Akinobu Matsunaga

Analysis of condensed phosphates in food products by ion chromatography with an on-line hydroxide eluent generator

An ion chromatographic method with gradient elution using an automated eluent generator was developed for the simultaneous determination of condensed phosphates (CPs) such as orthophosphate (P1), pyrophosphate (P2), polyphosphate, trimetaphosphate and phytate in food products. The linear calibration curves for P1, P2, tripolyphosphate, and tetrapolyphosphate in the range 0.5-500 microM had a correlation factor of 0.999 or better. The precision of the method for the CP peak areas obtained with the hydroxide eluent generator was better than that obtained with potassium hydroxide eluents prepared off-line. This method was applied to the determination of CPs in food products such as ham, fish paste, and cheese extracted by trichloroacetic acid.

Direct chiral resolution of tartaric acid in food products by ligand exchange capillary electrophoresis using copper(II)-D-quinic acid as a chiral selector.

Chiral resolution of native DL-tartaric acid was performed by ligand-exchange capillary electrophoresis using copper(II)-D-quinic acid as a chiral selector. Factors affecting chiral resolution, migration time, and peak area of tartaric acid were studied. The running conditions for optimum separation of tartaric acid were found to be 1 mM copper(II) sulfate-10 mM D-quinic acid (pH 5.0) with an effective voltage of -15 kV at 30 degrees C, using direct detection at 250 nm, and resolution of racemic tartaric acid was approximately 1.3. With this system, chiral resolution of DL-tartaric acid in food products was conducted successfully.

Direct chiral resolution of lactic acid in food products by capillary electrophoresis.

Chiral resolution of native DL-lactic acid was performed by capillary electrophoresis using 2-hydroxypropyl-beta-cyclodextrin as a chiral selector. Various factors affecting chiral resolution, migration time, and peak area of lactic acid were studied. The running conditions for optimum separation of lactic acid were found to be 90 mM phosphate buffer (pH 6.0) containing 240 mM 2-hydroxypropyl-beta-cyclodextrin with an effective voltage of -30 kV at 16 degrees C, using direct detection at 200 nm. In order to enhance the sensitivity, sample injection was done under a pressure of 50 mbar for 200 s. On-line sample concentration was accomplished by sample stacking. With this system, D- and L-lactic acids in food products were analyzed successfully.

Direct chiral resolution of malic acid in apple juice by ligand-exchange capillary electrophoresis using copper(II)-L-tartaric acid as a chiral selector

Chiral resolution of native DL‐malic acid was achieved by ligand‐exchange capillary electrophoresis using copper(II)‐L‐tartrate as a chiral selector. Factors affecting chiral resolution, migration time, and peak area of malic acid were studied. The running conditions for optimum separation of malic acid were found to be 1 mM copper(II) sulfate‐1 mM L‐tartrate (pH 5.1) with an effective voltage of –20 kV at 30°C, using direct detection at 280 nm, and resolution (Rs) of racemic malic acid was approximately 4. With this system, D‐ and L‐malic acids in apple juice were analyzed successfully.

Direct chiral resolution of aliphatic α-hydroxy acids using 2-hydroxypropyl-β-cyclodextrin in capillary electrophoresis

Chiral resolution of α-hydroxy acids (lactic acid, 2-hydroxybutyric acid, 2-hydroxy-3-methylbutyric acid, 2-hydroxyisocaproic acid) without derivatization was performed by capillary electrophoresis using 2-hydroxypropyl-β-cyclodextrin (2HP-β-CD). An increase in the bulkiness of the alkyl group in these acids enhanced the resolution. The association constants for complexes of 2HP-β-CD with the α-hydroxy acids were determined by spectrophotometric and electrophoretic methods. Good agreement was found between the two methods. An increase in the bulkiness of the alkyl group in these acids brought about an increase in the association constants. When cyclohexanol that was included in 2HP-β-CD was added to the background electrolyte, chiral separation of these compounds was completely prevented. These results suggest that α-hydroxy acids having a short alkyl chain, and also chiral compounds having aromatic rings, could be included in 2HP-β-CD to be chiroptically separated.

Retention model of multiple eluent ion chromatogrphy: A priori estimations of analyte capacity factor and peak intensity

In multiple eluent ion chromatography, the analyte elution behaviour still remains unclear. In this work, the inter-eluent selectivity coefficient was accurately determined by re-interpreting Hoovers model. Obtaining the inter-eluent selectivity coefficient was greatly simplified by introducing the concept of an “inter-eluent separation factor”. From the coefficient obtained, analyte capacity factors in polyprotic eluent systems can be estimated a priori. Moreover, this new factor permits the calculation of eluent species with different charges and, through stoichiometric simulation of the chromatogram, makes possible the a priori estimation of analyte peak intensities.

