High Throughput Titration Based on Variable and Fixed Triangular Wave Controlled Flow Ratiometry with LED-Photodiode Detector

Unprecedented high throughput flow titration (maximally 43.1 titrations/min) has been realized by a triangular wave controlled flow ratiometry using an in-house LED-photodiode detector. The detector was fabricated mainly with quartz tubing, an LED, a photodiode and a DC power supply. While the total flow rate is held constant, a titrand (acid) is merged with a titrant (base) containing an indicator, the flow rate of which is linearly varied by the control voltage Vc supplied from a computer. Downstream, the intensity of the transmitted light is monitored with the detector and acquired in the computer as detector output voltage Vd. In the initial feedback-based mode, the lamp direction of Vc is changed from upward to downward, or vice versa, when the detector senses the equivalence point. In the subsequent fixed triangular wave controlled mode, the scan range and the scan rate of Vc are further limited and quickened, respectively, in order to increase the throughput rate. Equivalence point is determined by offsetting the effect of the lag time between the upstream merging and the downstream sensing. Although the present approach is an absolute method, calibration curves have been constructed for practical operation. The linearity of the curve is satisfactory (r2 › 0.993). The present method is well applicable to various titrations of acids and bases including acetic acid in commercial vinegars

Unprecedented High Throughput Titration by Feedback-Based and Subsequent Fixed Triangular Wave-Controlled Flow Ratiometry and Its Application to Quantification of Japanese Pharmacopoeia Drugs

Throughput rate of flow ratiometric titration has further been enhanced by shortening the lag time from the confluence of solutions upstream to the sensing of signal downstream and by optimizing analytical parameters. Feedback-based upward and downward scans of titrand/titrant flow ratio were repeated in order to offset the effect of the lag time and thus to locate the equivalence point. Subsequent faster fixed triangular wave-controlled scans in narrower range further increased the throughput rate. Analytical parameters such as scan rate and scan range were optimized. Maximally, 46.9 titrations/min was realized with reasonable precision (RSD = 1.79%). Applicability of the method to the quantitation of the Japanese Pharmacopoeia drugs (furosemide, isoniazid and prochlorperazine maleate) was verified, where the latter two drugs were determined by nonaqueous titrations

Ionic multilayers at the free surface of an ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide, probed by x-ray reflectivity measurements

The presence of ionic multilayers at the free surface of an ionic liquid, trioctylmethylammonium bis nonafluorobutanesulfonyl amide TOMA+ C4C4N− , extending into the bulk from the surface to the depth of 60 Å has been probed by x-ray reflectivity measurements. The reflectivity versus momentum transfer Q plot shows a broad peak at Q 0.4 Å−1, implying the presence of ionic layers at the TOMA+ C4C4N− surface. The analysis using model fittings revealed that at least four layers are formed with the interlayer distance of 16 Å. TOMA+ and C4C4N− are suggested not to be segregated as alternating cationic and anionic layers at the TOMA+ C4C4N− surface. It is likely that the detection of the ionic multilayers with x-ray reflectivity has been realized by virtue of the greater size of TOMA+ and C4C4N− and the high critical temperature of TOMA+ C4C4N−

Analysis of hydroxy sphingomyelin

Sphingomyelin (SM) with N-α-hydroxy fatty acyl residues (hSM) has been shown to occur in mammalian skin and digestive epithelia. However, the metabolism and physiological relevance of this characteristic SM species have not been fully elucidated yet. Here, we show methods for mass spectrometric characterization and quantification of hSM. The hSM in mouse skin was isolated by TLC. The hydroxy hexadecanoyl residue was confirmed by electron impact ionization-induced fragmentation in gas chromatography-mass spectrometry. Mass shift analysis of acetylated hSM by time of flight mass spectrometry revealed the number of hydroxyl groups in the molecule. After correcting the difference in detection efficacy, hSM in mouse skin and intestinal mucosa were quantified by liquid chromatography-tandem mass spectrometry, and found to be 16.5 ± 2.0 and 0.8 ± 0.4 nmol/μmol phospholipid, respectively. The methods described here are applicable to biological experiments on hSM in epithelia of the body surface and digestive tract

Inner Product of RGB Unit Vectors for Simple and Versatile Detection of Color Transition

We propose a novel concept for detecting color transition by the inner product (IP) of RGB unit vectors. A digital microscope-based detector and a Visual Basic program were developed in-house. The concept is applied to indicator-based flow titration. The IP is 1 or < 1 if the vector’s direction is the same or different, respectively. The IP’s change can be used as a criterion for the indicator’s color transition. The present IP-based approach is simple, economical, and versatile because it is applicable to any color transition without selecting an analytical wavelength