the unknown ph values is performed by at least one multivariate algorithm using two or more variables and at least one calibration model the determined ph values are within the physiological ranges observed in blood containing tissue application_number US 13145898 A description as discussed above spectroscopic detection of ph variation is dependent on a sensitive and appropriate indicator species in blood there are four main systems responsible for buffering i e combining with hydrogen or hydroxyl ions while maintaining a constant ph hemoglobin bicarbonate plasma proteins and phosphate each of these was considered as the source of ph signal during the examination of lysed blood discussed below phosphate buffers are minimal in their buffering capacity are in low concentration provide essential no signal in the near infrared and thus were eliminated as a possible spectral source of ph information plasma proteins while in significant concentration do not provide a large variation in spectral signal to be a sufficient indicator species for ph support for this comes from the near infrared spectra examined which indicated only minimal correlation with ph titration data supports this finding see c tanford s a swanson and w s shore 34 hydrogen ion equilibria of bovin serum albumin 34 j amer chem soc 77 6414 6420 1955 the bicarbonate buffer is not an appropriate indicator species for spectroscopic determination of ph the relationship between bicarbonate ion and ph is defined by the chemical.