Core Concepts
In this article, we will discuss what analytical chemistry is, where this branch of chemistry originated, its foundational principles, and some of its uses across various fields.
What is analytical chemistry?
Analytical chemistry is a branch of chemistry focused on using laboratory methods and instruments to analyze substances. At its core, it seeks to answer the questions “What is this substance?” and “How much of this substance exists?” by understanding the composition and structure of matter. We can consider analytical chemistry a combination of applying chemical knowledge and developing new methods and instrumentation to aid in chemical analysis. In discussing this fascinating field, we should first start by exploring how it came to be.
Origins of Analytical Chemistry
Analytical chemistry has a somewhat tumultuous history, due to its relationship with the broader chemistry field. One could claim that it started with philosophers questioning possible connections between the elements, their properties, and how they change. This notable pursuit at the time, called alchemy, actually served as a strong foundation for what we now understand as analytical chemistry.
Starting with simple tools like a balance and weights, grains were used a standard to explain the weights of other things (like gold, which was weighed in terms of mustard seeds). The term “carats,” now a well-known unit for measuring gold’s weight, has its roots in the old practice of using carob seed to weigh things like diamonds!
Over time, information about various substances and emerging scientific methods slowly but surely began to move across the world. This set the stage for our modern understanding of analytical chemistry, because it organized this once-scattered knowledge and inspired curiosity that drove people to seek more of it. If we take a step back and look at the bigger picture, there are two major, complementary approaches to analytical chemistry: quantitative analysis and qualitative analysis.
Quantitative Methods of the Past
Math, statistics, and calculations abound in quantitative methods, which use numerical data to draw conclusions about chemistry. In the early days of chemistry, quantitative methods were prominent as researchers actively sought new insights about the world around them.
Scientists like Lorenzo Amedeo Avogadro (recognized as a father of physical chemistry) and John Dalton investigated the nature of atoms and molecules through gases. In particular, they wanted to determine what molecules are made of and how gas molecules react under different conditions. Avogadro’s findings culminated in Avogadro’s Law, a means of explaining his observations, which would not have been considered an analytical chemistry endeavor during his time. Around the same period, Swedish chemist Jöns Jacob Berzelius became noteworthy for his determination of atomic weights! His work lead to a better understanding of stoichiometric principles that we still use in chemistry today.
Qualitative Methods of the Past
The other family of chemical methods are qualitative ones, which emphasize conceptual theories more so than numerical data. During the 19th century, significant progress was made in these qualitative analytical techniques! In France, organic chemist Jean-Baptiste Dumas specialized in organic analysis. His aim was to determine the proportion of nitrogen present when combined with other elements within organic compounds. To do this, he first took the initial mass of the sample, and then combusted it to ensure that all present nitrogen would form the elemental N2. That combusted N2 was then pushed into a stream of carbon dioxide (CO2) in a strong alkali solution. Doing so causes the nitrogen to precipitate out into a vessel like a graduated cylinder. Here, the mass can be calculated based on the volume it occupies, the temperature, and the pressure.
The search for answers didn’t end there. Another key development came in 1901. Agricultural chemist Joseph Kastle found that, when in contact with biological material, phenolphthalein oxidizes in an alkaline solution. This was essentially the first crude blood test, like those often used in forensic science to determine the presence of blood.
In chemistry and other scientific fields, quantitative and qualitative methods are two halves of the same coin. Researchers in the past and present utilize both to create a comprehensive, well-rounded understanding of the world around us.
Formalization of Analytical Chemistry
It was also during the 19th century that analytical chemistry was finally formally recognized as a distinct discipline within the wider chemistry field. Credit to its formalization is given to Izaak Kolthoff, who notably combined fundamental chemistry theory with practical applications. Considered the father of modern analytical chemistry, Kolthoff founded the analytical chemistry division of the American Chemical Society in 1938. He tirelessly advocated for scientific distinction between analytical chemistry and other disciplines that had previously overlapped with it. Kolthoff utilized his international connections to push forward the idea that analytical chemistry and the process of chemical analysis were unique enough to deserve their own discipline. This served to solidify analytical chemistry as a concrete area of study, as opposed to the unstandardized methodologies that characterized its past.
