Instrumental Methods Of Analysis
Joke Grinman
Instrumental methods of analysis rely on machines. There are several different types of instrumental analysis. Some are suitable for detecting and identifying elementscloseelementA substance made of one type of atom only., while others are better suited to compoundsclosecompoundA substance formed by the chemical union of two or more elements..
The flame emission spectroscopeclosespectroscopeInstrument used to measure properties of light, usually to identify materials. is a scientific instrument based on flame testing. DataclosedataValues, typically letters or numbers. from a spectroscope can be used to:
In the flame emission spectroscope, the coloured light from a vaporisedclosevaporiseTo turn from a liquid to a gas or a vapour. sample can be split to produce an emission spectrumcloseemission spectrumLight given off by a substance, split into its component colours or wavelengths.. The different lines in an emission spectrum look like a coloured barcode. Each metal ion produces a unique emission spectrum.
The metal present in a sample is identified by comparing its spectrumclosespectrumA series of similar waves arranged in order of wavelength or frequency. with reference spectra. These are emission spectra from known metal ions. If two spectra match, they must be from the same metal ion.
A reading is taken from the flame spectroscope for different concentrations of a metal ion in solution. These readings are used to plot a calibration curveclosecalibration curveGraph with the readings from a machine plotted against known amounts of a substance..
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Background: Shade determination is a critical step for the fabrication of a satisfactory restoration. Visual shade selection with conventional shade guides is subjective and influenced by variables related to light, observer, and object. Shade selection devices have been introduced to provide subjective and quantitative shade values. This systematic review and meta-analysis aimed to compare the color difference for shade selection with visual and instrumental methods.
Methods: An initial search was conducted on databases (MEDLINE via PubMed, Scopus, and Web of Science) in addition to a manual search through references of identified articles. Studies comparing the accuracy of visual and instrumental shade selection based on ΔΕ were included in data synthesis. Mean differences (MDs) and 95% confidence intervals (CIs) were calculated to estimate the effect size for global and subgroup meta-analysis using the inverse variance weighted method and random-effects model (P 0.05). Results were presented as forest plots.
Results: The authors identified 1776 articles from the initial search. Seven in vivo studies were included in the qualitative analysis of which six studies were included in the meta-analysis. For the global meta-analysis, the pooled mean (95% CI) was - 1.10 (- 1.92, - 0.27). Test for overall effect showed that instrumental methods were significantly more accurate than visual methods with significantly less ΔΕ (P = 0.009). Test for subgroup difference showed that the type of instrumental shade selection method used had a significant effect on accuracy (P 0.001). Instrumental methods including spectrophotometer, digital camera, and smartphone showed significantly better accuracy compared with visual shade selection (P 0.05). The greatest mean difference was found between the smartphone and visual method with a mean (95% CI) of - 2.98 (- 3.37, - 2.59) with P 0.001 followed by digital camera and spectrophotometer. There was no significant difference in accuracy between IOS and visual shade selection (P = 1.00).
Conclusions: Instrumental shade selection with a spectrophotometer, digital camera, and smartphone showed significantly better shade matching compared with a conventional shade guide, whereas IOS did not improve the shade matching significantly compared with shade guides.
Compared to the classical methods of analysis, advanced instrumental methods have received increasing attention due to their highly precise analysis of food micro-/macro-structure. Due to its widespread popularity, yogurt has been the subject of numerous studies. This article discusses major advanced instrumental methods applied to the analysis of set/stirred yogurt reported in the literature. Discussed analytical methods have been categorized into two parts, namely chemical analysis methods (including flavor analysis of yogurt, analysis of milk constituents, and assays of indexes), and structural analysis methods (including textural and rheological analysis as well as microstructural analysis).
The many thousands of Aboriginal rock art sites extending across Australia represent an important cultural record. The styles and materials used to produce such art are of great interest to archaeologists and those concerned with the protection of these significant works. Through an analysis of the mineral pigments utilised in Australian rock art, insight into the age of paintings and practices employed by artists can be gained. In recent years, there has been an expansion in the use of modern analytical techniques to investigate rock art pigments and this paper provides a review of the application of such techniques to Australian sites. The types of archaeological information that may be extracted via chemical analysis of specimens collected from or at rock art sites across the country are discussed. A review of the applicability of the techniques used for elemental analysis and structural characterisation of rock art pigments is provided and how future technological developments will influence the discipline is investigated.
The rock art that exists in many parts of the world reflects human behaviour, relationships and experiences and can date back to prehistoric times. The oldest continuous tradition of rock art in the world exists in Australia and this provides an important component of the culture of Aboriginal Australia. Rock art sites exist is many parts of the country, with a high concentration spectacular rock art sites located in the tropical north of the country from Western Australia across to northern Queensland. Australian rock art is represented by many different artistic styles and techniques, often reflecting artistic practices during particular time periods. As such, Australian rock art is of great archaeological interest.
In addition to chronological information, the analysis of rock art pigments can provide insight into production methods, a link between a painting and a source. Different methods of paint production are employed in different regions and by different groups. Mixing with extenders (e.g. ochre with kaolinite), the use of binders (e.g. plant resins, wax) and/or heat treatment to alter the colour of a pigment can be determined via pigment analysis. A link between the composition of paint and a source material (e.g. a local ochre mine) has the potential provide valuable archaeological information. Additionally, a connection between archaeological fragments and rock art can be facilitated by the cross-correlation of the chemical and physical properties. The analysis of the pigments contained in superimposed images (an example painting is illustrated in Fig. 1) provides details about the relative age of particular paintings and also when and if pigment use has changed over time. The identification of conversion products that result from weathering processes of pigments can also provide supporting information about age and preservation.
Ochre is an important component of paint used in traditional, as well as modern, Australian indigenous art. The source material was extensively traded across Australia in the past and it has been established that the chemical composition of ochres is dependent on the source [5, 6]. Ochre is a mixture of natural minerals including iron oxide and clays [7]. Iron oxides, including haematite [Fe2O3] and goethite [FeOOH], in their different forms and combined with other minerals are responsible for the characteristic red, yellow and orange colours associated with this pigment source. Kaolinite [Al2Si2O5(OH)4], huntite [CaMg3(CO3)4], gypsum [CaSO42H2O] and/or calcite [CaCO3], for example, are minerals present in Australian white pigments. The specific compositions of such minerals vary by source location. Black pigments have been widely produced from charcoal, but mineral pigments such as manganese dioxide can be the source of this colour in certain parts of Australia. As there is not generally a history of chemical or thermal modification of pigments in Aboriginal art, the variation in elemental composition and morphology resulting from different geological formations of ochre has the potential to be linked to a source.
The transformation of particular minerals as a result of environmental exposure may also provide insight into the history of particular rock art. The oxalates, whewellite [Ca(C2O4)H2O] and weddelite [Ca(C2O4)2H2O], form deposits on rock surfaces [8, 9]. The oxalates may be produced by the reaction of calcite with oxalic acids formed by microorganisms including algae, fungi and lichens or is formed from bat guano, which contains ammonium oxalate. When the Ca2+ ion diffuses into oxalate-rich environment, the monohydrate whewellite is formed, while the dihydrate weddelite is formed when the \(\textC_2 \textO_4^2 - \) ion diffuses into a calcium-rich environment. Any weddelite that does form eventually transforms into whewellite in the presence of water as the latter is the more thermodynamically stable form. The oxalate minerals in white paint are believed to be a result of the microbiological alteration of huntite and calcite [10]. The oxalate materials that cover (or lie beneath) rock art have proven to be a source of information about when a painting was produced (e.g. [9]).
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