X-Ray Fluorescence in Biological Sciences. Группа авторов

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Название X-Ray Fluorescence in Biological Sciences
Автор произведения Группа авторов
Жанр Химия
Серия
Издательство Химия
Год выпуска 0
isbn 9781119645580



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elements are determined using the standard calibration curve method, which is mostly used in cases where standards are unavailable.

      The ICP‐AES method is also used to determine the content of metals in wines and alcoholic beverages, heavy metals such as arsenic (As) in food stuffs, and trace elements in complex biomolecules such as proteins. It is capable to determine traces of oil additives which further indicate the service life left for the motor oil. It is capable to detect Li (Z = 3) to U (Z = 92) except gases, halogens, low contents of P and S. However in XRF, P and S can be easily determined and quantified. The combined use of ICP‐AES and ICP‐MS is very powerful and gives highly accurate and precise results for a broad range of elements from the major (percentage, %) to trace levels (typically sub ppb) [3].

      The disadvantage of this technique is that the emission spectra are complex and subject to spectral interferences for some elements. Matrix effects also create many challenges to quantifying the elements of interest. Some of the lither elements such as C, H, N, O, and halogens cannot be determined using this technique. Some elements cannot be detected by ICPs but often are subject to be analyzed exclusively by XRF such as S, Br, and Cl.

      In case of the limits of quantification equal to or above 1 ppm (μg/g), or where non‐destructive analysis is required, XRF is the most popular and attractive technique to analyze the solid samples, powders, oils, and slurry samples. As opposed to ICP‐AES, ICP‐MS, and AAS, it does not require sample dissolution or digestion and allows essentially non‐destructive analysis. In that case, XRF ensures accurate and reliable results by avoiding the potential for inaccuracies caused by incomplete dissolution and large dilutions.

      1.3.4 Ion Chromatography (IC)

      Ion Chromatograhy (IC) is a versatile analytical technique that is generally applied to detect positive and negative ions. It utilizes an ion's intrinsic affinity for both an “eluent” (typically buffered water) and a “stationary phase” (porous solid support with charge‐bearing functional groups) [3, 7]. It works on any kind of charged molecule, including large proteins, small nucleotides and amino acids.

      IC has industrial applications too. Its main advantages in this sector include good precision and accuracy, reliability, high separation efficiency, high selectivity, good speed, and low operating cost. Applications of IC particularly in the field of pharmaceutical industry are being developed. These applications are typically focused on the determination of detection limits in the field of pharmaceuticals. The detection limits corresponding to oxalates, sulfamates, sulfates, iodide, phosphate, and electrolytes like sodium and potassium can be determined too. The IC can also be used for the analysis of drugs having pharmaceutical importance for the development of products with quality control testing. It can be used in pharmaceutical drugs in tablet or capsule form for the determination of the actual dosage of the drugs that can be dissolved within some time. IC can also be utilized for the detection as well as quantification of the inactive or undesirable ingredients that are being used in the pharmaceutical formulations. Sugar and associated alcohol have been detected in such formulations with the help of IC as they are easily resolved in an ion column due to having polar groups. IC can also analyze the impurities present in the drug substances and products. Impurities in the drug can be easily estimated and help to provide an intuition for the minimum and maximum dosage of drugs needed by a person on daily basis.

Advantages Limitations
Small sample quantity required.Rapid determination of anions and cations (inorganic as well as organic)Sensitivity: μg/l levelAnalysis of ionic speciesStability of the separator columns Buffer requirementDetermination of only ionic analytesIdentification of peaks based on a retention time match to a standard solutionSmall change in pH greatly alters binding profile of stationary phase and ion statesSamples applied to the IC under conditions of low ionic strength and controlled pHResistant to salt‐induced corrosion

      1.3.5 Laser‐Induced Breakdown Spectroscopy (LIBS)

      LIBS is more advantageous for depth analysis due to its refocused capability on the same location of a sample surface and its ability to provide depth profiling at a resolution of hundreds of nanometers per pass. In addition, the laser beam can be focused from 20 to 200 μm and thus allows the laser beam to scan across the whole sample surface that provides spatially resolved elemental mapping. It can detect nearly all the naturally occurring element down to down to ppm level, depending on the sample matrix.

Schematic illustration of a setup of laser-induced breakdown spectroscopy (LIBS).

      LIBS and XRF alike are generally used for positive material identification (PMI). For most of the applications, LIBS provides the same information as XRF, just using a laser source instead of radiation. But, in