Methods of Analytical Chemistry
In exploring analytical chemistry, you will find that there are a myriad of techniques that fall under its umbrella. While we can’t discuss every technique, we can point out some key ones that are frequently used in everyday science! Most analytical chemistry techniques fall into two categories: classical analytical methods and instrumentation methods.
Classical Analytical Methods
First, let’s delve into classical analytical methods, which refer to methods used before instrumentation was advanced. These methods are generally quite simple and accessible, meaning they can be employed in many lab settings!
Chemical Tests
A basic classical analytical method is the flame test, a chemical test that takes advantage of the properties of inorganic compounds! Flame tests identify metals present in a compound. In essence, the flame’s heat causes ions to enter an excited (energetic) state, and that energy is subsequently released as light!
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Volumetric Analysis
Volumetric analysis refers to the process of determining the concentration of an analyte within a solution. A common technique, titration, involves two main components: the analyte and the titrant. The titrant is a prepared solution of known concentration and volume. By reacting with the solution, the titrant determines the analyte’s concentration within it.
When thinking of titration, acid-base titration most commonly comes to mind. This technique determines the concentration of an acid and base by fully neutralizing it with an acid or base of known concentration. These kinds of titrations can also be used to determine the purity of chemicals!
Additionally, there are redox titration that utilize redox reactions to assess the concentrations of inorganic analytes. This technique originated in France from chemist François-Antoine-Henri Descroizilles during the late 18th century.
Chromatography
Volumetric analysis is a good starting point. Still, sometimes we want to know more about the chemical makeup of our sample. This is where techniques like chromatography come in. There are many forms of chromatography, including approaches that are tailored toward liquid or gas samples.
Either way, these techniques focus on separating a sample into its individual parts by having it interact with a stationary phase (often a column) and a mobile phase. Mobile phase is a substance that carries the sample through the stationary phase, which stays put. A column can be packed with a solid absorbent material and then, depending on the nature of the sample, may be filled with dry stationary phase and flushed with the mobile phase.
Alternatively, a slurry of the stationary phase is made and poured onto the column. Then, the scientist slowly introduces mobile phase to it. This technique takes advantage of the polarity of the sample’s components. After the sample enters the column, its components pass through the column at different speeds, based on their affinity to the mobile phase. Components with a greater affinity for the mobile phase get retained in the column for longer periods of time, so they pass through later than components with less affinity.
Another chromatography technique is thin-layer chromatography, which can be performed before making of a column to pre-determine which substances will pass through the column first. In thin-layer chromatography, the stationary phase is fused with a material that will have a small amount of sample present, and then soaked in the mobile phase. Through this test, you can see how far the samples components move off of their initial placement.
Gravimetric Analysis
Lastly, gravimetric analysis refers to studying the changes in mass over the course of a reaction, and determining an analyte based on mass. At its core, this type of analysis focuses on precipitating the analyte from an aqueous solution. The precipitate is separated and then weighed. If the chemical formula for the precipitate is known, then the mass of the original analyte can be determined via stoichiometry! This methodology, which can be traced all the way back to 1540 in a publication of Vannoccio Biringuccio studying metal ores, works not only with precipitate but also through volatilization.
A common theme among classical analytical techniques is that they tend to observe the change in a compound over a reaction. However, their key drawback is their lack of specificity. Classical analytical methods do not give us the freedom to target a specific analyte within the compound, which limits how much information we can glean. Fortunately, we have instrumentation to help decrease this informational gap!
Instrumentation Analytics
In analytical chemistry, instrumentation serves to measure physical and chemical properties of compounds. In doing so, they provide a wide scope of information about compounds that can be further investigated if necessary. Unfortunately, these methods are more expensive, so not quite as accessible to all labs as classical analytical methods typically are. In some cases, instrumentation methods can address the same principles as classical analytical ones. However, they can also address a wider breadth of the discipline.
