Electrochemical Analysis for Total Alkalinity of Water by the Measurement of Cathodic Prepeak of Quinone Caused by Surplus Acid.

In this study, an electrochemical analysis, coupled with the concept of back neutralization titration and the voltammetric determination of surplus acid, is proposed for determining the total alkalinity of water samples. When linear sweep voltammetry of 3,5-di-tert-butyl-1,2-benzoquinone (DBBQ) with H2SO4 in a water and ethanol (44 : 56, v/v) mixture was carried out using a bare glassy carbon working electrode, a cathodic prepeak of DBBQ caused by H2SO4 was observed on the voltammogram at a more positive potential than when compared with the original cathodic peak of DBBQ. When similar voltammetry was carried out in the presence of Na2CO3 and H2SO4, the cathodic prepeak height of DBBQ was decreased with an increase in the Na2CO3 concentration. The decrease of the cathodic prepeak height of DBBQ was found to be linearly related to the Na2CO3 concentration ranging from 0.025 to 2.5 mM (r2 = 0.998). The total equivalent concentrations of inorganic bases in samples of mineral water and tap water were determined, and then the results were converted to the total alkalinities of the water samples (mg/L CaCO3). The total alkalinities of the water samples determined by the present electrochemical analysis were essentially the same compared with those by the neutralization titration method. From these results, we were able to demonstrate that the present electrochemical analysis with accuracy and precision could be applied to determine the total alkalinity, which is one of the indicators to examine water quality. The present electrochemical analysis would contribute to achieving the sustainable development goals (SDGs) of #6 and #14.

Determination of oxalic acid in herbal medicines by semi-micro hydrophilic interaction liquid chromatography coupled with electrochemical detection.

In this study, the determination of oxalic acid in herbal medicines was performed by using a hydrophilic interaction liquid chromatography coupled with electrochemical detection (HILIC-ECD) method. A semi-micro column packed with amide-silica particles and an acetonitrile-30 mM phosphate buffer (pH 6.8) mixture (65:35, v/v) were used as the stationary and mobile phases, respectively, in the HILIC-ECD. A potential of + 1.1 V vs. Ag/AgCl was applied to a glassy carbon working electrode. The ratio of the peak height of oxalic acid to that of the internal standard (synephrine) was proportional to the concentration of 0.45 µg L-1 to 1.8 mg L-1 with a correlation coefficient of 0.999. The detection limit (signal-to-noise ratio, S/N = 3) of oxalic acid was 0.17 µg L-1. By the HILIC-ECD, the oxalic acid content in crude drugs and Kampo medicine extract granules (Zingiberis Rhizoma Processum, Pinelliae Tuber, Sho-seiryu-to, Hange-shashin-to, etc.) were determined with less than 2.9% relative standard deviation (RSD, n = 6), and their recoveries were more than 88.7% with less than 3.3% RSD (n = 6). In conclusion, we demonstrated that the HILIC-ECD performed measurements that were quite selective, accurate, and precise for the determination of oxalic acid in herbal medicines.

Gradient elution of hydroxyacetophenones by supercritical fluid chromatography with electrochemical detection.

Linear gradient elution supercritical fluid chromatography with electrochemical detection was developed using hydroxyacetophenones as analytes. Separation was carried out with a diol column (4.6 mm id × 250 mm length, 5 µm) as a stationary phase and a mixture of supercritical carbon dioxide and methanol as a mobile phase, where the ratio of carbon dioxide and methanol was changed from 99:1 (v/v) to 60:40 (v/v). For the electrochemical detection, methanol containing 1.0 mol L-1 ammonium acetate was used as a supporting electrolyte solution and + 1.2 V was applied to the electrochemical cell. We compared the performance of the present method to isocratic elution supercritical fluid chromatography, and the repeatability, linearity, and detection capability all showed better analytical parameters in the gradient elution. As such, we found that gradient elution supercritical fluid chromatography can achieve the faster separation and save resources compared to isocratic elution. Thus, the present method may contribute to the development of green analytical methods.

Electrochemical determination of free amino nitrogen in aged lean beef by the measurement of surplus acid after neutralization.

