Podcast
Questions and Answers
What trend may indicate a process issue when observed in data points?
What trend may indicate a process issue when observed in data points?
- 7 points alternating in value
- 3 consecutive points on the same side of the mean
- 5 points remaining constant
- 7 consecutive points rising or falling (correct)
Which of the following is NOT a typical cause of increased variability in data?
Which of the following is NOT a typical cause of increased variability in data?
- Variation from SOP
- Incorrect instrument calibration (correct)
- Poor technique
- Lack of training
What is a common cause of a downward trend in mean?
What is a common cause of a downward trend in mean?
- Poor instrument maintenance
- Evaporative concentration of calibration material (correct)
- Excessive training of personnel
- Improper reagent preparation
Which issue might cause an upward trend in mean?
Which issue might cause an upward trend in mean?
Which of the following could be a cause of a shift in mean?
Which of the following could be a cause of a shift in mean?
What is indicated by a pattern of 7 points on the same side of the mean?
What is indicated by a pattern of 7 points on the same side of the mean?
What could be a consequence of reference material contamination?
What could be a consequence of reference material contamination?
Which factor could potentially lead to increased variability in data collection?
Which factor could potentially lead to increased variability in data collection?
What is the difference between IDL and MDL determination?
What is the difference between IDL and MDL determination?
What does the Linear Dynamic Range refer to in analytical measurements?
What does the Linear Dynamic Range refer to in analytical measurements?
What is the purpose of a Method Blank in quality control?
What is the purpose of a Method Blank in quality control?
Which option describes a Field Blank accurately?
Which option describes a Field Blank accurately?
When is a Method Blank considered acceptable?
When is a Method Blank considered acceptable?
What is one of the main roles of Quality Control (QC) samples?
What is one of the main roles of Quality Control (QC) samples?
What happens in the event of a QC failure?
What happens in the event of a QC failure?
Which of the following statements about Duplicates is true?
Which of the following statements about Duplicates is true?
What is the calculated Method Detection Limit (MDL) based on the provided results?
What is the calculated Method Detection Limit (MDL) based on the provided results?
Under what conditions should Dixon's Test be applied?
Under what conditions should Dixon's Test be applied?
How is the standard deviation (SD) impacted by concentration levels?
How is the standard deviation (SD) impacted by concentration levels?
What happens if the MDL determination is conducted at a concentration greater than 10 x MDL?
What happens if the MDL determination is conducted at a concentration greater than 10 x MDL?
What is the rule regarding the number of times Dixon's Test can be used on a data set?
What is the rule regarding the number of times Dixon's Test can be used on a data set?
How often should MDL be redetermined according to laboratory policy?
How often should MDL be redetermined according to laboratory policy?
What is the difference between Method Detection Limit (MDL) and Instrument Detection Limit (IDL)?
What is the difference between Method Detection Limit (MDL) and Instrument Detection Limit (IDL)?
What should you do if a single result deviates significantly from a set of 7 results?
What should you do if a single result deviates significantly from a set of 7 results?
Why is it important to prepare the Spiked Blank independently from the calibration standards?
Why is it important to prepare the Spiked Blank independently from the calibration standards?
What defines an acceptable Spiked Blank according to historical data?
What defines an acceptable Spiked Blank according to historical data?
What is a Matrix Spike or Spiked Sample used for?
What is a Matrix Spike or Spiked Sample used for?
What can matrix effects lead to in the measurement process?
What can matrix effects lead to in the measurement process?
Which of the following best explains the significance of using a second source for preparing reagents?
Which of the following best explains the significance of using a second source for preparing reagents?
What does a laboratory analyze to check for matrix effects?
What does a laboratory analyze to check for matrix effects?
When preparing a matrix spike, what should be added to the sample?
When preparing a matrix spike, what should be added to the sample?
How are standard solutions typically characterized in a laboratory setting?
How are standard solutions typically characterized in a laboratory setting?
