UBC CHEM 211 1/3 EXAM QUESTIONS
AND ANSWERS GRADED A+ 2026
Assay - ANS Process of determining the amount of analyte in a sample.
Analyte - ANS The chemical substance being measured. Can be gasses, proteins etc.
Signal - ANS Analyte + Chemical or Physical Stimulus.
Observable change in some property.
A measured quantity that is correlated to the amount of analyte.
Qualitative analysis - ANS correlate signal to WHAT is in a sample
Quantitative analysis - ANS correlate signal to HOW MUCH is in a sample
Noise - ANS Unwanted variation in a measured quantity. Often takes the form of random
fluctuations in a measured signal.
Signal-to-noise ratio - ANS Magnitude of signal divided by magnitude of noise.
S/N is proportional to the sqrt(# of measurements)
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
1
, Required S/N ratio to Resolve an analytical signal - ANS S/N > 3
Detection limit - ANS The amount of analyte that corresponds to a signal just greater than
the mean of the background plus three standard deviations of its noise:
S>= u(bkg) + 3*stdev(bkg)
Background - ANS An approximately constant signal, measured in the absence of analyte.
Blank - ANS A measured sample that lacks the analyte, but otherwise contains the solvent,
reagents, etc., used in the analysis.
Sample Matrix - ANS All the components of a sample EXCEPT the analyte. A blank tries to
approximate the sample matrix.
ex.) Measuring amino acid content in ground beef.
Blank - artificial meat w/o amino acids
Sample Matrix - phospholipids, cholesterol etc in meat.
Positive Control - ANS Makes sure the analyte is there. A standard sample that contains a
known quantity of the analyte of interest. Helps prevent false negative results.
Negative Control - ANS Makes sure the analyte isn't there. A standard sample that does NOT
contain any analyte. Helps prevent false positive results.
Interference - ANS A specific chemical substance in a sample matrix that causes a systematic
error in a measured quantity.
May act on the analyte, a reagent used in the detection method, be the source of large
background signal, cause negative or positive bias, cause absolute or proportional errors.
Selectivity - ANS The extent to which other substances interfere with the determination of an
analyte. Good selectivity - analysis method has minimal interferences.
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
2
AND ANSWERS GRADED A+ 2026
Assay - ANS Process of determining the amount of analyte in a sample.
Analyte - ANS The chemical substance being measured. Can be gasses, proteins etc.
Signal - ANS Analyte + Chemical or Physical Stimulus.
Observable change in some property.
A measured quantity that is correlated to the amount of analyte.
Qualitative analysis - ANS correlate signal to WHAT is in a sample
Quantitative analysis - ANS correlate signal to HOW MUCH is in a sample
Noise - ANS Unwanted variation in a measured quantity. Often takes the form of random
fluctuations in a measured signal.
Signal-to-noise ratio - ANS Magnitude of signal divided by magnitude of noise.
S/N is proportional to the sqrt(# of measurements)
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
1
, Required S/N ratio to Resolve an analytical signal - ANS S/N > 3
Detection limit - ANS The amount of analyte that corresponds to a signal just greater than
the mean of the background plus three standard deviations of its noise:
S>= u(bkg) + 3*stdev(bkg)
Background - ANS An approximately constant signal, measured in the absence of analyte.
Blank - ANS A measured sample that lacks the analyte, but otherwise contains the solvent,
reagents, etc., used in the analysis.
Sample Matrix - ANS All the components of a sample EXCEPT the analyte. A blank tries to
approximate the sample matrix.
ex.) Measuring amino acid content in ground beef.
Blank - artificial meat w/o amino acids
Sample Matrix - phospholipids, cholesterol etc in meat.
Positive Control - ANS Makes sure the analyte is there. A standard sample that contains a
known quantity of the analyte of interest. Helps prevent false negative results.
Negative Control - ANS Makes sure the analyte isn't there. A standard sample that does NOT
contain any analyte. Helps prevent false positive results.
Interference - ANS A specific chemical substance in a sample matrix that causes a systematic
error in a measured quantity.
May act on the analyte, a reagent used in the detection method, be the source of large
background signal, cause negative or positive bias, cause absolute or proportional errors.
Selectivity - ANS The extent to which other substances interfere with the determination of an
analyte. Good selectivity - analysis method has minimal interferences.
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
2
