Preface Free

Trace element determination at abundance levels is highly significant in geochemical exploration due to their multiple roles in the geochemical cycle such as pathfinders, deciphering depositional environment, tectonic setting, differentiation trends in acidic rocks, an indicator of the source of magma, geo-thermometry, in petrogenesis, etc., usually at ppm to ppb levels. The analytical data of trace elements are sought on the samples collected from areas with favourable geological-settings and usually pertain to transition elements, rare earth (ppm to sub-ppm), platinum group and hydride forming metalloid elements at ppb levels. Vital elements of an analysis constitute collection of true representative samples, contamination-free transportation of the samples to the laboratory without any deterioration (water samples) in the absence of adequate on-site analysis, obtaining 50 mg to 500 mg of true representative samples of suitable mesh size for destructive (DT) and nondestructive (NDT) analytical techniques (except for fire assay), and preparation of a sample solution with total dissolved solids (TDS) within the tolerance level for destructive techniques, making the preparation of a sample solution a key component.

The solution preparation techniques vary with matrices (and exploration needs), preferably utilizing a wet acid combination and fusion with a minimal amount of suitable flux (to keep the TDS within tolerance levels) for subsequent feeding through a nebulizer in DTs, and therefore, the solution preparation techniques have been given due emphasis in the book.

DTs have all the advantages of solution chemistry including homogeneity and reduced matrix, in contrast to NDTs, which suffer from both needing samples to be pulverized to higher mesh sizes such as in XRF or synchrotron XRF. The centre stage of the analytical arena is surrounded by numerous flame-, plasma- and laser-based techniques, AAS, HR-CS AAS, MP-AES, ICP-OES, ICP-MS and different improved versions of ICP-TOF-MS, HR-ICP-MS, ICP-QQQ-MS (alone or hyphenated with a vapour generation kit, electrothermal atomization, or a multisample introduction system avoiding nebulization deficiency), LIBS, LA-ICP-MS, INAA and RNAA and other nuclear analytical techniques (NATs) besides electroanalytical, ion and various chromatography techniques; but most of the techniques are beyond reach, especially in developing countries due to their unaffordable high cost. The analytical load of the large throughput of samples in such places is shared mostly by UV-Vis molecular absorption spectrophotometry due to its modest aperitive needs, adequate sensitivity for many purposes and ability to be enhanced by the sensitization of a metal–ligand reaction by utilizing surfactant or catalytic effects, formation of a ternary complex, extractive and derivative spectrometry and of late flame atomic absorption spectroscopy (FAAS) with mostly deuterium background correction. A chapter on UV-Vis molecular spectrophotometry keeping this in view has been included.

Similarly, a chapter on laser, LED and conventional pellet fluorometry has been included due to their high detection power for uranium determination. It is useful for the selection of a suitable technique to obtain analytical data of an analyte, to list the orders of magnitude of detection power, matrix effects, multielement capability and the possibility of local, micro- and in-depth and high-precision analysis of the existing techniques. Almost all instrumental techniques are relative techniques and the quality of analytical data depends on the use of a properly validated standard of the analyte with the use of certified research materials (CRM), international Geo standards (IGC) with similar matrix observing all the analytical quality assurance (AQA) and analytical quality control (AQC) measures with adequate statistical treatment of data.

On-site analysis provides information on the chemical composition of the samples in the field in real time or near real time and thus helps in deciphering the rock type and identification and quantification of the elements sought, rapidly cutting down the transport time and expense both from the site and the laboratory; besides, the immediate availability of data helps in screening, dynamic sampling, grid mapping and further course of exploration. A chapter on in situ analysis with an emphasis on pXRF and LIBS, used more commonly due to ease of performance out of the available on-site techniques, is included.

The most important point to keep in mind is that even the most sensitive and accurate analytical techniques would be a waste if proper care to obtain a true representative sample is lacking at any stage. Besides, geochemical data contain variance from sampling error (due to cheap sampling strategies compensated by sampling density), analytical error and geochemical variation. For geochemical variation to be recognizable it must be significantly greater than the combined sampling and analytical errors.

Raghaw Saran