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Question 1Bioanalytical Chemistry

In a validated LC-MS/MS bioanalytical method, what does the calibration curve establish?

  1. The mass accuracy of the high-resolution instrument
  2. The relationship between detector response and analyte concentration Correct answer.
  3. The identity of unknown metabolites in a sample
  4. The stability of the analyte in whole blood

Explanation

A calibration curve models detector response as a function of known analyte concentrations, typically by weighted least-squares regression. It is then used to back-calculate concentrations in study samples. Identity, stability, and mass accuracy are assessed by other experiments.

Question 2Bioanalytical Chemistry

Which parameter of a chromatographic peak is most directly used to quantify an analyte in LC-MS/MS?

  1. Retention time
  2. Column backpressure
  3. Peak area or peak area ratio Correct answer.
  4. Peak symmetry factor

Explanation

Quantitation relies on the magnitude of the detector response, expressed as peak area or as the ratio of analyte area to internal standard area. Retention time supports identification, not quantitation. Symmetry and pressure are system suitability attributes.

Question 3Bioanalytical Chemistry

What is the primary purpose of an internal standard in a bioanalytical assay?

  1. To convert the analyte into a more stable derivative
  2. To increase the ionization efficiency of the analyte
  3. To correct for variability in sample preparation and instrument response Correct answer.
  4. To reduce the run time of the chromatographic method

Explanation

An internal standard compensates for variability in extraction recovery, injection volume, and detector response. A stable-isotope-labeled analog is often used because it behaves nearly identically to the analyte. It does not inherently boost ionization or shorten runs.

Question 4Bioanalytical Chemistry

Which sample type is most commonly used for measuring systemic drug exposure in a pharmacokinetic study?

  1. Urine
  2. Saliva
  3. Plasma Correct answer.
  4. Feces

Explanation

Plasma is the standard matrix for systemic exposure because it is well characterized and directly reflects circulating drug. Serum is also used, but plasma is typical. Urine and feces are used for excretion and mass balance studies.

Question 5Bioanalytical Chemistry

In regulated bioanalysis, what does the lower limit of quantification (LLOQ) represent?

  1. The lowest concentration that can be detected but not quantified
  2. The lowest concentration that can be reliably quantified with acceptable accuracy and precision Correct answer.
  3. The concentration of the internal standard in the sample
  4. The concentration at which the assay saturates the detector

Explanation

The LLOQ is the lowest concentration validated to meet predefined accuracy and precision criteria, typically within 20% of nominal. The limit of detection is lower but does not require the same quantitative rigor. Saturation relates to the upper limit of quantification.

Question 6Bioanalytical Chemistry

What is matrix effect in LC-MS/MS bioanalysis?

  1. Degradation of analyte during storage
  2. Drift in the mass spectrometer calibration over time
  3. Alteration of analyte ionization by co-eluting sample components Correct answer.
  4. Loss of analyte during sample extraction

Explanation

Matrix effect is the change in ionization efficiency caused by co-eluting endogenous or exogenous components from the sample matrix. It can cause ion suppression or enhancement and is assessed by comparing responses in matrix versus neat solution.

Question 7Bioanalytical Chemistry

Why is a stable-isotope-labeled internal standard often preferred in LC-MS/MS assays?

  1. It co-elutes with and ionizes similarly to the analyte Correct answer.
  2. It produces a different product ion that avoids interference
  3. It increases the analyte's extraction recovery
  4. It eliminates the need for a calibration curve

Explanation

A stable-isotope-labeled analog has nearly identical physicochemical behavior, so it co-elutes and ionizes similarly to the analyte. This makes it highly effective at correcting for matrix effects and recovery variability. It does not remove the need for calibration.

Question 8Bioanalytical Chemistry

Which document typically defines the acceptance criteria and procedures for a regulated bioanalytical method?

