IA 1-3

I. Analytical Chemistry, Signal & Noise

#	Front	Back
1	What are the two fundamental questions of analytical chemistry?	What is it? (qualitative analysis) and how much is there? (quantitative analysis).
2	What is the main distinction between qualitative and quantitative analysis?	Qualitative determines identity; quantitative determines amount/concentration.
3	Why are separation techniques important in analytical chemistry?	Many analytical techniques require pure compounds, so components often must be separated before analysis.
4	What is the difference between precision and accuracy?	Precision describes reproducibility; accuracy describes closeness to the true value.
5	How can precision be assessed experimentally?	By making replicate measurements and examining their standard deviation.
6	How is percent error calculated?	(measured−true)/true×100%.
7	When is absolute error more appropriate than percent error?	When the measurement error is approximately constant regardless of the magnitude of the measurement.
8	Why does every instrumental measurement contain noise?	Noise-free data do not exist; measurements contain both signal and random/systematic fluctuations.
9	What does the signal-to-noise ratio tell you?	It indicates the quality of an instrumental measurement.
10	How does increasing S/N affect measurement uncertainty?	A larger S/N corresponds to smaller error/uncertainty.
11	What approximate minimum S/N should generally be exceeded for a useful measurement?	About 2–3.
12	What are three ways a signal can be quantified?	Peak height, peak area, or total current, depending on the instrument.
13	What is chemical noise?	Uncontrollable variables affecting the system, such as temperature/pressure fluctuations or chemical interferences.
14	What is instrumental noise?	Noise arising from components of the instrument.
15	What causes Johnson (thermal) noise?	Movement of electrons in electronic components such as resistors and capacitors.
16	What causes shot noise?	Random variations in photons reaching a detector or electrons generated in a semiconductor.
17	When is shot noise especially important?	In low-signal applications.
18	What is flicker noise?	Noise whose magnitude is inversely related to frequency, commonly called 1/f noise.
19	When is flicker noise especially significant?	At low frequencies.
20	What is environmental noise?	Noise from the surroundings picked up by components of the instrument.
21	How can grounding and shielding improve S/N?	They reduce electronic noise.
22	Why can difference measurements reduce noise?	Noise tends to cancel when the difference between measurements is taken.
23	How does signal averaging affect S/N?	S/N improves approximately as the square root of the number of measurements.
24	What is ensemble averaging?	Co-adding successive datasets point-by-point and plotting the average value at each x-coordinate.
25	What is boxcar averaging?	Averaging a fixed number of adjacent data points, then moving to the next non-overlapping group.
26	What is moving averaging?	A running average in which the averaging window moves one point at a time.
27	What fraction of a Gaussian distribution lies within ±1 standard deviation?	68.3%.
28	What fraction lies within ±2 standard deviations?	95.5%.
29	What fraction lies within ±3 standard deviations?	99.7%.
30	What is the relationship between FWHM and σ for a Gaussian peak?	FWHM = 2.335σ.

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II. Figures of Merit

#	Front	Back
31	What six major figures of merit govern analytical-method selection?	Precision, accuracy, sensitivity, detection limit, dynamic range, and selectivity.
32	What other factors besides figures of merit influence method selection?	Speed, ease of use, required skill, and cost.
33	What is instrument sensitivity?	The slope of the response vs. concentration calibration curve.
34	What does a steeper calibration curve imply?	Greater sensitivity to small changes in concentration.
35	What is the limit of detection (LOD)?	The smallest concentration that can be measured reliably at a specified confidence level; statistically distinguishable from the blank.
36	What primarily limits the detection limit?	Statistical fluctuations in the signal of the blank.
37	According to the lecture, what is one estimate for detection-limit signal?	Average blank signal + 3 × standard deviation of the blank.
38	What is the limit of quantification (LOQ)?	The smallest amount of analyte that can be reliably quantified.
39	According to the lecture, what signal criterion is given for LOQ?	Average blank signal + 10 × standard deviation of the blank.
40	What is dynamic range?	The concentration region over which the calibration curve remains linear.
41	Why can a sample that is too concentrated be problematic?	It may fall outside the linear dynamic range, so it must be diluted.
42	How does selectivity affect chemical interference?	Greater selectivity means less concern about chemical interferences.
43	What is the tradeoff associated with high selectivity?	A highly selective technique may not be broadly applicable to many compounds.

