Monitoring and control of critical process parameters (CPPs) in various bioprocesses is a prerequisite to gain a safe product and hence, is a major topic in Process Analytical Technology (PAT). The most widespread methods for process monitoring are linked to sampling. Sample-based monitoring has various advantages: direct measurement of specific analytes; usage of highly automated offline analyzers; reliability through application of reference methods; extensive parallelization; flexibility and storage of reference samples for later analysis.