  1. The chromatogram printout
  2. The study protocol only
  3. A validated standard operating procedure and method validation report Correct answer.
  4. The certificate of analysis for the reference standard

Explanation

Regulated bioanalysis relies on validated SOPs and a method validation report that document procedures and acceptance criteria. These govern how runs are accepted and samples are quantified. Other documents support but do not define the method.

Question 9Bioanalytical Chemistry

A calibration curve uses a weighted 1/x² linear regression across a wide range. What is the main reason for applying weighting?

  1. To force the intercept through zero
  2. To convert peak area into concentration directly
  3. To remove the need for replicate standards
  4. To give low-concentration standards appropriate influence on the fit Correct answer.

Explanation

Weighting compensates for heteroscedasticity, where variance in response increases with concentration. A 1/x² weighting gives lower standards proportionally more influence, improving accuracy at the low end. It does not force a zero intercept or eliminate replicates.

Question 10Bioanalytical Chemistry

A run's calibration standards all meet criteria except one mid-level standard, which deviates by 18% from nominal. With at least six standards, what is the standard regulatory approach?

  1. Reject the entire run and repeat all samples
  2. Accept the failing standard because it is close to the limit
  3. Recalibrate the detector mid-run and continue
  4. Exclude the failing standard and refit if the remaining standards meet criteria Correct answer.

Explanation

Guidance allows a limited number of calibration standards to be excluded, provided enough standards remain to define the curve and all remaining standards meet criteria. The curve is then refit without the excluded point. Rejecting the whole run is unnecessary if criteria can still be met.

Question 11Bioanalytical Chemistry

During method validation, the same quality control sample is analyzed and gives a coefficient of variation of 4.5% across six replicates. This result primarily demonstrates acceptable:

  1. Precision Correct answer.
  2. Selectivity
  3. Carryover
  4. Dilution integrity

Explanation

Precision describes the closeness of repeated measurements to each other and is expressed as percent CV. A low CV across replicates indicates good precision. Selectivity, carryover, and dilution integrity are assessed by different experiments.

Question 12Bioanalytical Chemistry

How is carryover typically evaluated in a validated LC-MS/MS method?

  1. By measuring the retention time of the internal standard
  2. By calculating the slope of the calibration curve
  3. By comparing extracted blank response to the LLOQ response after a high-concentration sample Correct answer.
  4. By determining the extraction recovery at three concentrations

Explanation

Carryover is assessed by injecting blank samples immediately after a high-concentration sample and comparing any residual response to the LLOQ response. Acceptance is typically that carryover in the blank is no more than 20% of the LLOQ.

Question 13Bioanalytical Chemistry

A high-concentration study sample exceeds the upper limit of quantification and must be diluted. Which validation experiment supports this practice?

  1. Bench-top stability
  2. Dilution integrity Correct answer.
  3. Matrix effect
  4. Selectivity

Explanation

Dilution integrity demonstrates that diluting a sample above the upper limit of quantification still yields accurate and precise results. It validates the dilution procedure and diluent. Selectivity, matrix effect, and stability address different concerns.

Question 14Bioanalytical Chemistry

Which experiment best assesses whether endogenous matrix components interfere with the analyte measurement?

  1. Comparing peak areas of standards prepared in neat solvent
  2. Analyzing blank matrix from multiple individual sources and checking for interference at the analyte retention time Correct answer.
  3. Determining the slope of the calibration curve
  4. Measuring the internal standard recovery

Explanation

Selectivity is evaluated by analyzing blank matrix from several individual sources to confirm no interfering response at the analyte retention time. Using multiple sources captures biological variability in matrix composition.

Question 15Bioanalytical Chemistry

A bioanalytical method reports recovery of approximately 65% for the analyte. What does this value describe?

  1. The efficiency of extracting the analyte from the matrix Correct answer.
  2. The proportion of internal standard degraded during storage
  3. The fraction of analyte lost to matrix suppression
  4. The accuracy of the calibration curve

Explanation

Recovery measures how efficiently the analyte is extracted from the matrix and is determined by comparing extracted samples to post-extraction spiked samples. It is distinct from matrix effect, which concerns ionization. Recovery need not be near 100% if it is consistent.

