Environmental samples like waste waters are generally known to contain calcium, magnesium, sodium and potassium as major constituents. It is important to assess the amount of interference at analysis wave length arising from the matrix as well as other analyses to select suitable analysis lines. This paper report the measurement of partial sensitivities of 49 prominent lines of 17 impurities of interest in waste water (Ag, Al, As, B,, Ba, Be, Cd, Co, Cr,Cu, Fe, Hg, Mn, Ni, Pb, V, Zn) using indecisively coupled plasma atomic emission spectroscopy. Spectra scans for 300 pm wide windows centered (± 150pm) around analyses wavelengths, were obtained under compromise operating conditions. Using the criterion of “true detection limit”..Q–values for line interference [QIJ(la)] and Q-values for wing background inference [QWJ(Dla)] due to Ca, K, Mg and Na have been worked out. The Q-value s give a quantative estimate of the extent of spectral inference and thus permit a rational selection in a multi-component matrix is more complex than in a single element matrix. Therefore, prior quantitative knowledge of the matrix elements is inevitable for selection of a suitable line for trace element analysis. Trace element analysis in synthetically prepared samples indicates the presence of non-spectroscopic matrix effects.