Understanding Quantitative Analysis in Chemistry

Scientist looking at liquid in beaker.
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Quantitative analysis refers to the determination of how much of a given component is present in a sample. The quantity may be expressed in terms of mass, concentration, or relative abundance of one or all components of a sample. Here are a few sample results of quantitative analysis:

  • Ore contains 42.88% silver by mass.
  • The chemical reaction yielded 3.22 moles of product.
  • The solution is 0.102 M NaCl.

Quantitative Versus Qualitative

Qualitative analysis tells 'what' is in a sample, while quantitative analysis is used to tell 'how much' is in a sample. The two types of analysis are often used together and are considered examples of analytical chemistry.

Methods Used in Quantitative Analysis

Several methods are used to quantify a sample. These may be broadly classified as either physical or chemical methods.

Physical methods measure a physical property, such as adsorption of light, density, and magnetic susceptibility. Examples of physical methods include:

  • Fourier Transform Infrared Spectroscopy (FTIR)
  • Atomic Emission Spectroscopy (AES)
  • Energy Dispersive X-ray Spectroscopy (EDS)
  • trace element analysis
  • x-ray fluorescence spectroscopy
  • ICP-AES
  • ICP-MS

Chemical methods involve chemical reactions, such as oxidation, precipitation, or neutralization to form a new chemical compound. Examples of chemical methods include:

  • Titration (volumetric analysis)
  • Gravimetric analysis
  • Various wet chemistry tests
  • Combustion analysis
  • Inert gas fusion

Often physical and chemical methods overlap. In addition, mathematics is used in quantitative analysis. Statistics is particularly useful for analyzing data.

The primary tool for quantitative analysis is the analytical balance or scale, which is used to measure mass precisely. Glassware, such as the volumetric flask, is also important. For analytical chemistry, a typical balance measures mass to 0.1 of a milligram. A sensitivity of about a thousand times is needed for microanalytical work.

Why Quantitative Analysis Is Important

It's important to know the quantity of all or part of a sample for several reasons.

If you're performing a chemical reaction, quantitative analysis helps you predict how much product to expect and to determine your actual yield.

Some reactions take place when the concentration of one component reaches a critical level. For example, an analysis of a radioactive material might indicate there is enough of a key component for the specimen to undergo spontaneous fission!

Quantitative analysis is crucial to the formulation and testing of food and drugs, as it is used to measure nutrient levels and provide an accurate accounting of dosage.

It is also critical in determining the level of contaminants or the impurity of a sample. While qualitative analysis might be able to determine the presence of lead in the paint on a toy, for example, it is quantitative analysis that detects how much concentration exists.

Medical tests rely on quantitative analysis for information about a patient's health. For example, quantitative analysis could determine blood cholesterol levels or the ratio of lipoproteins in plasma or the amount of protein excreted in urine. Here again, quantitative analysis complements qualitative analysis, since the latter identifies the nature of a chemical while the former tells you how much there is.

Quantitative tests of a mineral may be used to determine whether it's practical to mine it for a specific element or compound.

Quantitative tests are used to verify that products meet manufacturer or regulatory specifications.