Question 16Bioanalytical Chemistry

Which stability experiment evaluates whether an analyte remains intact in the autosampler before injection?

  1. Freeze-thaw stability
  2. Long-term stability
  3. Stock solution stability
  4. Processed-sample (autosampler) stability Correct answer.

Explanation

Processed-sample stability, often called autosampler or extract stability, tests the analyte in prepared extracts held in the autosampler. Long-term and freeze-thaw stability concern stored samples, and stock stability concerns reference solutions.

Question 17Bioanalytical Chemistry

What is the purpose of a matrix effect experiment comparing post-extraction spiked samples to neat standards?

  1. To quantify extraction recovery
  2. To measure analyte stability in the autosampler
  3. To establish the LLOQ
  4. To determine whether co-eluting matrix components alter ionization Correct answer.

Explanation

Comparing the response of post-extraction spiked samples to neat standards isolates the effect of the matrix on ionization. A ratio near unity indicates little matrix effect, while deviations indicate suppression or enhancement.

Question 18Bioanalytical Chemistry

A batch contains calibration standards, blanks, and QCs. According to common regulatory expectations, what proportion of QCs must typically be within ±15% of nominal for a run to be accepted?

  1. At least 90%
  2. At least 67% Correct answer.
  3. Exactly 100%
  4. At least 50%

Explanation

Common acceptance criteria require at least two-thirds (about 67%) of QCs to be within ±15% of nominal, with at least 50% at each concentration level. A run failing these criteria is generally rejected.

Question 19Bioanalytical Chemistry

An analyst observes that a deuterated internal standard shows a different retention time than the unlabeled analyte on a reversed-phase column. What is the most likely explanation?

  1. The column temperature was too low
  2. The mass spectrometer was miscalibrated
  3. The internal standard has degraded completely
  4. A deuterium isotope effect altered the physicochemical behavior Correct answer.

Explanation

Although stable-isotope analogs usually co-elute closely, a significant isotope effect can shift retention, especially with multiple labels. This can compromise the internal standard's ability to track the analyte. Degradation, temperature, and calibration would not specifically cause a small retention shift of a labeled analog.

Question 20Bioanalytical Chemistry

Why is it important to prepare calibration standards in the same biological matrix as study samples?

  1. To account for matrix-dependent extraction and ionization behavior Correct answer.
  2. To eliminate the need for an internal standard
  3. To reduce the cost of reference standards
  4. To shorten the chromatographic run time

Explanation

Matrix composition affects both extraction recovery and ionization, so standards prepared in the same matrix better reflect study sample behavior. This improves the accuracy of back-calculated concentrations.

Question 21Bioanalytical Chemistry

A surrogate matrix is used for calibration because the true matrix is difficult to obtain. What additional validation is essential?

  1. Repeating the calibration curve daily
  2. Demonstrating parallelism between the surrogate and authentic matrix Correct answer.
  3. Determining the internal standard's molecular weight
  4. Measuring column backpressure

Explanation

When a surrogate matrix is used, parallelism experiments compare responses in surrogate versus authentic matrix to confirm the calibration applies to real samples. This ensures accurate quantitation in the actual study matrix.

Question 22Bioanalytical Chemistry

An incurred sample reanalysis (ISR) is performed on study samples. What does ISR primarily assess?

  1. The reproducibility of the reported concentrations in actual study samples Correct answer.
  2. The selectivity of the chromatographic method
  3. The stability of the analyte in stock solution
  4. The accuracy of the reference standard purity

Explanation

ISR evaluates reproducibility of study sample results by reanalyzing a subset of incurred samples and comparing original and repeat concentrations. A high percentage of pairs within ±20% indicates acceptable reproducibility in the study matrix.

Question 23Bioanalytical Chemistry

A method shows acceptable precision at the LLOQ but poor accuracy at low concentrations with a positive bias. Which factor is most likely responsible?