Spectroscopic Techniques
A common example of analytical chemistry instrumentation lies in the utilization of spectroscopy techniques — and there are many of them! Spectroscopic methods measure the exchange of energy between the sample and the electromagnetic spectrum. This includes instruments like UV-Vis spectrophotometers, which introduce light to the sample and then measure the absorbance of that light. Through this method, UV-Vis can give information on the concentration of a sample!
Along the absorption spectra theme, X-ray diffraction observes X-ray beams’ interactions with electrons. This leads researchers to identify a sample’s composition or crystalline structure! Fourier-transform infrared spectroscopy (FTIR) can determine the IR absorption of a sample in the solid, liquid, or gas phase. An FTIR assay can provide information specifically on the molecular structure of chemical compounds. Because of this, it’s commonplace in organic chemistry as a strategy to determine functional groups present.
Chromatographic Techniques
Recall from earlier that chromatography has a special role in analytical chemistry because it can separate a compound’s components. There are instruments that combine spectroscopy and chromatography techniques together, like the gas chromotography mass spectrometer (GCMS). The GCMS instrument identifies and measures the concentrations of compounds. It achieves this by heating liquid compounds and pushing them through the stationary phase. This separates the compound into its components based on their chemical properties. Then, the components get ionized and their mass is measured!
On a more focused look at chromatography, high-performance liquid chromatography (HPLC) can also be combined with spectroscopic methods. HPLC utilizes high-pressure pumps to deliver the mobile phase, which carries the sample, into the stationary phase (a column’s interior). Then, the mobile phase and sample flow out of the column and pass through a detector, which is sometimes a UV detector. The output describes the respective time each component came off the column and its intensity, which are key pieces of information that the scientist can use to analyze the sample’s components and their affinities.
Magnetic Techniques
The final analytical chemistry instrumentation method that we’ll tour is nuclear magnetic resonance. Abbreviated as NMR, this method utilizes a large magnet and magnetic fields to examine the spin properties of atomic nuclei. It also uses electromagnetic radiation to promote transition between nuclear energy levels. Typically, hydrogen or carbon isotopes are used, but others (like fluoride or silicone) can be employed instead. NMR is valuable for determining the structures of smaller molecules, a tricky science in and of itself.
Applications of Analytical Chemistry
By this point, we’ve covered a lot of ground. We described how analytical chemistry came to be and how it emerged from older chemistry disciplines. Analytical chemistry also plays a significant role in fields outside of chemistry, so let’s briefly discuss its applications.
A simple example lies in the field of pharmaceuticals. Tools like the UV-Vis spectrophotometer can determine the purity and potency of drugs before they go to market. HPLC is a crucial technique when checking for any cross-contamination during the drug production process. Electrochemical analyzers assess for redox reactions so scientists can simulate how drugs will interact with the body before production even begins! This gives researchers a solid starting point for designing and developing new medicines.
In the environmental sciences, analytical tools like gas chromatography equipped with photoionization detectors can monitor ambient air. Metal oxide-based sensors are one way of sampling air pollutants, allowing for a clearer picture of the mechanisms behind how pollutants interact in the atmosphere. Far from the lab, mass spectrometers can even help researchers study the ocean to track biological productivity markers for information about energy flow!
Moving beyond the sciences, spectroscopic techniques, specifically, play a role in fields like art, history, and archeology. This is because spectroscopic tools like IR spectroscopy allow for a non-destructive way of determining the makeup of a sample. This includes the chemical composition of paint pigments, which can help a historian date and locate the origin of a piece. Additionally, FTIR has the capacity to reveal the composition of multilayer structures! This way, we can study an artwork, even if it has been painted or sculpted over, without destroying its components.
Conclusion
All in all, analytical chemistry is an expansive branch of chemistry that contains hundreds of analytical processes. From gravimetry to spectrometry, it helps us better understand compounds. Since its formal recognition, these techniques have been used in various capacities. From fields like pharmaceuticals, ensuring that medicines are safe, to fields like art, analytical chemistry is making an impact! As this science continues to improve at an rapid pace, there is seems to be no limit to its reach.