Analytical Chemistry
What is Analytical Chemistry?
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Analytical Chemistry is the science of measurements and characterization.
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It is the study of the separation, identification, and quantification of chemical components in a sample.
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It also focuses on the improvements of experimental design and the creation of new measurement tools to provide better chemical information.
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Qualitative analysis determines which substances are in a sample.
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Quantitative analysis determines how much of each substance is present.
The Role of Analytical Chemistry
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Analytical chemistry plays a vital role in various fields, including medicine, industry, government, and academia.
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Examples:3
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Diagnose and treat illnesses: Determine the concentration of oxygen and carbon dioxide in a blood sample.
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Determine the effectiveness of emission-control devices: Measure quantities of hydrocarbons, nitrogen oxides, and carbon monoxide in automobile exhaust gases.
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Diagnose parathyroid disease: Measure ionized calcium in blood serum.
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Determine nutritional value in food: Determine nitrogen content in food to establish protein content.
Analytical Procedure
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An analytical procedure typically involves several steps, but not all steps are required for every analysis.4
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Factors to consider for a successful analysis:
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Target species: What is being measured?
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Detection method: How can the target species be detected? Can it be detected in the presence of other substances?
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Concentration: What concentration needs to be measured? Is the chosen technique appropriate for this concentration?
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Accuracy: What level of accuracy is required?
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Purpose of results: How will the results be used?
Steps in a Typical Quantitative Analysis:
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Choosing a Method: This decision depends on factors like the desired level of accuracy, the number of samples, and the complexity of the sample.
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Acquiring the Sample: The sample must accurately represent the larger material being analyzed. Biological samples present unique challenges.
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Processing the Sample: This may involve grinding, mixing, storing, and preparing replicate samples (portions analyzed simultaneously).
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Dissolving the Samples: This step ensures the sample is in a suitable form for analysis. It may involve acid-base additions, heating, or other chemical processes.
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Eliminating Interferences: Interferences are substances that can affect the accuracy of the analysis. Techniques are used to separate the analyte (substance of interest) from interfering components.
Important Terms
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Analyte: The specific substance in a sample that is being analyzed.
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Matrix: Everything else in the sample besides the analyte. The matrix can influence the analysis, so a selective method is needed.
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Selective method: A technique that responds only to the analyte of interest.
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Blank: An analysis of a sample without the analyte, used for calibration and checking the method.
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Reference materials: Samples with accurately known concentrations used to calibrate instruments and ensure accuracy.
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Replicate samples: Multiple portions of the same sample analyzed to assess the repeatability and precision of the method.
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Detection limit: The smallest concentration of a substance that can be reliably distinguished from a blank sample. A low detection limit indicates a more sensitive method.
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Accuracy: How close a measurement is to the true value.
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Precision: How close repeated measurements are to each other, indicating the reproducibility of the results.
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Systematic errors: Affect all measurements in the same way, often due to instrument calibration issues, impacting accuracy.
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Random errors: Cause variations in measurements even under identical conditions, affecting precision.
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Interference: A substance that affects the measurement of the analyte, leading to inaccurate results.
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Specific techniques: Techniques that only work for one specific analyte.
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Selective techniques: Techniques that work for a small number of analytes.
Define the Problem & Analyte: Clearly state the objective of the analysis. What specific substance, the analyte, needs to be identified or quantified?13
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Choose the Analytical Method: Select a suitable method based on factors like the required accuracy, analyte concentration, potential interferences, and available resources.13
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Acquire the Sample: Obtain a representative sample that accurately reflects the composition of the bulk material being studied. This step is crucial, especially for heterogeneous materials and biological samples.4
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Process the Sample: Prepare the sample for analysis. This might involve grinding, mixing, drying, or creating replicate samples to ensure homogeneity and facilitate analysis.5
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Dissolve the Sample: Convert the sample into a suitable form for the chosen analytical method, typically a solution. This may involve acid digestion, heating, or other chemical treatments.6
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Eliminate Interferences: Remove any substances from the sample that could interfere with the accurate measurement of the analyte. This often involves separation techniques or chemical reactions selective for the analyte.7
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Make Measurements: Employ the selected analytical method to measure the desired property of the analyte, such as its concentration or presence. This may involve techniques like spectroscopy, chromatography, or electrochemical methods.2
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Estimate Significance of Results: Analyze the collected data, considering factors like accuracy, precision, and detection limits, to draw meaningful conclusions about the analyte and address the initial problem