# Photon density wave spectroscopy as process analytical technology: a review of recent advances in technology and application

## TL;DR

This paper reviews recent advances in photon density wave spectroscopy as a tool for real-time monitoring in chemical and food processes.

## Contribution

The paper provides a comprehensive review of PDW spectroscopy's recent developments and applications in process analytical technology.

## Key findings

- PDW spectroscopy enables absolute quantification of optical properties in highly scattering materials.
- It allows dilution-free particle sizing in concentrated systems.
- Applications in chemical, biotech, and food processing are reviewed.

## Abstract

Photon density wave (PDW) spectroscopy is a calibration-free method for the simultaneous, absolute, and independent quantification of the optical absorption coefficient and the reduced scattering coefficient of highly light scattering materials. It allows for dilution-free particle sizing in concentrated liquid systems. Thus, it is beneficial as an inline process analytical technology (PAT). A brief comparison to other particle sizing technologies, the theoretical background of PDW spectroscopy, the current technical status, and limitations and technical challenges are reviewed. In addition, a comparative overview of the recent applications of PDW spectroscopy as PAT for chemical, biotechnological, and food processing is provided.