Sample Requirement and Submission for the EA and OR Analysis

Please submit the samples to the building A, in front of the room 181 (second floor). The samples have to be labelled and accompanied by a corresponding submission form. There are special forms for elemental analysis elemental analysis and for the measurement of optical rotation. Blank forms can be found also in the box outside of room 181. A record of each sample has to be written in a logbook located in front of the room 181.

The results of the analysis are fulfilled in the submission form and placed in the box outside of room 181. They are also available on the internal Novell network in the directory I:\MISC\ElemAnal.

Sample requirements for Elemental Analysis

A sample should be submitted as the dry (homogeneous) solid or the neat (non-volatile) liquid. In case of XRF-analysis it is possible to treat also volatile compounds and liquids. The minimum sample amount for elemental analysis depends on which elements are to be analyzed and which method is used (see the table bellow). Please, use labelled glass vials for the samples; preferred are labels containing only capital letters and numbers, which are the only characters accepted by the instruments. The expected elemental composition (molecular formula) should be filled in the submission form. It help us by the calibration of the machines and by the option of optimal charge and elaborating process. In case the expected elemental composition differs more than 0.3% from results obtained (CHN automatic analysis), the measurement is repeated.

Sample requirements for Optical Rotation

A sample should be submitted as the dry solid or the 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 analysed 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 as 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, the usual value is 589 nm.

The elemental analysis in brief

CHN 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 loaded in the instrument. When the tin is dropped into the high-heat oxygen environment of the combustion tube (heated at 925 °C), it creates a vigorous exothermic reaction. The sample temperature can reach 1700 °C, which aids in the combustion process. The sample is first oxidized in a pure oxygen environment. Final products produced on the combustion zone include CO₂, H₂O and N₂. Element such as halogens and sulphur, are removed by scrubbing reagents in the combustion zone. The whole procedure excludes determination of ash. The resulting gases are homogenized and controlled to exact conditions of pressure, temperature and volume. N₂, CO₂ and H₂O are moved by helium into the column, separated by a frontal chromatography and detected by thermal conductivity detector. The whole procedure is controlled by a microprocessor taking into account data from analysis of blanks, internal and external standards. The analysis is finished in approx. 6 min.

XRF-analysis (SPECTRO iQII)

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. The innermost electrons of various atoms are ejected from the inner shells creating vacancies in the process called the photoelectric effect. The vacancies represent unstable condition for the atomic system. Electrons from outer shells occupy the vacancies; the corresponding energy differences cause an emission of characteristic secondary (fluorescence) X-rays. The radiation frequencies are characteristic for individual elements. The intensity of a particular line corresponds to the content of an element in the sample. All element specific X-ray fluorescence signals from the sample are detected simultaneously in a fixed mounted semiconductor detector and evaluated. Hence, an X-ray fluorescence spectrum is obtained. SPECTRO iQ II instrument uses a polarized primary radiation for increased sensitivity and the noise reduction (especially important for determination of the light elements). The analysis is non-destructive, thus the sample after analysis (eventually after a solvent evaporation) can be used further.

Qualitative analysis: The SPECTRO iQ II spectrometer allows a qualitative detection of elements from Na to U in different types of samples (e.g. liquids, solutions, solid (powders) samples (except gases). We have got the cups for analyses of liquid samples (solutions, emulsions and suspensions) and furthermore for powder samples and solid pressed tablets. The limits of detection are different depending on individual elements; commonly they are in range from one to tens ppm.

Quantitative analysis: Currently, we can perform quantitative analyses of the elements, which we have been doing with titration methods, i.e. P, S, Cl, Br and I. A new methods for the determination of Al, Si, K, Cr, Fe, Co, Ni, Cu, Zn, Se, Ru, Pd, Ag, Cd, Sn, Cs, Pt, Au, Hg and Pb are established (Al in toluene/oil matrix and Pt in water). Nowadays the quantitative analyses are limited to sample solutions in methanol, because the calibration models for methanolic solutions are developed. Thus at least a minimal solubility of analyzed sample in methanol is required to prepare a defined sample solution. For simultaneous analyses of the all elements required we need 1 - 5mg of a sample. Of course, this value depends on the content of determined elements in a particular sample. Considering the results of many performed tests, both precision and accuracy of results obtained via X-ray fluorescence method is comparable to the current methods' performance characteristics. In fact, we can develop methods for determination of any element (from Na to U) but we need an appropriate standard (or standards) with a known (certified) content of the element to be determined. In future, it is possible to develop various quantitative methods in several other non-volatile solvents with proper elemental compositions (water, ethanol…) with respect to your requirements.

Determination of F and P, S, Cl, Br and I (by "classical" titrimetric way)

For analysis of F the sample is combusted by Schöniger method (i.e. in quartz Erlenmeyer flask in oxygen atmosphere). Formed F- is determined potentiometrically by using ion-selective electrode.
Determination of P is performed after Kjeldahl digestion of the samples with a mixture HClO₄ + HNO₃. After necessary adjustments of the sample, PO₄^2- is titrated using a standard solution of La(NO₃)₃; the indicator is eriochromblack T.
For analysis of Cl and Br the sample is combusted by Schöniger method. Formed Cl^- or Br^- are titrated by a solution of Hg(NO₃)₂ for sodium nitroprusside as an indicator. It is impossible to determine Cl and Br, when they are both present in the sample.
For analysis of I the sample is combusted by Schöniger method. Iodine is determined by Leipert method described by following steps: (1) absorption of iodine in NaOH solution, (2) oxidation of various iodine forms to iodate by bromine, (3) reduction of the excessive bromine by formic acid, (4) reduction of iodate by iodine forming elemental iodine, (5) titration of iodine by a standard solution of thiosulphate.
For analysis of S the sample is combusted by Schöniger method and formed SO42- ions are titrated in the presence of 2-propanol by a standard solution of Ba(ClO4)2 with thorin as an indicator.

Downloadable application forms (pdf files):

elemental analysis measurement of optical rotation