Stability studies of vitamins in three food reference materials

Summary Stability in storage and shipment of retinol, -tocopherol, vitamins B₁, B₂ and C in three foods was studied to assess the feasibility of certifying the vitamin content of three food RMs, whole milk powder (CRM 380), pork muscle (CRM 384) and freeze-dried haricot beans (CRM 383); these were recently certified for major dietary components and major elements. Interpretation of the long-term stability data was complicated by a dominant analytical variability over the measurement period. The long-term stability study (24 months) gave evidence of deterioration of vitamin B₂ in pork muscle. The other vitamins studied seemed to be acceptably stable at –18°C and +4°C. Additional studies showed stability of retinol in milk powder for 34 months and of vitamin C in haricot beans for 31 months at –18°C and +4°C. Long-term storage seems to be possible at a temperature not higher than +4°C except for vitamin B₂. A short-term stability study at +25°C and +30°C for 6 weeks showed acceptable stability of retinol and -tocopherol in milk powder (CRM 380) and of vitamin C in haricot beans (CRM 383). However, storage at +42°C induces degradation of retinol, -tocopherol and vitamin C.     

The stability of water‐ and fat‐soluble vitamin in dentifrices according to pH level and storage type

The purpose of this study is to evaluate the vitamin stabilities in dentifrices by analyzing various vitamins according to the level and storage temperature. The stabilities of water‐ and fat‐soluble vitamins were investigated in buffer solution at different pH values (4, 7, 8, 10 and 11) for 14 days and in dentifrices at different pH (7 and 10) for 5 months at two temperature conditions (room and refrigeration temperature) by analyzing the remaining amounts using HPLC methods. In the buffer solution, the stability of vitamins B₁, B₆ and C was increased as the pH values increased. Vitamins E and K showed poor stability at pH 4, and vitamin B₃ showed poor stability at pH 11. In dentifrices, the storage temperature highly influenced vitamin stability, especially vitamins C and E, but the stabilities of vitamins B₁ and C according to pH values did not correspond to the buffer solution tests. Vitamin B group was relatively stable in dentifrices, but vitamin C completely disappeared after 5 months. Vitamin K showed the least initial preservation rates. Vitamins were not detected in commercial dentifrices for adults and detected amounts were less than the advertised contents in dentifrices for children. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation and testing for homogeneity of spiked strawberry and cabbage candidate reference materials

Strawberry and cabbage candidate reference materials (RMs) have been prepared by our laboratory during 1992–1993. Fresh materials have been homogenized and spiked with known concentrations of pesticides representing compounds commonly used for strawberries and cabbages. The candidate RMs have been then freeze-dried, homogenized, bottled under a stream of nitrogen and stored frozen at –20°C. Homogeneity and stability of the candidate RMs have been studied during the storage period. Homogeneity of the candidate RMs for 5 g samples has been within 10%. Homogeneity and stability studies have been carried out using the conventional multiresidue method of Luke et al. [1]. Instrumental analysis have been performed by gas chromatography mass spectrometry (GC-MS) employing selected ion monitoring (SIM).     

Potentiometric Membrane Sensors for the Selective Determination of Pyridoxine Hydrochloride (Vitamin B6) in Some Pharmaceutical Formulations

The construction and general performance characteristics of two novel potentiometric PVC membrane sensors responsive to the pyridoxine hydrochloride known as vitamin B₆ (VB₆) are described. These sensors are based on the use of the ion-association complexes of the pyridoxine cation with molybdophosphate and tungstophosphate counter anions as ion pairs in a plasticized PVC matrix. The electrodes show a stable, near-Nernstian response for 6 × 10^–5–1 × 10^–2 M VB₆ at 25°C over the pH range 2–4 with a cationic slope of 54.0 ± 0.5 and 54.5 ± 0.4 mV per concentration decade for pyridoxine–molybdophosphate and pyridoxine–tungstophosphate, respectively. The two electrodes have the same lower detection limit (4 × 10^–5 M), and the response times are 45–60 and 30–45 s in the same order for both. Selectivity coefficients for VB₆ relative to a number of interfering substances were investigated. There is negligible interference from many cations, some vitamins, and pharmaceutical excipients. The determination of VB₆ in some pharmaceutical preparations using the proposed electrodes gave an average recovery of 98.0 and 99.0% of the nominal value and a mean standard deviation of 1.1 and 0.9% (n = 3) for pyridoxine–molybdophosphate and pyridoxine–tungstophosphate electrodes, respectively. The results compare favorably with data obtained by the British pharmacopoeia method.     

