Quality Control Techniques and Procedures

Questions and Answers

What is the primary disadvantage of a photocell?

Need for external voltage

Low sensitivity and fatigue (correct)

High sensitivity

Complex design

Which component of a vacuum phototube is negatively charged?

Wire

Cathode (correct)

Anode

Envelope

What is the maximum sensitivity wavelength for a typical photocell?

550 nm (correct)

700 nm

450 nm

600 nm

How does a photomultiplier tube (PMT) amplify radiant energy?

Employing multiple dynodes Signup and view all the answers

Which photodetector type offers the fastest response times?

Photomultiplier tube (PMT) Signup and view all the answers

What is the primary function of a diffraction grating?

To separate light into its component wavelengths Signup and view all the answers

What is a key advantage of using a photodiode compared to a PMT?

Size and speed Signup and view all the answers

What is meant by the term 'spectral bandwidth'?

The range of wavelengths above one-half peak transmittance Signup and view all the answers

What condition can damage the photoelectric surface of a photomultiplier tube?

Intense light exposure Signup and view all the answers

Which photodetector's performance is limited by external voltage requirements?

Vacuum phototube Signup and view all the answers

Which type of cuvette is the most commonly used for spectrophotometry?

Alumina silica cuvette Signup and view all the answers

What does the exit slit determine in a monochromator?

The specific wavelength of light selected Signup and view all the answers

What is the significance of having plane-parallel optical surfaces in a square cuvette?

It minimizes refraction errors and maintains a constant light path Signup and view all the answers

Which statement accurately describes photodetectors?

They convert radiant energy into electrical energy Signup and view all the answers

What is the disadvantage of using scratched optical surfaces in a cuvette?

They scatter light and affect accuracy Signup and view all the answers

What type of diffraction grating is formed by using two laser beams and photoresist?

Holographic grating Signup and view all the answers

What type of mercury lamp emits a sharp-line spectrum and both UV and visible light?

Low-pressure mercury lamp Signup and view all the answers

What property makes lasers particularly useful in analytic instrumentation?

High intensity and narrow bandwidth Signup and view all the answers

Which type of filter is known for passing a relatively wide band of radiant energy but has low transmittance of the selected wavelength?

Colored-glass filter Signup and view all the answers

What function does a monochromator serve in a spectroscopic setup?

Isolates individual wavelengths of light Signup and view all the answers

How do interference filters produce monochromatic light?

Through constructive interference of waves Signup and view all the answers

What causes the dispersion of white light into a continuous spectrum when using a prism?

The difference in refractive index for different wavelengths Signup and view all the answers

What defines a shift in the control values according to the Shewhart Levey–Jennings chart?

Six or more consecutive values on one side of the mean Signup and view all the answers

Which of the following is a critical factor that may alter the results in a spectroscopic measurement?

Stability of radiant energy Signup and view all the answers

What occurs when there are 10 consecutive results on the same side of the target mean?

10x violation Signup and view all the answers

What is a common application of a xenon lamp in analytical techniques?

Fluorescence applications Signup and view all the answers

Which situation indicates a trend in the Levey–Jennings chart?

Six or more values crossing the mean in one direction Signup and view all the answers

What does a 22s violation indicate?

Two consecutive values exceed +/- 2SD Signup and view all the answers

When is a control value considered to be outside of acceptable limits?

When it exceeds +3SD or -3SD Signup and view all the answers

Which of the following is NOT an essential element of a Quality Assurance (QA) program?

Training protocols for staff Signup and view all the answers

What results when an analytical method is not in control related to the +/- 2SD limits?

New controls should be run, and testing needs to be repeated. Signup and view all the answers

What is indicated by a 41s violation?

Four consecutive values are above or below 1SD Signup and view all the answers

What is the main purpose of quality control?

To detect and repair performance issues. Signup and view all the answers

Which characteristic of quality control refers to the closeness of measurement to the true value?

Accuracy Signup and view all the answers

Which quality control indication involves the method's ability to maintain consistency over time?

Reliability Signup and view all the answers

What does specificity in quality control primarily focus on?

Identifying a substance without interference from others. Signup and view all the answers

What does diagnostic sensitivity measure in a quality control context?

The proportion of correctly identified diseases. Signup and view all the answers

Which of the following best describes 'precision' in the context of quality control?