  1. An interfering endogenous peak co-eluting at the analyte retention time Correct answer.
  2. Insufficient detector saturation
  3. A calibration range that is too narrow at the high end
  4. Excessive internal standard concentration

Explanation

A co-eluting interference elevates the measured response at low concentrations, producing a positive bias that is most apparent near the LLOQ. Improving chromatographic separation or selectivity resolves this. Detector saturation and high-end range do not cause low-end positive bias.

Question 24Bioanalytical Chemistry

Why must the calibration range be validated separately from the LLOQ alone?

  1. Because the linearity and accuracy must be demonstrated across the entire range, not just at the lowest point Correct answer.
  2. Because internal standards interfere only at high concentrations
  3. Because the LLOQ is always the most accurate point
  4. Because calibration standards are not required in regulated work

Explanation

Validation must demonstrate that the method is accurate and precise across the full calibration range, including linearity and the upper limit of quantification. The LLOQ is only one point and does not establish performance at higher concentrations.

Question 25Bioanalytical Chemistry

In a cross-validation between two bioanalytical methods or laboratories, what is the primary acceptance goal?

  1. That both methods use the same internal standard
  2. That both methods use identical instrument models
  3. That both methods have the same run time
  4. That both methods yield comparable results on the same samples within predefined criteria Correct answer.

Explanation

Cross-validation confirms that results from two methods or sites are comparable within predefined acceptance criteria, enabling data to be combined. Identical instruments, run times, or internal standards are not the objective.

Question 26Bioanalytical Chemistry

In regulated bioanalysis, what does the lower limit of quantification (LLOQ) of a method represent?

  1. The midpoint concentration of the validated calibration range
  2. The lowest concentration that can be measured with acceptable accuracy and precision Correct answer.
  3. The concentration at which the analyte response equals the internal standard response
  4. The lowest concentration that produces any detectable signal above background noise

Explanation

The LLOQ is defined by demonstrated performance: the lowest concentration validated to meet predefined accuracy and precision criteria, typically within ±20% of nominal. Mere detection of signal is a different concept (the limit of detection) and does not require quantitative acceptance.

Question 27Bioanalytical Chemistry

Which sample type is analyzed to confirm that reagents, solvents, and the extraction procedure introduce no measurable analyte signal?

  1. A study sample diluted above the upper limit of quantification
  2. A post-extraction spiked matrix sample
  3. A zero standard containing internal standard but no analyte
  4. A double blank sample containing neither analyte nor internal standard Correct answer.

Explanation

A double blank (matrix without analyte or internal standard) is used to demonstrate that the overall procedure contributes no interfering signal at the analyte retention time. The zero standard tests for interference with the internal standard channel rather than the analyte channel.

Question 28Bioanalytical Chemistry

A chromatographic peak shows fronting. Which characteristic of the peak shape does this describe?

  1. The peak is symmetrical but unusually broad
  2. The peak has two resolved maxima
  3. The trailing edge of the peak is less steep than the leading edge
  4. The leading edge of the peak is less steep than the trailing edge Correct answer.

Explanation

Peak fronting means the rising (leading) edge is shallower and the falling (trailing) edge is steeper, often linked to column overload or extra-column effects. Tailing is the opposite pattern, where the trailing edge is drawn out.

Question 29Bioanalytical Chemistry

Which detector type is most commonly coupled to liquid chromatography for quantitative small-molecule bioanalysis because of its sensitivity and selectivity?

  1. Tandem mass spectrometry Correct answer.
  2. Refractive index detection
  3. Fluorescence detection
  4. Conductivity detection

Explanation

Tandem mass spectrometry (MS/MS) provides sensitive, selective detection based on precursor-to-product ion transitions, making it the standard for quantitative LC bioanalysis. Refractive index and conductivity detectors are far less sensitive and selective for trace analysis.

Question 30Bioanalytical Chemistry

Which anticoagulant is commonly used to prepare plasma samples for bioanalysis?

