Analytical Sciences

An amperometric alcohol-sensing electrode was prepared by immobilizing alcohol oxidase (AOx) in a polyion complex membrane. Three kinds of aqueous solutions (poly(4-styrenesulfonate)-, AOx- and poly-L-lysine-containing solutions) were successively placed on the surface of a glassy carbon electrode and the electrode was allowed to dry. The anodic current (at 1 V vs. Ag/AgCl) of the enzyme electrode increased immediately after the addition of alcohols (e.g., ethanol), and reached a steady state within 5 s. A linear response to ethanol was observed up to 0.4 mM with a detection limit of 0.5 μM. The polyion complex membrane showed permselectivity based on the solute size with a molecule weight cut-off of ca. 100, which was very effective in suppressing the electrochemical interference by L-ascorbic acid and uric acid. The enzyme electrode was applied to the determination of ethanol in alcoholic drinks and soy sources. The electrode could be used for two weeks.

A systematic classification method for polymers is not yet available in case of using near infrared spectra (NIR). That is why we have been searching for a systematic method. Because raw NIR spectra usually have few obvious peaks, NIR spectra have been pretreated by 2nd derivation for taking well modulated spectra. After the pretreatment, we applied classification and regression trees (CART) to the discrimination between the spectra and the species of polymers. As a result, we obtained a relatively simple classification tree. Judging from the obtained splitting conditions and the classified polymers, we concluded that obtained knowledge on the chemical function groups estimated by the important wavelength regions is not always applicable to this classification tree. However, we clarified the splitting rules for polymer species from the NIR spectral point of view.

Official Methods of Analysis of AOAC International (OMA) 2006.07 was originally designed for quantifying flavonol aglycones in ginkgo dietary supplements. To determine whether the method is applicable to the quantification of flavonol aglycones in lyophilized onion samples, single- and multi-laboratory validation studies were performed. Triplicated measurements on 3 different days revealed that the mean quercetin content was 3.48 g/kg dry weight, and the relative repeatability standard deviation (RSDr) and the relative intermediate standard deviation (RSDint) were 0.8 and 1.8%, respectively. The recovery of quercetin-3-O-glucoside spiked at 3 different amounts (1.56, 3.12, and 6.24 g/kg dry weight of onion) ranged from 98.42 to 100.31%, and the RSDr and RSDint ranged from 2.2 to 5.9%, and from 3.4 to 5.2%, respectively. A multi-laboratory validation study showed that the mean quercetin contents were 2.80 and 6.61 g/kg dry weight, and that satisfactory inter-laboratory precision (RSDr and RSDR ranged from 0.41 to 0.92%, and from 6.73 to 7.62%, respectively); all HorRat values were less than 2. These results indicate that OMA 2006.07 is applicable to the determination of the quercetin content of lyophilized onion samples.

Digital PCR (dPCR) enables sensitive and precise quantification of template nucleic acid without calibration. However, dPCR is not yet in widespread use, probably due to the need for expensive specialized instruments. In this paper, we describe a dPCR system using a simple microfluidic chip and common laboratory tools. The microfluidic chip consists of two parts: a PDMS part with 24,840 × 0.25 nL microwells and a PDMS-coated flat glass plate. Human RNase P gene was adopted as the model template. Commercial products of human genomic DNA and real-time PCR reagents were mixed to make a PCR mixture. The PCR mixture was confined to the microwells by the PDMS degas-driven liquid control technique. The thermal cycling was performed on a common well-type thermal cycler with a minor modification. During the thermal cycling, evaporation of the PCR mixture was prevented with a handmade water holder. In the fluorescence image, bright (positive) microwells and dim (negative) ones were clearly discriminated. The number of the positive microwells was counted using software, and was used for estimation of the template concentration in the sample based on the theory of the Poisson distribution. The estimated concentrations well agreed with the input template concentrations in the range from 1.32 copies/µL to 13 200 copies/µL. The techniques presented in this paper will pave the way for facile dPCR in a broad range of laboratories without the need for expensive instruments.

The resolution method for overlapped peaks based on fractional-order differentiation (FOD) of the Gaussian function is described. Its main idea stems from a variation of the maximum and the zero-crossing of the Gaussian peaks signal at different differential orders. I obtained two kinds of estimators for estimating the characteristic parameters of the Gaussian peak based on the above relationship. The resolution of several kinds of overlapped peaks simulated by computer has been performed and discussed in detail. The proposed method has been used to resolve overlapped voltammetric peaks obtained in the analysis of binary mixtures of Cd(II) and In(III) metal ions. The results indicate that the proposed method can be used to resolve overlapped peaks which can be modeled by the Gaussian peaks both effectively and satisfactorily.