The ability to consistently produce the same results. Signup and view all the answers

What factor is primarily assessed by checking the stability of machines in quality control?

Consistency of performance over time. Signup and view all the answers

The concept of practicability in quality control refers to which of the following?

The method's usability in real-world settings. Signup and view all the answers

Study Notes

Quality Control Overview

Quality Control (QC) employs techniques and procedures to monitor performance characteristics and ensure accurate analytical results.
Primary goal of QC is to detect and correct performance deviations to maintain quality.
Focuses on identifying errors and minimizing mistakes, forming a part of Quality Assurance (QA).

Purposes/Objectives of QC

Assess quality of reagents.
Ensure stability of analytical instruments.
Check for technical errors made by operators.

Core Indications of QC

Accuracy: Reflects how close a measurement is to the true value, typically within a range of ±1.
Specificity: Ability to detect a particular substance without interference from other substances.
Sensitivity: Capability to identify even minute amounts of a specific substance.
Reliability: Consistency in maintaining accuracy over time and across different conditions.
Precision: Reproducibility of results from multiple tests on the same sample.
Practicability: Practical capability to yield reliable results under normal operational conditions.
Diagnostic Sensitivity: The test's ability to accurately identify true positive results among diseased individuals.

Quality Control Charts

Shewhart Levey-Jennings Chart:
- In control: Results within confidence limits.
- Out of control: Identifies outliers, shifts, or trends indicating errors.

Outliers, Shifts, and Trends

Outlier: A control value that lies outside confidence limits, often due to random error.
Shift: A series of 6 consecutive values on one side of the mean indicates systematic error, commonly from instrument calibration issues.
Trend: Six or more values increasing or decreasing across the mean, typically indicating reagent deterioration.

Westgard Multirule Interpretation

12s Violation: Random error warning (1 value outside ±2SD).
13s Violation: Indicates random error (1 value outside ±3SD).
22s Violation: Systematic error warning (2 consecutive values outside ±2SD).
41s Violation: Systematic error indication (4 consecutive values above/below 1SD).
10x Violation: Systematic error (10 consecutive results on one side of target mean).
R4S Violation: Random error indication (widespread result variation within 4SD).

Quality Assurance Program Elements

Involves commitments, facilities, and resources for effective operation.
Essential for tracking specimen acquisition and turnaround times.

Light Sources in Analysis

Low-pressure mercury lamps: Emit sharp line spectra.
Xenon lamps: High-intensity, stable, suitable for fluorescence applications.
Lasers: Provide high intensity for precise analytical instrumentation.

Sample Holder (Cuvette)

Holds samples and must allow transparency in the spectral range of interest; can be round or square.
Common types include alumina silica, quartz/plastic, and borosilicate glass, with the former being most widely used.

Photodetectors

Converts radiant energy into electrical signals; varies in type and sensitivity.
Visual Observation: Basic detection method.
Photovoltaic Cells: Detect visible radiation; low sensitivity.
Vacuum Phototubes: Require outside voltage; enables strong photoelectric response.
Photomultiplier Tubes (PMT): Highly sensitive and fast, ideal for low-light detection.
Photodiodes: Fast and small, offering excellent linearity, though less sensitive than PMTs.

Important Factors Affecting Results

Range and spectral distance.
Stability of radiant energy and temperature.
Proper alignment of optical components, such as the entrance slit and monochromator which isolates specific wavelengths for analysis.

Characteristics of Monochromators

Colored-glass filters: Transparency in broad spectrum, simple and low-cost.
Interference filters: Narrow wavelength transmittance based on constructive interference principles.
Prisms: Separate light into continuous spectra through refraction.
Diffraction gratings: Commonly used for spectral separation; efficiency determined by parallel grooves on a surface.

Key Metrics for Quality Control Components

Nominal Wavelength: Wavelength at peak transmittance.
Spectral Bandwidth: Range of wavelengths above half of peak transmittance.
Bandpass: Defined as width at more than half the maximum transmittance.

Cuvette Requirements

Transparent materials that do not absorb light at the specified wavelengths, avoiding errors from scratched surfaces.

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Description

This quiz focuses on the principles and techniques of quality control, including methods to monitor performance characteristics. It explores the importance of ensuring accurate results and the strategies to detect and correct performance issues.