Instrumental chemistry

The Instrumental Analysis (IA ) is the field of analytical chemistry, which performs the analysis and identification of unknown substances ( "sample" ) or their molecular structures by means of modern analytical instruments. For this purpose, a sample is typically prepared (e.g., by extraction and elution ), placed in the device and irradiated or cut in order to detect specific values ​​in a detector. These can include the type, concentration or amount of the unknown substance - often to areas in tiny quantities inside.

Development and characteristics

Instrumental analysis is based on high-precision measurement principles that have been redeveloped in the last 40 years in order to confront explosively growing demands of research, environmental analysis and product control can. The handling of the devices ( laboratory technology ) was developed in this period. In comparison to classical wet chemical methods, there are features instrumental methods of analysis, that the measurements can be quickly with the help of advanced analytical instruments, inexpensive, accurate, precise, selective and performed with small quantities. Many substances ( test compounds ) have thus become measurable from a few picograms well into the layman hardly imaginable area.

For a detailed description of each instrumental method of analysis (for example, in the investigation of a finished dish to a pesticide in vegetables) include in addition to the testing facility ( laboratory ) and the test system ( here: the finished dish ) the indication of the test instrument (eg gas chromatograph, GC) of the substance ( the pesticide ) and the sample (brand of ready-prepared meal "gypsy schnitzel with mashed potatoes ," Preparation of the extract of eg 10 g pepper with a help of an extractant such as 50 ml dichloromethane).

The quality of an analytical method is described by (eg by elution or extraction) and the method validation is done in addition to the documentation of sample preparation, ie, the detection and documentation of the reliability of a method of analysis. For this, the correctness, accuracy and precision of the method is investigated and in the case of accuracy by means of the Gaussian function is also calculated (eg in the measured value display in the "peak" shape). The calibration establishes a relationship between the measured size and analysis result, the reliability of the result is described by the arithmetic mean ( " average " ), the standard deviation and the recovery rate.


The generic term instrumental analysis covered four categories of procedures: optical, spectroscopic, chromatographic and electroanalytical methods.

Optical methods of analysis

→ Introductory article: Optics

Optical methods and devices are those in which the sample is irradiated with light or light similar electromagnetic radiation. A part of this radiation is diffracted or reflected thereby in a given angle. This can then be measured in a refractometer ( left figure).

These methods include addition of refractometry (Measurement of refractive index), the polarimetry (measurement of the optical activity / the amount of rotation ), and photometry ( measurement of light absorption in the form of the absorbance or transmittance at a specific wavelength ). Polarimetry is, for example, a method in which a sample solution is illuminated with linearly polarized light of a certain wavelength. Certain substances have the ability to rotate the plane of vibration of linearly polarized light ( specific optical rotation, optical activity). This specific rotation is often used in pharmacy and chemistry for the identification and purity control of chiral substances. Particular importance has the indication of the specific rotation of natural products such as amino acids, terpenes and sugars, since the majority of these compounds is optically active.

Spectroscopic Methods

In spectroscopic methods and devices, the sample interacts with the electromagnetic radiation (absorption and emission). The various instrumental methods of analysis of spectroscopy are divided by:

Atomic spectroscopy in an atomic absorption spectrometer (abbreviation: AAS ) is generally a measurement of the wave number, wavelength or frequency of absorbed radiation for the determination of atomic energy levels, atomic emission spectroscopy in atomic emission spectrometer / flame photometer (AES ) measures energy emitted, the IR spectroscopy ( infrared spectrometer IR) and the UV / visible spectroscopy ( UV / VIS spectrometer ) measured in the infrared, visible and ultraviolet region of the spectrum elrektromagnetischen.

Fluorescence spectroscopy measures the light emitted by a fluorescent light in the sample fluorescence spectrometer, while an X-ray fluorescence analysis ( XRF) is X-ray radiation used. The nuclear magnetic resonance ( NMR) is measured in the NMR spectrometer, the electron spin resonance in Elektronenspinresonanzspektrometrie (ESR or EPR).

The mass spectrometer (MS), however, is a device that is not operating spectroscopy ( no use of electromagnetic radiation ), but the molecules of the sample substance divided into fragments, which are then captured by a magnetic field, and sorted by calculated mass numbers.

Chromatographic methods

Chromatographic methods and devices aim the sample to enable ( a mixture of substances ) under certain conditions into a movement, so that the components can be separated and identified on the basis of different flow or migration velocity (gas, high pressure liquid chromatography and the similar. , separation by adsorption and desorption as well as different retention times of the individual components). This is so highly precise micro method for separating substances (compared to the classical macro - separation processes of distillation, sublimation, extraction, recrystallization, reprecipitation and filtration).

Important analytical instruments for chromatography are gas chromatograph (GC, often for the determination of peak areas and retention factors and times of certain substances ), HPLC instruments ( for high performance liquid chromatography ), ion chromatography ( for ion chromatography / electrophoresis IC / EP ) and electrophoresis equipment for gel electrophoresis, specifically 2D - gel electrophoresis and IEF gel electrophoresis (IEF = isoelectric focusing ).

Electroanalytical and other instrumental methods of analysis

Furthermore, there are electro- analytical and other physical methods, and devices for which the sample is electrically charged, for example, exposed to the electric current ( electrolysis potentiometry or conductimetry and the like. ) Or molecular fragments (fragments) smashed and separated is ( mass spectrometry ). The nine most important methods of this group are:

  • Electrogravimetry for determining the concentration of the electrolyte deposited mass
  • Potentiometry ( voltammetry ) to measure the electrochemical potential and the voltage
  • Polarography / Voltammetry recording of current-voltage curves for quantitative and qualitative analysis
  • Amperometry registration of the electrolysis current at constant potential
  • Coulometry registration of the electrical charge that is transmitted in an electrolysis
  • Conductometry, such as an automated Leitfähigkeitstitration
  • Osmometry for measuring the osmotic pressure
  • Viscometer for measuring the viscosity
  • Mass spectrometry for the determination of the molar mass of a molecule and its key fragments

Wet chemical and classical analytical methods such as volumetric analysis ( volumetric analysis ) and gravimetry ( precipitation analysis) should only be accounted to the instrumental methods of analysis, when electronic instruments are being introduced. In volumetric analysis that would be instrumental indication of the equivalence point example by means of potentiometric or conductometric. An instrumental version of gravimetry is thermogravimetry.

Coupled methods

In recent times the direct coupling of different analysis methods has become increasingly important. A classic example is the so-called GC-MS, is in a mass spectrometer (MS) using a gas chromatograph (GC) connected (GC -MS). Through the chromatograph, a separation of a complex substance mixture is often obtained, while the continuously -fed with the gas flow of the chromatograph mass spectrometer allowing identification of individual sample components. Similar combinations are couplings of the high performance liquid chromatography (HPLC) and mass spectrometry or by HPLC and NMR.