Effects of γ-irradiation and cooking on vitamins B6 and B12 in grass prawns (Penaeus monodon)

The effects of irradiation doses, irradiation temperature and a combined treatment of irradiation and cooking on the vitamin B₆ and B₁₂ contents of grass prawns have been studied. Grass prawns were irradiated at refrigerated (4°C) or frozen (-20°C) temperatures with different doses. A domestic cooking procedure was followed after irradiation. The changes in vitamins B₆ and B₁₂ of both raw and cooked grass prawns were evaluated. Results showed no significant changes of vitamin B₆ and B₁₂ in grass prawns with a radiation dose up to 7 kGy at either 4°C or -20°C. Irradiation at 4°C caused more destruction of vitamin B₁₂ but not vitamin B₆ than did irradiation at -20°C in grass prawns. There was significant destruction of both vitamins B₆ and B₁₂ in unirradiated samples during cooking. The introduction of the irradiation process before cooking had no effect on either vitamin. These results indicate that the loss of vitamins B₆ and B₁₂ in the combined treatments was caused mainly by thermal destruction.     

Das Gleichgewicht zwischen oktaedrisch und tetraedrisch koordiniertem Kobalt(II) in N,N-Dimethylacetamid

Zusammenfassung In Lösung von [Co(DMA)₆](ClO₄)₂ in wasserfr. N,N-Dimethylacetamid (DMA) wird spektrophotometrisch ein Gleichgewicht zwischen tetraedrisch und oktaedrisch koordiniertem Co²⁺ festgestellt. Die GleichgewichtskonstanteK=[Co _tetr ²⁺ ]/[Co _oct ²⁺ ] wurde bei 25°C zu 0,028 und bei 70°C zu 0,19 bestimmt. Bei –8°C zeigen die Elektronenspektren keinen meßbaren Anteil der tetraedrischen Species. Für den oktaedrischen Komplex ergibt sichD _q =805 cm^–1,B=834 cm^–1.

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The equilibrium between octahedral and tetrahedral coordinated cobalt(II) in N,N-dimethylacetamide

Spectrophotometric results establish an equilibrium between tetrahedral and octahedral coordinated cobalt(II) in anhydrous N,N-dimethylacetamide (DMA). The equilibrium constantK=[Co _tetr ²⁺ ]/[Co _okt ²⁺ ] has been found to be 0,028 at 25°C and 0,19 at 70°C. Electronic spectra indicate no measurable amount of the tetrahedral species at –8°C. For the octahedral complexD _q =805 cm^–1 andB=834 cm^–1.

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A Thermodynamic Study Between 18-Crown-6 with Mg2+, Ca2+, Sr2+and Ba2+ Cations in Water–Methanol and Water–Ethanol Binary Mixtures Using The Conductometric Method

The complexation reactions between Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ cations with the macrocyclic ligand, 18-Crown-6 (l8C6) in water–methanol (MeOH) binary systems as well as the complexation reactions between Ca²⁺ and Sr²⁺ cations with 18C6 in water–ethanol (EtOH) binary mixtures have been studied at different temperatures using conductometric method. The conductance data show that the stoichiometry of all the complexes is 1:1. It was found that the stability of 18C6 complexes with Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ cations is sensitive to solvent composition and in all cases, a non-linear behaviour was observed for the variation of log K _f of the complexes versus the composition of the mixed solvents. In some cases, the stability order is changed with changing the composition of the mixed solvents. The selectivity order of 18C6 for the metal cations in pure methanol is: Ba²⁺ > Sr²⁺ > Ca²⁺ > Mg²⁺. The values of thermodynamic parameters (Δ H _c ° and Δ S _c °) for formation of 18C6–Mg²⁺, 18C6–Ca²⁺, 18C6–Sr²⁺ and 18C6–Ba²⁺complexes were obtained from temperature dependence of the stability constants. The obtained results show that the values of (Δ H _c ° and Δ S _c °) for formation of these complexes are quite sensitive to the nature and composition of the mixed solvent, but they do not vary monotonically with the solvent composition.This revised version was published online in July 2005 with a corrected issue number.     

