Laser Induced Breakdown Spectroscopy of Complex Materials
We have used LIBS to determine the elemental compositions of samples such as soils, biological fluids, organic compounds, and more recently water solutions of various elements and organic compounds [1-5]. Previously we obtained LIBS spectrum of bovine serum albumin (BSA) to determine its elemental composition. For purpose of quantification the pure deuterium oxide (D2O), pure water and their mixtures were used as a source of standard H and D elements. These data were used for the following deconvolution of superimposed H and D LIBS peaks of deuterized BSA solution (see Figure 1). From these data we have determined the number of hydrogen atoms in the BSA molecules.
Knowledge about elemental composition can shed some light on the structure of molecules. While the number of carbon atoms provides one with information about molecular backbone size, the number of sulfur atoms directly relates to disulfide bonds (S-S bonds) formed between cysteine residues in peptide chains and determines the secondary structure of proteins. The same time the quantity of disulfide bonds for some proteins (e.g., thioredoxin) declares the number of possible cycles between a few disulfide states as part of their function.
A principal component analysis (PCA) was developed to classify experimental LIBS data and demonstrate that organic molecules can be identified despite their similar elemental composition. The PCA of experimental data (stars) is in a good agreement with the known molecular composition (dots) (Figure 2). We have demonstrated the ability of LIBS in providing not only qualitative information about the molecule but also in performing precise stoichiometry data about its composition .