Prerequisite For Accurate Results Research Articles

Absorption Coefficients of Phenolic Structures in Different Solvents Routinely Used for Experiments.

Phenolic structures are of great interest due to their antioxidant properties and various postulated benefits on human health. However, the quantification of these structures in fruits and vegetables, as well as in vivo or in vitro experiments, is demanding, as relevant concentrations are often low, causing problems in exactly weighing the respective amounts. Nevertheless, the determination of used concentrations is often a prerequisite for accurate results. A possibility to quantify polyphenol is the use of UV/vis spectroscopy. Therefore, the absorption coefficients of selected phenolic structures were determined in three different solvents relevant for polyphenol research (water/methanol (50/50, v/v), water, and phosphate buffer at pH 7.5). To confirm the values based on weight and to avoid errors due to impurities, hygroscopic effects, and inadequate balance care, the mass concentrations were additionally determined by quantitative NMR (q-NMR). The coefficients presented in this article can help to quickly and easily determine accurate concentrations in a laboratory routine without wasting the often-precious standard compounds.

Modelling of the tributary momentum contribution to predict confluence head losses

ABSTRACTThis paper proposes a new model to determine the head losses at confluences in one-dimensional models of open channel networks, making use of a momentum conservation approach. Momentum conservation has been applied in several theoretical models for confluence head losses, giving satisfactory results in general. However, for larger confluence angles between the main channel and the incoming tributary, the model accuracy diminished. Many authors identified that a correct estimation of the tributary momentum contribution is a prerequisite for accurate results. This work reports on the development and application of a theoretical model for the tributary momentum contribution, based on similarities with the flow upstream of a circular bend in a straight open channel. It describes the two-dimensional depth-averaged flow features in the tributary under the assumption of a 90° angle confluence in which all channels have equal widths, in order to obtain the resulting momentum contribution. The proposed model predicts head losses within the same order of accuracy as a numerical model solving the shallow water equations in two dimensions throughout the confluence.

A simple and fast approach for the determination of inorganic and total mercury in aqueous slurries of biological samples using cold vapor atomic absorption spectrometry and in situ oxidation

A simple, fast and reliable method for the determination of inorganic and total mercury in biological samples directly from slurries prepared in water has been developed using cold vapor atomic absorption spectrometry. The method does not require any standing time or heating of the slurries. Samples are simply mixed with water and measurement can be carried out immediately. For inorganic mercury determination, no additional preparation is required. For total mercury determination the samples have to be oxidized previously with a 2% m/v KMnO4 solution for 2 minutes. After that, the measurement can be carried out similarly to that for inorganic mercury determination. The methylmercury concentration can be calculated as the difference between total and inorganic mercury. The greatest advantage of this method is that only a minimum of reagents and sample handling steps are required, which stands as a prerequisite for accurate results in routine analysis, particularly for the determination of mercury. The results were in good agreement with the 95% confidence level of the certified or close to the informed value for the reference materials investigated. The relative standard deviation was better than 7% for most of the samples. The limits of detection in the sample were determined as 0.020 and 0.016 µg g−1 for inorganic and total mercury, respectively.

Uncertainty of species unspecific quantification strategies in hyphenated ICP-MS analysis

Owing to the lack of standards and certified reference materials for a variety of elemental species in specific matrices the application of species unspecific quantification strategies employing ICP-MS detection has gained more and more importance. The comparison of different calibration strategies by assessing their main sources of uncertainty is a prerequisite for accurate results. A flow injection (FI) model experiment, using a constant spike flow provided by a HPLC pump, and the chromatographic separation of three platinum species were conducted for fundamental evaluation of on-line isotope dilution mass spectrometry (IDMS) used for species unspecific quantification. A cisplatin standard solution was injected into a flow supplied by a HPLC pump for the FI study. This flow was mixed with a constant make-up flow containing an isotopically enriched 196Pt standard. A make-up (fsp) flow of 117 mg min−1 was determined gravimetrically. In comparison, a make-up flow calculation based on reverse ID calibration, i.e., injection of a standard solution of natural isotopic composition, was found to produce significantly biased results. Make-up flow values of 174, 148 and 143 mg min−1 were obtained depending on the peak width of the FI signal (0.7, 1.22, 1.39 min, respectively). A full combined uncertainty calculation, accounting for possible sources of uncertainty in the measurement process, was carried out for both methods and compared with an uncertainty budget which was set up for single point external calibration with internal standardization. On-line IDMS based on gravimetric spike mass flow determination showed a total combined uncertainty of 8%. A comparable uncertainty of 9% was calculated for single point external calibration with internal standardization, since with the investigated FI experiment sources of uncertainty such as gradient elution did not need to be considered. The high total combined uncertainty of 17% of the second investigated on-line IDMS procedure is mainly determined by mass-flow determination. Generally, the final combined uncertainty of on-line IDMS quantification was found to critically depend on the number of measured data points s−1 defining the peak. The species unspecific quantification methods were evaluated for HPLC-ICP-MS analysis of cisplatin and two of its hydrolysis products. On-line IDMS based on gravimetrical mass flow determination was an absolute prerequisite for obtaining accurate results in terms of total platinum concentration.

Determination of mercury in mineral coal using cold vapor generation directly from slurries, trapping in a graphite tube, and electrothermal atomization

A rugged and reliable method for the determination of mercury in coal without sample digestion, based on chemical vapor generation (cold vapor technique) from slurried coal samples has been developed. It involves collection of the mercury vapor in a graphite tube, treated with gold or rhodium as permanent modifier, and determination by electrothermal atomic absorption spectrometry. Mercury quantitatively leached out of the investigated coal reference materials into 1 mol l −1 nitric acid within 48 h when the coal was ground to a particle size of ≤50 μm, except for one sample (BCR 180), which had to be ground to ≤30 μm, or a leaching time of 72 h had to be used. No detectable quantity of mercury was generated directly from the slurry particles, but it was not necessary to filter the solution. The greatest advantage of the method is that only a minimum of reagents and sample handling steps are required, a prerequisite for accurate results in routine analysis. The results were well within the 95% confidence level of the certificate or close to the information value of the reference materials investigated. The characteristic mass of 110 pg obtained with gold as the permanent modifier is close to values reported for direct analysis of solutions, showing close to 100% trapping efficiency for mercury. A limit of detection (LOD) of 90 pg absolute was obtained with this modifier, which corresponds to an LOD of 0.009 μg g −1 Hg in coal. This is based on 1 ml of slurry containing 10 mg of coal, and is an order of magnitude lower than the lowest mercury content in the investigated reference materials.

Age estimation in biopsy specimens of dentin.

Determination of age at death on the basis of aspartic acid racemization in dentin is one of the most reproducible and accurate methods. In Germany, age estimation by this method has so far generally not been applied to living persons, since the extraction of a tooth exclusively for age estimation when it is not medically indicated is regarded as ethically and legally problematic. The development of a biopsy technique applicable to dentin took place against this background. Testing the technique and analysis of dentinal biopsy specimens revealed that the biopsy technique is a low-risk procedure that causes only minor discomfort to the affected person. It is readily practicable and facilitates standardized specimen removal. The relationship between the extent of aspartic acid racemization in dentinal biopsy specimens and age is very close, facilitating age estimation. A prerequisite for accurate results is the performance of biopsies under strictly standardized conditions. If this is guaranteed, age determination on the basis of aspartic acid racemization in dentinal biopsy specimens appears to be superior in precision to most other methods in living persons and can be used for all age groups.