Advantages and Disadvantages of Common Spectrophotometric Methods in Biochemical Analyzers

Biochemical analyzers are instruments that use Beer-Lambert's law to measure the concentration of specific substances in samples. Their core component is a device capable of separating mixed light into monochromatic light for detection, commonly known as a spectrophotometer. Depending on the application and implementation, biochemical analyzers primarily use the following spectrophotometric methods:

Pre-Filter Beam Splitting

Pre-filter beam splitting was a common spectrophotometric method in early low-speed analyzers. A filter wheel with different wavelength filters is installed in the incident light path before the reaction cup. Driven by a motor, the filter wheel rotates to position the appropriate filter in the light path when a specific wavelength is required. The light passes through the filter, the reaction cup, and eventually reaches the detection device, enabling measurement of the substance's absorbance.

This method was widely used in early low-speed analyzers but is now largely obsolete in high-speed systems due to its reliance on mechanical movement, which is time-consuming and inefficient.

Post-Filter Beam Splitting

Post-filter beam splitting uses fiber optics and filters to achieve spectrophotometry. Light from the reaction cup is guided to corresponding detection channels via a bundle of optical fibers. Each channel has a filter of a specific wavelength at the fiber's exit point. These filters split the full-spectrum light signal, allowing for simultaneous measurement of absorbance at multiple wavelengths.

This method improves efficiency by eliminating mechanical movement and enables multi-wavelength detection. However, light transmission through fibers reduces light efficiency, potentially affecting the lifetime of light sources. Therefore, high-efficiency optical fibers must be used. Additionally, the accuracy of wavelengths depends on the filter's performance, requiring filters with sufficient cut-off depth.

Post-filter beam splitting is particularly advantageous in space-constrained setups, as fiber optics allow flexible light path adjustments.

Post-Beam-Splitter Beam Splitting

Post-beam-splitter beam splitting is a widely used optical system in the market. It employs a beam splitter that reflects specific wavelengths while allowing others to pass. This changes the path of the desired wavelength without relying on fiber optics. The system is highly efficient, compact, and easy to calibrate, making it suitable for medium-speed biochemical analyzers.

However, the beam splitter only changes the light path. The accuracy of wavelengths and control of stray light still depend on filters, requiring filters with sufficient cut-off depth and half-wave width to ensure wavelength accuracy and minimize stray light.

Post-Grating Beam Splitting

Post-grating beam splitting is the dominant method in medium-to-high-speed biochemical analyzers. It uses a core optical component to separate composite light into a spectrum arranged by wavelength. A metal mask with narrow slits is placed in the spectrum's path to allow only specific wavelengths to pass. The light passing through the mask reaches the detection unit, enabling accurate signal collection and conversion.

This method is highly efficient, with excellent wavelength accuracy, low stray light, and a wide linear range, making it ideal for high-sensitivity and high-precision measurements.