Services

C-H-N determination

The determination of C, H and N in solid/liquid samples is performed using an automatic PE 2400 Series II CHNS/O Analyser. The sample weighed in a tin capsule is combusted in oxygen atmosphere. Final combustion products include N₂, CO₂ and H₂O. Elements such as halogens and sulphur are removed by scrubbing reagents in the combustion zone. The resulting gases are separated by a frontal chromatography and detected by a thermal conductivity detector. The whole procedure excludes determination of the ash.

ED-XRF analysis

Method principle: A solid, liquid or powder sample is excited in a sample compartment of the analyzer with X-rays emitted from an X-ray tube. During the relaxation, the atoms emit secondary X-rays. The radiation frequencies are characteristic for each element. The intensity of a particular line corresponds to the content of the element in the sample. SPECTRO XEPOS P instrument uses adapted primary radiation for increased sensitivity if specific groups of elements are determined. The analysis is non-destructive, thus the sample can be used further after the analysis.

The method allows rapid screening of the present elements, whether they are desirable or not in the sample, e.g. residual halogenated reagents, heavy metals from the catalysts used in the synthesis (Pd, Pt, Ni…) etc. Detection limits are most often in the range from 0.1 to 10 mg/kg. Quantitative determination of P, S, Cl, Br and I or other elements is most often done after dissolving a precisely weighed sample amount in methanol as a well-defined matrix against external calibration. Water or other solvents that do not contain interfering elements can be used, too.

Optical emission spectrometry with inductively coupled plasma (ICP-OES)

Method principle: The sample is transformed into a solution (dissolved or burned in O₂ atmosphere and then dissolved). The solution is nebulized and aerosol is carried to high-temperature plasma by a stream of argon. In the plasma, compounds are atomized and atoms are excited to higher energy states. During following relaxation, the atoms emit characteristic radiation in visible and ultraviolet region. Radiation´s wavelength is characteristic for each element and its intensity is related to the element´s concentration in the sample. The method can determine most chemical elements. Limits of detection vary among different matrices and elements, in general they are between 0.01 and 10 µg/L (in analyzed solution). In comparison with “classic” titrimetric methods, ICP-OES offers faster analysis, lower limits of detection, lower sample consumption, simultaneous determination of multiple elements and lower risk of interferences.

Optical emission spectrometry with inductively coupled plasma and electrothermal vaporization (ETV-ICP-OES)

Method principle: Electrothermal vaporization represents an alternative way of sample introduction to ICP-OES. The sample is weighted into graphite boats and inserted into a graphite furnace. In the furnace, sample is heated according to chosen temperature program up to a maximum of 3000 °C. During this heating sample decomposes and analytes evaporate. A small amount of CCl₂F₂ (freon R12) is added to the furnace during heating to transform elements into their more volatile compounds. A stream of argon flows through the furnace, carrying vapors and dry aerosol to high-temperature plasma.

Unlike in the common ICP-OES, when ETV is used, element´s signal is not constant during the analysis (compounds evaporate at different temperatures and therefore at different moments) and therefore transient signal needs to be recorded. Electrothermal vaporization improves limits of detection of ICP-OES (up to units of µg/kg in the material itself), lowers sample consumption and enables analysis without sample preparation. Another advantage is removal of interferences by optimization of temperature program so that interfering elements evaporate at different moments.

Measurement of optical rotation

By default, measurements are made in cell A (1.5 mL) at a wavelength of 589 nm, alternatively it can be measured at wavelengths of 365, 405, 436, 546 and 633 nm.

Infrared spectroscopy

We provide measurement and evaluation of infrared (IR) spectra, including their detailed interpretation. IR spectra could be measured by the transmission technique in solutions in cuvettes (most often from KBr) or in the solid phase in the form of pressed KBr tablets. Measurements in KBr tablets could also be performed by microtechnique which requires less than 1 mg of sample. All the mentioned measurements could be performed using reflectance techniques such as Attenuated total reflection (ATR) or Diffuse reflection method (DRIFTS). It is also possible to measure temperature-dependent IR spectra of substances in solution or in a tablet in the temperature range of 5-95 °C. The infrared spectrometer is also equipped with accessories enabling the measurement of aqueous solutions (transmission measurement in H₂O or D₂O, or the ATR technique can be used). Moreover, it is possible to combine infrared spectrometer with gas chromatography (GC-FTIR) which enables the analysis of volatile samples, including the identification of components in mixtures.