Über die thermische Stabilität der Eta-Carbide

Zusammenfassung Das Auftreten von -Carbiden vom TypusA ₃B₃C,A ₂B₄C undA ₆B₆C (A=Fe, Co, Ni,B=Mo, W) wurde untersucht. Mit Ausnahme des Systems Fe–Mo–C konnten in allen Systemen -Carbide des TypsA ₆B₆C beobachtet werden. Im System Co–Mo–C ist die Phase Co₆Mo₆C oberhalb 1000° C thermisch nicht mehr stabil, sondern zerfällt in Co₃Mo₃C+-Phase (Co₇Mo₆). Im System Co–W–C treten im Temperaturbereich 1100–1350° C drei strukturell eng verwandte -Carbide der Zusammensetzungen CO₆W₆C, Co₃W₃C und Co₂W₄C auf. Unterhalb 1000° C ist Co₃W₃C nicht beständig und zerfällt in Co₆W₆C, WC und Kobalt. Isotherme Schnitte durch das System Co–W–C bei 1100° C und 1300° C werden entworfen.

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About the thermal stability of eta-carbides

The occurence of -carbides of typeA ₃B₃C,A ₂B₄C, andA ₆B₆C (A=Fe, Co, Ni), (B=Mo, W) has been investigated. With the exception of the system Fe–Mo–C the formation of a phaseA ₆B₆C could be observed in all systems. The phase Co₆Mo₆C is not stable at temperatures exceeding 1000°C, but undergoes a decomposition to Co₃Mo₃C and -phase (Co₇Mo₆). Three structurally related -phases are observed in the system Co–W–C in the temperature range 1100 to 1350° C: Co₆W₆C, Co₃W₃C, and Co₂W₄C. Below 1100° C the phase Co₃W₃C is unstable and decomposes, forming Co₆W₆C, WC, and Co. Isothermal sections of the systems Co–W–C are drawn for the temperatures 1100 and 1300° C.

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Herrn Prof. Dr.R. Kieffer zum 65. Geburtstag gewidmet.     

RP-HPLC determination of water-soluble vitamins in honey

The assessment and validation of reliable analytical methods for the determination of vitamins in sugar-based matrices (e.g. honey) are still scarcely explored fields of research. This study proposes and fully validates a simple and fast RP-HPLC method for the simultaneous determination of five water-soluble vitamins (vitamin B₂, riboflavin; vitamin B₃, nicotinic acid; vitamin B₅, pantothenic acid; vitamin B₉, folic acid; and vitamin C, ascorbic acid) in honey. The method provides low detection and quantification limits, very good linearity in a large concentration interval, very good precision, and the absence of any bias. It has been successfully applied to 28 honey samples (mainly from Sardinia, Italy) of 12 different botanical origins. While the overall amount of the analytes in the samples is quite low (always below 40 mg kg⁻¹), we have observed a marked dependence of some of their concentrations (i.e. vitamin B₃ and vitamin B₅) and the botanical origin of the honey. This insight might lead to important characterization features for this food item.     

Effect of the B Vitamins on the Radiolysis of Aqueous Ethanol and Ethylene Glycol Solutions

The effects of vitamins B₁, B₂, and B₆ and pyridoxal phosphate on the formation of the final radiolysis products of aqueous ethanol and ethylene glycol solutions were studied. It was found that vitamin B₂ and pyridoxal phosphate effectively oxidize R^·CHOH species to suppress their recombination and fragmentation reactions, thereby increasing the yields of corresponding oxidation products. Vitamins B₁ and B₆ are capable of reducing alcohol radicals to the parent molecules and, hence, decreasing the yields of the main radiolysis products.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 5, 2005, pp. 325–329.Original Russian Text Copyright © 2005 by Lagutin, Shadyro.     

