addition of brij 35 results in a larger bathochromic shift of the wavelength maxima upon complexation of the ionophore with calcium which effect is desirable to reduce endogenous spectral interferences non ionic surfactants were found to cause a substantial increase in the absorptivity of the calcium complex and attendant increase in sensitivity of the reagent the following table shows the effect of brij 35 on the calcium response to a reagent formulation of 1 0 u00d7 10 4 m dilabeled chromogenic tetraacid diphenol 9 0 1 m ches ph 9 0 2 0 ml reagent 0 08 ml sample for different levels of calcium ______________________________________ sup u03b4a 500 nmca sup 2 mg dl no surfactant 0 1 brij 35______________________________________0 0 0 0 0 04 0 0 134 0 44308 0 0 2456 0 740012 0 0 3466 0 965116 0 0 4446 1 1410______________________________________ a series of experiments was conducted to assess performance of the reagent containing the preferred chromogenic dilabeled tetraacid diphenol 9 in the analysis of calcium the following formulation was used samples were evaluated on a technicon ra xt u00ae analyzer available from miles inc the assignee of the present application technicon ra xt is a registered trademark of miles inc tarrytown n y the following instrument parameters were used ______________________________________reagent volume 390 ulsample volume 6 uldelay 2 min filter 550 nmtype endpointcell pathlength 7.