  1. Formalin
  2. Sodium fluoride only
  3. Sodium azide
  4. K2-EDTA Correct answer.

Explanation

K2-EDTA is a standard anticoagulant for plasma collection in bioanalysis. Formalin is a fixative and sodium azide is a preservative, neither being used as an anticoagulant for plasma preparation.

Question 31Bioanalytical Chemistry

What is the primary purpose of a calibration curve in a bioanalytical assay?

  1. To relate detector response to analyte concentration for quantifying unknown samples Correct answer.
  2. To measure the protein binding of the analyte
  3. To establish the melting temperature of the analyte
  4. To determine the isoelectric point of the analyte

Explanation

A calibration curve models the relationship between instrument response and known analyte concentrations, enabling interpolation of unknown sample concentrations. Protein binding, isoelectric point, and melting temperature are unrelated physicochemical measurements.

Question 32Bioanalytical Chemistry

Which term describes the process of releasing analyte from binding proteins or tissues before extraction?

  1. Sample homogenization and disruption Correct answer.
  2. Ion suppression
  3. Chromatographic separation
  4. Post-column addition

Explanation

Homogenization and disruption break down tissue structure and release bound analyte so it can be extracted reproducibly. Chromatographic separation and post-column addition occur after extraction, and ion suppression is a matrix phenomenon, not a release step.

Question 33Bioanalytical Chemistry

What does the term 'accuracy' describe in a bioanalytical method?

  1. The closeness of repeated measurements to each other
  2. The retention time reproducibility of the analyte
  3. The slope of the calibration curve
  4. The closeness of the measured concentration to the true or nominal concentration Correct answer.

Explanation

Accuracy reflects systematic agreement between the measured value and the true or nominal value, often expressed as percent bias. Closeness of repeated measurements to each other is precision, a distinct characteristic.

Question 34Bioanalytical Chemistry

A QC sample is prepared at a nominal concentration of 40.0 ng/mL and measured at 43.2 ng/mL. What is the percent bias?

  1. +92.0%
  2. +3.2%
  3. +7.4%
  4. +8.0% Correct answer.

Explanation

Percent bias equals (measured minus nominal) divided by nominal, multiplied by 100: (43.2 − 40.0)/40.0 × 100 = +8.0%. The sign is positive because the measured value exceeds nominal.

Question 35Bioanalytical Chemistry

A solid-phase extraction method is being developed for a basic analyte. Which condition would most favor retention of the protonated analyte on a cation-exchange sorbent?

  1. Loading at the analyte's isoelectric point
  2. Loading at a pH at least two units below the analyte pKa Correct answer.
  3. Loading in pure organic solvent
  4. Loading at a pH at least two units above the analyte pKa

Explanation

For cation exchange, the analyte must be positively charged, which requires the pH to be well below its pKa so the protonated form predominates. Loading above the pKa deprotonates the analyte and reduces ionic interaction with the sorbent.

Question 36Bioanalytical Chemistry

A laboratory needs to measure a volatile analyte in blood with minimal sample preparation and high sensitivity. Which technique is most appropriate?

  1. Capillary electrophoresis with UV detection
  2. Reverse-phase LC with UV detection
  3. Headspace gas chromatography with mass spectrometry Correct answer.
  4. Size-exclusion chromatography with refractive index detection

Explanation

Headspace gas chromatography isolates volatile analytes from the matrix and, with mass spectrometry, provides sensitive selective detection. LC with UV, CE with UV, and size-exclusion with refractive index are poorly suited to volatile analytes or trace sensitivity.

Question 37Bioanalytical Chemistry

During method development, an analyst observes poor reproducibility of extraction recovery from plasma. Which change is most likely to improve reproducibility?

  1. Switching from mass spectrometry to UV detection
  2. Adding a structurally related internal standard before extraction to normalize recovery Correct answer.
  3. Increasing the injection volume without other changes
  4. Reducing the number of calibration standards

Explanation

An internal standard added before extraction compensates for variability in extraction recovery and ionization. Increasing injection volume or reducing calibration points does not address recovery variability, and UV detection generally worsens selectivity.