Direct chiral resolution of pantothenic acid using 2-hydroxypropyl-β-cyclodextrin in capillary electrophoresis

Abstract Chiral resolution of native dl -pantothenic acid was performed by capillary electrophoresis using 2-hydroxypropyl-β-cyclodextrin as a chiral selector. Various factors affecting chiral resolution and migration time of pantothenic acid were studied. The optimum running conditions for separation of pantothenic acid were found to be 60 mM phosphate buffer (pH 7.0) containing 60 mM 2-hydroxypropyl-β-cyclodextrin and 10% (v/v) methanol with an effective voltage of 20 kV at 15°C, using direct detection at 200 nm. With this system, pantothenic acid in a soft drink was analyzed successfully.

Enantiomeric purity determination of malic acid in apple juices by multi-beam circular dichroism detection.

A multi-beam circular dichroism (CD) detector which is easily constructed by inserting inexpensive optics into a conventional photo-diode array detector has an advantage of simultaneous detection of the absorbance and CD. The enantiomeric purity determination of malic acid in beverages was performed by this detection system. Malic acid when complexed with Cu(II) was found to have an absorbance maximum at around 750 nm. The L-malic acid-Cu(II) complex showed a positive Cotton effect in its absorbance band and its anisotropy factor (delta epsilon/epsilon) was relatively large at about 1/170. This complex was retained on a reversed-phase column with the addition of racemic 2-hydroxy-3-methylbutyric acid to the mobile phase as the ligand. A plot of the relative peak areas between the CD and the absorption (delta abs/abs) versus optical purity showed good linearity with a correlation coefficient of 0.999, and the precision expressed as the relative standard deviation of the errors from the regression line was +/-2.7% (2sigma). The accuracy of the proposed method was assessed by capillary electrophoresis. Eight commercially available juice products were analyzed using this method. Five of them were thought to be adulterated with synthetic malic acid.

Enantioselective analysis of thiobencarb sulfoxide produced by metabolism of thiobencarb by hydroxypropyl‐γ‐cyclodextrin modified micellar electrokinetic chromatography

Cyclodextrin-modified micellar electrokinetic chromatography was applied to the enantioseparation of thiobencarb sulfoxide, which is produced by S-oxygenation of thiobencarb, a herbicide, using γ-cyclodextrin together with sodium dodecyl sulfate. Factors affecting chiral resolution and migration time of thiobencarb sulfoxide were studied. The optimum running conditions were found to be 20 mM phosphate-5 mM borate buffer (pH 8.5) containing 60 mM hydroxypropyl-γ-cyclodextrin and 100 mM sodium dodecyl sulfate with an effective voltage of +20 kV at 20°C using direct detection at 220 nm. Under these conditions, the resolution (Rs) of racemic thiobencarb sulfoxide was approximately 1.7. Thiobencarb was treated with a rat liver microsomal fraction containing cofactors (known as S9mix). The ratio between (+)- and (-)-thiobencarb sulfoxide was found to be 15:85. It was also found that the ratio between (+)-and (-)-thiobencarb sulfoxide produced in soil spiked with thiobencarb was 3:7. These results indicated marked enantioselectivities for these metabolisms. The activities of thiobencarb, (+)- and (-)-thiobencarb sulfoxides on 5α-dihydrotestosterone-and 17β-estradiol-induced transcriptions were also investigated. Whereas thiobencarb and (+)-thiobencarb sulfoxide did not show any activities, (-)-thiobencarb sulfoxide showed significant anti-estrogenic and anti-androgenic activities, suggesting that thiobencarb sulfoxide can act as both an enantioselective anti-estrogen and an enantioselective anti-androgen.

Theoretical considerations on the appearance of sample and system peaks in ion chromatography with photometric detection

Abstract A general model is proposed for interpreting the appearance of sample and system peaks in ion-exchange chromatography with photometric detection. In this theory, a changed fraction of organic acid in the mobile phase resulting from the ion-exchange process with a sample ion migrates through the column from plate to plate in accordance with the ionic and partition equilibria. This perturbation of UV-detectable components yields the sample and system peaks. Simulation of this theory by computer accounts well for the sample peaks observed in real ion chromatography. An equation expressing the sample response—capacity factor relationship at low mobile phase pH was derived.