Spatial distribution of radiant intensity from primary sources for atomic absorption spectrometry. Part II: Electrodeless discharge lamps

The spatial distribution of radiant intensity from electrodeless discharge lamps (EDLs) used as radiation sources in atomic absorption spectrometry is investigated with a digital photodiode array imaging system. Intensity distribution over the radial and longitudinal sections of Pb and Hg lamps is measured for both atomic and ionic lines of the analyte and the filler gas. The plasma in the EDLs is highly structured, with metal and filler gas excited species being distributed nonuniformly but in different ways. The clouds of emitting metal and Ar atoms are spatially separated in the volume of the Pb EDL. The excited Pb atoms detected from both the resonance and nonresonance lines have the form of a thin layer concentric to the bulb walls located near the surface of the bulb ("optical skin effect"). In contrast, the emission distribution for Ar atomic lines is bell-shaped with a maximum at the center of the plasma. The spatial distribution of emitting Ar ions is more complex - there is a bulk maximum coinciding with Ar atomic emission maximum and another maximum concentric to the walls coinciding with the maximum of metal atom emission. In the Hg EDL the difference between the spatial intensity profiles of metal and filler gas (Ar) lines is less pronounced because of the use of an increased filler gas pressure in the lamp. Emitting species of both Ar and metal are primarily located in the bulk of the plasma with, however, a small depletion in the vicinity of the lamp axis. Evolution of the spatial intensity profiles during warm-up of the lamps is investigated as well. In both lamps the radial and longitudinal intensity distributions of metal lines are established during the first minutes after lamp ignition, after which there is a slow and monotonic increase of the established intensity profiles. This result implies thermal vaporization as a mechanism of analyte supply to the plasma. The spatial intensity profiles for Ar lines are established in the first seconds after lamp ignition, after which only the absolute values of the established distributions change. The approach to the steady-state intensity of Ar atomic and ionic lines is nonmonotonic; there is a clearly pronounced initial overshoot in intensity of Ar atomic lines that coincides with a decline in the intensity of Ar ion lines. An interpretation for the observed spatial intensity profiles is given on the basis of radial cataphoresis theory

Three-dimensional structure of the radiation beam in atomic absorption spectrometry

The results of an investigation of the three-dimensional distribution of radiant intensity in the probing radiation beam produced in a conventional atomic absorption spectrometer by hollow cathode lamps and electrodeless discharge lamps are presented. The investigation is based on the use of a photodiode array-based digital imaging system. The results obtained revealed that the probing radiation beam is highly non-uniform, both longitudinally and radially. The character of the non-uniformities is greatly dependent on the type of the primary source. An interpretation of the results is given and the possible consequences of the radiation beam non-uniformities for the application of Beer-Lambert's law are discussed

Future challenges in colloid and interfacial science

This article deals with topics where I expect special future challenges, exemplifying these by experiments out of my own department. One area where I expect large progress also in view of many technical developments in the past concerns the understanding of the structure of fluid interfaces at the atomic level. It is shown by non-linear optical spectroscopies that the free water surface is ice-like and can be “liquefied” by ion adsorption. X-ray fluorescence from the interface demonstrates that ion binding is very specific which cannot be explained by existing theories. A second major area are nonequilibrium features, and one of the old and new ones here is nucleation and growth. This presentation concentrates on effects produced by ultrasound, a well-defined trigger of gas bubble formation. It exhibits high potential for chemistry at extreme conditions but with a reactor at normal conditions. It has special importance for treatment of surfaces that can be also manipulated via controlled surface energies. A third area will concern complex and smart systems with multiple functions in materials and biosciences. As next generation, I anticipate those with feedback control, and examples on this are self-repairing coatings

Insulin resistance and its association with the components of the metabolic syndrome among obese children and adolescents

