There are countless fields where analytical chemistry finds applications, ranging from health sciences to industrial research and, last but not least, agriculture, where it plays a fundamental role not only with the analysis of crops, water, and soils but also with guiding new farming practices.
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Analytical chemistry enables the separation and identification of the components present in a given sample. For decades it has been strongly embedded in agriculture, both in terms of research and production processes, and over the years it has also contributed to shaping practical agricultural procedures.
This branch of chemistry provides the essential tools for the analysis of agricultural resources, such as water, soil, and crops, with new technologies being developed and adapted to accommodate farmers’ and consumers’ needs, namely the increasing demand for food of a growing population.
As an example, having information on soil composition is fundamental for guiding the fertilization process, taking also into account the necessity of protecting the environment from undesirable effects of agricultural practices. In this regard, efforts are made towards developing more reliable and efficient methods of analysis.
Analysis of pesticides
Pesticides are chemicals used to eliminate pests, and their use is compulsory to maximize agricultural productivity and face the increasing food demand. They enable the control of both the quantity and the quality of crops, but despite their helpful role in agriculture, they are extremely toxic for the environment and pose a risk for human health.
Pesticides are particularly dangerous in fruits and vegetables since people are exposed to them and the chemicals can therefore accumulate in the body. Their analysis is particularly challenging, especially concerning the discrimination in complex matrices and the usually low concentrations, making them difficult to detect.
The usual techniques for the analysis of pesticides include gas chromatography (GC) and high-performance liquid chromatography (HPLC), often coupled with mass spectrometry (MS) as a detection method. Depending on the type of pesticide and matrix, different extraction techniques can be used.
As an example, the analysis of pesticide residues in tuber crops can be done using pressurized liquid extraction (PLE) and GC-MS. PLE is more efficient than other preparation methods such as supercritical fluid extraction (SFE) and soxhlet extraction.
PLE GC-MS was used for the analysis of 150 pesticide residues in three commonly cultivated tuber crops. The method complied with the regulatory requirements and performed better than the conventional methods, with the identification and quantification of the chemicals at concentrations ≤10 ng/g.
Determination of toxic metals and nutrients in soils
One of the main issues in agriculture is toxic metals contamination. Metals can bind to sulfur, oxygen, and nitrogen present in the functional groups of many proteins and other biological molecules, altering their chemistry and interfering with their normal function.
Exposure to high levels of arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg) – to name a few – can cause severe health problems. On the other hand, iron (Fe), boron (B), and copper (Cu) are micronutrients essential for plants growth.
The most common techniques for the analysis of such metals are inductively coupled plasma with mass spectrometry (ICP-MS), inductively coupled plasma optical emission spectroscopy (ICP-OES), atomic absorption spectrometry (AAS).
An interesting atomic spectroscopy technique that is developing fast is laser-induced breakdown spectroscopy (LIBS). A high-power laser focuses on a small area of the sample, producing plasma by heating and ionizing matter on the surface layer. Emission spectra are then measured with a spectrometer.
LIBS is starting to find applications in agriculture with the analysis of soils for the detection of heavy metals. The results are comparable with those from the other more established techniques (i.e. AAS), and limits of detection (LOD) of 1 ppm can be achieved. Further work is in progress for the development of commercially viable devices to use LIBS for the analysis of real crops.
Spectroscopic approaches for the analysis of fungal contaminations in crops
Infrared (IR) spectroscopy is a rapid, non-destructive technique, and requires minimal sample preparation. It is among the most commonly used techniques in analytical chemistry and it is strongly involved in agriculture for the quality assessment of fruits and vegetables.
Healthy apples can be distinguished from those with moldy cores without damaging the product, and there is a lot of research in progress aimed at developing methods for the in-line analysis of a wide range of goods.
An interesting potential application of IR spectroscopy is in the determination of fungal contamination in crops, which could be indirectly assessed by the analysis of the medium infrared (MIR) spectrum.
In particular, mycotoxins (produced by filamentous fungi) are natural contaminants present in numerous agricultural products. Some of them (e.g. aflatoxins, ochratoxins, fumonisins) are of special interest because of their frequent occurrence and harmful effects on health.
Mycotoxins cause alterations in the carbohydrate and protein content of crops. Such alterations can be investigated by examining differences in the spectral bands in the regions 900–1200 cm–1 and 1200–1750 cm–1. However, these observations need to be correlated to reference measurements of known mycotoxin concentrations.
Analytical chemistry can offer a wide range of techniques suitable for different substrates and serving various purposes. Its role in agriculture is crucial, and as practices and needs evolve, analytical techniques and methods continue to develop accordingly, to adapt to the changing times.
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