In this study, an electroanalytical method, which is based on the concept of acid-base back titration and the electrochemical sensing of acids by means of the reduction of quinone, is proposed for determining free amino nitrogen (FAN) in lean beef samples. To perform the electrochemical determination of FAN in beef samples, the following voltammetric behaviors of 3,5-di-tert-butyl-1,2-benzoquinone (DBBQ) in the presence of acid have been applied: (1) A cathodic prepeak height of DBBQ caused by HCl (iH) is proportional to the HCl concentration in the electrolyte solution. (2) iH is linearly decreased with an increase in amino acids concentration in the electrolyte solution after the amino acids are neutralized by excess HCl. By the present electroanalytical method, FAN in a lean beef sample was determined to be 4.70 mgN g-1 with a repeatability of 3.4% relative standard deviation (n = 5). This result by the present electroanalytical method was in good agreement with a colorimetric method using a ninhydrin reagent. Moreover, the present electroanalytical method was able to monitor increases of FAN in lean beef samples during wet-aging. These results demonstrate the present electroanalytical method could help in the development of an on-site analysis for estimating aged beef samples via the determination of FANs.

Simultaneous determination of deuterium-labeled ergosterol and brassicasterol in stroke-prone spontaneously hypertensive rats by ultra-high performance liquid chromatography-electrospray ionization-tandem mass spectrometry.

A previous study has shown that brassicasterol-d1 was detected in the serum of stroke-prone spontaneously hypertensive rats after oral administration of ergosterol-d1. To quantitatively evaluate the serum concentration of brassicasterol-d1, an ultra-high performance liquid chromatography-electrospray ionization-tandem mass spectrometry method was developed for the simultaneous determination of picolinyl ester-derivatized ergosterol-d1 and brassicasterol-d1. The separation was performed on an ODS column (Waters Acquity UPLC BEH C18) with a mobile phase consisting of methanol and water containing 0.1% acetic acid (95/5, v/v). Linear calibration curves in the presence of the serum were obtained in a concentration range of 0.04-8 µg mL-1. Recovery rates of 95.6-119% were obtained with an RSD (n = 6) of less than 7.5%. The method was applied to the determination of time-concentration curves of ergosterol-d1 and brassicasterol-d1 in stroke-prone spontaneously hypertensive rats, showing a pharmacokinetic profile of ergosterol-d1 where the peak serum concentration of brassicasterol-d1 was 3-fold higher than that of ergosterol-d1.

Electrochemical determination of emodin in acidic media by high-performance liquid chromatography and its application to Polygoni Multiflori Radix samples.

Electrochemical reduction of emodin under acidic media occurs at a less negative potential when compared with that under neutral media. When emodin is electrochemically detected at a less negative potential, a decrease in background noise and improvement in specificity benefit the development of high-performance liquid chromatography with electrochemical detection (HPLC-ECD) for its determination. HPLC-ECD was performed using an octadecyl silica column, acetonitrile-water (60:40, v/v) containing 5 mmol L-1 hydrochloric acid and 10 mmol L-1 lithium perchlorate, as a mobile phase, and an applied potential at - 0.4 V vs. Ag/AgCl. Under these optimal HPLC-ECD conditions, the detection limit (signal-to-noise ratio, S/N = 3) of emodin was 0.61 µg L-1. When this HPLC-ECD system was applied to the determination of emodin in Polygoni Multiflori Radix (PMR) samples, other peaks did not appear close to the emodin peak on a chromatogram. The emodin contents in PMR samples were determined with relative standard deviations (RSDs, n = 6) of less than 3.9%, and their recoveries ranged from 92 to 106%. We have shown that our HPLC-ECD system performed an accurate, precise, and specific determination of emodin in PMR samples.

Effects of digital processing on repeatability assessment of a multiple reaction monitoring liquid chromatography-tandem mass spectrometry system by ISO 11843-7.

ISO 11843 part 7 (ISO 11843-7) can provide a standard deviation (SD) of area measurements of a target peak through the stochastic behaviors of instrumental noises. The purpose of this study is to demonstrate that ISO 11843-7 can be applied to assess repeatability in an isocratic liquid chromatography-tandem mass spectrometry (LC-MS/MS) system without repetitive measurements. The relative standard deviation (RSD) of the peak area of ergosterol picolinyl ester, which was used as an example, on a multiple reaction monitoring (MRM) chromatogram was determined by ISO 11843-7. The RSD by ISO 11843-7 (N = 1) was within a 95% confidence band of the RSD by repetitive measurements (N = 6). Moreover, the effects of digital smoothing, such as moving average, were also examined on the repeatability assessment in LC-MS/MS by ISO 11843-7. From the results of the comparisons of the RSDs obtained by ISO 11843-7 and the repetitive measurements, it was shown that suitable RSDs of the peak area were obtained from the smoothed MRM chromatograms by the moving average for narrow data point windows (e.g., one-sixth of the peak width). In conclusion, the utility of repeatability assessment based on ISO 11843-7 has been expanded for the validation of an LC-MS/MS system.

