| Analytical Chemistry |
Article Index for Analytical |
Shopping Analytical |
Articles about Analytical Chemistry |
Website Links For Analytical |
Information AboutAnalytical Chemistry |
| CATEGORIES ABOUT ANALYTICAL CHEMISTRY | |
| analytical chemistry | |
| materials science | |
| materials analysis methods | |
| science-related listsanalytical chemistry | |
| materials science | |
| materials analysis methods | |
| science-related lists | |
| chemistry | |
|
Analytical chemistry is the of material samples to gain an understanding of their Chemical Composition and Structure . TYPES Analytical chemistry can be split into two main types, qualitative and quantitative: # Qualitative Inorganic Analysis seeks to establish the presence of a given Element or Inorganic Compound in a sample. #Qualitative organic analysis seeks to establish the presence of a given Functional Group or Organic Compound in a sample. # Quantitative Analysis seeks to establish the amount of a given element or compound in a sample. Most modern analytical chemistry is quantitative. Quantitative analysis can be further split into different areas of study. The material can be analyzed for the amount of an element, or for the amount of an element in a specific chemical species. The latter is of particular interest in biological systems; the molecules of life contain carbon, hydrogen, oxygen, nitrogen, and others, in many complex structures. TECHNIQUES There are a bewildering array of techniques available to separate, detect and measure chemical compounds. These can be grouped into four main categories: # Separation Of Chemicals in order to measure the weight or volume of a final product. This is an older process and can be quite painstaking, but is an essential first step when dealing with certain mixtures of substances, like extracts from organisms. Modern separation techniques such as HPLC often seek to separate and determine amount or identity in a single automated analysis by integrating a detector. # Titration is a technique used to determine amounts present in solution or a physical characteristic of a molecule such as an Equilibrium Constant . # Spectroscopy measures the absorption or emission of various types of Radiation . From the radiation energy, we can infer the chemical compositions and quantities. Methods include Atomic Absorption Spectroscopy (AAS), Nuclear Magnetic Resonance (NMR) and Neutron Activation Analysis (NAA). # Mass Spectrometry is used to determine the Molecular Mass , the elemental composition, structure and sometimes amount of chemical species in a sample by Ionizing the analyte molecules and observing their behavior in electric and magnetic fields. "Hybrid" or "hyphenated" techniques combine two or more analytical methods such as ICP-MS (Inductively-Coupled Plasma - Mass Spectrometry), where Volatilisation of a sample occurs in the first step, and measuring of the concentration occurs in the second. The first step may also involve a separation technique, such as Chromatography , and the second a detection / measuring device. Another example of a hybrid technique is Gas Chromatography-Mass Spectrometry {Link without Title} , which is primarily used for non-ionic, volatilizable organic compounds. The compounds are separated on a chromatographic column, and introduced directly, or via a specialized interface, to an ionization chamber in a mass spectrometer. The compounds are then ionized (typically by electron impact, or chemical ionization) and accelerated through a carefully controlled electromagnetic field. The time of flight, or the voltage applied at the exact moment of impact is unique for compounds of the same mass. In this manner, the retention time and mass are measured for each compound. Techniques that involve volatilisation aim to produce free atoms of the elements making up the sample, which can then be measured in concentration by the degree to which they absorb or emit at a characteristic spectral frequency. These methods have the disadvantage of completely destroying the sample, and any species contained within it. These techniques include Atomic Absorption Spectroscopy and ICP-MS / ICP-AES . These techniques can still be used to study speciation, however by the incorporation of a separation stage before volatilisation. METHODS Analytical methods rely on scrupulous attention to cleanliness, sample preparation, Accuracy And Precision . Many practitioners will keep all their glassware in acid to prevent contamination, samples will be re-run many times over, and equipment will be washed in specially pure solvents. A standard method for analysis of concentration involves the creation of a Calibration Curve . If the concentration of element or compound in a sample is too high for the detection range of the technique, it can simply be diluted in a pure solvent. If the amount in the sample is below an instrument's range of measurement, the method of addition can be used. In this method a known quantity of the element or compound under study is added, and the difference between the concentration added, and the concentration observed is the amount actually in the sample. TRENDS Analytical chemistry research is largely driven by performance (sensitivity, selectivity, robustness, linear range, accuracy, precision, and speed), and cost (purchase, operation, training, time, and space). A lot of effort is put in shrinking the analysis techniques to Chip size. Although there are few examples of such systems competitive with traditional analysis techniques, potential advantages include size/portability, speed, and cost. ( Total Analysis System or lab on a chip) Much effort is also put into analyzing biological systems. Examples of rapidly expanding fields in this area are:
SEE ALSO
|
|
|