FI Method Research Articles

Flow injection spectrophotometric determination of acetylsalicylic acid in tablets after on-line microwave-assisted alkaline hydrolysis

The proposed method is based on the on-line microwave-assisted alkaline hydrolysis of acetylsalicylic acid (ASA) to salicylic acid (SA) that reacts with FeIII to form a complex that absorbs at 525 nm. Samples merged with NaOH were passed continuously through a domestic microwave oven in order to accelerate the hydrolysis of ASA. Under the best analytical conditions, the linearity of the calibration equation for ASA ranged from 25 to 250 µg ml–1. The precision for ten successive measurements of 200 µg ml–1 ASA presented a relative standard deviation of 0.40%. The detection limit was 4.0 µg ml–1 and recoveries of 99.1–101.0% were obtained for ASA. No interference was observed from the common excipients of tablets and other active substances such as ascorbic acid and caffeine. The proposed FI method is adequate for a large number of samples because it is not time consuming and permits the determination of ASA in 90 samples per hour.

Immobilization of xanthine oxidase and its use in the quantitation of hypoxanthine in fish muscle tissue extracts using a flow injection method

Fish muscle extracts (Scomberomorus— brasiliensis- carite) were analyzed for their hypoxanthine content using a flow injection system incorporating an immobilized xanthine oxidase bioreactor. The xanthine oxidase was immobilized under mild conditions to a 2-fluoro-1-methylpyridinium Fractogel support. The uric acid produced from the oxidation of hypoxanthine by the immobilized xanthine oxidase at pH 7.0 and 35‡C was monitored at 290 ran. Hypoxanthine concentrations as low as 4.4 Μmol/L can be detected. Up to 30 samples per hour can be analyzed at a flow rate of 1 mL/min, using 150 ΜL sample volumes and a bioreactor dimension of 1.0 cm x 2.0 mm id. Recovery yields were between 92 and 99%. Both within day and between day precisions gave CVs < 5.00% (n = 30). Good correlation (r = 0.998) is obtained when 78 fish samples were analyzed for their hypoxanthine content both by this FI method and a reference HPLC method.

Development of a Numerical Solution Method for Advection Terms and Its Application to the Atmospheric Dynamic Model, PHYSIC

A numerical solution method, HIFI, for advection terms was developed. The method is a hybrid of the newly developed FI method, the first- and second-order upwind schemes. The excursion of the solution caused by the FI method is suppressed by applying the first- and second-order upwind schemes only at the grid points where the excursion of the solution is predicted. This limited use of the high-numerical-diffusion schemes can suppress the numerical diffusion to a reasonably low level. The FI method was designed so as to maximize on accuracy without loosing any stability due to the linear analysis. The accuracy and stability of the FI method vary according to the Courant number and other parameters. HIFI was adopted based on the meteorological sub-model of the numerical atmospheric dispersion model, PHYSIC. Predictability of wind speed in the lower atmosphere could be improved. It is considered that the HIFI method can be applied not only to the meteorological sub-mode in PHYSIC but also to the diffusion ca...

Development of a Numerical Solution Method for Advection Terms and Its Application to the Atmospheric Dynamic Model, PHYSIC.

A numerical solution method, HIFI, for advection terms was developed. The method is a hybrid of the newly developed FI method, the first- and second-order upwind schemes. The excursion of the solution caused by the FI method is suppressed by applying the first- and second-order upwind schemes only at the grid points where the excursion of the solution is predicted. This limited use of the high-numerical-diffusion schemes can suppress the numerical diffusion to a reasonably low level. The FI method was designed so as to maximize on accuracy without loosing any stability due to the linear analysis. The accuracy and stability of the FI method vary according to the Courant number and other parameters.HIFI was adopted based on the meteorological sub-model of the numerical atmospheric dispersion model, PHYSIC. Predictability of wind speed in the lower atmosphere could be improved. It is considered that the HIFI method can be applied not only to the meteorological sub-mode in PHYSIC but also to the diffusion calculation of atmospheric radioactive materials.

Determination of inorganic phosphate by flow injection with fluorescence quenching

An FI method using fluorescence quenching for the determination of phosphate ions is proposed. The method is based on the ability of phosphates to inhibit the formation of a strongly fluorescent complex of scandium ions with 2-hydroxy-1-naphthaldehyde-p-methoxy-benzoylhydrazone (HNAMBH) in weakly acidic (pH 4) water–ethanol (50% v/v) mixtures. The optimal chemical conditions for fluorescence quenching of the HNAMBH–Sc complex by phosphates were studied, and a simple FI manifold was developed. The method has been applied to the determination of phosphate in blood serum. The sensitivity of the method allows a 1:1000 dilution of the serum samples, so that interferences from other serum constituents are suppressed. The measurement throughput was 120 h–1. The ranges of application (as phosphorus) are 3.0–15 µg l–1 and 15–150 µg l–1. The detection limit of the method is 3.0 µg l–1(3.0 mg l–1 for serum, high concentration range) and 0.8 µg l–1(0.8 mg l–1 for serum, low concentration range). Within-run sr values for 6.0, 9.0 and 15.0 µg l–1 of phosphorus were 5.7, 5.2 and 1.8%, and for 30.0, 60.0 and 120 µg l–1 of phosphorus were 2.6, 2.5 and 1.8%, respectively. Analytical recoveries from serum samples range from 95.5 to 103.9%(mean 99.1%).

Relationship between the amount and the activity of the microbial biomass in Dutch grassland soils: Comparison of the fumigation-incubation method and the substrate-induced respiration method

The aim of this study was to test whether soil texture and amount of available carbon affect microbial activity and the percentage of the soil microbial biomass that is active. Total and active microbial biomass were determined by the fumigation-incubation method (FI) and the substrate-induced respiration method (SIR), respectively. The ratio biomass-SIR:biomass-FI, indicating the percentage of active microbial biomass, and the ratio C mineralization: biomass-FI, indicating the activity of the microbial biomass, were both higher in soils with a coarse texture than in soils with a fine texture. The ratio C mineralization :biomass-SIR was not affected by soil texture. The ratios biomass-SIR:biomass-FI and C mineralization : biomass-FI were higher in the upper 10-cm soil layer than in the 10–25 cm layer, while the ratio C mineralization :biomass-SIR was not affected by soil depth. During 25 weeks incubation, the amount of biomass-SIR as well as the C mineralization rate decreased significantly. The amount of biomass-FI, however, did not change significantly during incubation. Assuming that the amount of available C decreases both with soil depth and during incubation, the observations indicate that smaller amounts of available carbon coincide with a reduced activity of the biomass and a lower percentage of active biomass. The close similarity between C mineralization rate and amount of biomass-SIR shows that biomass-SIR is a good indicator of microbial activity, whereas the FI method is not suitable for this purpose.