Determination of energizers in energy drinks

The method of UV/VIS derivative spectrophotometry for the determination of caffeine and B vitamins in energy drinks after solid phase extraction has been developed. Caffeine has been determined in the mixture with B₂ vitamin with zero-crossing technique from the I derivative spectra (λ = 266.8 nm), and B₃ in mixture with B₆ vitamin from the II derivative spectra (λ = 280.1 nm). B₁₂ vitamin has also been determined in a three-component mixture with vitamins B₃ and B₆. Taurine in drinks has been determined from the basic spectra after derivatization with ninhydrin (λ = 570 nm).     

Potentiometric Determination of the First Hydrolysis Constant of Gallium(III) in NaCl Solution to 100°C

The hydrolysis equilibrum of gallium (III) solutions in aqueous 1 mol-kg^–1 NaCl over a range of low pH was measured potentiometrically with a hydrogen ion concentration cell at temperatures from 25 to 100°C at 25°C intervals. Potentials at temperatures above 100°C increased gradually because of further hydrolysis of the gallium(III) ion, followed by precipitation. The results were treated with a nonlinear least-squares computer program to determine the equilibrium constants for gallium(III)–hydroxo complexes using the Debye–Hückel equation. The log K (mol-kg^–1) values of the first hydrolysis constant for the reaction, Ga³⁺ + H₂O GaOH²⁺ + H⁺ were –2.85 ± 0.03 at 25°C, –2.36 ± 0.03 at 50°C, –1.98 ± 0.01 at 75°C, and –1.45 ± 0.02 at 100°C. The computed standard enthalpy and entropy changes for the hydrolysis reaction are presented over the range of experimental temperatures.     

Zirconium-Containing Compositions with a Component Ratio Characteristic of the Garnet Structure: Physicochemical and Catalytic Properties

The possibility for the formation of garnet structures in the Mn–Fe–Zr–O and Ca–Sm–Zr–O systems obtained by the precipitation of the corresponding salts is studied. It is shown that, in the Mn–Fe–Zr–O system, garnet is crystallized at 860–920°C, for which probable cation distribution is estimated to be {Zr_2.5 ⁴⁺Mn_0.5 ²⁺}[Mn₂ ²⁺](Fe_2.5 ³⁺Mn_0.5 ³⁺)O₁₂. In the Ca–Sm–Zr–O system, the perovskite CaZrO₃, pyrochlore Sm₂Zr₂O₇, and CaO are formed at 900–1200°C, but compounds with garnet structures are not found. The reported systems are characterized by surface areas of 300–450 m²/g at 450°C, and they have the polydisperse distribution of pores over sizes. The introduction of surfactants at the stage of component mixing enables an increase in the overall pore volume and mechanical strength of these systems. The Mn–Fe–Zr and Ca–Sm–Zr compositions are active catalysts for the complete oxidation of hydrocarbons.     

Mechanism of the Formation of O2? Radical Anions on CeO2 and (0.5–10)%CeO2/ZrO2 during the Adsorption of an NO-O2 Mixture

It is established by ESR that the adsorption of an NO + O₂ mixture at 20°C on oxidized CeO₂ (O₂, T = 400–700°C) produces radical anions O ₂ ⁻ located both on isolated Ce⁴⁺ cations (O ₂ ⁻ (1)) and in associated anionic vacancies (O ₂ ⁻ (2)). These species differ in thermal stability. For example, O ₂ ⁻ (2) decomposes at 20°C, while O ₂ ⁻ (1) decomposes at 50°C. Only O ₂ ⁻ (1) species are observed at −196°C in ZrO₂-supported CeO₂. In the case of NO + O₂ adsorption at 20°C, O ₂ ⁻ is stabilized on Zr⁴⁺ cations and decomposes at 270°C. Increasing the cerium oxide content of the ZrO₂ surface from 0.5 to 10% only partially inhibits the formation of O ₂ ⁻ -Zr⁴⁺. The Zr⁴⁺ cation is shown to possess a higher Lewis acidity than the Ce⁴⁺ cation, and the ionic bond in O ₂ ⁻ -Zr⁴⁺ complexes is stronger than that in O ₂ ⁻ -Ce⁴⁺ complexes. ESR, temperature-programmed desorption, and IR spectroscopic data for various adsorption complexes of NO on CeO₂ suggest that, in the key step of O ₂ ⁻ formation, free electrons appear on the surface owing to the conversion of adsorbed NO molecules into nitrito chelates on coordinately unsaturated ion pairs Ce⁴⁺-O ₂ ⁻ .__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 414–422.Original Russian Text Copyright © 2005 by Il’ichev, Shibanova, Ukharskii, Kuli-zade, Korchak.     

