Enzymatic Spectrophotometric Determination of Ascorbic Acid in Commercial Vitamin C Tablets

Esteban, Maria R.; Ho, Chu-Ngi

doi:10.1006/mchj.1996.1442

Cited by 20 publications

(17 citation statements)

References 11 publications

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“…The first mechanism proposed to explain the abundance discrepancy assumes that the AD is produced by electron temperature, T e , fluctuations as proposed by Peimbert (1967) (see Peimbert & Peimbert 2011 for a recent reassessment). However, these temperature variations cannot be reproduced by photoionization models and different mechanisms have been invoked to explain their presence in ionized nebulae (see Esteban 2002;Peimbert & Peimbert 2006). According to this scenario, RLs should provide the true abundances because their emissivities are much less dependent on temperature that those of CELs.…”

Section: Recombination Lines and The Abundance Discrepancy Problemmentioning

confidence: 99%

“…However, the faint RL of C II 4267Å provides an alternative method to derive C abundances in ionized nebulae. Our group has been pioneer measuring the C II 4267Å line in Galactic and extragalactic H II regions using intermediate-high spectral resolution spectroscopy (Esteban et al 2002(Esteban et al , 2009(Esteban et al , 2013López-Sánchez et al 2007). In particular, we have obtained -for the first time-the C/H and C/O radial gradients of the ionized gas in the Milky Way (MW), and preliminary estimates for the spiral galaxies M31, M33, M101 and NGC 2403.…”

Section: And O Radial Abundance Gradients In Galaxiesmentioning

confidence: 99%

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Deep high spectral resolution spectroscopy and chemical composition of ionized nebulae

et al. 2014

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High spectral resolution spectroscopy has proved to be very useful for the advancement of chemical abundances studies in photoionized nebulae, such as H II regions and planetary nebulae (PNe). Classical analyses make use of the intensity of bright collisionally excited lines (CELs), which have a strong dependence on the electron temperature and density. By using high resolution spectrophotometric data, our group has led the determination of chemical abundances of some heavy element ions, mainly O ++ , O + and C ++ from faint recombination lines (RLs), allowing us to deblend them from other nearby emission lines or sky features. The importance of these lines is that their emissivity depends weakly on the temperature and density structure of the gas. The unresolved issue in this field is that recombination lines of heavy element ions give abundances that are about 2-3 times higher than those derived from CELs −in H II regions− for the same ion, and can even be a factor of 70 times higher in some PNe. This uncertainty puts into doubt the validity of face values of metallicity that we use as representative not only for ionized nebulae in the Local Universe, but also for star-forming dwarf and spiral galaxies at different redshifts. Additionally, high-resolution data can allow us to detect and deblend faint lines of neutron capture element ions in PNe. This information would introduce further restrictions to evolution models of AGBs and would help to quantify the chemical enrichment in s-elements produced by low and intermediate mass stars. The availability of an echelle spectrograph at the E-ELT will be of paramount interest to: (a) extend the studies of heavyelement recombination lines to low metallicity objects, (b) to extend abundance determinations of s-elements to planetary nebulae in the extragalactic domain and to bright Galactic and extragalactic H II regions. . However, high spectral resolution spectroscopy permits to obtain proper measurements of very faint lines of much interest for abundance studies due to their closeness to other lines or telluric emission features, specially in the reddest part of the op-⋆ Corresponding author. e-mail: cel@iac.es tical range or the near infrared (NIR). In most PNe, high spectral resolution is necessary in order to resolve their usually complex velocity structure, where velocity splitting of the order of few to several tens of km s −1 is the common rule. Since the velocity structure of H II regions is normally much simpler, spectral resolutions of about R∼10,000 are necessary to resolve their line widths and thus optimize the contrast of the faint lines with respect to the underlying continuum. The continuum may be very intense in the case of the spectra of extragalactic H II regions, where most of the contribution comes from the stellar underlying population we are including in our observing area and may even contain absorption features. Moreover, there are also important bright collisionally excited emission lines that need the use of high spectral resolution −R∼3000 ...

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Section: Recombination Lines and The Abundance Discrepancy Problemmentioning

confidence: 99%

Section: And O Radial Abundance Gradients In Galaxiesmentioning

confidence: 99%

Deep high spectral resolution spectroscopy and chemical composition of ionized nebulae

et al. 2014

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“…These large-scale temperature gradients play a role analogous to the small-scale temperature fluctuations proposed by Peimbert (1967) and used by very many others since then (e.g., Esteban 2002;Peña-Guerrero et al 2012). Kingdon & Ferland (1995) attempted to reproduce temperature fluctuations in the context of detailed photoionization models, and the whole thorny issue of their existence and theoretical justification was discussed by Stasińska (2004).…”

Section: Introductionmentioning

confidence: 99%

NEW STRONG-LINE ABUNDANCE DIAGNOSTICS FOR H II REGIONS: EFFECTS OF Κ-Distributed ELECTRON ENERGIES AND NEW ATOMIC DATA

Dopita

Sutherland

Nicholls

et al. 2013

ApJS

298

466

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Recently, Nicholls et al., inspired by in situ observations of solar system astrophysical plasmas, suggested that the electrons in H ii regions are characterized by a κ-distribution of energies rather than a simple Maxwell-Boltzmann distribution. Here, we have collected together new atomic data within a modified photoionization code to explore the effects of both the new atomic data and the κ-distribution on the strong-line techniques used to determine chemical abundances in H ii regions. By comparing the recombination temperatures (T rec ) with the forbidden line temperatures (T FL ), we conclude that κ ∼ 20. While representing only a mild deviation from equilibrium, this result is sufficient to strongly influence abundances determined using methods that depend on measurements of the electron temperature from forbidden lines. We present a number of new emission line ratio diagnostics that cleanly separate the two parameters determining the optical spectrum of H ii regions-the ionization parameter q or U and the chemical abundance, 12+log(O/H). An automated code to extract these parameters is presented. Using the homogeneous data set from van Zee et al., we find self-consistent results between all of these different diagnostics. The systematic errors between different line ratio diagnostics are much smaller than those found in the earlier strong-line work. Overall, the effect of the κ-distribution on the strong-line abundances derived solely on the basis of theoretical models is rather small.

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“…Enzymic [33][34][35] colorimetric determinations of ascorbic acid in commercial vitamin C tablets and in fruits and vegetables were made by measuring the absorbance at 358 nm or 320 nm of the resulting products obtained by oxidation of o-phenylenediamine/1,4-diaminobenzene using ascorbate oxidase or peroxidase in presence of H 2 O 2 at pH 5.3. Ascorbic acid is determined after oxidation with mercuric chloride and condensing the DHAA with 4,5-disubstituted phenylenediamine 36 , which gives the quinoxaline derivative used for absorbance measurement.…”

Section: Resultsmentioning

confidence: 99%

Photometric Methods for the Determination of Vitamin C

1998

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Enzymatic Spectrophotometric Determination of Ascorbic Acid in Commercial Vitamin C Tablets

Cited by 20 publications

References 11 publications

Deep high spectral resolution spectroscopy and chemical composition of ionized nebulae

Deep high spectral resolution spectroscopy and chemical composition of ionized nebulae

NEW STRONG-LINE ABUNDANCE DIAGNOSTICS FOR H II REGIONS: EFFECTS OF Κ-Distributed ELECTRON ENERGIES AND NEW ATOMIC DATA

Photometric Methods for the Determination of Vitamin C

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