Raman microspectroscopy

Raman microscopy enables the measurement of biological, biochemical and organic samples in the solid phase and in solutions. The Raman microspectrometer is equipped with a confocal and inverted microscope, an attachment for measuring the solution in standard cuvettes and an adapter for macro sample studies. There are five lasers with excitation wavelengths of 325 nm, 532 nm, 633 nm, 785 nm, 1064 nm. A polarization set is available for each laser which allows measuring of polarized Raman spectra to obtain additional information about the studied system (for example symmetry of vibrational modes, orientation of molecules). Accessories also allows the photoluminescence of a wide variety of compounds to be studied. Experiments can be performed on macro and/or microscopic samples including measurement of temperature dependencies (in the range of 5-95 °C). Microscopic samples such as living cells and monolayers can be studied and electrochemical experiments can be also performed.

Electronic circular dichroism (ECD) spectroscopy

Electronic circular dichroism spectroscopy is measured in the UV/VIS spectral range (180 nm – 800 nm) in solutions, solid samples and on layers at laboratory temperature. The linear dichroism could be measured when studying layers. It is also possible to measure temperature dependences (in the range of 5-95 °C). An absorption spectrum is measured in parallel to each ECD spectrum which is necessary to avoid artifacts in samples with low intensity or relatively high diffraction. Magnetic circular dichroism (MCD) can be studied at laboratory temperature using a permanent magnet (1 Tesla). ECD spectroscopy can be used to measure kinetics (including fast ones) and monitor equilibrium states in chiral systems. Furthermore, ECD spectroscopy can be used for conformational studies (especially of peptides, proteins, nucleic acids) and for determining the secondary structure of peptides and proteins. The ECD spectrometer also enables the measurement of fluorescence in solution and is also equipped with an attachment for stop-flow measurements.

Vibrational circular dichroism (VCD) spectroscopy

After previous agreement, it is possible to provide measurements of vibrational circular dichroism using the transmission technique in solutions or solids (pressed KBr tablets) at laboratory temperature.

Raman Optical Activity (ROA)

Raman optical activity can be measured in solutions at laboratory temperature.

Thermodynamic / kinetic solubility

There are two protocols generally used for the solubility measuring, the thermodynamic and the kinetic protocol. The first one can be defined as the concentration of compound in a saturated solution when the excess of solid material is in equilibrium with the solution at the end of dissolution process. The kinetic solubility is the concentration of a solution when the first precipitate appears after adding the highly concentraced solution of compound (most often using the dimethyl sulphoxide as a pre-solvent) in the solvent. The main advantage of the kinetic protocol is short time of sample preparation in comparison to the thermodynamical protocol. Although the thermodynamic protocol takes a longer time to reach equilibrium and is difficult to automate, it provides more accurate data because the solvent is not influenced by the other aditives such as dimethyl sulphoxyde.

The solubility measuring is performed using chromatographic system (Vanquish UHPLC, Thermo Fisher Scientific, Germany) connected to the diode array detector and consequently to the charged aerosol detector (both Vanquish, Thermo Fisher Scientific, Germany). Samples and calibration standards are prepared using automated system of robotic arm (PAL-RTC, Switzerland). This method is powerful in detecting possible impurities and measuring the solubility of the analyte of interest. The charged aerosol detector is a universal detector for non- and semi-volatile compounds. It also detects analytes with a lack of chromophore, such as steroids and its derivatives.

Differential Scanning Calorimetry (DSC)

Differential scanning calorimetry is a thermoanalytical method in which the difference between the amount of heat required to raise the temperature of a sample and a reference is measured as a function of temperature. Both the sample and the reference are kept at nearly the same temperature during the experiment. The method can determine the temperature and possibly also the enthalpy of phase transitions of the studied molecules. Indirectly, this technique can be used to control the quality and purity of substances. Therefore, it is also possible to use DSC for the development and research of materials, to identify and specify the possible polymorphic character of substances which can also affect the solubility of various forms (essential, e.g., for the bioavailability of substances).

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