WorksheetsAnachem 3 Second Shifting Review
Total questions: 10
Worksheet time: 10mins
When performing an analysis where the sample matrix significantly affects the signal (e.g., viscosity or ionic strength changes instrument response), the most appropriate calibration technique to mitigate this effect is the:
External standard method
Standard additions method
Single-point standardization
Linear regression calibration
An analyst prepares a five-point external standard calibration curve for a spectrophotometric assay. After performing the least-squares regression, they obtain an R2 = 0.925. The correct evaluative action the analyst should take is to:
Proceed with the analysis, as the R2 value is high enough for most quantitative work.
Reject the calibration and repeat the standardization, as the linearity is questionable.
Use a single-point standardization instead, since the R2 value suggests error in multiple standard preparations.
Extrapolate the calibration curve to force an R2 closer to 1.00.
A single-point standardization is least reliable when:
The detector response is known to be linear over the entire working range.
A primary standard of high purity is used for the calibration.
The instrument's zero reading is unstable or drifts over time.
The analytical signal is likely to deviate from Beer's Law at high concentrations.
A major source of error unique to the external standard method (compared to standard additions) is:
Errors due to volumetric glassware inaccuracies.
Errors from the non-linearity of the detector response.
Errors arising from a significant difference between the matrix of the standard solutions and the sample matrix.
Errors introduced by weighing the primary standard.
Which of the following practices represents good practice in the development of a calibration curve?
Including the origin (0,0) as a fixed point in the regression, even if a blank was not measured.
Preparing all standards from the highest concentration by serial dilution.
Ensuring the analyte concentration in the samples falls within the range of the established standards
Performing the regression using only the two points furthest from each other.
A chemist is tasked with analyzing a sample where the target analyte is present at a concentration of 50 parts per million (ppm). Based on the constituent classification, this analyte should be classified as a:
Major constituent
Micro constituent
Trace constituent
Ultratrace constituent
A pharmaceutical company needs to verify the concentration of a drug in a large batch of tablets. To ensure they get a representative sample from the entire batch, they randomly select tablets from the top, middle, and bottom of the mixing tank. This approach is an example of which type of sampling plan?
Random sampling
Systematic sampling
Stratified sampling
Intuitive sampling
Which of the following scenarios is most likely to lead to a large sampling error?
Analyzing a liquid solution that is continuously stirred and well-mixed.
Using an analytical method that has a high measurement variance.
Sampling a large pile of coal where the quality varies significantly by location and particle size.
Preparing a laboratory sample from a gross sample that is already homogeneous.
An analyst determines that for a specific material, the measurement variance is significant, but the sampling variance is insignificant. To achieve a better overall estimate of the population mean, the analyst should prioritize:
Increasing the size of the gross sample.
Analyzing more laboratory samples from the existing gross sample.
Increasing the number of increments in the initial sampling plan.
Switching to a standard additions calibration method.
Suppose a One-Way ANOVA yields a significant result (p < 0.05). What is the necessary next step in the statistical analysis?
Conclude that the mean of the largest group is significantly different from all other groups.
Stop the analysis, as the primary hypothesis has been proven
Conduct a post-hoc test to determine which specific pairs of group means are different.
Re-run the test using a higher significance level to confirm the finding.
