Control Charts Quiz
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Questions and Answers

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?

  • Variation from SOP
  • Incorrect instrument calibration (correct)
  • Poor technique
  • Lack of training

    • 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?

    <p>Deterioration of reference material</p> Signup and view all the answers

    Which of the following could be a cause of a shift in mean?

    <p>Improper reagent preparation</p> Signup and view all the answers

    What is indicated by a pattern of 7 points on the same side of the mean?

    <p>Possible process issue</p> Signup and view all the answers

    What could be a consequence of reference material contamination?

    <p>Shift in mean</p> Signup and view all the answers

    Which factor could potentially lead to increased variability in data collection?

    <p>Inconsistent application of techniques</p> Signup and view all the answers

    What is the difference between IDL and MDL determination?

    <p>IDL is the same as MDL when there is no sample preparation.</p> Signup and view all the answers

    What does the Linear Dynamic Range refer to in analytical measurements?

    <p>The range of concentrations maintaining linearity in calibration.</p> Signup and view all the answers

    What is the purpose of a Method Blank in quality control?

    <p>To detect any contamination from reagents or the laboratory environment.</p> Signup and view all the answers

    Which option describes a Field Blank accurately?

    <p>It is a sample filled with water and sent to a sampling site and back.</p> Signup and view all the answers

    When is a Method Blank considered acceptable?

    <p>When it is measured as 'not detected' or below the Reporting Limit.</p> Signup and view all the answers

    What is one of the main roles of Quality Control (QC) samples?

    <p>To validate the results of real samples without interference.</p> Signup and view all the answers

    What happens in the event of a QC failure?

    <p>Further investigation is required to determine the cause.</p> Signup and view all the answers

    Which of the following statements about Duplicates is true?

    <p>They help identify random errors during sample analysis.</p> Signup and view all the answers

    What is the calculated Method Detection Limit (MDL) based on the provided results?

    <p>0.11 mg/L</p> Signup and view all the answers

    Under what conditions should Dixon's Test be applied?

    <p>If any number appears significantly higher or lower than the other values.</p> Signup and view all the answers

    How is the standard deviation (SD) impacted by concentration levels?

    <p>Higher concentrations lead to a higher SD.</p> Signup and view all the answers

    What happens if the MDL determination is conducted at a concentration greater than 10 x MDL?

    <p>The MDL determined will be too high, not reflecting true MDL.</p> Signup and view all the answers

    What is the rule regarding the number of times Dixon's Test can be used on a data set?

    <p>It can be applied only once per set of 8 numbers.</p> Signup and view all the answers

    How often should MDL be redetermined according to laboratory policy?

    <p>Every year or every 2 years.</p> Signup and view all the answers

    What is the difference between Method Detection Limit (MDL) and Instrument Detection Limit (IDL)?

    <p>IDL is sometimes determined but is not as useful as MDL.</p> Signup and view all the answers

    What should you do if a single result deviates significantly from a set of 7 results?

    <p>Recalculate the results without the outlier.</p> Signup and view all the answers

    Why is it important to prepare the Spiked Blank independently from the calibration standards?

    <p>To ensure accuracy and avoid contamination.</p> Signup and view all the answers

    What defines an acceptable Spiked Blank according to historical data?

    <p>A result that is within 3 SD of the mean.</p> Signup and view all the answers

    What is a Matrix Spike or Spiked Sample used for?

    <p>To evaluate the effect of the matrix on recovery efficiency.</p> Signup and view all the answers

    What can matrix effects lead to in the measurement process?

    <p>Results that are artificially low or high.</p> Signup and view all the answers

    Which of the following best explains the significance of using a second source for preparing reagents?

    <p>It minimizes the risks of contamination or decomposition.</p> Signup and view all the answers

    What does a laboratory analyze to check for matrix effects?

    <p>Spiked samples or Matrix Spikes.</p> Signup and view all the answers

    When preparing a matrix spike, what should be added to the sample?

    <p>A known volume of a target analyte.</p> Signup and view all the answers

    How are standard solutions typically characterized in a laboratory setting?

    <p>As pure compounds diluted in RO water.</p> Signup and view all the answers

    What does a control chart indicate when a point is outside the predetermined limits?

    <p>There is likely an intermittent variation from an assignable cause.</p> Signup and view all the answers

    What is the purpose of plotting mean and standard deviations in a control chart?

    <p>To monitor process performance and identify trends.</p> Signup and view all the answers

    How often should control charts be updated and interpreted?

    <p>In real time, each day the instrument is run.</p> Signup and view all the answers

    What is the minimum percentage of compounds that must be monitored in a multi-element/compound method?

    <p>10%</p> Signup and view all the answers

    What action should be taken if an out of control situation is detected?

    <p>Address the situation immediately before reporting data.</p> Signup and view all the answers

    What does the '+3 δ' represent in a control chart?

    <p>The upper control limit to identify variations.</p> Signup and view all the answers

    What is a key benefit of maintaining control charts?

    <p>They provide a historical view of process performance for proactive change.</p> Signup and view all the answers

    What should happen to results from a 'second source' standard each day?

    <p>They are used to update the control charts.</p> Signup and view all the answers

    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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    Related Documents

    Introduction To Analytical Chemistry PDF

    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.

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