On-line automated high-performance liquid chromatographic determination of total riboflavin phosphates using immobilized acid phosphatase as a pre-column reactor

Supercritical fluid extraction as an on-line clean-up technique for determination of riboflavin vitamins in food samples by capillary electrophoresis with fluorimetric detection

An automatic method for the separation and determination of riboflavin (RF) vitamins (RF, flavin mononucleotide and flavin adenine dinucleotide) in food samples (chicken liver, tablet and powder milk) is proposed. The method is based on the on-line coupling of a supercritical fluid extractor (SFE) with a continuous flow-CE system with guided optical fiber fluorimetric detection (CF-CE-FD). The whole SFE-CF-CE-FD arrangement allowed the automatic treatment of food samples (clean-up of the sample followed by the extraction of the analytes), and the direct introduction of a small volume of the extracted plug to the CE-FD system for the determination of RF vitamins. Fluorescence detection introduced an appropriated sensitivity and contributed to avoid interferences of nonfluorescent polar compounds coming from the matrix samples in the extracted plug. Electrophoretic responses were linear within the 0.05-1 microg/g range, whereas the detection limits of RF vitamins were in the 0.036-0.042 microg/g range. The proposed arrangement opens up interesting prospects for the direct determination of polar analytes in complex samples with a good throughput and high level of automation.

Immobilization of arginase and its application in an enzymatic chromatographic column: Thermodynamic studies of nor-NOHA/arginase binding and role of the reactive histidine residue

A biochromatographic approach is developed to measure for the first time changes in enthalpy, heat capacity change and protonation for the binding of nor-NOHA to arginase in a wide temperature range. For this, the arginase enzyme was immobilized on a chromatographic support. It was established that this novel arginase column was stable during an extended period of time. The affinity of nor-NOHA to arginase is high and changes slightly with the pH, because the number of protons linked to binding is low. The determination of the enthalpy change at different pH values suggested that the protonated group in the nor-NOHA-arginase complex exhibits a heat protonation of approximately -33 kJ/mol. This value agrees with the protonation of an imidazole group. Our result confirmed that active-site residue Hist 141 is protonated as imidazolium cation. Hist 141 can function as a general acid to protonate the leaving amino group of L-ornithine during catalysis. The thermodynamic data showed that nor-NOHA-arginase binding, for low temperature (<15 degrees C), is enthalpically unfavourable and being dominated by a positive entropy change. This result suggests that dehydration at the binding interface and charge-charge interactions contribute to the nor-NOHA-arginase complex formation. The temperature dependence of the free energy of binding is weak because of the enthalpy-entropy compensation caused by a large heat capacity change, DeltaC(p)=-2.43 kJ/mol/K, of arginase. Above 15 degrees C, the thermodynamic data DeltaH and DeltaS became negative due to van der Waals interactions and hydrogen bonding which are engaged at the complex interface confirming strong enzyme-inhibitor hydrogen bond networks. As well, by the use of these thermodynamic data and known correlations it was clearly demonstrated that the binding of nor-NOHA to arginase produces slight conformational changes in the vicinity of the active site. Our work indicated that our biochromatographic approach could soon become very attractive for studying other enzyme-ligand binding.

Application of immobilized enzyme reactor in on-line high performance liquid chromatography: A review

This review summarizes all the research efforts in the last decade (1994-2003) that have been spent to the various application of immobilized enzyme reactor (IMER) in on-line high performance liquid chromatography (HPLC). All immobilization procedures including supports, kind of assembly into chromatographic system and methods are described. The effect of immobilization on enzymatic properties and stability of biocatalysts is considered. A brief survey of the main applications of IMER both as pre-column, post-column or column in the chemical, pharmaceutical, clinical and commodities fields is also reported.