Supercritical fluid chromatography with post-column addition of supporting electrolyte solution for electrochemical determination of tocopherol and tocotrienol isomers.

A supercritical fluid chromatography with electrochemical detection system was developed for the simultaneous determination of tocopherol and tocotrienol isomers. The supercritical fluid chromatography with electrochemical detection system was connected with an additional pump to create a flow path to add a supporting electrolyte solution. The supporting electrolyte solution was mixed with a mobile phase in a post-column fashion, enabling the independent control of the separation and detection. After optimization of the measurement conditions, vitamin E isomers and an internal standard substance (2,2,5,7,8-pentamethyl-6-hydroxychroman) were separated within 30 min using a mixture of supercritical carbon dioxide and methanol (99:1, v/v) as a mobile phase and a cyanopropyl column (4.6 mm inner diameter × 250 mm length, 5 µm). For the electrochemical detection, methanol containing 1.0 mol/L ammonium acetate was used as a supporting electrolyte solution, and the applied potential was set at +0.8 V. This analytical method showed good linearity (5-100 µg/mL) and repeatability (less than 2.5% relative standard deviation, n = 6) and was applicable to the determination of tocopherol and tocotrienol isomers in nutrition supplements.

Effects of sampling rate and noise filter processing on repeatability assessment in UHPLC with ultraviolet detection based on the ISO 11843-7.

The present study examines whether short measurement time and noise filter processing in an ultra-high-performance liquid chromatography with ultraviolet detection (UHPLC-UV) contribute to limitations for repeatability assessment based on the ISO 11843 part 7 (ISO 11843-7), which can stochastically provide a measurement standard deviation (SD) caused by baseline noise (SB). In this study, ergosterol was used as an example in UHPLC-UV analysis. From the results of power spectrum analysis of baseline noise, 1024 consecutive digital data points provided a suitable SB. Thus, it was found that an SB can be obtained from about 1 min of baseline when a chromatogram was recorded at sampling rate of 20 points s-1 in the present UHPLC-UV system. The relative SDs (RSDs) of the peak area obtained by the ISO 11843-7 were within 95% of the confidential intervals of the RSDs obtained by repetitive measurements, indicating the ISO 11843-7 is applicable to estimate repeatability in a UHPLC-UV system. In a similar way, we found that the RSD of the peak area obtained from a chromatogram with noise filter processing in UHPLC-UV could also be estimated by the ISO 11843-7. In conclusion, we experimentally demonstrate that short measurement time and noise filter processing are not limitations for repeatability assessment based on the ISO 11843-7.

Determination of Phenolic Compounds in Beverages by Three-Flow Channel Isocratic HPLC with Electrochemical Detections Using a Column-Switching Technique.

For the quantitative analysis of phenolic compounds in beverage samples, a three-flow channel isocratic HPLC with electrochemical detection (3LC-ECD) system was devised using a column-switching technique. Phenolic compounds with significantly different hydrophobicity (the range of calculated log P: -0.77 to 3.02) were simultaneously measured to draw three chromatograms by the 3LC-ECD; the peaks of gallic acid (GA), protocatechuic acid (PCA), and gallocatechin (GC) were observed at electrochemical detector 1 (D1) within 42 min, the peaks of procyanidin B3 (B3), epigallocatechin (EGC), catechin (C), epicatechin (EC), procyanidin B2 (B2), ethyl gallate (Eg), and epigallocatechin gallate (EGCg) were observed at D2 within 50 min, and the peaks of epicatechin gallate (ECg), gallocatechin gallate (GCg), catechin gallate (Cg), propyl gallate (Pg), and resveratrol (RVT) were observed at D3 within 70 min. The relationships between the phenolic compound concentrations and their chromatographic peak heights gave good linearity with correlation coefficients of more than 0.998. The detection limits of the phenolic compounds by the 3LC-ECD ranged from 0.6 to 3.0 µg/L. Further, the phenolic compound concentrations of commercially available teas and wines were determined with a relative standard deviation (RSD) of less than 4.9% (n = 6), and their recoveries ranged from 91 to 109%. These results indicate that the 3LC-ECD system provided an accurate, precise, and specific determination of the phenolic compounds in beverages without affecting the matrices derived from these samples.