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III. Chromatography Fundamentals

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44	What three features are required for chromatographic separation?	A mobile phase, a stationary phase, and a phase boundary across which analytes partition.
45	What is the mobile phase?	The phase that moves through the chromatographic system; it may be a gas or liquid.
46	What is the stationary phase?	The phase that remains stationary; it may be a solid or liquid.
47	What causes chromatographic separation?	Different analytes interact differently with the stationary and mobile phases.
48	What equilibrium is established in chromatography?	An equilibrium between molecules in the mobile and stationary phases.
49	What does a distribution coefficient Kc>1 imply?	More analyte is in the stationary phase than in the mobile phase.
50	Why does stronger interaction with the stationary phase generally increase retention?	The molecule spends more time in the stationary phase, delaying its movement through the column.
51	What is tm?	The time required for the mobile phase to traverse the column.
52	Why do all compounds share the same mobile-phase travel time?	They all spend the same amount of time moving with the mobile phase.
53	Where does chromatographic separation primarily occur?	In the stationary phase, because compounds differ in their stationary-phase interactions.
54	What defines adsorption chromatography?	The stationary phase is a solid, and molecules adsorb onto it.
55	Give two examples of adsorption chromatography.	TLC and column chromatography.
56	What defines partition chromatography?	The stationary phase is a liquid on a solid support, and analytes dissolve into it.
57	In normal-phase LLC, how do mobile and stationary-phase polarities compare?	The mobile phase is nonpolar/less polar and the stationary phase is polar/more polar.
58	In reverse-phase LLC, how do mobile and stationary-phase polarities compare?	The mobile phase is polar/more polar and the stationary phase is nonpolar/less polar.
59	What is ion-exchange chromatography designed to separate?	Ions, based on interactions with charged stationary-phase sites.
60	What is size-exclusion chromatography based on?	Differences in molecular size and access to pores in the stationary phase.
61	In size-exclusion chromatography, which molecules enter the pores more easily?	Smaller molecules.
62	Why do larger molecules elute before smaller ones in size-exclusion chromatography?	Large molecules are excluded from the pores and therefore spend less time in the stationary phase.

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IV. Plate Theory, HETP & Van Deemter

#	Front	Back
63	What does the number of theoretical plates, N, measure?	Chromatographic efficiency.
64	What does a larger N indicate?	Better separation / greater efficiency.
65	Why can't N alone be used to compare columns of different lengths?	N generally increases as column length increases.
66	What is HETP?	Height equivalent to a theoretical plate, H=L/N.
67	What does a smaller HETP indicate?	A more efficient separation.
68	Why is HETP more useful than N when comparing columns of different lengths?	HETP normalizes efficiency for column length.
69	What factors can affect HETP?	Technique, mobile/stationary phases, temperature, and flow rate.
70	What does the Van Deemter equation describe?	The relationship between peak broadening/efficiency and flow velocity.
71	What does the A term represent in the Van Deemter equation?	Eddy diffusion from different paths through packed particles.
72	What factors affect the A term?	Packing-particle size and how tightly the column is packed.
73	What does the B term represent?	Longitudinal diffusion of analyte along the column.
74	Why does the B term become smaller at higher flow velocity?	There is less time for longitudinal diffusion to broaden the band.
75	What does the C term represent?	Mass-transfer broadening caused by differences in how quickly analyte molecules equilibrate with the stationary phase.
76	How does the C term depend on flow rate?	It is directly proportional to flow rate.
77	Why is there an optimal flow rate in chromatography?	One source of broadening decreases with flow velocity while another increases, producing a minimum H at an intermediate velocity.
78	What is the consequence of operating far below the optimal flow rate?	Longitudinal diffusion becomes increasingly important.
79	What is the consequence of operating far above the optimal flow rate?	Mass-transfer broadening becomes increasingly important.

