Instrumental Analysis
ACS Exam
Which of the following is the correct order of wavelengths from shortest to longest?
A. UV → Visible → IR → Microwave
B. Gamma → X‐ray → UV → Visible → IR → Microwave → Radio
C. Visible → UV → X‐ray → IR → Microwave
D. Radio → Microwave → IR → Visible → UV → X‐ray → Gamma
Answer: B
Explanation: Shortest wavelengths (highest energy) begin with gamma, then x-ray,
etc.
In atomic absorption spectroscopy (AAS), which of the following is the most common
source of line broadening?
A. Doppler broadening
B. Instrumental (monochromator) broadening
C. Pressure broadening
D. Natural linewidth
Answer: A
Explanation: Atoms in a flame move, giving Doppler shifts and hence broadening.
Which technique uses multiply charged ions produced by a high‐voltage spray of
solution into vacuum?
A. Electron Impact Mass Spectrometry
,B. Matrix‐Assisted Laser Desorption Ionization (MALDI)
C. Electrospray Ionization (ESI)-MS
D. Thermal Ionization MS
Answer: C
Explanation: ESI involves spraying a solution under high voltage, producing multiply
charged ions.
In a HPLC separation using a reverse‐phase column (nonpolar stationary phase),
increasing the mobile phase polarity will
A. increase retention times of strongly retained nonpolar analytes
B. decrease retention times of strongly retained nonpolar analytes
C. have no effect on retention time
D. cause immediate elution of all analytes
Answer: B
Explanation: In RP-HPLC, nonpolar stationary phase retains nonpolar analytes;
increasing mobile phase polarity reduces the analyte–stationary interaction, so
retention decreases.
Which of the following detectors is most commonly used in GC for general organic
compounds?
A. Flame Ionization Detector (FID)
B. Thermal Conductivity Detector (TCD)
C. Photomultiplier Tube (PMT)
D. Coulometric detector
Answer: A
Explanation: FID is widely used for organics in GC because of high sensitivity and
broad applicability.
For a spectrophotometric method following Beer's law, absorbance
,𝐴
A is related to concentration
𝑐
c by:
𝐴
=
𝜀
𝑏
𝑐
A=εbc. What happens if you double the path length
𝑏
b, everything else remaining constant?
A. Absorbance doubles
B. Absorbance halves
C. Absorbance remains the same
D. Cannot determine
Answer: A
Explanation: Doubling path length doubles absorbance proportionally.
Which of the following is a qualitative figure of merit, rather than a quantitative one?
A. Detection limit
B. Precision
C. Dynamic range
D. Selectivity
Answer: D
Explanation: Selectivity refers to how well the method distinguishes analyte from
interferents – a qualitative characteristic.
, In voltammetry, what is the term for the potential at which the current begins to
increase rapidly due to redox of the analyte?
A. Half-wave potential
B. Peak potential
C. Limiting current
D. Switching potential
Answer: B
Explanation: In techniques like cyclic or differential pulse voltammetry, the peak
potential is where current sharply increases because the redox reaction occurs.
Which of the following sources would be most appropriate for mid‐infrared (MIR)
spectroscopy?
A. Hollow cathode lamp
B. Nernst glower (infrared emitter)
C. Deuterium lamp
D. Xenon lamp
Answer: B
Explanation: A Nernst glower emits IR radiation suitably for MIR spectroscopy.
In inductively coupled plasma mass spectrometry (ICP-MS), what is one major
advantage over flame atomic absorption?
A. Lower detection limits
B. Larger sample size required
C. Simpler instrumentation
D. Only works for inert gases
Answer: A
Explanation: ICP-MS offers much lower detection limits (trace/ultra‐trace) compared
to flame AAS.
ACS Exam
Which of the following is the correct order of wavelengths from shortest to longest?
A. UV → Visible → IR → Microwave
B. Gamma → X‐ray → UV → Visible → IR → Microwave → Radio
C. Visible → UV → X‐ray → IR → Microwave
D. Radio → Microwave → IR → Visible → UV → X‐ray → Gamma
Answer: B
Explanation: Shortest wavelengths (highest energy) begin with gamma, then x-ray,
etc.
In atomic absorption spectroscopy (AAS), which of the following is the most common
source of line broadening?
A. Doppler broadening
B. Instrumental (monochromator) broadening
C. Pressure broadening
D. Natural linewidth
Answer: A
Explanation: Atoms in a flame move, giving Doppler shifts and hence broadening.
Which technique uses multiply charged ions produced by a high‐voltage spray of
solution into vacuum?
A. Electron Impact Mass Spectrometry
,B. Matrix‐Assisted Laser Desorption Ionization (MALDI)
C. Electrospray Ionization (ESI)-MS
D. Thermal Ionization MS
Answer: C
Explanation: ESI involves spraying a solution under high voltage, producing multiply
charged ions.
In a HPLC separation using a reverse‐phase column (nonpolar stationary phase),
increasing the mobile phase polarity will
A. increase retention times of strongly retained nonpolar analytes
B. decrease retention times of strongly retained nonpolar analytes
C. have no effect on retention time
D. cause immediate elution of all analytes
Answer: B
Explanation: In RP-HPLC, nonpolar stationary phase retains nonpolar analytes;
increasing mobile phase polarity reduces the analyte–stationary interaction, so
retention decreases.
Which of the following detectors is most commonly used in GC for general organic
compounds?
A. Flame Ionization Detector (FID)
B. Thermal Conductivity Detector (TCD)
C. Photomultiplier Tube (PMT)
D. Coulometric detector
Answer: A
Explanation: FID is widely used for organics in GC because of high sensitivity and
broad applicability.
For a spectrophotometric method following Beer's law, absorbance
,𝐴
A is related to concentration
𝑐
c by:
𝐴
=
𝜀
𝑏
𝑐
A=εbc. What happens if you double the path length
𝑏
b, everything else remaining constant?
A. Absorbance doubles
B. Absorbance halves
C. Absorbance remains the same
D. Cannot determine
Answer: A
Explanation: Doubling path length doubles absorbance proportionally.
Which of the following is a qualitative figure of merit, rather than a quantitative one?
A. Detection limit
B. Precision
C. Dynamic range
D. Selectivity
Answer: D
Explanation: Selectivity refers to how well the method distinguishes analyte from
interferents – a qualitative characteristic.
, In voltammetry, what is the term for the potential at which the current begins to
increase rapidly due to redox of the analyte?
A. Half-wave potential
B. Peak potential
C. Limiting current
D. Switching potential
Answer: B
Explanation: In techniques like cyclic or differential pulse voltammetry, the peak
potential is where current sharply increases because the redox reaction occurs.
Which of the following sources would be most appropriate for mid‐infrared (MIR)
spectroscopy?
A. Hollow cathode lamp
B. Nernst glower (infrared emitter)
C. Deuterium lamp
D. Xenon lamp
Answer: B
Explanation: A Nernst glower emits IR radiation suitably for MIR spectroscopy.
In inductively coupled plasma mass spectrometry (ICP-MS), what is one major
advantage over flame atomic absorption?
A. Lower detection limits
B. Larger sample size required
C. Simpler instrumentation
D. Only works for inert gases
Answer: A
Explanation: ICP-MS offers much lower detection limits (trace/ultra‐trace) compared
to flame AAS.
