X-Ray Fluorescence Spectrometry

(or XRF spectrometry) an analytical method in geology for determination of a wide range of elements in bulk rock specimens. Rock samples are prepared as ground powder compressed into flat cylinders or fused into coin-like flat discs and then excited with X-ray radiation. The radiation causes the removal of an ELECTRON from an ORBITAL, and when it is replaced, the surplus energy is emitted as a characteristic, secondary, X-ray. The X-ray is measured by the spectrometer and the intensity of the radiation compared to a standard to enable concentrations to be calculated. The technique is widely used in analysing rock samples both for major elements and certain TRACE ELEMENTS. Concentrations of trace elements as low as 1 to 10 parts per million can be detected although, in many instances, the quantities are higher.

Taken from Dictionary of Science

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X-ray fluorescence (XRF) is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis and chemical analysis, particularly in the investigation of metals, glass, ceramics and building materials, and for research in geochemistry, forensic science and archaeology.

Taken from Wikipedia

Quantitative Analysis

the examination of a sample to discover the amounts of the substances present.

Taken from Dictionary of Science

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In chemistry, quantitative analysis is the determination of the absolute or relative abundance (often expressed as a concentration) of one, several or all particular substance(s) present in a sample.

Once the presence of certain substance(s) in a sample is known, the study of their absolute or relative abundance can help in determining specific properties. Knowing the composition of a sample is very important and several ways have been developed to make it possible, like gravimetric and volumetric analysis. Gravimetric analysis yields more accurate data about the composition of a sample than volumetric analysis does, but the first one takes more time to perform in the laboratory. Volumetric analysis in the other side doesn't take that much time and the results that we obtain are in the most cases satisfactory. Volumetric analysis can be simply a titration based in a neutralization reaction but it can also be a precipitation or a complex forming reaction as well as a titration based in an redox reaction. However, each method in quantitative analysis has a general specification, in neutralization reactions, for example, the reaction that occurs is between an acid and a base, which yields a salt and water, hence the name neutralization. In the precipitation reactions the standard solution is in the most cases silver nitrate which is used as a reagent to react with the ions present in the sample and to form a high insoluble precipitate. Precipitation methods are often called simply as Argentometry. In the two other methods the situation is the same. Complex forming titration is a reaction that occurs between metal ions and a standard solution that is in the most cases EDTA (ethylene diamine tetra acetic acid). In the redox titration that reaction is carried out between an oxidizing agent and a reduction agent.

For example, quantitative analysis performed by mass spectrometry on biological samples can determine, by the relative abundance ratio of specific proteins, indications of certain diseases, like cancer.

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X-chromosome

one kind of CHROMOSOME that is involved in the determination of the sex of an individual. A woman has a pair of X-chromosomes, whereas a man has one X-chromosome and one Y-chromosome. There are many GENES on the X-chromosome which have nothing to do with the sex of the individual. For example, red-green colour blindness is determined by a RECESSIVE gene on the X-chromosome. If a woman carrying this gene has a son (X,Y) then he will inherit colour blindness as the Y-chromosome will have no corresponding gene to suppress (over-ride) the effect. If she has a daughter (X,X), and the father has normal vision, then the recessive gene is still inherited but its effect is suppressed (hidden) as the X-chromosome from the father will carry the dominant gene for normal vision.

Taken from Dictionary of Science