Sweet potato acid phosphatase immobilized on glutaraldehyde-activated aminopropyl controlled-pore glass: activation, repeated use and enzyme fatigue

Sweet potato acid phosphatase was covalently coupled with glutaraldehyde to aminopropyl controlled-pore glass, and used as a pre-column enzyme reactor. The immobilized enzyme reactor (IMER) was continuously operated using an automated chromatographic detection system we developed. Functional evaluation of the IMER was carried out by injecting ten samples on the same day at an injection amount of 1.25 nmol (62.5 nmol per ml) using riboflavin sodium phosphate (FMNs) as a substrate, and by prolonged use for ten months. The IMER exhibited decreased activity after repeated use for a total of 3000 samples, but about 75% of its original activity remained. The conversion rate of FMNs to riboflavin by IMER was increased from 89 to 97% by adding citrate, ethylenediaminetetraacetic acid disodium salt, etc., but especially by adding citrate. The increased conversion of FMNs to riboflavin due to the addition of citrate was probably not due to the chelation of heavy metal ions by citrate. We also investigated complex formation of acid phosphatase with the substrate FMNs using surface plasmon resonance to determine the effect of citrate on the processes of association and/or dissociation between the enzyme and substrate. Enzyme fatigue was also observed during the course of prolonged and repeated use.

Simultaneous determination of water-soluble vitamins in a vitamin-enriched drink by an in-capillary enzyme reaction method

The in-capillary enzyme reaction method was used to determine riboflavin phosphate in a vitamin-enriched drink based on its conversion to riboflavin (vitamin B2) with alkaline phosphatase. Simultaneously, three water-soluble vitamins [thiamine nitrate (vitamin B2 mononitrate), pyridoxine hydrochloride (vitamin B6 hydrochloride) and nicotinamide (vitamin PP)] and anhydrous caffeine in the drink were subjected to quantitative analysis. In the system, electrophoretic migration was used to mix zones containing the substrate (riboflavin phosphate) and the enzyme (alkaline phosphatase). The reaction was then allowed to proceed in the presence of a weak electric field and, finally, the product (riboflavin) of enzyme reaction and other water-soluble vitamins migrated under the influence of an applied electric field to the detector. All the active ingredients and the formulation excipients were successfully separated by micellar electrokinetic chromatography with 135 mM sodium dodecyl sulfate. To prevent inhibition of enzyme reaction by the addition of sodium dodecyl sulfate to the reaction zone, sandwich mode injection, in which plugs of sandwich solution without sodium dodecyl sulfate were introduced into the capillary on both sides of the reaction zone, was utilized as a barrier to protect the enzyme reaction from the inhibitor. The relationship between the peak area of the product and the concentration of the substrate was calculated in the in-capillary enzyme reaction method. Excellent linearity was obtained, with correlation coefficients of 0.9999. The established method was validated and demonstrated to be applicable to the determination of the five active ingredients, including riboflavin phosphate, in a commercial vitamin-enriched drink. No interference from the formulation excipients was observed. Good linearities were obtained, with correlation coefficients above 0.999. Recoveries and precisions ranged from 99.3 to 101.8%, and from 0.1 to 2.5% RSD, respectively. Good agreement was obtained between the established method and traditional high-performance liquid chromatographic methods. These results suggest that the in-capillary enzyme reaction method can be used for the simultaneous determination of riboflavin phosphate and other water-soluble vitamins in pharmaceuticals.

Simultaneous determination of riboflavin phosphate and other ingredients in a multivitamin pharmaceutical preparation by on-line automated LC coupled with pre-column immobilized enzyme reactor

An automated chromatographic detection system for the simultaneous determination of riboflavin phosphate, caffeine, nicotinamide and pyridoxine hydrochloride in a multivitamin pharmaceutical preparation was constructed. Hydrolytic pretreatment of riboflavin phosphate to riboflavin was carried out using a pre-column enzyme reactor, in which immobilized sweet potato acid phosphatase was packed, and then enzymatically hydrolyzed riboflavin and other ingredients in the pharmaceutical preparation were concentrated in an ODS trap column. The concentrated riboflavin and other ingredients were back-eluted from the trap column using a mobile phase containing 1-decanesulfonate as an ion-pair reagent, and then subsequently chromatographed on an ODS analytical column. It was necessary to wash the ODS trap column with aqueous acetonitrile to remove 1-decanesulfonate in the trap column, which is advantageous to concentrate the riboflavin and other ingredients for the subsequent analysis. The calibration curves for riboflavin phosphate and other ingredients were linear over the concentration ranges tested, and correlation coefficients for standard curves were 0.9999 for all four ingredients. Analytical recoveries of the four ingredients at different levels of concentration added to the ordinary pharmaceutical preparation were also in the range of 99.1-101.2%. The present method was superior to the ordinary manual and batch-wise enzymatic methods in being harmless to the environment, rapid and accurate under continuous autoanalysis.