Semi-quantitative analysis

A semi-qnantitative mnlti-element analysis - limited in accuracy and precision - is performed in solid-state mass spectrometry if the concentration of at least one element - used as an internal standard element - is known. Eor example, if trace impurities have to be analyzed in high pnrity copper metal, then Cn with a known concentration of 100% is chosen as the internal 

Trace element concentrations are obtained in the semi-quantitative mode by ICP-MS, LA-ICP-MS, SSMS or SNMS with an error factor of about 0.3-3 for most elements. The results of semi-quantitative trace analysis, e.g., for high purity materials, are sometimes sufficient to estimate the purity of the matrix investigated. 

2 One Point Calibration in Solid-state Mass Spectrometry Using a Certified Reference Material 

Certified reference materials (CRMs) are mainly applied to validate the analytical procedure developed for routine analysis in order to determine the accuracy of analytical data, the recovery for selected elements, the uncertainty of trace element determination and the detection limits. Otherwise, in solid-state mass spectrometric techniques, such as SSMS, LA-ICP-MS, GDMS, SNMS or SIMS, one point calibration using CRMs has been established as an important calibration strategy to obtain reliable analytical data. The one point cahbration is performed using the experimentaUy determined relative sensitivity coefficients (RSCs) on a suitable CRM with a similar trace/matrix composition. An RSC of a chemical element is defined as the ratio of the measured element concentration (experimentally determined) divided by the certified element concentration (accepted or recommended value of element concentration) in a given matrix. 

Experimentally measured element concentration Certified element concentration 

Qualitative analysis may be extended to provide semi-quantitative determination of concentrations. This may be carried out by addition of internal standards at known concentrations. Quantitation for each analyte detected is achieved by ratio of the total ion current for the analyte to that of the closest eluting internal standard. However, as the response of different compounds to mass selective detectors can vary considerably, this approach can lead to significant errors. A complementary approach that has found favour and can reduce the uncertainty involves the analysis of standards of tentatively identified compounds, in order to calculate response factors to the nearest internal standard. Standards are usually analysed several times over a period of time to calculate a mean response factor. This enables a semi-quantitative analysis of reasonable accuracy to be performed by reference to an in-house database of response factors. This eliminates the need for extensive calibrations for every batch and also reduces the errors from widely varying response factors. 

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Somsen et al. [796] have reported the use of SERR spectroscopy for the in situ selective determination and semi-quantitative analysis of structurally similar dyes separated by TLC. The limits of identification of the TLC-SERRS method (ca. 5ng applied) were sufficient for acquisition of spectra of impurities present in the certified dye standards. SERRS may also be used for in situ identification of highly fluorescent molecules on HPTLC plates. 

Thin-layer chromatography (TLC)2 has become a valuable tool for the qualitative and semi-quantitative analysis of various organic and mor-... 

Synopsis of Experiment and Results. The material is irradiated during straining and relaxation. The example shows that a nanostructure which is hard to interpret from a series of scattering patterns may clearly reveal its complex domain structure after transformation to the CDF. Different structural entities are identified which respond each in a different way on mechanical load. The shape of the basic particles is identified (cylinders). The arrangement of the cylinders is determined. Thus the semi-quantitative analysis of the CDF provides the information necessary for the selection and definition of a suitable complex model which is required for a... 

Fig. 6.3.7. Semi-quantitative analysis of C6-Ci2-SPC in investigated surface waters (sample batch from December 1999) (from Ref. [23]).

For the time being, qualitative or semi-quantitative analysis of the influence of the medium on the electronic factor value rest on the description given by the... 

This notion of occasional ion hops, apparently at random, forms the basis of random walk theory which is widely used to provide a semi-quantitative analysis or description of ionic conductivity (Goodenough, 1983 see Chapter 3 for a more detailed treatment of conduction). There is very little evidence in most solid electrolytes that the ions are instead able to move around without thermal activation in a true liquid-like motion. Nor is there much evidence of a free-ion state in which a particular ion can be activated to a state in which it is completely free to move, i.e. there appears to be no ionic equivalent of free or nearly free electron motion. 

