Quantitative SERS Methods

Reproducibility and sensitivity represent a major preoccupation of researchers interested in developing practical quantitative SERS methods (Bell and Sirimuthu 2008 Bell and Stewart 2011). In the case of quantitative analysis and sensing, the prerequisites to SERS substrates were postulated by Natan in his concluding remark at Faraday Discussion 132 (Natan 2006). According to it, we can summarize the main features of SERS enhancing metallic substrate for sensing ... 

S.E.J. Bell, A. Stewart, Quantitative SERS methods, in Surface Enhanced Raman Spectroscopy Analytical, Biophysical and Life Science Applications, ed. by S. Schliicker (Wiley, Weinheim, 2011), pp. 71-86... 

The main features of PC are low cost, need for small sample amount, high level of resolution, ease of detection and quantitation, simplicity of apparatus and use, difficult reproducibility (because of variation in fibres) and susceptibility to chemical attack. Identification of the separated components is facilitated by the reproducible Rj values. Detection methods in PC have been reviewed [368]. Fluorescence has been used for many years as a means of locating the components of a mixture separated by PC or TLC. However, also ATR-IR and SERS are useful. Preparative PC is unsuitable for trace analysis because filter paper inevitably contains contaminants (e.g. phthalate esters, plasticisers) [369]. For that purpose an acceptable substitute is glass-fibre paper [28]. 

Since SERS and SERRS are substance specific, they are ideal for characterisation and identification of chromatographically separated compounds. SE(R)R is not, unfortunately, as generally applicable as MS or FUR, because the method requires silver sol adsorption, which is strongly analyte-dependent. SE(R)R should, moreover, be considered as a qualitative rather than a quantitative technique, because the absolute activity of the silver sol is batch dependent and the signal intensity within a TLC spot is inhomogeneously distributed. TLC-FTIR and TLC-RS are considered to be more generally applicable methods, but much less sensitive than TLC-FT-SERS FT-Raman offers p,m resolution levels, as compared to about 10p,m for FTIR. TLC-Raman has been reviewed [721],... 

An application of the method to Alzheimer s A l-42 revealed that the O-acyl isopeptide of Api-42 (in which the Gly -Ser sequence of A 31-42 was isomerized to a P-ester bond) could be synthesized effectively and stored without spontaneous self-assembly (1-3). Intact monomer A -A2 could then be obtained from the isopeptide under physiologic experimental conditions. The water solubility of the TFA salt of the isopeptide was 100-fold higher than that of A 1 2 (0.14mg mL ). Purified isopeptides could be converted quantitatively... 

ICP emission spectroscopy is used primarily for the qualitative and quantitative analysis of samples that arc dissolved or suspended in aqueous or organic liquids. I he techniques for preparation of such solutions are similar lo tho.se described in. Section 9D-1 for flame absorption methods. With plasma emission, however, it is possible to analyze solid samples direclly. These procedures include incorporating electrothermal vaporization, la.ser and S[)ark ablation, and glow-discharge vaporization, all of which were described in Section 8C-2. Suspensions of solids in solutions can... 

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