Determination of sulfur forms in wine including free and total sulfur dioxide based on molecular absorption of carbon monosulfide in the air–acetylene flame

A new method for the determination of sulfur forms in wine, i.e., free SO₂, total SO₂, bound SO₂, total S, and sulfate, is presented. The method is based on the measurement of the carbon monosulfide (CS) molecular absorption produced in a conventional air–acetylene flame using high-resolution continuum source absorption spectrometry. Individual sulfur forms can be distinguished because of the different sensitivities of the corresponding CS molecular absorption. The sensitivity of free SO₂ is about three times higher than the value for bound SO₂ and sulfate. The method makes use of procedures similar to those used in classic reference methods. Its performance is verified by analyzing six wine samples. Relative standard deviations are between 5 and 13% for free SO₂ and between 1 and 3% for total SO₂. For the validation of the accuracy of the new method, the results are compared with those of reference methods. The agreement of the values for total SO₂ with values of the classic method is satisfactory: five out of six samples show deviations less than 16%. Due to the instability of free SO₂ in wine and the known problems of the used reference method, serious deviations of the free SO₂ results are found for three samples. The evaluation of the limits of detection focuses on the value for free SO₂, which is the sulfur form having by far the lowest concentration in wine. Here, the achievable limit of detection is 1.8 mg L⁻¹. Figure Detection of non-metal elements using continuum source flame absorption spectrometry     

Selective synthesis and derivatization of alkali metal silanides MSi(SiH3)3

Greetings from silicon valley: Alkali metal silanides (H(3)Si)(3)Si(-)M(+) were shown to be selectively accessible for the first time by the reaction of neopentasilane Si(SiH(3))(4) with tBuOM or iPr(2)NLi. The method allows the convenient derivatization of higher silicon hydrides and provides a simple access for unprecedented systematic studies on the chemical behavior of hydropolysilanes (see scheme).     

Spin-lock techniques and CPMG imaging sequences: a critical appraisal of T1p contrast at 0.15 T

The addition of a spin-lock preparatory sequence to a Carr-Purcell-Meiboom-Gill (CPMG) imaging sequence provides a method which allows an accurate and simple comparison of T1p and T2 contrast. Sagittal and axial brain images, produced with the application of a three pulse preparatory spin-lock sequence prior to a sixteen-echo CPMG imaging sequence, are compared with images acquired without the spin-lock sequence. The CPMG sequence uses non-selective refocusing pulses. Therefore, observed echo signals accurately reflect T2 relaxation. This allows a convenient method for assessing the degree to which T1p and T2 contrast differ. The spin-lock CPMG (SL-CPMG) images were acquired with a spin-locking field amplitude of 0.4 G and resemble heavily T2-weighted images at 0.15 T. Quantitative analyses of signal intensities from edema and normal brain tissue confirm the qualitative observations. This in vivo method should prove useful for determining when the additional RF power deposition associated with spin-locking techniques will provide an alternate form of tissue contrast than that available from additional echo collection.     

Scales of Nucleophilicity and Electrophilicity: A System for Ordering Polar Organic and Organometallic Reactions

Contrary to widely held opinion, for many reactions in organic and organometallic chemistry it is possible to define nucleophilicity and electrophilicity parameters that are independent of the reaction partners. This phenomenon, discovered by Ritchie during the early 1970s for reactions of highly stabilized carbenium and diazonium ions with n-nucleophiles, also occurs with reactions of carbenium ions with aliphatic and aromatic π-electron systems and in hydride transfer reactions. With the aid of the scales of nucleophilicity and electrophilicity set out here, which extend over eighteen orders of magnitude, forecasts can be made about the feasibility and rate of a given CC bond formation, ionic reduction, or diazo coupling. Linkage with the reactivity scales of Ritchie and Sweigart/Kane-Maguire enables a unified treatment of a large number of polar reactions.     

Wine Storage at Cellar vs. Room Conditions: Changes in the Aroma Composition of Riesling Wine

Storage temperature is one of the most important factors affecting wine aging. Along with bottling parameters (type of stopper, SO₂ level and dissolved O₂ in wine), they determine how fast wine will evolve, reach its optimum and decline in sensory quality. At the same time, lowering of the SO₂ level in wine has been a hot topic in recent years. In the current work, we investigated how Riesling wine evolved on the molecular level in warm (~25 °C) and cool (~15 °C) conditions depending on the SO₂ level in the wine (low, medium and high), flushing of the bottle’s headspace with CO₂ and three types of stoppers (Diam 30, Diam 30 origin and Diam 5) with different OIR levels (0.8–1.3 mg) and OTR levels (0.3–0.4 mg/year). It was demonstrated that the evolution of primary and secondary aromas, wine color and low molecular weight sulfur compounds (LMWSCs) during the two years of aging mainly depended on the storage temperature. Variation in the SO₂ level and CO₂ in the headspace affected mostly certain LMWSCs (H₂S, MeSH) and β-damascenone. New aspects of C₁₃-norisprenoids and monoterpenoids behavior in Riesling wine with different levels of SO₂ and O₂ were discussed. All three types of stoppers showed very close wine preservation properties during the two years of storage. The sensory analysis revealed that, after only six months, the warm stored wines with a low SO₂ level were more oxidized and different from the samples with medium and high SO₂ levels. A similar tendency was also observed for the cool stored samples.     

