A fifth spectrophotometric method for the quantitative determination of the concentration of Pb^2+ in blood uses a multiple-point standard addition based on equation 5.6. The original blood sample has a volume of 1.00 mL, and the standard used for spiking the sample has a concentration of 1560 ppb

Question

A fifth spectrophotometric method for the quantitative determination of the concentration of $Pb^{2+}$ in blood uses a multiple-point standard addition based on equation 5.6. The original blood sample has a volume of 1.00 mL, and the standard used for spiking the sample has a concentration of 1560 ppb $Pb^{2+}$ . All samples were diluted to 5.00 mL before measuring the signal. A calibration curve of $S_{spike}$ versus $V_s$ is described by

$S_{spike} = 0.266 + 312 mL^{–1} × V_s$

Determine the concentration of $Pb^{2+}$ in the original sample of blood.

$S_{spike}=k\left\lgroup C_A\frac{V_0}{V_\mathrm{f}}+C_S\frac{V_s}{V_\mathrm{f}} \right\rgroup$ (5.6)

[latex]S_{spike} = 0.266 + 312 mL^{–1} × V_s[/latex]

Determine the concentration of [latex]Pb^{2+}[/latex] in the original sample of blood.

[latex]S_{spike}=k\left\lgroup C_A\frac{V_0}{V_\mathrm{f}}+C_S\frac{V_s}{V_\mathrm{f}} \right\rgroup[/latex] (5.6)

Accepted Answer

To find the x-intercept we let [latex]S_{spike}[/latex] equal 0

[latex]0 = 0.266 + 312 mL^{–1} × ( ext{x-intercept})[/latex]

and solve for the ×-intercept’s absolute value, giving a value of 8.526 × [latex]10^–4[/latex] mL.

Thus

[latex] ext{x-intercept}=8.526 imes 10^{-4} ml =\frac{C_AV_0}{C_S} =\frac{C_A imes (1.00 ml)}{1560 ppb}[/latex]

and the concentration of [latex]Pb^{2+}[/latex] in the blood sample, [latex]C_A[/latex], is 1.33 ppb.

Question 5.7: A fifth spectrophotometric method for the quantitative deter...

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