30 Questions
What is the advantage of measuring a decrease in reagent absorbance at a particular wavelength?
It increases the sensitivity of the determination.
How is the normal measurement process of spectrophotometry reversed in certain cases?
The blank solution is measured against zero absorbance set with the test solution.
What is the purpose of the preliminary qualitative examination of the color reaction?
To provide a guide to the optimum pH range for color development.
Why is it necessary to measure the absorbance of each solution against a reagent blank at the same pH?
To account for any shift in band maxima with pH.
What is the range of wavelengths over which the absorbance of each solution should be measured?
A relatively wide band of 30-40 nm.
What is the purpose of allowing a definite time interval for color development?
To allow for the reaction to reach completion.
Why is it necessary to periodically check the photometric accuracy of the spectrophotometer absorbance scale?
To ensure the accuracy of absorbance values at different wavelengths
What is the purpose of using standard copper sulphate, ammonium cobalt sulphate, or potassium chromate solutions?
To check the photometric accuracy of the spectrophotometer absorbance scale
What is Sandell's expression or sensitivity index?
The number of micrograms of constituent determined, converted to the colored product
Why should the absorbance of the reagent and product be measured separately against a solvent blank?
To study the causes of instability in the reagent blank
What is the molar absorptivity of the colored compound?
The amount of light absorbed by the colored compound at a specific wavelength
What is the recommended temperature range for studying the effect of temperature on the absorbance?
15○ to 35○
What is the minimum amount of a colored substance dependent on?
The reproducibility of the measurement of the absorbance
What is the limiting factor in detecting the minimum amount of a colored substance?
The precision of reading a scale
What is the purpose of constructing a calibration curve for the constituent?
To determine the optimum concentration range for the constituent
Why is it necessary to specify the temperature when publishing the sensitivity of the procedure?
Because the absorbance varies with the temperature of color development and measurement
What is the purpose of studying the effect of temperature on the absorbance?
To determine the optimum conditions for the reaction
What should be plotted to construct a calibration curve for the constituent?
The absorbance against the concentration of the constituent
What is the usual method to calculate the sensitivity of an instrument?
By calculating the concentration that produces a given absorbance in the optimum range of least photometric error
What is the assumption behind the first method of stating sensitivity?
That Beer's Law holds to very low concentrations
What is the unit of measurement for the sensitivity of an instrument?
pg of element/cm²
What is the value of absorbance difference that represents a more attainable practical value?
0.005
What is the equation used to calculate the molar absorptivity of the colored compound?
ε = A l c
Why is the second method of designation of sensitivity based on the molar absorptivity of the colored compound?
Because it is directly related to the concentration of colored species
What is the optimal range of absorbance values for measurements on a spectrophotometer to minimize photometric error?
0.248 units
What is the purpose of stating the range of linearity in a calibration curve?
To provide an alternative to presenting a straight line calibration curve
What is the significance of recording the slit width at which the measurements were made?
It is necessary for good precision in spectrophotometric measurements
What is the consequence of projecting a calibration curve beyond the tested range without experimental verification?
It may lead to errors in the calibration curve
What is the primary advantage of a system that follows Beer's Law?
It permits greater accuracy in spectrophotometric measurements
What is the significance of the analytical concentration of the species determined in relation to the absorbance values?
It represents the optimal range of concentration for the determination
Understanding the stability of reagent blanks and its effects on analytical reactions. Learn how to study the causes of instability and the impact of temperature, atmosphere, and light on reactions.
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