Deck 17: Interferences in Chemical Analysis

Question 1

Suppose a colorimetric analysis that utilizes a highly colored reagent is to be performed.Which type of blank should be prepared to ensure the correct sample results?

A)sample blank
B)reagent blank
C)instrument blank
D)diluent blank

Answer 1

reagent blank

Question 2

The interference in a hemolyzed sample results from the presence of ______, which results in ______ of incident light in colorimetric assays.

A)hemoglobin, absorbance
B)hemoglobin, scatter
C)hemopexin, absorbance
D)hemopexin, scatter

Answer 2

hemoglobin, absorbance

Question 3

Which of the following statements is/are correct regarding percent error of absorbance readings in spectrophotometry?

A)Percent error is large at very low absorbance readings.
B)Percent error is large at mid-range absorbance readings.
C)Percent error is large at high absorbance readings.
D)both a and c

Answer 3

both a and c

Question 4

Which of the following techniques would be useful for the correction of protein buildup on a spectrophotometer flow cell in an automated analyzer?

A)two-point kinetic analysis
B)bichromatic analysis
C)sample dilution
D)both a and b

Question 5

The following laboratory data were collected utilizing a chemical reaction to measure the concentration of estrogen in a patient's urine sample.Given the wavelength of maximum absorbance for the assay is 525 nm, and the background is known to be linear between 490 nm and 560 nm, calculate the concentration of estrogen in the patient sample using the Allen correction.
Patient sample absorbance at 490 nm = 0.298
Patient sample absorbance at 525 nm = 0.405
Patient sample absorbance at 560 nm = 0.140
Standard absorbance at 490 nm = 0.180
Standard absorbance at 525 nm = 0.492
Standard absorbance at 560 nm = 0.036
Standard concentration = 25 mg/L

A)12.1 mg/L
B)24.0 mg/L
C)26.0 mg/L
D)51.6 mg/L

Question 6

One method to eliminate many nonspecific chemical interferents involves increasing the specificity of the reaction used for measurement.This can be accomplished by:

A)the use of specific buffers to maintain the correct reaction pH
B)the use of specific immunoassays for the material being measured
C)the use of reagent and sample blanks in the same assay
D)all of the above

Question 7

It is recommended that fluorescence intensity measurements be made below what absorbance level?

A)0.100
B)0.500
C)1.000
D)none of the above

Question 8

Given the following data for bichromatic analysis in which the analytical wavelength is 510 nm, determine the concentration of analyte in the patient sample.
Patient sample absorbance at 510 nm = 0.715
Patient sample absorbance at 550 nm = 0.113
Standard absorbance at 510 nm = 0.500
Standard absorbance at 550 nm = 0.113
Standard concentration = 25 mg/L

A)25 mg/L
B)112.5 mg/L
C)134 mg/L
D)602 mg/L

Question 9

Which of the following interferences will have the greatest impact on nephelometric and turbidimetric measurements?

A)hemolysis
B)lipemia
C)icterus
D)both a and c

Question 10

The most common source of interference in spectrophotometric analyses results from:

A)the presence of drugs in the patient sample
B)the presence of unexpected increases of compounds associated with disease processes in the patient sample
C)the presence of hemolysis, icteria, or lipemia in the patient sample
D)the anticoagulant used to collect the patient sample

Question 11

It is recommended that spectrophotometric measurements be made in which of the following absorbance ranges?

A)0.100 - 1.100
B)0.200 - 0.500
C)0.500 - 1.500
D)0.100 - 2.000

Question 12

The interference in a lipemic sample results from the presence of excessive ______, which results in ______ of incident light in colorimetric assays.

A)carbohydrates, absorbance
B)carbohydrates, scatter
C)lipoproteins, absorbance
D)lipoproteins, scatter

Question 13

Suppose you have a lipemic patient sample for analysis by a colorimetric technique.Which of the following actions should be taken to eliminate the interference caused by the lipemia?

A)Use a sample blank.
B)Dilute the patient sample.
C)Convert the method of analysis to a nephelometric technique.
D)Convert the method of analysis to a fluorometric technique.

Question 14

Given the following data for bichromatic analysis in which the analytical wavelength is 510 nm, what is the most likely interference?
Patient sample absorbance at 510 nm = 0.715
Patient sample absorbance at 550 nm = 0.113
Standard absorbance at 510 nm = 0.500
Standard absorbance at 550 nm = 0.113
Standard concentration = 25 mg/L

A)spectrophotometer flow-cell contamination
B)hemolysis
C)the matrix in which the standard is dissolved
D)non-visual interference in the patient sample

Question 15

Suppose the result for a particular analyte by HPLC was much higher than anticipated, and the patient's physician questioned the result.Which of the following analytical modifications would be most useful in investigating the reason for the unexpectedly high patient result?

A)Reanalyze the patient sample with the use of a refractive index detector.
B)Reanalyze the patient sample with the use of a photo diode array (PDA) detector.
C)Dilute the patient sample and reanalyze with the current HPLC system.
D)Verify linearity and reanalyze the patient sample.

Question 16

The most difficult type of immunochemical interference to detect is the presence of:

A)heterophilic anti-immunoglobulin antibodies
B)iatrogenic antibodies
C)rheumatoid factor
D)complement

Question 17

The effect of stray light on fluorescence measurements is best described by which of the following statements?

A)Stray light may result in a false increase in fluorescence intensity.
B)Stray light may result in a false decrease in fluorescence intensity.
C)Stray light will not influence fluorescence detected because of the use of two monochromators.
D)A blank must be used to negate the effect of stray light in fluorescence measurements.