A gas diffusion sequential injection system for the determination of sulphur dioxide in wines

In the present work, a sequential injection system with spectrophotometric detection was developed for the determination of free and total sulphur dioxide in wines. It was based on the formation of a coloured product from the reaction among SO2, formaldehyde and pararosaniline. A gas diffusion unit (GDU) was incorporated into the manifold to prevent the wine matrix interference in the spectrophotometric measurement. An acid solution was added to the sample prior to its passage through the donor channel of the GDU to promote gaseous SO2 formation. For the free SO2 determination, the sample was directly aspirated into the holding coil; for the total SO2 determination, the sample was processed after previous in-line hydrolysis of bound SO2 with an alkali solution. Two second-order calibration curves were established, defining two concentration ranges: 2–40 mg l−1 for the free SO2 determination and 25–250 mg l−1 for the total SO2 determination. Relative standard deviations (n=10) were lower than 1.2% for the determination of free SO2 and lower than 2.3% for the determination of total SO2. The sample frequency was about 16 h−1. This methodology was applied to the determination of free and total sulphur dioxide in 10 table wines and the results were statistically comparable with those furnished by the recommended procedure

On The Gould’s Formula for Stirling Numbers of The Second Kind

We present an alternative deduction of the Gould’s relation for Stirling numbers of the second kind. Our approach is based in the Nörlund polynomials and in the duality property between the Stirling numbers

Multi-syringe flow injection system with in-line microwave digestion for the determination of phosphorus

A multi-syringe system for spectrophotometric determination of total phosphorus involving in-line digestion is proposed. Sample and digestion solution were dispensed and directed towards a digestion vessel located inside a domestic microwave oven (MWO) where sample digestion took place. Afterwards, the digested sample was merged with the necessary reagents for the colorimetric determination based on the molybdenum blue method. Several digestion conditions were studied regarding composition of digestion solution, digestion time and power set on theMWO. The system was applied to waste water samples and results shown a good agreement with the reference method. Repeatable results (R.S.D. < 2.41%) and determination frequency of 12 h−1 were obtained.info:eu-repo/semantics/acceptedVersio

Multi-syringe flow injection system for the determination of available phosphorus in soil samples

Considering the importance of monitoring the levels of nutrients present in soils and their availability to plants, an automatic methodology is proposed based on multi-syringe flow injection analysis (MSFIA) for the spectrophotometric determination of available phosphorus in soil extracts. This fully computerized flow technique allowed the development of a flow network where sample and reagents were intercalated and sent further towards the detection system. The colorimetric determination was based on the molybdenum blue method with ascorbic acid as reducing reagent and the Egner–Riehm method was applied to extract phosphorus from soil samples. A linear calibration curve was obtained between 0.75 and 15.0mgL-1. A determination frequency of 15 h-1 was achieved, with good repeatability for 12 consecutive injections of soil extracts (RSD<1.7%). The results obtained from 12 soil samples were statistically comparable to those attained by the usual batch method

Real-time phase-shift detection of the surface plasmon resonance

We investigate a method to directly measure the phase of a laser beam reflected from a metallic film after excitation of surface plasmon polaritons. This method permits real time access to the phase information, it increases the possible speed of data acquisition, and it may thus prove useful for increasing the sensitivity of surface plasmon based sensors

Total Degree Formula for the Generic Offset to a Parametric Surface

We provide a resultant-based formula for the total degree w.r.t. the spatial variables of the generic offset to a parametric surface. The parametrization of the surface is not assumed to be proper.Comment: Preprint of an article to be published at the International Journal of Algebra and Computation, World Scientific Publishing, DOI:10.1142/S021819671100680

Spectrophotometric determination of iron and boron in soil extracts using a multi-syringe flow injection system

In the last decade, significant advances in flow analysis have been reported, namely the extensive use of computer-controlled devices to enhance the autonomy and performance of analysers. In the present work, computer-controlled multi-syringe flow injection systems are proposed to perform the spectrophotometric determination of available iron and boron in soil extracts. The methodologies were based on the formation of ferroin complex (determination of iron) and azomethine-H reaction (determination of boron). Both determinations were performed in manifolds with similar configurations by changing the reagents present in the different syringes. In the determination of iron, elimination of Schlieren effect in the detection system was achieved through the binary sampling approach, where a three-way valve was actuated to intercalate small slugs of sample and reagent, promoting better mixing conditions for solutions with different values of refractive index. In the determination of boron, in-line sample blank measurement was attained by omitting the introduction of reagent through software control, without manifold reconfiguration. Linear calibration curves were established between 0.50 and 10.0 mg Fe l−1 and between 0.20 and 4.0 mgBl−1. No systematic difference was found when soil extracts were analysed by the proposed methodologies and compared to the respective reference procedures.info:eu-repo/semantics/acceptedVersio

Fluorometric method based on molecular recognition solid-phase extraction for determination of riboflavin in milk and infant formula

Riboflavin (vitamin B2) is involved in several biological processes, particularly in energy production, and it is acquired from food ingestion, principally from supplemented food during the first years of life. Therefore, a simple, fast and cost-effective high-throughput method for determination of riboflavin in milk and infant formula is proposed, based on selective extraction using commercially available molecularly imprinted polymers targeted to riboflavin, followed by direct fluorometric determination. Several aspects were studied, namely microplate assay conditions, the composition of eluting solution and the stability of riboflavin in the eluate. Hence, elution using 1% (v/v) acetic acid in methanol or in acetonitrile is recommended, followed by immediate analysis or solvent evaporation, with reconstitution and analysis within 24 h. The proposed method provided a LOD of 0.03 mg L−1, with working range for undiluted samples between 0.125 and 2 mg L−1, and sample throughput of 24 h−1. It was successfully applied to certified reference material NIST-1846 and also to commercial milk and infant formula samples.info:eu-repo/semantics/publishedVersio