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Chapter 5: Q5-22 P (page 116)

Why is it desirable in the method of standard addition to add a small volume of concentrated standard rather than a large volume of dilute standard?

Short Answer

Expert verified

  • The large volume of dilute standard will alter the concentration of the matrix and will possibly result to matrix effect.

  • The addition of diluted standards may also cause a difficulty in detection.

  • The large volume of dilute standard may also affect the sensitivity of the instruments being used.

  • The measurements made will be nearly similar to each other when only a small volume of concentrated standard is added.

Step by step solution

01

Step 1:Concentrated and dilute standard definition

  • A standard solution is a solution that has a precisely known concentration of an element or compound in analytical chemistry.
  • A dilution is a solution that decreases the concentration of a solute by adding additional solvent to a more concentrated solution (stock solution).
02

Key points

There are a couple of reasons why it is desirable to add only a small volume of concentrated standard rather than a large volume of dilute standard:

  • The large volume of dilute standard will alter the concentration of the matrix and will possibly result to matrix effect.

  • The addition of diluted standards may also cause a difficulty in detection.

  • The large volume of dilute standard may also affect the sensitivity of the instruments being used.

  • The measurements made will be nearly similar to each other when only a small volume of concentrated standard is added.

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Most popular questions from this chapter

How is a control chart used? State six indications that a process is going out of control.

1.00 mL of blood serum was diluted to 25.00 mL in each flask of a standard addition experiment like Figure 5-7 to measure a hormone with a molecular mass of 373 g/mol. The x-intercept of the graph was 4.2 ppb (parts per billion). Find the concentration of hormone in the serum and express your answer in ppb and molarity. Assume that the density of serum and all solutions is close to 1.00 g/mL

Here is a use objective for a chemical analysis to be performed at a drinking water purification plant: "Data and results collected quarterly shall will be used to determine whether the concentrations of haloacetates in the treated water demonstrate compliance with the levels set by the Stage 1 Disinfection By-products Rule using Method 552.2"(a specification that sets precision, accuracy, and other requirements).

Which one of the following questions best summarizes the meaning of the use objective?

(i) Are haloacetate concentrations known within specified precision and accuracy?

(ii) Are thehaloacetates detectable in the water?

(iii) Dothehaloacetate concentrations exceed the regulatory limit?

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 bindEu(III)are required to enhance the emission. The figure shows standard addition experiments in which10.00mLof sample and20.00mLcontaining a large excess of organic additive were placed in 50-mL volumetric flasks. Then Eu(III) standards (0,5.00,10.00,or15.00mL) were added and the flasks were diluted to50.0mLwithH2O. Standards added to tap water contained0.152ng/mL(ppb) of Eu(III), but those added to pond water were 100 times more concentrated (15.2 ng/mL).


(a) Calculate the concentration of Eu(III)(ng/mL) in pond water and tap water.

(b) For tap water, emission peak area increases by.4.61units when 10.00mL of 0.152ng/mL standard are added. This response is4.61 units/1.52ng = 3.03units per ng ofEu(III). For pond water, the response is12.5units when10.00mLof15.2ng/mLstandard are added, or0.0822units per ng. How would you explain these observations? Why was standard addition necessary for this analysis?

What is the difference between an instrument detection limit and a method detection limit? What is the difference between robustness and intermediate precision?
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