Simultaneous determination of nitrite and nitrate ions by air-segmented amplitude-modulated multiplexed flow analysis

Triangular-wave controlled amplitude-modulated flow analysis for extending dynamic range to saturated signals

We have applied our amplitude-modulated flow analysis concept to extend the dynamic range to saturated analytical signals. Sample solution, the flow rate F_S of which is periodically varied with a triangular control signal V_c, is merged with a reagent solution delivered at a constant flow rate F_R. While the total flow rate F_T is kept constant, a diluent with F_T-(F_S + F_R) flow rate is aspirated from the third channel. The analytical signal V_d obtained downstream is processed by fast Fourier transform to obtain the amplitudes of the wave components in V_d. When the sample concentration C_S is low, V_d shows a triangular profile like V_c; the sum of the amplitudes ΣA is proportional to C_S. When C_S is high, V_d shows a trapezoidal profile because of the V_d saturation. A linear calibration curve can also be obtained for such saturated signals by plotting C_SΣA against C_S. The proof of the concept is validated by applying it to spectrophotometric determinations of a dye (Methylene Blue) and colored complexes of Fe²⁺ - phenanthroline and Fe³⁺ - Tiron.

Introduction of Air-Segmentation Approach to Flow Titration by Feedback-based and Subsequent Fixed Triangular Wave-controlled Flow Ratiometry

An air-segmentation approach has been introduced to a feedback-based and subsequent fixed triangular wave-controlled flow ratiometry to suppress axial dispersion in flow titration. The flow rate of a base solution containing an indicator is linearly varied with a control signal, Vc, supplied by a computer. The solution is merged with an acid solution under a constant total flow rate. Air is introduced to the merged solution in order to segment the solution with air bubbles. Both phases are led to a UV/Vis detector without phase separation. Air signals are removed by signal processing. The effect of the lag time between the merging of solutions upstream and the sensing of the corresponding signal downstream is offset by feedback-based upward and downward Vc scans, and thus the Vc that gives the equivalence composition is determined. Subsequently, fixed triangular wave control is applied to a narrower Vc range with a higher scan rate to enhance the throughput rate (maximally 11.8 titrations/min). Air-segmentation has been found to be effective to reduce axial dispersion and to preserve the titrand/titrant composition upon their just being merged. Consequently, the applicable range is extended especially to lower titrand concentration. The proposed method has been successfully applied to various acid-base titrations, including the nonaqueous titration of the Japanese Pharmacopoeia drug.

Design of analytical systems based on functionality of doped ice

Ice plays an important role for the circulations of some compounds in the global environment. Both the ice surface and the liquid phase developed in a frozen solution are involved in such reactions of the molecules of environmental importance. This leads to the idea that ice can be used to design novel analytical reaction systems. We devised ice chromatography, in which ice particles are used as the liquid chromatographic stationary phase, and have subsequently developed various analytical systems utilizing the functionality of ice. This review focuses our attention on the analytical facets of ice containing impurities such as salts; hereinafter, we call this "doped ice". The design of novel separation systems and use as microreactors with doped ice are mainly discussed.

Air segmented amplitude modulated multiplexed flow analysis with software-based phase recognition: determination of phosphate ion

Amplitude modulated multiplexed flow analysis (AMMFA) has been improved by introducing air segmentation and software-based phase recognition. Sample solutions, the flow rates of which are respectively varied at different frequencies, are merged. Air is introduced to the merged liquid stream in order to limit the dispersion of analytes within each liquid segment separated by air bubbles. The stream is led to a detector with no physical deaeration. Air signals are distinguished from liquid signals through the analysis of detector output signals, and are suppressed down to the level of liquid signals. Resulting signals are smoothed based on moving average computation. Thus processed signals are analyzed by fast Fourier transform. The analytes in the samples are respectively determined from the amplitudes of the corresponding wave components obtained. The developed system has been applied to the simultaneous determinations of phosphate ions in water samples by a Malachite Green method. The linearity of the analytical curve (0.0-31.0 μmol dm(-3)) is good (r(2)>0.999) and the detection limit (3.3 σ) at the modulation period of 30s is 0.52 μmol dm(-3). Good recoveries around 100% have been obtained for phosphate ions spiked into real water samples.

A review of the phytochemistry and pharmacological activities of raphani semen

The dried ripe seed of Raphanus sativus L., commonly known as radish seed (or Raphani Semen), is used as traditional Chinese medicine (TCM) to treat constipation, chronic tracheitis, and hypertension. The major active compounds in Raphani Semen are alkaloids, glucosinolates, brassinosteroids, and flavonoids. Fatty acids are its main nutritional contents. Raphani Semen has been demonstrated to have beneficial effects on hypertension, obesity, diabetes mellitus, constipation, and cough. So far, there is no report about the adverse/toxic effects of this herb on humans. However, Raphani Semen processed by roasting was reported to exhibit some adverse effects on mice. Additionally, erucic acid, the main fatty acid in Raphani Semen, was shown to enhance the toxicity of doxorubicin. Thus, Raphani Semen has a potential risk of causing toxicity and drug interaction. In summary, Raphani Semen is a valuable TCM herb with multiple pharmacological effects. More studies on Raphani Semen could help better understand its pharmacological mechanisms so as to provide clear scientific evidence to explain its traditional uses, to identify its therapeutic potential on other diseases, and to understand its possible harmful effects.