It is easy to generalize this to the case, under a reasonably close approximation, when we have asymmetric distributions which are assumed to be normal in each of the four quadrants of the coordinate system centered at (l l 2 ,l l 1 ). Then the confidence region is made of union of four quadrant-wise elliptic regions. Let the asymmetric confidence intervals for specified z c and the two concentrations be [l l 1 {H B ,l l 1 zH T ] and [l l 2 {W L , l l 2 zW R ].