Question

7 The fluorescence of each of a series of acidic solutions of quinine was deter mined five times. The results are given below. Concentration, ng m 01020 304050 Fluorescence intensity 422 4460 75 104 32046 63 81109 42145 6079107 5 2244 6378 101 4 2144 6377105 (arbitrary units) Determine the slopes and intercepts of the unweighted and weighted regression lines. Calculate, using both regression lines, the confidence limits for the con centrations of solutions with fluorescence intensities of 15 and 90 units. 8 An ion-selective electrode (ISE) determination of sulphide from sulphate reducing bacteria was compared with a gravimetric determination. The results obtained were expressed in milligrams of sulphide. Sample: Sulphide (ISE method): 108 12 152 3106 11128 12 160 128 123 45 6789 10 Sulphide (gravimetry): 105 16 113 0 108 11 141 11 182 118 Comment on the suitability of the ISE method for this sulphide determination. (Al-Hitti, I.K., Moody, G.J and Thomas, J.D.R, 1983, Analyst, 108: 43)

Answer 1

The ISE method is one of the simplest known method and is inexpensive as compared to the gravimetric method of determination. Also the results obtained are quite accurate by ISE methods. Thus, ISE method is best suitable in this scenario.