A Tool for Rapid, Accurate Concentration Measurement of Biological Samples

Conventional ultraviolet–visible spectroscopy (UV-vis) instruments use fixed optical pathlengths to measure analyte concentrations in biological samples. As Paul Mania (bioanalytics application specialist at Repligen) pointed out during an April 2022 presentation, such an approach requires sample dilution, which introduces risks for error and increases operator workload. Mania explained how the CTech SoloVPE instrument measures analyte concentrations at line without need for dilution, simplifying and accelerating analysis of samples from several downstream operations.

Mania’s Presentation
Traditional UV-vis instruments measure analyte absorbance one time across a fixed pathlength, then use that value to determine analyte concentration. But absorbance values from biological samples exceed the linear range of most such systems. Thus, samples must be diluted. That complicates concentration measurement, Mania explained. Operators need to estimate an analyte’s concentration, perform volumetric or gravimetric dilution, take measurements, plot out results, calculate analyte concentrations, and define assay acceptance criteria. That process can take 30 minutes to three hours. Mania added that manual dilution increases requirements for operator training and introduces risks for errors, with the possibility of skewing measurements by 5–20%.

The SoloVPE system leverages variable-pathlength technology (VPT) to determine analyte concentrations using a fiberoptic probe suspended from a flow cell. Upon application, the sensor gathers data from up to 10 pathlengths. Then, the system software uses a proprietary algorithm to analyze absorbance values across the different pathlengths, calculating a slope value indicative of the analyte’s concentration. Because samples come within 5 µm of the instrument detector, values can be measured without need for sample dilution. Thus, dilution workflows are eliminated, as are the errors introduced by them. Results are generated in less than two minutes.

Mania emphasized the SoloVPE system’s accuracy and robustness. In addition to collecting more data than a conventional UV-vis instrument does, the SoloVPE system requires those data to be linear. Noting the instrument’s suitability for good manufacturing practice (GMP) environments, Mania added that ASTM International now considers VPT to be a standard method for quantitative UV-vis analysis.

Mania presented two case studies to demonstrate the instrument’s utility. In one example, Bristol Myers Squibb (BMS) sought to validate a SoloVPE system for testing of in-process samples at a clinical manufacturing facility. The company had been using a conventional UV-vis system for concentration measurement, diluting samples gravimetrically. Using samples with known analyte concentrations, BMS compared measurements from both conventional and SoloVPE systems. On average, values from the conventional instrument differed from the known concentration by 3.5%. Values from the SoloVPE system differed by <1%, with high linearity and precision. Equally important, the workflow’s rapidity helped BMS to streamline its manufacturing process from three hours to 30 minutes. That amounted to labor savings of 33 days per year.

Downstream scientists at Biogen confirmed the potential for such savings in separate experiments. They needed a method for analyzing in-process samples with analyte concentrations of 0.5–270 mg/mL. During validation, Biogen determined that the SoloVPE system obtained data with a margin of error <1%. Replacing a traditional UV-vis instrument with a SoloVPE system also reduced costs related to instrument use, time, and labor by >50%. That amounted to yearly time and cost savings of 59 days and >US$318,000, respectively.

The SoloVPE system has been validated for in-process testing of
>100 monoclonal antibodies (MAbs) and for clinical-manufacturing testing of >80 such products. Although MAb concentration analysis remains the most frequent application, the system also serves as a platform for “gold-particle” testing of viral filters and measurement of polysorbate, antisense oligonucleotide (ASO), and hemoglobin concentrations. Other applications include evaluation of adenoassociated virus (AAV) titers during process development.

Questions and Answers
What support is provided during system installation? Application specialists work on site with users to assist with system installation and operational qualification (IQ/OQ), software validation, and training. Repligen provides a standard operating procedure (SOP) template that users can adapt to their needs. Support specialists also perform periodic maintenance (PM) and requalification according to United States Pharmacopia (USP) guidelines.

What kind of audit trail can the system generate? Because the software tracks all assay parameters and data, the system provides complete audit logs that can be exported to Microsoft Excel files using Viper software.

Find the full webinar online at www.bioprocessintl.com/category/webinars.