Gas chromatography (GC) and mass spectrometry (MS) can be coupled to the TGA instrument for online identification of the evolved gases during heating pyrolysis-GC/MS is a popular technique for the evaluation of the mechanism and the kinetics of thermal decomposition of polymers and rubbers. Moreover, it allows a reliable detection and (semi)quantitative analysis of volatile additives present in an unknown polymer sample. 

There are, fortunately, several properties that do correlate well with the bond valence as discussed below. They include the bond length and its thermal expansion as well as a bond force constant that can be used for a semi-quantitative analysis of the Raman and infrared spectra of crystals. 

Densitometric scanning of the dried gels with integration of the optical density of the peaks allows then the semi-quantitative analysis of the different lipoproteins. 

In contrast to SIMS, in SNMS - where the evaporation and ionization processes are decoupled -the matrix effects are significantly lower, because the composition of sputtered and post-ionized neutrals corresponds more closely to the composition in the solid sample (compared to the sputtered secondary ions in SIMS), which means the RSCs of elements vary by about one order of magnitude. Consequently, a semi-quantitative analysis by SNMS can also be carried out if no suitable matrix matched CRM is available. This is relevant for thin film analysis, especially for the determination of elemental concentration profiles in depth, for studying the stoichiometric composition of thin films and interdiffusion effects. 

Table I. Semi-quantitative Analysis of Red Clay (Done by Emission Spectroscopy)...

This method is well adapted to qualitative analysis where automatic identification of the lines can be made by very sophisticated visual displays. For semi-quantitative analysis, software can be used to estimate a composition that is very close to that of the sample. However, for quantitative analysis, serious problems can be encountered and reference standards have to be analysed in matrices that are almost identical in composition to that of the sample. 

Besides plasmas, which are at the forefront of thermal atomisation devices, other excitation processes can be used. These methods rely on sparks or electrical arcs. They are less sensitive and take longer to use than methods that operate with samples in solution. These excitation techniques, with low throughputs, are mostly used in semi-quantitative analysis in industry (Fig. 15.2). Compared to the plasma torch, thermal homogeneity in these techniques is more difficult to master. 

Whenever quantitative analysis is desired, care must be taken to use proper standards and account for interelement matrix effects since the inherent sensitivity of the method varies greatly between elements. Methods to account for matrix effects include standard addition, internal standard and matrix dilution techniques as well as numerous mathematical correction models. Computer software is also available to provide semi-quantitative analysis of materials for which well-matched standards are not available. 

The elemental composition of unknown materials such as engine deposits can be determined qualitatively and the information used to develop dissolution methods prior to analysis by inductively coupled plasma atomic emission spectroscopy (ICPAES). Alternatively, a semi-quantitative analysis can be provided by XRF alone, especially important when only a limited quantity of sample is available and needed for subsequent tests. The deposit does not even have to be removed from the piston since large objects can be placed directly inside an EDXRF spectrometer. 

The dynamic mechanical response of a material can be characterised through the loss modulus, the loss tangent, tan S, or the loss compliance, However, as already mentioned for Ar-Al-PA (Sect. 6), the loss compliance can be considered the most relevant parameter for quantitatively comparing different materials, at least for additive purposes. For this reason, the semi-quantitative analysis and the comparison of viscoelastic data determined for different systems have been performed [63] in terms of /", whereas the determination of activation energies and entropies are based on loss modulus data. 

The use of LC-ARC or 96-well microtiter plates containing solid scintillant, in contrast, represents low-cost methodologies to improve the sensitivity of the semi-quantitative analysis of metabolites. The LC-ARC and 96-well microtiter plate approaches have similar LOD for 14C and 3H and both can be used in combination with MS to generate quantitative and structural data. Both approaches are particularly useful in cases where the sample is limited. The throughput of LC-ARC is higher than for the plate approach due to the need to dry and count the plates offline. However, the 96-well plate approach is nondestructive, such that drug-related components can be subsequently eluted from the plates for further analysis, if necessary. 

Although samples are taken and prepared in the same way here as in the semi-quantitative analysis, in the evaluation of the complex spectra of the substances, the multi-dimensional GC technique (GCGC—MS) is employed. This consists of two series-connected GCs combined with an MS detector. As a rule, the process... 

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