A measurement chamber extension for a spectrophotometric characterization with a NIR-spectrophotometer or a Raman-spectrophotometer of a liquid in a polymer container comprising a tubular section, wherein the measurement chamber extension comprises: - an adapter plate having an adapter opening; - a container holder comprising a receptacle; and - an optical element comprising a mirror; wherein the adapter plate is light-tightly connectable to the measurement chamber of the NIR-spectrophotometer or of the Raman-spectrophotometer by its outer contour being adapted to an outer contour of the measurement chamber of the spectrometer, and the adapter opening is arranged to encompass a measurement window of the NIR-spectrophotometer or Raman-spectrophotometer to provide exposure of the liquid to a measurement light beam emitted from the measurement chamber of the NIR-spectrophotometer or Raman-spectrophotometer through the measurement window; wherein the receptacle of the container holder is configured to arrange the optical element adjacent to a surface of the polymer container containing the liquid providing a loss-free transmission or transflection of the measurement light beam from the optical element to a detector of the NIR-spectrophotometer or Raman-spectrophotometer; wherein the receptacle is configured to hold the tubular section of the polymer container so as to allow a reproducible layer thickness for the transflection measurement; wherein the container holder comprises an optical element support structure comprising a light guiding channel, wherein a width of the light guiding channel is adapted to fit with a width of the measurement window of the NIR-spectrophotometer or Raman-spectrophotometer, wherein the mirror comprises a gold layer, and wherein the polymer container is selected from: a syringe, an infusion pump or a cartridge for such, and an infusion bag. - an adapter plate having an adapter opening; - a container holder comprising a receptacle; and - an optical element comprising a mirror; wherein the adapter plate is light-tightly connectable to the measurement chamber of the NIR-spectrophotometer or of the Raman-spectrophotometer by its outer contour being adapted to an outer contour of the measurement chamber of the spectrometer, and the adapter opening is arranged to encompass a measurement window of the NIR-spectrophotometer or Raman-spectrophotometer to provide exposure of the liquid to a measurement light beam emitted from the measurement chamber of the NIR-spectrophotometer or Raman-spectrophotometer through the measurement window; wherein the receptacle of the container holder is configured to arrange the optical element adjacent to a surface of the polymer container containing the liquid providing a loss-free transmission or transflection of the measurement light beam from the optical element to a detector of the NIR-spectrophotometer or Raman-spectrophotometer; wherein the receptacle is configured to hold the tubular section of the polymer container so as to allow a reproducible layer thickness for the transflection measurement; wherein the container holder comprises an optical element support structure comprising a light guiding channel, wherein a width of the light guiding channel is adapted to fit with a width of the measurement window of the NIR-spectrophotometer or Raman-spectrophotometer, wherein the mirror comprises a gold layer, and wherein the polymer container is selected from: a syringe, an infusion pump or a cartridge for such, and an infusion bag.