Continuous glucose monitoring in interstitial fluid using glucose oxidase-based sensor compared to established blood glucose measurement in rats

Glucose monitoring is of importance for success of complex therapeutic interventions in diabetic patients. Its impact on treatment and glycemic control is demonstrated in large clinical trials. Up to eight blood glucose measurements per day are recommended. Notwithstanding, a substantial number of diabetic patients cannot or will not monitor their blood glucose appropriately. Considerable progress in control of disturbed metabolism in diabetic patients can be expected by continuous glucose monitoring. The aim of the study was to evaluate the performance of a new amperometric glucose oxidase-based glucose sensor in vitro and in vivo after subcutaneous implantation into rats.For in vitro testing current output of sensors was measured by exposure to increasing and decreasing glucose concentrations up to 472 mg dL⁻¹ over a time period of 7 days. After subcutaneous implantation of sensors into interscapular region of male rats glucose in interstitial fluid was evaluated and compared to glucose in arterial blood up to 7 days. Hyper- and hypoglycaemia were induced by intravenous application of glucose and insulin, respectively. Current of each implanted sensor was converted into glucose concentration using the first blood glucose measurement only.A change of current with glucose of 0.35 nA mg⁻¹ dL⁻¹ indicates high sensitivity of the sensor in vitro. The response time (90% of steady state) was calculated by approximately 60 s. Test strips for blood glucose measurement as reference for sensor readings was found as an appropriate and rapidly available method in rats by comparison with established hexokinase method in an automated lab analyzer with limits of agreement of +32.8 and −25.7 mg dL⁻¹ in Bland-Altman analysis. In normo- and hypoglycaemic range sensor readings in interstitial fluid correlated well with blood glucose measurements whereas hyperglycaemia was not reflected by the sensor completely when blood glucose was changing rapidly.The data given characterize a sensor with high sensitivity, long term stability and short response time. A single calibration of the sensor is required only in measurement periods up to 7 days. The findings demonstrate that the sensor is a highly promising candidate for assessment in humans.     

Clinical experience with rapid 2DFT SSFP imaging at low field strength

A retrospective analysis of clinical imaging using 2DFT SSFP at 0.14 T is presented. The technique's potential for tissue characterization and its utility for clinical diagnosis were tested by both in vitro measurements of various tissues and in vivo clinical images. Different pulse angles not only influenced image contrast, but also helped characterize lesions, particularly those containing fat. In addition, the pulse angle changed the signal from venous flow perpendicular to the imaged slice. The slow flow sensitivity of the 2DFT SSFP technique was demonstrated in the detection of CSF motion. Rapid SSFP offers flow sensitivity and adequate lesion detecting ability, along with high patient throughput.     

Explicit one-step time discretizations for discontinuous Galerkin and finite volume schemes based on local predictors

We consider a family of explicit one-step time discretizations for finite volume and discontinuous Galerkin schemes, which is based on a predictor-corrector formulation. The predictor remains local taking into account the time evolution of the data only within the grid cell. Based on a space–time Taylor expansion, this idea is already inherent in the MUSCL finite volume scheme to get second order accuracy in time and was generalized in the context of higher order ENO finite volume schemes. We interpret the space–time Taylor expansion used in this approach as a local predictor and conclude that other space–time approximate solutions of the local Cauchy problem in the grid cell may be applied. Three possibilities are considered in this paper: (1) the classical space–time Taylor expansion, in which time derivatives are obtained from known space-derivatives by the Cauchy–Kovalewsky procedure; (2) a local continuous extension Runge–Kutta scheme and (3) a local space–time Galerkin predictor with a version suitable for stiff source terms. The advantage of the predictor–corrector formulation is that the time evolution is done in one step which establishes optimal locality during the whole time step. This time discretization scheme can be used within all schemes which are based on a piecewise continuous approximation as finite volume schemes, discontinuous Galerkin schemes or the recently proposed reconstructed discontinuous Galerkin or P_NP_M schemes. The implementation of these approaches is described, advantages and disadvantages of different predictors are discussed and numerical results are shown.