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V. Retention, Selectivity & Resolution

#	Front	Back
80	Why do two compounds separate chromatographically?	They have different interactions with the stationary phase.
81	What does the retention factor k indicate?	The extent to which a compound is retained relative to the mobile phase.
82	What is chromatographic resolution, Rs, used to describe?	How well two neighboring peaks are separated.
83	What does Rs≈0.6 indicate?	A valley between the peaks can be distinguished.
84	What does Rs≈1.5 indicate?	The peaks are baseline resolved.
85	What is the selectivity/separation factor α used to describe?	The relative retention/selectivity between two compounds.
86	If two compounds have identical stationary-phase interactions, what happens to their separation?	Their chromatographic separation decreases because their retention becomes similar.
87	What generally improves resolution: broader or narrower peaks?	Narrower peaks, because overlapping decreases.
88	Why can simply increasing column length have diminishing benefits?	Although N increases, peak widths also increase with the longer time spent in the column.

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VI. Gas Chromatography (GC)

#	Front	Back
89	What is the mobile phase in GC?	A gas.
90	What major property must analytes have to be useful in GC?	They must be volatile enough to enter and remain in the gas phase under operating conditions.
91	What is the carrier gas in GC?	A high-purity gas serving as the mobile phase.
92	What carrier gases are commonly used in GC?	He, H₂, N₂, or Ar.
93	Why must GC carrier gas be highly pure?	Impurities can degrade the column and cause false signals.
94	Why is the GC injector heated?	To vaporize the sample.
95	Why is the injector typically hotter than the oven?	The lecture specifies roughly 30–50°C above the highest oven temperature to ensure vaporization.
96	What can happen to a GC sample before it enters the column?	It is often split before entering the column.
97	What is the purpose of an oven in GC?	To maintain elevated temperature so analytes remain gaseous and to control elution.
98	What is an isothermal GC experiment?	The oven remains at one temperature throughout the run.
99	What is a temperature-programmed GC experiment?	The oven ramps temperature during the run.
100	In GC, which compounds generally elute first?	More volatile compounds.
101	What is the main difference between packed and open-tubular GC columns?	Packed columns contain packing material; open-tubular columns have no solid support and stationary phase bonded directly to the capillary interior.
102	Why are open-tubular columns generally more efficient?	They have a very small contribution from the A term of the Van Deemter equation.
103	What must a GC stationary phase be able to withstand?	It must be thermally stable, nonvolatile, and nonreactive toward the analyte.
104	What is a major advantage of open-tubular columns?	They provide more efficient separations.

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VII. GC Detectors

#	Front	Back
105	What does a thermal conductivity detector (TCD) measure?	Changes in the resistivity of a heated wire in the gas stream.
106	What is a major advantage of TCD?	It is universal and non-destructive.
107	What is a major disadvantage of TCD?	Poor sensitivity.
108	Why does a TCD require a reference flow?	It compares the sample stream against the mobile phase/reference gas.
109	What is the most widely used GC detector?	Flame ionization detector (FID).
110	How does FID detect analytes?	Analytes are burned in an H₂/air flame, ionized, and the resulting ion current is measured.
111	Compared with TCD, how sensitive is FID?	More sensitive.
112	Is FID destructive or non-destructive?	Destructive.
113	What kinds of structural information does FID provide?	None according to the lecture.
114	What is the principle of an electron-capture detector (ECD)?	Electronegative analytes capture electrons, reducing the measured current.
115	What compounds are particularly well suited to ECD?	Compounds containing halogens, NO₂, or phosphorus.
116	What is the major strength of ECD?	Selectivity for electronegative compounds.
117	What is an FPD selective for?	Sulfur- and phosphorus-containing compounds.
118	How does an FPD generate its signal?	Combustion produces excited species that emit photons.
119	What does an MS detector measure in GC?	Ions according to their mass-to-charge ratio (m/z).
120	What major advantage does GC-MS have over many other GC detectors?	It provides qualitative structural information about analytes.
121	What major disadvantage does MS have relative to simple GC detectors?	It is expensive and destructive.

