In this paper, we deal with generalized Diophantine quadruples called
Diophantine quadruples with the property D(r), where r ∈ R, i.e. with the
sets of four distinct non-zero elements in R such that the product of each
two distinct elements increased by r is a perfect square in R. Often, we use
the shorter term D(r)-quadruples. The natural problem that arises here is to
describe the set of all r ∈ R such that D(r)-quadruple exists. This problem
has been solved in certain rings. In the ring of integers Z, Brown in [3],
Gupta, Singh in [10] and Mohanty, Ramasamy in [14] proved independently