (relative error within ±3.5%). We prospect that the fs-VOSM can be widely adopted in many advanced instruments such as process analyzer, flow injection analyzer, and turbidity meter.