The present invention relates to a spectroscopic apparatus for non-invasive in vivo analysis of blood and to a corresponding analysis method, in particular for direct determination of the pH value of the blood. From a Raman signal detected from an excited target region containing blood at least one predetermined pH sensitive signal portion is determined, from which the pH value of the blood in the target region by use of a relationship between pH value and one or more band parameters of pH sensitive vibrations of at least one molecule or part of a molecule present in blood, in particular heme vibrations of hemoglobin, is determined.