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VIII. Liquid Chromatography & HPLC

#	Front	Back
122	What is the fundamental difference between GC and LC in how analytes interact with the phases?	In LC, analytes interact with both mobile and stationary phases, while GC uses a gaseous mobile phase and analyte volatility is essential.
123	In liquid-solid chromatography, what is the stationary phase?	A solid, onto which analytes adsorb.
124	In liquid-liquid chromatography, what is the stationary phase?	A liquid in which analytes dissolve.
125	In normal-phase LC, which compounds generally elute first?	Less-polar compounds.
126	In reverse-phase LC, which compounds generally elute first?	More-polar compounds.
127	Why do nonpolar analytes elute first in normal-phase LC?	They have greater affinity for the nonpolar mobile phase than for the polar stationary phase.
128	What happens to mobile-phase polarity in a normal-phase gradient?	It is increased to help elute more-polar analytes.
129	What happens to mobile-phase polarity in reverse-phase gradient elution?	It is decreased to help elute less-polar analytes.
130	Why must solvents in a mobile-phase gradient remain miscible?	The changing solvent composition must remain a single usable mobile phase.
131	What is isocratic LC?	Mobile-phase composition remains constant throughout the run.
132	What is gradient LC?	Mobile-phase composition changes during the run.
133	What is the conceptual LC analogue of GC temperature programming?	Gradient elution.
134	What are typical normal-flow HPLC flow rates given in the lecture?	Approximately 0.1–10 mL/min.
135	Why must HPLC injectors maintain pressure during injection?	The analyte must be introduced into the flowing mobile phase without losing system pressure.
136	Why must HPLC columns withstand high pressure?	High flow through packed particles creates substantial pressure.
137	What type of HPLC pump is most common?	A reciprocating pump.
138	What is a major advantage of a reciprocating pump?	Excellent flow control.
139	What is the purpose of an HPLC sample loop?	To introduce a defined sample into the flowing mobile phase without losing pressure.
140	Why are columns often made of stainless steel in normal-flow HPLC?	They must tolerate the high pressures used in the system.

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IX. LC Detectors & Fluorescence

#	Front	Back
141	How does a refractive-index detector work?	It compares the refractive index of the solvent with that of the solvent + analyte.
142	What is a major advantage of a refractive-index detector?	It is the most universal LC detector.
143	What is a major limitation of a refractive-index detector?	It cannot be used with solvent gradients.
144	What does a UV-visible detector measure?	Absorption of light by analytes.
145	According to Beer’s law, how does absorbance depend on concentration?	A=εbc, so absorbance is proportional to concentration under the stated conditions.
146	In A=εbc, what does b represent?	Path length.
147	In A=εbc, what does c represent?	Concentration.
148	What is a major advantage of fluorescence detection?	It is very sensitive and selective with very low background.
149	Why is fluorescence highly selective?	Most molecules do not fluoresce.
150	Is fluorescence detection destructive?	No; it is non-destructive according to the lecture.
151	What is fluorescence tagging?	Derivatizing a nonfluorescent analyte to create a fluorescent compound.
152	What is pre-column derivatization?	Tagging the analyte before chromatographic separation.
153	What is post-column derivatization?	Tagging the analyte after separation but before detection.
154	Why must ninhydrin be used post-column for the example given?	The amine's R group is not retained in the product, so tagging before separation would interfere with the separation.
155	Why can dansyl chloride be used either pre- or post-column?	The R group is retained in the derivative.
156	What is anthranilic acid used to tag in the lecture?	Carbohydrates.
157	What is a major advantage of LC-MS?	It provides substantial structural information and is compatible with electrospray ionization.

