How scientists use advanced analytical methods to reveal the hidden chemical composition of matter
Every day, billions of liters of water flow through our pipelines. But how can we be sure that this water is not contaminated with invisible, dangerous heavy metals like lead or mercury? The answer lies in instrumental elemental analysis – a discipline that enables the precise identification and measurement of even the tiniest traces of elements in various materials 1 .
These analytical methods are now indispensable tools in nearly all scientific and technological fields. From environmental monitoring to the development of new materials with tailored properties, instrumental analytical methods provide crucial data that ensures our safety and enables technological progress 3 .
This article delves into the fascinating world of elemental analysis and deciphers how scientists make the invisible chemical composition of matter visible.
Instrumental elemental analysis encompasses a range of techniques used for the identification and quantification of chemical elements in a sample. Unlike classical "wet chemical" methods, these techniques use sophisticated instruments to measure physical phenomena associated with the presence of specific elements 1 3 .
The fundamental principle of all these methods is based on the fact that each element interacts with energy in a characteristic way. Whether it involves the absorption of light, emission of radiation, or formation of ions – these characteristic interactions generate signals that serve as "fingerprints" of the elements, enabling their detection and quantification .
The smallest amount of an element that can be reliably detected with a specific method. Modern techniques like ICP-MS achieve detection limits in the parts per trillion (ppt) range – comparable to a sugar cube in an Olympic swimming pool 6 .
Qualitative analysis answers the question "Which elements are present?", while quantitative analysis determines "How much" of each element is contained in the sample 3 .
Most analytical methods require careful sample preparation, often including digestion, where solid samples are converted into soluble forms to enable accurate analysis 4 .
AAS is an established method for determining metal concentrations in samples. In this technique, the sample is vaporized, and the atoms absorb light at specific, element-specific wavelengths 1 .
The amount of absorbed light is directly proportional to the concentration of the element in the sample, described by the Lambert-Beer's Law: A = ε × c × l (where A is absorption, ε is the molar absorption coefficient, c is concentration, and l is path length) 3 .
AAS finds application particularly for defined questions based on specific standards. For the determination of alkali elements like sodium and potassium or mercury in ultratraces, it is considered an unrivaled method 4 .
ICP-OES uses an extremely hot plasma (up to 10,000 K) to excite the atoms in the sample. When these excited atoms return to their ground state, they emit light with characteristic wavelengths specific to each element 4 .
Thanks to its flexibility and very large working range (from µg/L to g/L), ICP-OES has developed into a "workhorse" in instrumental elemental analysis. It enables the simultaneous determination of many elements from acidified aqueous solutions and after digestions of solid samples 4 .
ICP-MS combines an ionizing plasma with a mass spectrometer and represents the most sensitive available technique for elemental analysis. The plasma serves as an ion source here, while the mass spectrometer separates and detects the ions according to their mass-to-charge ratio 1 4 .
This technique is characterized by extremely low detection limits for ultratrace analysis. Due to the very short measurement times, it also enables rapid sequential overview analysis of over 80 elements simultaneously 4 .
X-ray fluorescence analysis is a non-destructive method in which a sample is irradiated with X-rays. This excites elements in the sample, which then emit characteristic secondary X-ray radiation (fluorescence) 1 .
The intensity of this radiation is proportional to the element concentration, described by the basic equation: I = k · C · e^(-μx) (where I is intensity, k is a constant, C is concentration, and μ is the absorption coefficient) 1 .
| Method | Principle | Detection Limit | Main Application Area |
|---|---|---|---|
| AAS | Absorption of light by atoms | µg/L range | Determination of alkali metals, mercury in ultratraces 4 |
| ICP-OES | Emission of light from excited atoms | µg/L range | Simultaneous multielement analysis, wide concentration range 4 |
| ICP-MS | Separation and detection of ions by mass/charge | ng/L to pg/L range | Ultratrace analysis, multielement analysis 4 |
| XRF | Emission of characteristic X-ray radiation | mg/kg range | Non-destructive analysis of solids, materials science 1 |
The monitoring of heavy metals in drinking water is a critical application of elemental analysis with direct impacts on public health. Lead, mercury, arsenic, and cadmium are among the particularly dangerous metals that can exert toxic effects even in minimal concentrations 1 .
