Matrix effects caused by Na and Al in the nitrogen Microwave-sustained, Inductively Coupled, Atmospheric-pressure Plasma (MICAP) were investigated. Easily ionizable elements, such as Na, can suppress or enhance the analyte signal; Al is shown here to produce a similar effect. The influence of these matrices was examined for 18 emission lines of 8 analyte atoms and ions having a wide range of excitation and ionization energies. The plasma operating conditions were fixed during all experiments at a total nitrogen flow of 19.4Lmin−1 and a microwave power of 1.5kW. An Fe solution was used to determine the excitation temperature of the plasma by the Boltzmann plot method at selected matrix concentrations. In addition, vertical emission profiles of the plasma were measured. The matrix effect becomes worse at higher concentrations of an easily ionizable element. The effect is caused not only by a shift in ionization equilibrium but also by a possible change in plasma ionization temperature. Correction methods to reduce the matrix effects were tested and are discussed. Display omitted •The spatial behavior of elemental emission from the MICAP is a function of concomitant elements present in a sample solution.•Unlike in the argon ICP, a concomitant does not produce a shift in the vertical distribution of emission intensity.•Rather, the result of adding an easily ionized matrix element to a sample solution is to lower emission intensity of ion lines and to boost emission from neutral-atom lines.•Overall, the effect appears to be due mainly to a shift in ion-atom equilibrium induced by electrons added to the discharge.•A secondary effect seems to be a modification of the ionization temperature of the MICAP.