Emerging Separation Techniques in Supercritical Fluid Chromatography.

Supercritical fluid chromatography (SFC) has unique separative characteristics distinguished from those of HPLC and gas chromatography. At present, SFC is widely used and there are many applications in various biological, medical, and pharmaceutical fields. In this review, we focus on recently developed novel techniques related to SFC separation including: new column stationary phases, microfluidics, two-dimensional separation, and gas-liquid separation. In addition, we discuss the application of SFC using a water-containing modifier to biological molecules such as amino acids, peptides, and small proteins that had been challenging analytes.

Electrochemical Determination of Titratable Acidity for the Discrimination of Schisandrae Chinensis Fructus and Schisandrae Sphenantherae Fructus.

A simple electrochemical procedure has been developed for determining the titratable acidity in Schisandrae Chinensis Fructus (SCF) and Schisandrae Sphenantherae Fructus (SSF) by means of reduction of quinone in the presence of acid compounds. To measure a voltammogram, a test solution was prepared by mixing a water extract from SCF or SSF and an electrolyte cocktail containing 3,5-di-tert-butyl-1,2-benzoquinone and NaCl. The quantitative results of titratable acidity in the SCF and SSF samples by the present voltammetry were in good agreement with those by neutralization titration using 0.1 M NaOH (r2 = 0.980): y = 1.003x + 0.010, where the y- and x-axes were the titratable acidity obtained by the present voltammetry and the neutralization titration, respectively. Further, the titratable acidities in the SSF samples were significantly lower than those in the SCF samples (p < 0.01). From these findings, we show that the titratable acidity is useful as an indicator to discriminate between SCF and SSF. Moreover, a prototype of electrochemical portable sensor for on-site analysis has been provided to perform this procedure.

Structure Revision of (22E)-Ergosta-7,22-diene-3ß,5α,6ß,9α,14α- pentol from the Spores of the Medicinal Mushroom Ganoderma lucidum.

Careful reexamination of the published ¹H and ¹³C NMR spectral data of (22E)-ergosta-7,22-diene-3ß,5α,6ß,9α,14α-pentol (1), isolated from the spores of the medicinal mushroom Ganoderma lucidum, indicates that, in reality, the compound is (22E)-ergosta-7,22-diene-3ß,5α,6ß,9α,14ß-pentol (5).

Structure Revision of (22E)-24-Methylcholesta-8(14),22-diene- 3ß,5α,6ß,7α-tetraol from the Marine-Derived Fungus Penicillium sp.

Careful reexamination of the published ¹H- and ¹³C-NMR spectral data of (22E)-24-methylcholesta-8(14),22-diene-3ß,5α,6ß,7α-tetraol (1), isolated from the marine-derived fungus Penicillium sp., indicates that, in reality, the compound is 5α,6α-epoxy-(22E,24R)-24-methylcholesta-8(14),22-diene-3ß,7α-diol (5).

Structure Revision of Two Polyoxygenated Sterols from the Marine Sponge Neofibularia nolitangere.

Careful reexamination of the published 1H- and 13C-NMR spectral data of (24S)-24-ethylcholest-8-ene-3ß,5α,6ß,7α-tetraol (1) and (24S)-24-ethylcholest-8(14)-ene-3ß,5α,6ß,7α-tetraol (2), isolated from the marine sponge Neofibularia nolitangere, indicates that, in reality, compounds 1 and 2 are (24S)-5α,6α- epoxy-24-ethylcholest-8-ene-3ß,7α-diol (9) and (24S)-5α,6α-epoxy-24-ethylcholest-(14)-ene-3ß,7α-dio (10), respectively.

Terpenoids and sterols from some Japanese mushrooms.

