The quantitative determination of SNF in the aqueous phase of fresh cement-water systems have been investigated by UV spectrophotometry and spectrofluorimetry. The conventional UV method gives a spectrum with three λ max values at ca. 227, 292 and 328nm, which may be used for analysis. However, different λ max values produce rather different results for the same species of SNF in the aqueous phase of fresh cement mixes although all follow the same trends. The SNF concentrations in solutions measured at ca. 227nm are significantly higher than those obtained at 292nm and 328nm. Alternatively, a method based on spectrofluorimetry may be used for SNF analysis. The results obtained using this method are in very good agreement with those produced by the UV method at 227nm, suggesting that true SNF concentrations in fresh or hardened cement pastes can be measured either by spectrofluorimetry or by UV spectrophotometry at 227nm. © 1992.