Methods & Sample Requirements
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.
The analysis is finished in approx. 6 min.
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Sample Requirements: The amount of substance required for 1 analysis is about 1.5 mg |
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.
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Sample Requirements: The amount of substance required for 1 analysis is about 1 - 3 mg, Please state the solubility of the substance in methanol or other solvents. |
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.
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Sample Requirements: Depending on content of elements to be determined, one analysis needs c.a. 1 5 mg of sample. The analysis is destructive. |
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.
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Sample Requirements: Depending on sample type and content of elements to be determined, one analysis needs 0.5-5 mg of sample. Analysis of such small amounts brings higher demands on sample homogeneity. |
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.
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Sample requirements for Optical Rotation: A sample should be submitted as a dry solid or a neat liquid. The minimum sample amount is 2 mg; the more sample you submit the higher accuracy of the measurement is obtained. On the other hand, compounds with high optical rotation can be analyzed at amounts of ca. 0.5 mg. In this case please indicate precisely weight of the sample or do not hesitate to contact the laboratory staff. The sample will be dissolved in the solvent specified in the submission form. Please pay attention to the solvent selection as only well dissolved samples give accurate results and eventual crystallization can damage rather expensive sample cell. If you want to get back your dissolved sample please provide us with an empty labelled bottle of appropriate size and indicate this fact in the submission form. Furthermore, you should specify the type of cell A (1.5 mL), B (0.5 mL) and C (2.8 mL). The cell A is ordinarily used. The required wavelengths values can be indicated in the submission form (365, 405, 436, 546, 589 and 633 nm), the usual value is 589 nm. |
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).