Podcast
Questions and Answers
What does the term 'precision' refer to in measurements?
What does the term 'precision' refer to in measurements?
- The ability to detect small differences.
- The mutual agreement of replicate measurements. (correct)
- The closeness of measurements to the true value.
- The measure of random errors in a dataset.
Which of the following describes 'bias' in an analytical method?
Which of the following describes 'bias' in an analytical method?
- It refers to the systematic error of the method. (correct)
- It reflects the uncertainty in measurements.
- It is the measure of random errors.
- It indicates the capability of an instrument to detect small amounts.
Sensitivity in measurement techniques is concerned with which of the following?
Sensitivity in measurement techniques is concerned with which of the following?
- The ability to avoid interference during measurement.
- The range of amounts that can be measured.
- The deviation of measurements from the true value.
- The smallest difference that can be detected. (correct)
What is meant by 'dynamic range' in the context of analytical measurements?
What is meant by 'dynamic range' in the context of analytical measurements?
What do figures of merit help analysts determine?
What do figures of merit help analysts determine?
Which factor could cause a shift in the measured mean value away from the true value?
Which factor could cause a shift in the measured mean value away from the true value?
Which of the following factors contributes to non-random errors affecting accuracy?
Which of the following factors contributes to non-random errors affecting accuracy?
What is the function of using guaranteed standards in an analytical method?
What is the function of using guaranteed standards in an analytical method?
What type of analysis indicates the presence of an analyte by measuring a property?
What type of analysis indicates the presence of an analyte by measuring a property?
Which of the following methods is primarily involved in measuring the magnitude of a property to determine concentration?
Which of the following methods is primarily involved in measuring the magnitude of a property to determine concentration?
Which of the following is a method of radiation absorption?
Which of the following is a method of radiation absorption?
Which instrumental method uses the mass to charge ratio for analysis?
Which instrumental method uses the mass to charge ratio for analysis?
What is the primary purpose of an instrument in the context of analytical methods?
What is the primary purpose of an instrument in the context of analytical methods?
Which method is categorized under radiation scattering?
Which method is categorized under radiation scattering?
What type of energy is often used to stimulate analytes for obtaining information?
What type of energy is often used to stimulate analytes for obtaining information?
Which analysis method involves the use of heat as a response in the analysis concept?
Which analysis method involves the use of heat as a response in the analysis concept?
What role does a transducer play in an analytical instrument?
What role does a transducer play in an analytical instrument?
Which of the following constitutes an electrical domain?
Which of the following constitutes an electrical domain?
In the process of domain conversion, what is typically the first step in analysis?
In the process of domain conversion, what is typically the first step in analysis?
What does a photocell primarily measure in spectrophotometry?
What does a photocell primarily measure in spectrophotometry?
What is chemical noise primarily characterized by?
What is chemical noise primarily characterized by?
What is the primary function of a sensor in an analytical instrument?
What is the primary function of a sensor in an analytical instrument?
Which type of noise is caused by thermal agitation of electrons?
Which type of noise is caused by thermal agitation of electrons?
Which of the following best describes an instrument in the context of analytical measurement?
Which of the following best describes an instrument in the context of analytical measurement?
In the context of the measurement process, which of the following options is NOT a data domain?
In the context of the measurement process, which of the following options is NOT a data domain?
Which phenomenon is described as having a magnitude inversely proportional to frequency?
Which phenomenon is described as having a magnitude inversely proportional to frequency?
What analytical response is observed in a spectrophotometer when using monochromatic light energy?
What analytical response is observed in a spectrophotometer when using monochromatic light energy?
What is a common method to reduce environmental noise in instrumentation?
What is a common method to reduce environmental noise in instrumentation?
What type of noise occurs when electrons cross a junction?
What type of noise occurs when electrons cross a junction?
What is the primary function of a difference amplifier in noise reduction?
What is the primary function of a difference amplifier in noise reduction?
In the context of modulation for noise reduction, what is the first step in the process?
In the context of modulation for noise reduction, what is the first step in the process?
What type of noise is considered to be emitted from surrounding electromagnetic radiation?
What type of noise is considered to be emitted from surrounding electromagnetic radiation?
What does the calibration sensitivity of the instrument measure?
What does the calibration sensitivity of the instrument measure?
What is the coefficient of variation at an analyte concentration of 5 ppm?
What is the coefficient of variation at an analyte concentration of 5 ppm?
How is the detection limit defined in relation to the standard deviation?
How is the detection limit defined in relation to the standard deviation?
At which concentration is the analytical sensitivity evaluated for the unknown sample?
At which concentration is the analytical sensitivity evaluated for the unknown sample?
What does a dynamic range of the technique refer to?
What does a dynamic range of the technique refer to?
How is the detection limit calculated from the standard deviation?
How is the detection limit calculated from the standard deviation?
What is the expected dynamic range to be considered worthwhile?
What is the expected dynamic range to be considered worthwhile?
What is the analytical concentration of the unknown sample determined from the data?
What is the analytical concentration of the unknown sample determined from the data?
What primarily determines the measurability of the signal level in analytical measurements?
