SoloVPE Application: Drug-to-Antibody Ratio (DAR)

Measure Antibody Drug Conjugates with VPT

Accurately measure antibody drug conjugates

CTech SoloVPE System can be used to accurately measure Antibody Drug Conjugates (ADC) by using variable pathlength technology.


There is potential for miscalculation due to optical density being affected by dilution and manual calculation when using traditional ultraviolet and visible (UV‐Vis) absorption spectroscopy methods.

The SoloVPE Solution

  • Allows users to get an accurate drug-to-antibody Ratio (DAR) value by measuring the payload and antibody wavelength simultaneously. 
  • Slope Spectroscopy manipulates Beer-Lambert’s law, allowing the system to accurately vary the absorbance with the change in pathlength.  
  • With near-perfect linear regression, the system can accurately measure a wide range of concentrations undiluted, ideal for process development, QC testing, and bioprocessing manufacturing risk mitigation.
  • The dedicated software’s MultiQ feature allows the user to measure the payload and antibody simultaneously. 
  • The User Result feature allows for built-in calculations of the DAR value that doesn’t need to be done outside of the software.

Application Case Study

ImmunoGen, Inc. and Magenta Therapeutics have integrated the SoloVPE System for determination of the DAR value of their products.

For Inline Testing

For inline testing using the same technology as the SoloVPE, consider learning more about the FlowVPX, which can measure the DAR value of ADCs “inline” during downstream process development and manufacturing, allowing you to measure the ratio between the payload and the protein in real time.


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Application Services

The passion for what we do is in the product and support services you receive

CTech is committed to our customers’ success. We design service offerings to supplement our standard support options and provide you with increased access to our highly knowledgeable and experienced professionals. We offer implementation, development, and educational guidance to maximize the benefits of your variable pathlength solutions and the Slope Spectroscopy® technique.

Application Services

  • 21 CFR Part 11 Guidance
  • Annex 11 Guidance
  • Validation Support
  • Qualification Service
  • Method Transfer Service


  • Method Design & Development
  • Comparability
  • On-Site Support
  • Custom Standards
  • Process Auditing


  • SOP Document Review
  • Advanced Slope Spectroscopy Training
  • Data Analysis
  • Maintenance & Troubleshooting

Contact a Bioanalytics Application Specialist

Your Partners in Method Development and Process Solutions.

Connect with our dedicated applications team. Our team can show you how to maximize the benefits of your variable pathlength solutions and the Slope Spectroscopy® technique. Let us help you expedite your SoloVPE Validation.

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