Über die Gewinnung und Thermostabilität der Chalkogenate von Antimon und Wismut, 2. Mitt.: Gewinnung und Untersuchung der Thermostabilität von Wismuttellurit

Zusammenfassung Wismuttellurit-Trihydrat Bi₂(TeO₃)₃·3H₂O wurde hergestellt und sein Verhalten thermisch, thermogravimetrisch, chemisch sowie phasen-röntgenographisch studiert. Es wurde festgestellt, daß bei 175–192°C das Trihydrat in das Dihydrat übergeht, das bei 275–300°C eine monotrope Umwandlung erfährt. Bei weiterem Erhitzen erfolgt eine partielle Oxidation des Te(IV) zu Te(VI), begleitet von einem exothermen Effekt, der bei 348–366°C auftritt. Die vollkommene Entwässerung der Substanz tritt bei 480–500°C ein. Bei 525–600°C wird Te⁶⁺ wieder zu Te⁴⁺ reduziert und schmilzt das Wismuttellurit.

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Preparation and thermostability of the chalkogenates of antimon and bismuth, II: Preparation and thermostability of bismuth tellurite

Bismuth tellurite—the tri-hydrate—has been prepared. By thermal, thermo-gravimetric, chemical, as well as phaseroentgenographic analysis, the behaviour of Bi₂(TeO₃)₃·3H₂O upon heating has been studied. It was found that at 175–192°C the tri-hydrate passes into the di-hydrate, which at 275–300°C undergoes a monotropic transformation. On further heating, a partial oxidation of Te(IV) to Te(VI) takes place, accompanied by an exothermal effect at 348–366°C. The complete desiccation of the substance takes place presumably at 480–500°C. At 525–600°C Te⁶⁺ is again reduced to Te⁴⁺ and the bismuth tellurite melts.

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Validation of a screening method for the simultaneous identification of fat-soluble and water-soluble vitamins (A,E, B<Subscript>1</Subscript>, B<Subscript>2</Subscript> and B<Subscript>6</Subscript>) in an aqueous micellar medium of hexadecyltrimethylammonium chloride

Simultaneous determination of the fat-soluble vitamins A and E and the water-soluble vitamins B₁, B₂ and B₆ has been carried using a screening method from fluorescence contour graphs. These graphs show different colour zones in relation to the fluorescence intensity measured for the pair of excitation/emission wavelengths. The identification of the corresponding excitation/emission wavelength zones allows the detection of different vitamins in an aqueous medium regardless of the fat or water solubility of each vitamin, owing to the presence of a surfactant which forms micelles in water at the used concentration (over the critical micelle concentration). The micelles dissolve very water insoluble compounds, such as fat-soluble vitamins, inside the aggregates. This approach avoids the use of organic solvents in determining these vitamins and offers the possibility of analysing fat- and water-soluble vitamins simultaneously. The method has been validated in terms of detection limit, cut-off limit, sensitivity, number of false positives, number of false negatives and uncertainty range. The detection limit is about g L^–1. The screening method was applied to different samples such as pharmaceuticals, juices and isotonic drinks.     