Over the past twenty years, our research group has been studying the chemical constituents of mushrooms. From nineteen species, namely, Amanita virgineoides Bas (Amanitaceae), Daedaleopsis tricolor (Bull.: Fr.) Bond. et Sing. (Polyporaceae), Grifolafrondosa (Fr.) S. F. Gray (Polyporaceae), Hericium erinaceum (Bull.: Fr.) Pers. (Hericiaceae), Hypsizigus marmoreus (Peck) Bigelow (Tricholomataceae), Lactarius piperatus (Scop.: Fr.) S. F. Gray (Russulaceae), Lentinula edodes (Berk.) Sing. (Pleurotaceae), Lyophyllyum connatum (Schum.: Fr.) Sing. (Tricholomataceae), Naematoloma sublateritium (Fr.) Karst. (Strophariaceae), Ompharia lapidescens Schroeter (Polyporaceae), Panellus serotinus (Pers.: Fr.) Kuhn. (Tricholomataceae), Pholiota nameko (T. Ito) S. Ito et Imai in Imai (Strophariaceae), Pleurotus eringii (DC.: Fr.) Quel. (Pleurotaceae), Polyporus umbellatus Fries (Polyporaceae), Russula delica Fr. (Russulaceae), Russula sanguinea (Bull.) Fr. (Russulaceae), Sarcodon aspratus (Berk.) S. Ito (Thelephoraceae), Tricholoma matsutake (S. Ito et Imai) Sing. (Tricholomataceae), and Tricholomaportentosum (Fr.) Quel. (Tricholomataceae), we isolated eight new sesquiterpenoids, six new meroterpenoids, three new triterpenoids, and twenty eight new sterols. In this review, structural features of these new compounds are discussed.

Three new lactarane sesquiterpenoids from the mushroom Russula sanguinea.

The family Russulaceae is one of the largest in the subdivision Basidiomycotina in Whittaker's Kingdom of Fungi [1] and comprises hundreds of species, worldwide distributed, belonging to the genera Lactarius and Russula. While secondary metabolites occurring in the fruiting bodies of Lactarius species have been well investigated [2], the Russula mushrooms have received less attention, notwithstanding the larger number of existing species [3]. In a previous paper, we reported the isolation and structural elucidation of sterols from the fruiting bodies of Russula sanguinea (Bull.) Fr. [4]. In the course of further studies on the constituents of the above mushroom, three new lactarane sesquiterpenoids, sangusulactones A-C (1-3), along with two known compounds have been isolated (Figure 1). This paper deals with the structural elucidation of the new compounds. The known compounds 4 and 5 were identified as blennin A (4) [5] and 15-hydroxyblennin A (5) [6], respectively, by comparison of their spectral data with those reported in the literature.

A new geranylated aromatic compound from the mushroom Hericium erinaceum.

A new geranylated aromatic compound, 5-[(2'E)-3',7'-dimethyl-2',6'-octadienyl]-4-hydroxy-6-methoxy-1-isoindolinone (1), was isolated from the fruiting bodies of the mushroom Hericium erinaceum (Bull.: Fr.) Pers. (Hericiaceae) together with three known sterols, 5alpha,6alpha-epoxy-(22E)-ergosta-8(14),22-diene-3beta,7alpha-diol (2), (22E)-ergosta-7,9(11),22-triene-3beta,5alpha,6beta-triol (3) and (22E)-ergosta-7,22-diene-3beta,5alpha,6alpha,9alpha-tetrol (4). The structure of the new compound was elucidated on the basis of spectral data.

Terpenoids and related compounds from plants of the family Compositae (Asteraceae).

This review will summarize the authors' studies on the structures of terpenoids and related compounds from plants of the family Compositae (Asteraceae). Eighty three new compounds have been obtained and characterized from seven species of the plants, namely, Erigeron annuus (L.) Pers., Erigeron philadelphicus L., Erigeron sumatrensis Retz, Ligularia dentata Hara, Ligularia stenocephala Matsum. et Koidz., Petasites japonicus Maxim. and Tussilago farfara L.

Six new secoiridoids from the dried fruits of Ligustrum lucidum.

Six new secoiridoid constituents, named isoligustrosidic acid (1), 6'-O-trans-cinnamoyl 8-epikingisidic acid (2), 6'-O-cis-cinnamoyl 8-epikingisidic acid (3), oleopolynuzhenide A (4), nuzhenals A (5) and B (6) were isolated from the dried fruits of Ligustrum lucidum AIT. Their structures were established on the basis of spectral and chemical data.