What does a control chart indicate when a point is outside the predetermined limits?
What does a control chart indicate when a point is outside the predetermined limits?
What is the purpose of plotting mean and standard deviations in a control chart?
What is the purpose of plotting mean and standard deviations in a control chart?
How often should control charts be updated and interpreted?
How often should control charts be updated and interpreted?
What is the minimum percentage of compounds that must be monitored in a multi-element/compound method?
What is the minimum percentage of compounds that must be monitored in a multi-element/compound method?
What action should be taken if an out of control situation is detected?
What action should be taken if an out of control situation is detected?
What does the '+3 δ' represent in a control chart?
What does the '+3 δ' represent in a control chart?
What is a key benefit of maintaining control charts?
What is a key benefit of maintaining control charts?
What should happen to results from a 'second source' standard each day?
What should happen to results from a 'second source' standard each day?
Study Notes
Control Charts
- Control charts are visual representations of data collected over time
- These charts help identify trends and potential process issues
- Key indicators to watch include:
- Abrupt change in data
- 7 consecutive points rising or falling
- 7 consecutive points on the same side of the mean
- Points outside of the control limits (+3 sigma and -3 sigma)
Common Causes of Violations
- Increased Variability:
- Variations from standard operating procedures
- Poor technique, lack of training
- Shift in Mean:
- Incorrect standard or reagent preparation
- Reference material contamination
- Incorrect instrument calibration
- Change in procedure/instrumentation
- Downward Trend in Mean:
- Evaporative concentration of calibration material
- Deterioration of reagents
- Upward Trend in Mean:
- Deterioration of reference material or reagents
- Evaporative concentration of reference material
Method Detection Limit (MDL)
- MDL is a measure of the lowest concentration of a substance that can be reliably detected by a specific analytical method
- Calculated using the standard deviation and a specific t-value (varies with number of replicates)
- Dixon's Test is used to identify and reject outlier results
- MDL should be determined annually or biannually, or when there are major changes to the method or instrumentation
- Instrument Detection Limit (IDL) is determined without considering the variability of the sample preparation steps
Linear Dynamic Range
- The range of concentrations that are still on the linear part of the calibration curve
Quality Control (QC)
- Routine, structured part of analysis conducted by the analyst
- Performed by analyzing QC samples alongside real samples within a batch or run
- QC samples include:
- Method Blank
- Duplicates or Repeats
- Spiked Blank or QC Standard
- Matrix Spike or Spiked Sample
- SRMs and CRMs
Method Blank
- An aliquot of reagent water or blank matrix that is treated exactly as a real sample
- Purpose is to determine if method analytes or other interferences are present in the laboratory environment, reagents, or apparatus
- An acceptable Method Blank has a result less than the Reporting Limit (i.e. “not detected.”)
Field Blank
- An aliquot of reagent water or blank matrix placed in a sample container in the laboratory and treated like a real sample
- Sent to the sampling site, exposed to sampling site conditions, and brought back
- Purpose is to determine if method analytes or other interferences are present in the field environment
Spiked Blank or QC Standard
- Prepared independently from the calibration standards, preferably from a different bottle and manufacturer
- Acceptance limits are based on historical data, with results within 3 standard deviations of the mean being acceptable
Matrix Effects
- Interferences caused by components in the sample matrix that can suppress or enhance measurement
- Can be determined by analyzing a Matrix Spike or Spiked Sample
Control Charts
- Used to assess the stability and control of a method over time
- Data collected from a “second source” standard is plotted against time to identify trends
- Points outside the limits (+3 sigma and -3 sigma) indicate a potential problem
- Out of control situations are addressed immediately to prevent data loss
- Control charts are audited regularly by QA
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Description
Test your knowledge of control charts and their applications in monitoring data trends over time. This quiz covers key indicators, common causes of violations, and implications for process control. Understand how variability and shifts in mean can impact your analysis.