Question 38Bioanalytical Chemistry

A method must quantify an analyte over a range spanning three orders of magnitude. Which approach best maintains acceptable accuracy across the range?

  1. Use a single-point calibration at the midpoint
  2. Use peak height only and ignore concentration-response linearity
  3. Use weighted regression and evaluate standards at each level against acceptance criteria Correct answer.
  4. Use unweighted regression and accept any standard within 30% of nominal

Explanation

Weighted regression with level-by-level evaluation against predefined criteria ensures accuracy is verified across the entire range. Unweighted regression may fit high concentrations well but distort low-end accuracy, and single-point calibration cannot cover a wide range.

Question 39Bioanalytical Chemistry

A study requires measuring an analyte in urine, but enzyme activity degrades the analyte after collection. Which practice best mitigates this?

  1. Collect into a container with an appropriate preservative or adjust pH at collection Correct answer.
  2. Dilute samples immediately with water
  3. Centrifuge samples only after prolonged storage
  4. Store samples at room temperature for extended periods

Explanation

Adding a preservative or adjusting pH at collection inhibits enzymatic degradation and preserves analyte integrity. Room-temperature storage and delayed processing promote degradation rather than preventing it.

Question 40Bioanalytical Chemistry

Two analytes in a method have similar precursor ions but different product ions. Which acquisition approach best maintains selectivity for both?

  1. Multiple reaction monitoring with distinct transitions for each analyte Correct answer.
  2. Selected ion recording of a common fragment
  3. Single ion monitoring of the shared precursor
  4. Full-scan acquisition without fragmentation

Explanation

Multiple reaction monitoring uses unique precursor-to-product transitions, providing selectivity even when precursor ions are similar. Monitoring a shared precursor or common fragment would not distinguish the analytes.

Question 41Bioanalytical Chemistry

A method reports a within-run precision of 6% and a between-run precision of 9%. What does the between-run value describe?

  1. Variability of replicate injections within a single run
  2. The recovery of the analyte from matrix
  3. Variability of measurements across separate analytical runs over time Correct answer.
  4. The systematic bias of the assay

Explanation

Between-run (inter-batch) precision captures variability across separate runs performed on different occasions. Within-run precision describes variability among replicates in one run, and bias and recovery are separate characteristics.

Question 42Bioanalytical Chemistry

An assay shows severe ion suppression in the analyte channel that varies among individual lots of plasma. Which strategy most directly addresses this?

  1. Remove the internal standard from the method
  2. Shorten the chromatographic run time
  3. Increase the spray voltage without changing cleanup
  4. Improve sample cleanup and evaluate multiple matrix lots during validation Correct answer.

Explanation

Improving cleanup reduces co-eluting matrix components, and testing multiple lots characterizes variability in matrix effects. Raising spray voltage or shortening run time may worsen co-elution, and removing the internal standard eliminates a key compensation tool.

Question 43Bioanalytical Chemistry

A calibration curve is linear at low concentrations but flattens at the high end. What is the most likely cause?

  1. Insufficient equilibration time at low concentrations
  2. Carryover affecting low-concentration standards
  3. Detector saturation at high concentrations Correct answer.
  4. Internal standard degradation at low concentrations

Explanation

Flattening at the high end of a curve typically reflects detector saturation, where response no longer increases proportionally with concentration. Low-end issues such as carryover or equilibration would affect the low end, not cause high-end flattening.

Question 44Bioanalytical Chemistry

A zero standard shows a large internal standard peak but a small analyte peak at the analyte retention time. What is the most appropriate interpretation?

  1. Analyte contamination or carryover is present and should be investigated Correct answer.
  2. The calibration curve slope is too steep
  3. The analyte is unstable in the autosampler
  4. The internal standard concentration is too low

Explanation

A zero standard should contain internal standard but no analyte; an analyte peak indicates contamination or carryover. Internal standard concentration, stability, and curve slope would not explain an unexpected analyte signal in a zero standard.

