Analytical Chem istry - DePauw University

Chapter 5 Standardizing Analytical Methods203kASstd0.0931= =−3C 316 . × 10std= 29.46 MM−1and then use this value of k A to solve for C A .CASsamp0.114= = = 387 . × 10−1k 29.46 MA−3MWhen using multiple standards, the indeterminate errors affecting thesignal for one standard are partially compensated for by the indeterminateerrors affecting the other standards. The standard selected for the onepointstandardization has a signal that is smaller than that predicted by theregression equation, which underestimates k A and overestimates C A .Click here to return to the chapter.Practice Exercise 5.2We begin with equation 5.8rewriting it as⎛S k C V o= + Cspike A A⎝⎜VfstdV VkCV0 = + k × ⎧ ⎨ ⎪ C V A A oA stdV⎩⎪Vfwhich is in the form of the linear equationstdfstdf⎞⎠⎟⎫⎬⎪⎭⎪Y = y-intercept + slope × Xwhere Y is S spike and X is C std ×V std /V f . The slope of the line, therefore,is k A , and the y-intercept is k A C A V o /V f . The x-intercept is the value of Xwhen Y is zero, orkCVClick here to return to the chapter.Practice Exercise 5.3A A o0 = + k ×{ x-intercept}VfkCVA A oV CVfAx-intercept=− =−k VAUsing the calibration equation from Figure 5.7a, we find that the x-interceptisAfo