Water-soluble vitamins detectors

Hou, W. Wang, E. Determination of water-soluble vitamins by hquid chromatography with a parallel dual-electrode electrochemical detector. Talanta 1990, 37, 841-844. 

Three methods of detection (UV absorbance, fluorescence, and electrochemical activity) are applicable for the analysis of water-soluble vitamins. Currently, UV absorption detection is used in many LC applications for water-soluble vitamins. A simultaneous assay of several vitamins with several wavelengths along with information of peak purity can be accomplished with a diode array absorbance detector. The detection limit of a UV detector is in the order of 1-10 ng (10-100 pmol), which is poorer than that of fluorescence and electrochemical detectors but often sufficient for analysis for many vitamins in foods and physiological samples (Table 4). The lack of selectivity of UV detection may cause problems with interfering and co-eluting contaminants especially in biological samples, thus necessitating sample purification prior to LC. 

Chen, P., Atkinson, R., and Wolf, W.R., 2009. Single-laboratory validation of a high-performance liquid chromatographic-diode array detector-fluorescence detector/mass spectrometric method for simultaneous determination of water-soluble vitamins in multivitamin dietary tablets. Journal of AOAC... 

The next generation of HPLC detectors, namely mass spectrometers, are now available and being deployed for water-soluble vitamin determinations in dietary supplements with electrospray ionization interface (ESI) (Holler et al. 2006). There remain obstacles to overcome for multivitamin analyses in complex food matrices, as co-elution of vitamins or excipients can compromise... 

Crevillen, A.G., Pumera, M., Gonzalez, M.C., and Escarpa, A. (2008) Carbon nanotubes disposable detectors in microchip capillary electrophoresis for water-soluble vitamins determination analytical possibilities in pharmaceutical quality control. 

Vitamin analyses in elemental diets are frequently required for process and quality control. Van der Horst et al. developed reversed phase methodology to determine the water-soluble vitamins, including PN, in total parenteral nutrition solutions (103). Iwase described a HPLC method to analyze the aqueous extract from an elemental pediatric diet for PN and nicotinamide (104). Chromatography involved a two-column, double-UV detector system to allow simultaneous determination of both PN and nicotinamide (104). 

A mixture of several water-soluble vitamins including calcium pantothenate was recently evaluated by CE by Jegle (83). The sample was analyzed in a 0.02 M sodium phosphate buffer (pH 7) and separated using a three-dimensional capillary zone electrophoresis system (flised-siUca, 50 pm i.d., straight, length to detector 400 mm, total length 485 mm, injection pressure 4.6 sec at 4 kPa, postinjection pressure 4 sec at 40 kPa, polarity positive, voltage 20 kV, capillary temperature... 

Vitamin Bi (thiamin) is related to beriberi, a disease associated with a deficiency of this vitamin. In fact, thiamin is a coenzyme in different biochemical reactions. Pork, legumes, as well as liver and kidney products are regarded as excellent sources of this vitamin. Thiamin, as well as other water-soluble vitamins, is frequently found bound to proteins or carbohydrates or even phosphorylated. Therefore, prior to their analysis, a sample treatment to release the free forms of the vitamin is common. A t)q)ical extraction protocol for water-soluble vitamins includes autoclaving the sample with hydrochloric acid for the acid hydrolysis of the vitamin followed by an adjustment in the pH to values around 4.0—4.5, adequate for an enzymatic treatment. This vitamin can be, subsequently, separated by ion-pair RP chromatography and detected with a fluorescence detector after postcolumn oxidation to thiochrome. MS detection through electrospray ionization is also used, although the separation pH should be adjusted to maximize the ionization of the vitamin. 

There is an obvious interest in the development of analytical methods able to determine multiple vitamins simultaneously. Nevertheless, as it has been described in this section, each water-soluble vitamin has different optimum conditions for extraction and analysis. Therefore, the most commonly employed strategy is the development of protocols for different groups of vitamins that can be simultaneously and properly analyzed under the same analytical conditions, grouping vitamins that can be treated and extracted imder the same conditions. For instance, the combination of a RP separation coupled to different detectors, namely, UV, fluorescence, and MS, allows the simultaneous determination of vitamins Bi, B2, B3, B6, B9, pantothenic acid, biotin, and vitamin C [7]. 

The use of a mass spectrometer as chromatographic detector offers a great advantage in vitamin analysis the possibility of simplifying the extraction procedure. The selectivity of the LC—MS technique reduces problems due to intrusive peaks from matrix components, while its sensitivity (ng or pg injected for real samples) allows the direct injection of an extract, eliminating the concentration step and the exposure to heat (most water-soluble vitamins posses low thermal stability). Sample preparation time is reduced as well as the duration of exposition to air and light (most vitamins and carotenoids are susceptible to these factors). 

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