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X. Ion Exchange & Size Exclusion

#	Front	Back
158	What is the stationary phase in ion-exchange chromatography?	A polymer/resin containing positively or negatively charged groups.
159	What determines retention in ion-exchange chromatography?	Charge density of the analyte.
160	Why do small compact ions generally bind more strongly than larger diffuse ions?	Their charge is more concentrated, producing stronger interaction with the stationary phase.
161	Why does a dication generally bind more strongly than a monocation?	It has greater charge density.
162	What charge state predominates at low pH in the amino-acid example?	Cations.
163	What charge state predominates at medium pH in the amino-acid example?	Zwitterions.
164	What charge state predominates at high pH in the amino-acid example?	Anions.
165	What is the stationary phase in size-exclusion chromatography?	A cross-linked polymer containing large, uniform pores.
166	What happens to small molecules in size-exclusion chromatography?	They enter the pores and become temporarily trapped.
167	What happens to large molecules?	They are excluded from the pores.
168	How is retention related to molecular mass in size-exclusion chromatography?	Retention is inversely related to molecular mass.
169	Why should size-exclusion chromatography not be used for small molecules according to the lecture?	The technique is intended to separate species based on size, particularly larger molecules.

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XI. Qualitative & Quantitative Chromatographic Analysis

#	Front	Back
170	How can chromatographic retention time be used for qualitative analysis?	Compare an analyte's retention time with that of a known standard under identical conditions.
171	Why is retention time alone not definitive identification?	Different compounds can have the same retention time.
172	How does mass spectrometry improve chromatographic qualitative analysis?	It provides substantially more structural information than retention time alone.
173	What chromatographic features are commonly used for quantitative analysis?	Peak height or peak area.
174	What is the basic calibration-curve procedure?	Run standards of known concentration, construct a response-vs-concentration curve, then run the unknown and interpolate its concentration.
175	Why must standards and unknown be run under the same conditions?	Their instrumental responses must be directly comparable.
176	What variables can complicate calibration-curve analysis?	Beer’s-law linearity, injection volume, dilution, and other experimental factors.
177	What is an internal standard?	A compound of similar structure added at a known concentration to standards and unknowns.
178	Why is an internal standard useful?	Using analyte/internal-standard response ratios helps correct for sample-to-sample injection-volume variation.
179	What quantity is typically compared when using an internal standard?	The ratio of peak areas or peak heights.

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XII. Electrophoresis

#	Front	Back
180	What are the two major types of electrophoresis covered?	Gel electrophoresis and capillary electrophoresis.
181	What is the basic principle of gel electrophoresis?	A voltage is applied across a cross-linked polymer gel, causing charged species to migrate.
182	What gels are listed in the lecture?	Agarose and polyacrylamide.
183	Which direction do anions migrate in gel electrophoresis?	Toward the anode.
184	What determines separation in gel electrophoresis?	Charge density/size.
185	What biological samples are specifically mentioned as applications?	DNA and proteins.
186	Why is there a practical limit to voltage in gel electrophoresis?	Increasing voltage causes resistive heating.
187	What replaces the gel in capillary electrophoresis?	A capillary filled with buffer solution.
188	What is the material of the capillary specified in the lecture?	Fused silica.
189	Why can capillary electrophoresis use much higher voltages than gel electrophoresis?	The capillary can tolerate much higher electric fields without melting.
190	What advantage does high voltage provide in CE?	Very efficient separations, with up to roughly 10⁶ theoretical plates.
191	Why do neutral compounds not normally separate by ordinary CE?	They lack electrophoretic mobility.
192	What major detectors can be coupled to CE?	UV/Vis, fluorescence, and MS.
193	What is electrophoretic flow?	Movement caused by the interaction of a charged species with the electric field.
194	Toward which electrode do cations move electrophoretically?	Toward the cathode.
195	Toward which electrode do anions move electrophoretically?	Toward the anode.
196	Why does electro-osmotic flow occur in a silica capillary?	Negatively charged silanol groups attract cations, forming an electrical double layer that drives net buffer flow toward the cathode.
197	In typical CE, which is larger: electro-osmotic or electrophoretic flow?	Electro-osmotic flow is generally larger.
198	How does the combination of electro-osmotic and electrophoretic flow permit separation of anions, cations, and neutrals?	Their net velocities differ because electrophoretic motion adds to or opposes the electro-osmotic flow.
199	Within a given charge class, what primarily determines CE separation?	Charge density.
200	Why can CE have exceptionally high efficiency?	There is no stationary phase, and peak broadening is dominated largely by longitudinal diffusion.