A Serum taken from a patient being treated with lithium for manic-depressive illness was analyzed for lithium concentration. A reading of 291 units was obtained for the intensity of the 671 nm red emission line. Then 1.00 mL of a 11.7 mM Lithium standard was added to 9.00 mL of serum, and this spiked serum gave an intensity reading of 729 units. What is the original concentration of Li in the serum?
You have posted this numerous times in the last day or so. I don't know how the units are displayed; if you have an answer post it. I may be able to help if I can figure out the units and I can do that if I have an answer.
To determine the original concentration of lithium in the serum, you can use the method of standard addition. This involves adding known amounts of a standard solution to the sample and comparing the changes in the measured signal.
Here's how you can solve this problem step by step:
Step 1: Calculate the change in intensity
Subtract the initial intensity reading from the spiked intensity reading to find the change in intensity:
Change in intensity = spiked intensity reading - initial intensity reading
Change in intensity = 729 units - 291 units
Change in intensity = 438 units
Step 2: Calculate the concentration change
Since 1.00 mL of a 11.7 mM lithium standard was added to 9.00 mL of serum, the amount of lithium added can be calculated as follows:
Amount of lithium added = (volume of added standard solution) x (concentration of standard solution)
Amount of lithium added = (1.00 mL) x (11.7 mM)
Amount of lithium added = 11.7 μmol
Step 3: Calculate the original concentration of lithium in the serum
To find the original concentration of lithium in the serum, you can set up a proportion using the changes in intensity and concentration:
Change in intensity / Amount of lithium added = Initial intensity reading / Original concentration
Plugging in the values we know:
438 units / 11.7 μmol = 291 units / Original concentration
Cross-multiply and solve for the original concentration:
(438 units) x (Original concentration) = (291 units) x (11.7 μmol)
Original concentration = (291 units) x (11.7 μmol) / (438 units)
Original concentration ≈ 7.80 μmol
Therefore, the original concentration of lithium in the serum is approximately 7.80 μmol.