Europium is a lanthanide element found at parts per billion levels in natural wa

Question

Europium is a lanthanide element found at parts per billion levels in natural waters. It can be measured from the intensity of orange light emitted when a solution is Illuminated with ultraviolet radiation. Certain organic compounds that bind Eu(III) are required to enhance the emission. The figure below shows standard addition experiments in which 10.00 mL of sample and 20.00 mL containing a large excess of organic additive were placed in 50-mL volumetric flasks. Then Eu(IIl) standards (0, 5.00, 10.00, or 15.00 mL) were added and the flasks were diluted to 50.0 mL with H, 0. Standards added to tap water contained 0.153 ng/mL (ppb) of Eu(III), but those added to pond water were 100 times more concentrated (15.3 ng/mL). Calculate the concentration of Eu(III) (ng/mL) in pond water and tap water. poked water mg/mL tap water mg/mL For tap water, emission peak area increases by 4.57 units when 10.00 mL of 0.153 ng/mL standard are added. This response is 4.57 units/1.53 ng = 2.99 units per ng of Eu(III). For pond water, the response is 12.6 units when 10.00 mL of 15.3 ng/mL standard are added, or about 0.0824 units per ng. How would you explain these observations? Why was standard addition necessary for this analysis? There is likely to be a in which something in the water the Eu(III) emission. The standard addition method allows us to accurately determine the analyte concentration in the .

Explanation / Answer

Q1.

x-intercept for TAP-water

Concentration of Eu(III) in tap water -->

intercept --> -6.0 mL

C = 6*0.100 ng/mL = 0.6 ng/mL

for the POND watert

intercept = -14.6 mL

then

C = 14.6*0.100 (ppb) * (100 times more) = 60 ng/mL

Q2.

choose A, since there is a matrix effect in which something in the tap water decreases the Eu(III) emission.

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