Sedimentation methods, high sensitivity

We have recently developed a microcalorimetric technique for quantifying the energetic changes of microorganisms colonizing a sea-water-sediment interface in experimental microcosms. The inherent low specificity of direct microcalorimetry and, moreover, the high sensitivity and reliability of modern microcalorimeters proved advantageous, since unknown and subtle events, not shown by more specific methods, may be detected. 

As stated in Section 8.2.1, only limited results concerning Mw determinations of lignins with the use of LALLS photometry have been published. This radically new and sophisticated technique constitutes an improvement over other methods, such as sedimentation equilibrium and size exclusion chromatography, for the evaluation of Mw. Its low angle capability, combined with high sensitivity, small sample size, and simplified clarification procedures, allow simple and accurate determinations to be made even on lignin samples which have been considered very troublesome. Moreover, as stated in Section 8.2.2, additional difficulties, inherent lignin properties, i.e., absorbance, fluorescence and anisotropy, may also be overcome. 

New High Sensitivity Sedimentation Methods Application to the Analysis of the Assembly of Bacteriophage P22... 

Modem analytical methods can provide a rapid and highly sensitive examination of contaminated soils, sediments, landfill, etc., provided that the samples presented for analysis are homogeneous and in an appropriate physical form. 

Limits of detection (LODs) reached were 0.4 ng/1 of uranium and 2.8 ng/1 of thorium. The reproducibility of the LOV—MSFIA—ICP-MS was 1.7% expressed as relative standard deviation (RSD). Moreover, a high sensitivity, a wide working range, e.g. 0—200 pg/1 for both U and Th, and an injection frequency up to 9/h (depending on the sample volume) should be highlighted. Different water sample matrices (seawater, well water, freshwater, tap water and mineral water), a phosphogypsum sample with natural uranium and thorium content and a channel sediment reference material were satisfactorily analyzed with the proposed method. 

Despite the advances made in high-performance liquid chromatography in recent years, there are still occasionally applications in which conventional column chromatography is employed. These methods lack the sensitivity, resolution and automation of HPLC. They include the determination of urea herbicides in soil, polyaromatic hydrocarbons, carbohydrates, chloroaliphatic compounds and humic and fulvic acids in non-saline sediments. The technique has also been applied in sludge analysis, e.g. aliphatic hydrocarbons and carboxylic acids. 

Three different detection methods (gas chromatography with electron capture, mass spectrometric and atomic emission detectors) have been compared for the determination of polychlorobiphenyls in highly contaminated marine sediments [74], Only atomic emission detection in the chlorine-selective mode provided excellent polychlorobiphenyl profiles without interferences. However, the lower sensitivity of the atomic emission detector, compared to the other two detectors required a 10 to 20g sample size for most analyses. 

The extraction and clean-up methods used for the recovery of organophosphorus derivatives do not differ basically from those applied to other groups of substances. However, because of the high toxicity of the compounds involved, the techniques must be extremely sensitive and able to detect sub-nanogram amounts. A number of reviews have been published on the subject164-171. As previously mentioned, the compounds to be analysed may be found in living matter as well as in soil, sediments, water and air the experimental methods vary accordingly. 

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