What primarily determines the measurability of the signal level in analytical measurements?
What is referred to as the background or baseline in analytical measurements?
What is referred to as the background or baseline in analytical measurements?
Which factor leads to the presence of noise in analytical instruments?
Which factor leads to the presence of noise in analytical instruments?
What happens to the signal-to-noise ratio when noise increases while signal remains constant?
What happens to the signal-to-noise ratio when noise increases while signal remains constant?
What does a large signal-to-noise ratio indicate regarding the quality of the analytical measurement?
What does a large signal-to-noise ratio indicate regarding the quality of the analytical measurement?
Which statement best describes the concept of drift in analytical measurements?
Which statement best describes the concept of drift in analytical measurements?
What is the primary goal when analyzing signal-to-noise ratio in analytical measurements?
What is the primary goal when analyzing signal-to-noise ratio in analytical measurements?
What can cause the linearity limit in an analytical instrument?
What can cause the linearity limit in an analytical instrument?
Flashcards
Qualitative analysis
Qualitative analysis
A type of analysis that focuses on identifying the presence of a substance without determining its amount.
Quantitative analysis
Quantitative analysis
A type of analysis that determines the amount or concentration of a substance.
Instrumental methods
Instrumental methods
Analytical methods that utilize instruments to measure physical or chemical properties of a sample.
Spectroscopy
Spectroscopy
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Scattering
Scattering
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Refractometry
Refractometry
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Diffraction
Diffraction
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Potentiometry
Potentiometry
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Data Domain Conversion
Data Domain Conversion
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Detector
Detector
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Transducer
Transducer
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Sensor (chemical)
Sensor (chemical)
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Data Processor
Data Processor
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Spectrophotometer
Spectrophotometer
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Stimulus
Stimulus
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Analytical Response
Analytical Response
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Precision
Precision
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Accuracy
Accuracy
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Bias
Bias
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Sensitivity
Sensitivity
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Dynamic range
Dynamic range
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Selectivity
Selectivity
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Figure of Merit
Figure of Merit
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Performance Characteristics
Performance Characteristics
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Calibration Sensitivity
Calibration Sensitivity
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Analytical Sensitivity
Analytical Sensitivity
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Coefficient of Variation (CV)
Coefficient of Variation (CV)
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Detection Limit (LOD)
Detection Limit (LOD)
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Quantitation Limit (LOQ)
Quantitation Limit (LOQ)
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Linearity Limit (LOL)
Linearity Limit (LOL)
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Concentration of Unknown
Concentration of Unknown
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Linearity Limit
Linearity Limit
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Analytical Signal
Analytical Signal
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Drift
Drift
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Noise
Noise
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Signal-to-Noise Ratio (S/N)
Signal-to-Noise Ratio (S/N)
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Thermal Noise (Johnson Noise)
Thermal Noise (Johnson Noise)
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Shot Noise (Quantum Noise)
Shot Noise (Quantum Noise)
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Flicker Noise (1/f Noise)
Flicker Noise (1/f Noise)
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Environmental Noise
Environmental Noise
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Chemical Noise
Chemical Noise
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Grounding and Shielding
Grounding and Shielding
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Difference Amplifier
Difference Amplifier
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Analog Filtering
Analog Filtering
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Study Notes
Introduction to Instrumental Methods
- Instrumental methods use instruments to identify and quantify analytes.
- Qualitative analysis determines the presence of an analyte.
- Quantitative analysis determines the concentration of an analyte.
- Classical methods involve separating components and treating them with reagents to identify them.
- Modern instrumental methods measure physical properties of analytes.
Classification of Analytical Methods
- Qualitative Analysis identifies the analyte by measuring a property which indicates its presence.
- Methods involve separation of components and treating them with reagents leading to product identification by color, solubility, odor, optical activity, boiling point (BP), or melting point (MP).
- Quantitative Analysis determines the amount (concentration) of the analyte by measuring a property proportional to its concentration.
- Involve measuring properties such as mass and volume to determine a concentration.
Instrumental Methods
- Instrumental methods use instruments to measure physical properties for quantitative analysis.
- They started with electrical and absorption measurements (early 20th century).
- Properties of analytes used for analysis include:
- Light absorption or emission
- Fluorescence
- pH
- Electric potential and current
- Mass to charge ratio
- New separation techniques replaced classical methods.
Types of Instrumental Methods
- Various methods for measuring radiation, electrical potential, charge, and mass based analysis methods.
The Analysis Concept
- Analytical process involves probing the sample with a probe (electrons, photons, atoms, molecules, ions, heat) that results in an observable response of the sample (e.g. heat, ions, molecules, atoms, photons, electrons or photons, heat).
- Analyzing a sample involves determining what is there, how much there is, and how it behaves.
Instrument
- Instruments convert chemical or physical characteristics of a sample into information that humans can manipulate.
- Stimuli such as EM, electrical or nuclear energy are used to obtain information from the analyte.
Data Domains
- Measurements are aided by devices that convert information from one form to another (e.g., non-electrical to electrical).