<p>Abstract</p> <p>Background</p> <p>Insulin resistance is the primary metabolic disorder associated with obesity; yet little is known about its role as a determinant of the metabolic syndrome in obese children. The aim of this study is to assess the association between the degree of insulin resistance and the different components of the metabolic syndrome among obese children and adolescents.</p> <p>Methods</p> <p>An analytical, cross-sectional and population-based study was performed in forty-four public primary schools in Campeche City, Mexico. A total of 466 obese children and adolescents between 11-13 years of age were recruited. Fasting glucose and insulin concentrations, high density lipoprotein cholesterol, triglycerides, waist circumference, systolic and diastolic blood pressures were measured; insulin resistance and metabolic syndrome were also evaluated.</p> <p>Results</p> <p>Out of the total population studied, 69% presented low values of high density lipoprotein cholesterol, 49% suffered from abdominal obesity, 29% had hypertriglyceridemia, 8% presented high systolic and 13% high diastolic blood pressure, 4% showed impaired fasting glucose, 51% presented insulin resistance and 20% metabolic syndrome. In spite of being obese, 13% of the investigated population did not present any metabolic disorder. For each one of the components of the metabolic syndrome, when insulin resistance increased so did odds ratios as cardiometabolic risk factors.</p> <p>Conclusions</p> <p>Regardless of age and gender an increased degree of insulin resistance is associated with a higher prevalence of disorders in each of the components of the metabolic syndrome and with a heightened risk of suffering metabolic syndrome among obese children and adolescents.</p

Spatially and temporally resolved detection of analytical signals in graphite furnace atomic absorption spectrometry

Spatial non-uniformities in analyte, atomizer gas phase temperature and radiant intensity distributions characteristic for graphite furnace atomic absorption spectrometry are briefly summarized and their effect on the analyte detection is analysed. It is shown that conventional detection of analyte based on the use of photomultiplier tubes provides excellent temporal resolution, sufficient wavelength isolation but totally ignores the spatial aspects of the interaction of the probing radiation beam with the analyte in the atomizer. A new, spatially resolved, method of analyte detection based on the use of a solid state detector located along the monochromator slit is presented. The approach is illustrated by the temporally and spatially resolved detection of Cd atomization and NaCl vaporization. It is shown that severe non-uniformities in atomic and/or background absorbance may be a potential source of analytical error. Advantages of spatially resolved detection as compared with conventional detection are discussed

Spatially and temporally resolved detection of analytical signals in graphite furnace atomic absorption spectrometry

Spatial non-uniformities in analyte, atomizer gas phase temperature and radiant intensity distributions characteristic for graphite furnace atomic absorption spectrometry are briefly summarized and their effect on the analyte detection is analysed. It is shown that conventional detection of analyte based on the use of photomultiplier tubes provides excellent temporal resolution, sufficient wavelength isolation but totally ignores the spatial aspects of the interaction of the probing radiation beam with the analyte in the atomizer. A new, spatially resolved, method of analyte detection based on the use of a solid state detector located along the monochromator slit is presented. The approach is illustrated by the temporally and spatially resolved detection of Cd atomization and NaCl vaporization. It is shown that severe non-uniformities in atomic and/or background absorbance may be a potential source of analytical error. Advantages of spatially resolved detection as compared with conventional detection are discussed

Spatially and temporally resolved detection of analytical signals in graphite furnace atomic absorption spectrometry

Spatial non-uniformities in analyte, atomizer gas phase temperature and radiant intensity distributions characteristic for graphite furnace atomic absorption spectrometry are briefly summarized and their effect on the analyte detection is analysed. It is shown that conventional detection of analyte based on the use of photomultiplier tubes provides excellent temporal resolution, sufficient wavelength isolation but totally ignores the spatial aspects of the interaction of the probing radiation beam with the analyte in the atomizer. A new, spatially resolved, method of analyte detection based on the use of a solid state detector located along the monochromator slit is presented. The approach is illustrated by the temporally and spatially resolved detection of Cd atomization and NaCl vaporization. It is shown that severe non-uniformities in atomic and/or background absorbance may be a potential source of analytical error. Advantages of spatially resolved detection as compared with conventional detection are discussed