Question 45Bioanalytical Chemistry

An analyte is light-sensitive and degrades during sample processing under laboratory lighting. Which measure best protects sample integrity?

  1. Increase processing temperature to speed the work
  2. Perform processing under yellow or reduced light and document the precaution Correct answer.
  3. Store samples in clear glass on the bench
  4. Expose samples to direct sunlight to verify degradation

Explanation

Conducting work under reduced or yellow light minimizes photodegradation, and documenting the precaution preserves traceability. Elevated temperature, direct sunlight, and clear-glass bench storage would accelerate degradation.

Question 46Bioanalytical Chemistry

A method is transferred to a second laboratory, and results for the same samples differ systematically from the originating laboratory. Which action best resolves this?

  1. Report both data sets without investigation
  2. Discard the originating laboratory's data
  3. Perform cross-validation comparing results and investigate sources of discrepancy Correct answer.
  4. Recalibrate the instrument without comparing results

Explanation

Cross-validation compares results from both laboratories against predefined criteria and identifies systematic discrepancies for investigation. Recalibrating without comparison, reporting discordant data, or discarding one data set does not resolve the underlying issue.

Question 47Bioanalytical Chemistry

Two internal standards are compared: one is a structural analog, the other a stable-isotope-labeled version of the analyte. In which situation would the structural analog be the more reasonable choice?

  1. When the labeled standard co-elutes with an interfering isobaric matrix component that the analog avoids
  2. When maximum compensation for ionization differences is required
  3. When the analyte is stable and the matrix is simple
  4. When the analyte has no available stable-isotope form and the analog tracks extraction well Correct answer.

Explanation

If a stable-isotope standard is unavailable, a well-behaved structural analog that tracks extraction and chromatography is a practical alternative. The labeled standard is generally preferred when available because it best compensates for ionization differences.

Question 48Bioanalytical Chemistry

A validation run shows acceptable accuracy for all QCs except the low QC, which shows a consistent negative bias of 22%. Which conclusion is most defensible?

  1. The method is acceptable because only one QC level failed
  2. The bias is acceptable because precision was good
  3. The low-concentration region fails accuracy criteria and requires investigation before the method is accepted Correct answer.
  4. The high QC should be reanalyzed to compensate

Explanation

A consistent bias beyond the predefined limit at any QC level indicates a failure of accuracy criteria in that region and requires investigation. Good precision does not offset unacceptable bias, and failures cannot be offset by other levels.

Question 49Bioanalytical Chemistry

An analyte binds strongly to plasma proteins, and recovery from plasma is low and variable. Which approach most directly improves extraction of total analyte?

  1. Shorten the extraction time
  2. Disrupt protein binding before extraction, for example by protein precipitation or pH adjustment Correct answer.
  3. Reduce the extraction solvent volume
  4. Increase the internal standard concentration

Explanation

Disrupting protein binding releases bound analyte so it can be extracted reproducibly, improving recovery of total analyte. Reducing solvent volume, altering internal standard concentration, or shortening extraction time would not address protein binding.

Question 50Bioanalytical Chemistry

A laboratory observes that an assay's LLOQ signal-to-noise ratio is adequate, but accuracy at the LLOQ fails because of a small interfering peak. Which action is most appropriate?

  1. Improve chromatographic separation or sample cleanup to resolve the interference Correct answer.
  2. Increase the injection volume to overwhelm the interference
  3. Accept the LLOQ because signal-to-noise is adequate
  4. Lower the LLOQ to increase the signal-to-noise ratio

Explanation

Adequate signal-to-noise does not guarantee accuracy when an interfering peak biases the measurement; improving separation or cleanup resolves the interference. Lowering the LLOQ or increasing injection volume does not remove the interference, and signal-to-noise alone is insufficient for acceptance.