- Data encoding can occur in non-electrical (physical, chemical properties like color, length) and electrical domains (current, voltage, charge, frequency, pulse width, phase, count, and serial).
Examples of Data Domains
- Non-electrical: physical properties (light intensity, color), chemical properties (pH), scale position (length), number (objects)
- Electrical: current, voltage, charge, frequency, pulse width, phase, count, serial, parallel
Domain Conversion
- Analysts measure physical/chemical properties of a system.
- The instrument produces an electrical signal representing that datum.
- Instruments use transducers to convert signals into different forms.
- The analysis of an instrument's behavior is characterized as a series of data domain converters.
Data Domains - Way of Encoding Analytical Responses
- Inter-domain conversions transform information from one domain to another (e.g., light energy to an electrical signal).
- Detector: detects changes in the environment.
- Transducer: converts non-electrical data to electrical data or vice versa.
- Sensor: converts chemical data into electrical data. Glass electrodes continuously monitor and reversibly measure specific chemical species.
Instrumental Measurement Example: Spectrophotometry
- Instrument: Spectrophotometer
- Stimulus: Monochromatic light energy
- Analytical response: Light absorption
- Transducer: Photocell
- Data: Electrical current
- Data processor: Current meter
How Do We Choose an Analytical Method?
- The choice of method is based on the performance characteristics: figures of merit.
- Assessing the method involves:
- Reproducibility (Precision).
- Closeness to the true value (Accuracy/bias).
- Measurement of the smallest difference (Sensitivity).
- The range of measurable amounts (Dynamic range).
- Interference from other components (Selectivity).
Performance Characteristics
- Figures of merit are used to identify suitable methods. These include:
- Precision
- Bias
- Sensitivity
- Quantitation limit
- Dynamic range
- Accuracy
- Detection limit
- Linearity limit
- Selectivity
Figure of Merit
- A numerical value derived from experimental data used for evaluating and comparing analytical instruments or methods. It helps determine the technique's applicability for particular analysis issues and is expressed in numerical terms.
- Performance characteristics are measured in terms of figures of merit.
Precision
- Mutual agreement of replicate measurements.
- Standard deviation and variance are common precision metrics.
- Includes RSD and CV (relative standard deviation and coefficient of variation)
Bias
- Bias measures the systematic/determinate error of an analytical method.
- Bias = μ − Xt , where μ is the mean/average value expected for the analyte and Xt is the experimentally observed value or true concentration.
Accuracy
- Accuracy measures the closeness of measured values to the true value or the error of the mean.
- It arises from determinate or non-random errors (e.g., instrument errors, analyst errors, method errors).
Sensitivity
- A measure of an instrument's ability to distinguish small differences (e.g., differences in analyte concentration).
- It depends on the slope of the calibration curve. A larger slope represents more sensitive measurements.
- Precision plays a key role in sensitivity.
Calibration Sensitivity
- Calculated using the slope (m) of the calibration curve.
- Slope is independent of concentration.
Analytical Sensitivity
- Accounts for precision.
- Independent of measurement units but concentration-dependent.
- Incorporates slope (m) and standard deviation (s) as analytical sensitivity factor (y = m/s).
Detection Limit
- The smallest detectable analyte amount.
- Dependent on signal-to-noise ratio.
- Analysis signal needs to be greater than the blank signal (usually 3 times the standard deviation of the blank).
Dynamic Range
- The concentration range over which the technique is useful (from Quantitation Limit to Linearity Limit).
- Ideally a two orders or more magnitude range is useful.
Quantitation Limit
- The analyte amount that can be reliably quantified.
- Ten times the standard deviation from the blank.
Linearity Limit
- The upper concentration limit at which the response of the detector is linear.
Signals and Noise
- Analytical measurements consist of a signal and noise component.
- Signal is the desired information about the analyte.
- Noise (N)- is the extraneous information that degrades analysis performance.
Signal
- Every analytical procedure relies on a signal taken from a detector.
- Output from detector has a baseline (non-zero output).
- Background or baseline varies over time, this variation is called drift.
- Signal is calculated by subtracting expected baseline from output amplitude
Noise
- Variations in an output signal are collectively termed noise.
- Unwanted time-dependent changes.
- Noise is measured in the same units as the signal. (e.g., current, voltage, or power)
Signal-to-Noise Ratio (S/N)
- The importance of ratio. It influences measurability.
- A large S/N is desired (more signal and less noise)
- The ratio of the mean signal and standard deviation of noise.
Sources of Instrumental Noise
- Chemical noise: Uncontrollable variables affecting the chemistry (temperature, pressure, humidity).
- Instrument noise:
- Thermal (Johnson) noise: thermal agitation of electrons.
- Shot Noise: random electron movement across junctions
Hardware Devices for Noise Reduction
- Grounding and shielding: surrounds circuit with a conductive material, attenuating environmental noise.
- Difference amplifiers: subtract out the noise.
- Analog filtering: uses low-pass filters to remove high-frequency interference, reducing noise.
- Modulation: converts low frequency signals into higher frequencies for filtering before demodulation to the original frequency for amplification.
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