In this experiment, the concentration of several heavy metals in a drinking water sample is to be determined simultaneously using the ICP-MS method. The goal is to demonstrate the performance capability of modern elemental analysis for environmental monitoring and to prove that the measured values are below the legally established limit values.
The water sample is filled into specially pretreated polyethylene bottles and immediately acidified with high-purity nitric acid to a pH value of <2 to prevent adsorption of metals to container walls 6 .
An aliquot of 50 mL of the sample is treated with 0.5 mL Suprapur® nitric acid and heated to 50°C to oxidize dissolved organic substances 2 .
The ICP-MS instrument is calibrated with a series of multielement standard solutions containing Certipur® reference materials and present in the same matrix as the samples (acidified water) 2 .
The ICP-MS analysis of the drinking water sample provides the results shown in Table 2. For comparison, the legal limit values of the Drinking Water Ordinance are given.
| Element | Measured Concentration (μg/L) | Limit Value (μg/L) | Compliance |
|---|---|---|---|
| Lead (Pb) | 0.8 | 10 | Yes |
| Mercury (Hg) | 0.02 | 1 | Yes |
| Arsenic (As) | 1.5 | 10 | Yes |
| Cadmium (Cd) | 0.15 | 5 | Yes |
| Copper (Cu) | 45.0 | 2000 | Yes |
The data show that all measured heavy metal concentrations are significantly below the legal limit values. Particularly noteworthy is the sensitivity of the method: Even mercury in a concentration of 0.02 μg/L (20 parts per trillion) can still be reliably detected 4 6 .
The scientific significance of these analyses lies not only in verifying compliance with limit values but also in the ability to detect even the slightest changes in environmental pollution at an early stage. This enables preventive measures long before health-hazardous concentrations are reached.
The reliability of elemental analytical measurements depends crucially on the quality of the reagents and materials used. The following table lists essential components for conducting elemental analyses:
| Reagent/Material | Specification | Function |
|---|---|---|
| Suprapur® Acids | High purity, with guaranteed trace element contents | Sample digestion and preservation without contamination 2 |
| Certipur® Standards | ISO 17025 accredited, ISO Guide 34 | Calibration and qualification of analytical instruments 2 |
| Ultrapure Water | Resistance >18 MΩ·cm | Preparation of dilutions and reagent solutions |
| Sample Containers | Specially pretreated polyethylene | Prevention of contamination and adsorption |
| Buffer and Detection Kits | For specific analysis methods | Sample preparation and signal amplification 2 |
Instrumental elemental analysis finds application in numerous areas:
Analysis of alloy composition and development of new materials with specific properties 1 .
Determination of essential trace elements and harmful contaminations in food 6 .
Purity control of active ingredients and detection of catalyst residues 6 .
Origin determination of materials and reconstruction of historical trade routes 1 .
Analysis of trace evidence and comparison of material samples for criminal investigations.
Instrumental elemental analysis has developed into an indispensable tool in science and industry. Methods like AAS, ICP-OES, ICP-MS, and XRF now enable the precise determination of elements over an extraordinarily large concentration range – from percentage levels down to ultratraces 4 6 .
The future of this discipline is characterized by several promising developments. These include:
Development of smaller analytical devices for on-site measurements with portable instrumentation.
Combination of different analytical methods for expanded analysis possibilities and complementary data.
Development of more intelligent data evaluation algorithms for faster and more reliable interpretation of complex results 5 .
Like the invisible elements it detects, instrumental elemental analysis usually works in the background – yet its importance for our safety, health, and technological development could hardly be greater. It is a silent guardian that ensures our water is clean, our food is safe, and our materials are reliable.