As per SciFinder the only reference I can find is: Jia, Rui; He, Yan-li; Xia, Er-ning "Differential spectrophotometric determination of polyquaternium-1 in ophthalmic preparations bacteriostatic agent" Yaowu Fenxi Zazhi, Volume 32, Issue 8, Pages 1465-1467, 2012 CODEN:YFZADL ISSN:0254-1793 The article is written in Chinese.
-L.E. Stevens, J.I. Eckardt. Spectrophotometric determination of polyquaternium-1 with Trypan Blue by a difference procedure. From Analyst 1987, 112, 1619-21.
-R. Jia, Y. He, E. Xia. Differential spectrophotometric determination of polyquaternium-1 in ophthalmic preparations bacteriostatic agent. Yaowu Fenxi Zazhi 2012, 32, 1465-1467.