Buffer Standards for the Physiological pH of Zwitterionic Compounds,MOBS and TABS from 5 to 55°C

The values of the second dissociation constant, pK₂, and related thermodynamic quantities of 4-(N-morpholino)butanesulfonic acid (MOBS) and N-tris(hydroxymethyl)-4-aminobutanesulfonic acid (TABS) have already been reported over the temperature range 5–55°C including 37{°}C. This paper reports the pH values of twelve equimolal buffer solutions at designated pH (s) with the following compositions: (a) mixtures of MOBS (0.05 mol-kg^–1) + NaMOBS (0.05 mol-kg^–1); (b) MOBS (0.08 mol-kg^–1) + NaMOBS (0.08 mol-kg^–1); (c) MOBS (0.08 mol-kg^–1) + NaMOBS (0.08 mol-kg^–1) + NaCl (0.08 mol-kg^–1); (d) TABS (0.05 mol-kg^–1) + NaTABS (0.05 mol-kg^–1); and (e) TABS (0.08 mol-kg^–1) + NaTABS (0.08 mol-kg^–1); and (f) TABS (0.08 mol-kg^–1) + NaTABS (0.08 mol-kg^–1) + NaCl (0.08 mol-kg^–1). Two buffer solutions have ionic strengths I= 0.05 mol-kg^–1, another two have I=0.08 mol-kg^–1, and the remaining two buffer solutions have I= 0.16 mol-kg^–1, which is close to that of the clinical fluids (blood serum). These buffers have been recommended as a useful pH standard for the measurements of physiological solutions. Conventional pH values of all six buffer solutions from 5–55°C, as well as those obtained from the liquid junction potential correction at 25 and 37{°}C have been calculated. The flowing-junction calomel cell has been utilized to measure E_j, the liquid junction potential.     

Sequential determination of fat- and water-soluble vitamins in Rhodiola imbricata root from trans-Himalaya with rapid resolution liquid chromatography/tandem mass spectrometry

A rapid method was developed to determine both types of vitamins in Rhodiola imbricata root for the accurate quantification of free vitamin forms. Rapid resolution liquid chromatography/tandem mass spectrometry (RRLC–MS/MS) with electrospray ionization (ESI) source operating in multiple reactions monitoring (MRM) mode was optimized for the sequential analysis of nine water-soluble vitamins (B₁, B₂, two B₃ vitamins, B₅, B₆, B₇, B₉, and B₁₂) and six fat-soluble vitamins (A, E, D₂, D₃, K₁, and K₂). Both types of vitamins were separated by ion-suppression reversed-phase liquid chromatography with gradient elution within 30 min and detected in positive ion mode. Deviations in the intra- and inter-day precision were always below 0.6% and 0.3% for recoveries and retention time. Intra- and inter-day relative standard deviation (RSD) values of retention time for water- and fat-soluble vitamin were ranged between 0.02–0.20% and 0.01–0.15%, respectively. The mean recoveries were ranged between 88.95 and 107.07%. Sensitivity and specificity of this method allowed the limits of detection (LOD) and limits of quantitation (LOQ) of the analytes at ppb levels. The linear range was achieved for fat- and water-soluble vitamins at 100–1000 ppb and 10–100 ppb. Vitamin B-complex and vitamin E were detected as the principle vitamins in the root of this adaptogen which would be of great interest to develop novel foods from the Indian trans-Himalaya.     

Characterization (certification) of three wheat flours and a wheat gluten reference material (NIST RM 8436, 8437, 8438 and 8418) for essential and toxic major, minor and trace element constituents

Summary Three wheat flours, Durum Wheat Flour (NIST RM 8436), Hard Red Spring Wheat Flour (NIST RM 8437), Soft Winter Wheat Flour (NIST RM 8438) and Wheat Gluten (NIST RM 8418) Reference Materials were characterized for essential and toxic major, minor and trace elemental composition by analysts in an interlaboratory cooperative characterization campaign. Extensive application of widely varied analytical methods yielded 16–27 best estimate and 3–8 informational concentration values for each of these materials. These reference materials are intended for analytical quality control of element determinations in flour and flour products as well as other agricultural/food materials with related matrices.Contribution No. 92–145 from Centre for Land and Biological Resources Research     

Interaction of tetrabutylammonium octahydrotriborate with aluminum chloride. A new method for the preparation of tetraborane(10)

Interaction of Bu₄NB₃H₈ with AlCl₃ at 45–50 °C results in the formation of BH₄ ^– and unstable borane B₂H₄, which is converted into a mixture of B₄H₁₀, B₅H₉, and B₂H₆. This reaction can be used for the preparation of tetraborane(10).