Analytical Chemistry

Analytical chemistry / Chemical analytics at abcr

Analytical ChemistryAnalytical Chemistry

Besides a broad spectrum for the needs of synthesis chemists, the abcr portfolio also comprises many important products for chemical analytics.

Chemists become familiar with pH indicators such as phenolphthalein, methyl orange or bromophenol blue right at the start of their studies. Their application for acid-base titrations in chemical analytics is based on a colour change, this relating to deprotonation or protonation at the relevant equivalence product of the indicator acid or base.

abcr also provides a large range of volumetric standard solutions for diverse analytic methods. These typically include titration methods such as complexometry. A colour change from free or only weakly coordinated complexes to strongly coordinated complexes is used here in order to determine the concentration of the analyte, usually metal ions. A familiar use of this method involves determining bivalent cations such as Cu, Pb, Hg, Ca and Mg via complexometric titration with a EDTA solution (= ethylenediaminetetraacetic acid).

Farbstoffe finden in der Analytik nicht nur Einsatz als Indikatoren. Sie können als Fluoreszenzmarker zudem helfen, bestimmte Strukturen und Strukturelemente selektiv sichtbar zu machen. So erlaubt beispielsweise der Einsatz von Nilrot und anderer ähnlicher Fluoreszenzfarbstoffe die spezifische und quantitative Bestimmung von Mikroplastikpartikeln in Abwasser - auch in Anwesenheit anderer Mikropartikel aus natürlichen Quellen. Dies erlaubt ein Monitoring, um gezielt Mikroplastik aus (Ab-) Wasser zu entfernen.

Fluoresce markers are used in biochemistry and medicine for marking biomolecules such as proteins or carbohydrates. This is done in many cases by the marker/fluorophore binding to amino or hydroxy groups of the target.

The abcr catalogue contains a wide range of different solvents for analytical purposes. Their diverse purities make them ideal for different analytical methods such as high-performance liquid chromatography (HPLC), gas chromatography (GC and GC/MS), UV/Vis spectrometry or IR spectrometry. The use of suitable reference standards is often indispensable for these chromatographic separation methods.

An important subgroup of these solvents is formed by the deuterated solvents for NMR spectroscopy (magnetic resonance spectroscopy). They are indispensable for the structural elucidation of organic and organometallic substances. At abcr they are available in different degrees of deuteration.

Further deuterated compounds, for instance some vitamin derivates, and other isotope-labelled compounds, above all with stable 13C and 15N isotopes, provide the option for a precise examination of reaction processes through to the mechanism for the metabolism of various substances. Deuterated salts such as lithium aluminium deuteride allow deuterium to be introduced into organic compounds, e.g. for the reduction of esters, ketones and aldehydes.

A particularly challenging field of NMR analytics involves the analysis of enantiomer mixtures. In many cases, both enantiomers exhibit the same NMR spectrum. To nevertheless be able to examine these via NMR spectroscopy, a suitable enantiomerically pure chiral derivatisation reagent is added. The resultant diastereomers exhibit different NMR spectra. A quantification of the enantiomers, determination of the ee value (“enantiomeric excess”) and optical purity is thus possible. For example, the carboxylic acid chloride of (R) or (S)-α-methoxy-α-(trifluormethyl)phenylacetic acid has proven effective for determining the enantiomeric purity of chiral amines and alcohols (CAS numbers 20445-33-4 and 39637-99-5). These are also referred to as Mosher’s acid chlorides. Harry S. Mosher et al., described their use for the first time in 1969 [1].

Atomic absorption spectrometry (AAS) and mass spectrometry as well as optical emission spectrometry with inductively coupled plasma (ICP-MS or ICP-OES) also require the use of corresponding standard solutions. Depending on the matrix to be investigated and desired application field, these standard solutions are suitable for both external calibration as well as standard addition. The wide spectrum of underlying methods attained in this way allows inorganic components to be monitored for both industrial quality control as well as for environmental analytics, particularly in respect to diverse heavy metals.

Besides the softening, resalination or partial desalination of water, a familiar application of ion exchange chromatography involves the separation of trivalent lanthanide and actinide ions. The application of this analytical method enabled a series of synthetically produced actinides to be verified chemically. Ion exchangers are divided into cation and anion exchangers. Both materials consist of synthetic resins with different functionalisation. Cation exchangers contain carboxylic or sulfonic acid groups, while anion exchangers contain quaternary ammonium groups.

Many analytical methods are sensitive to the parameters of the analysis itself. In particular the pH value can have major consequences here. To ensure that this remains constant during the course of an analysis, buffer solutions are used. Their pH value is chosen so as to correspond to the optimum of the desired method. The Karl Fischer titration used to determine the water content also utilises such a buffer system.

A range of 20 biological buffers is grouped together under the term “Good buffers”. The advantages of these buffer substances developed by Norman E. Good lie in the low interactions with proteins, a high solubility, a buffer range between pH 6 and 8, a low toxicity and UV absorption, the cost-effective manufacture and their metabolic and chemical stability. Examples of this substance class, which exhibit an amine function and a sulfonic acid group, are MOPS, MES, HEPES, PIPES or HEPPSO.

[1] Dale, James A.; Dull, David L.; Mosher, Harry S. „ α-Methoxy-α-trifluoromethylphenylacetic acid, a versatile reagent for the determination of enantiomeric composition of alcohols and amines”, Journal of Organic Chemistry (1969), 34(9), 2543-49