i_H = 1;
i_C = 2;
i_O = 3;
i_Na = 4;
i_Cl = 5;
i_Ca = 6;
i_Mg = 7;
i_S = 8;
i_P = 9;
i_SIZE = 9;

M_H  =  1.00794; % g/mol
M_C  = 12.0107;  % g/mol
M_O  = 15.9994;  % g/mol
M_Na = 22.9897;  % g/mol
M_Cl = 35.45;    % g/mol
M_Ca = 40.078;   % g/mol
M_Mg = 24.305;   % g/mol
M_S  = 32.06;    % g/mol
M_P  = 30.9738;  % g/mol

mol_masses = zeros(1, i_SIZE);
mol_masses(i_H) = M_H;
mol_masses(i_C) = M_C;
mol_masses(i_O) = M_O;
mol_masses(i_Na) = M_Na;
mol_masses(i_Cl) = M_Cl;
mol_masses(i_Ca) = M_Ca;
mol_masses(i_Mg) = M_Mg;
mol_masses(i_S) = M_S;
mol_masses(i_P) = M_P;