Organic Acid Species Research Articles

Interfacial reaction between organic acids and iron-containing clay minerals: Hydroxyl radical generation and phenolic compounds degradation

Reactive oxygen species, especially hydroxyl radicals (OH), exert a distinguished role in the transformation of contaminants, and their in-situ generation attracts wide attentions in environmental and geochemical areas. The present work explored the potential formation of OH during the interactions between iron-containing clay minerals and environmentally prevalent organic acids in dark environments. The results demonstrated that the accumulative OH concentrations were related to the solution pH, the types of clay minerals, and the nature of organic acid species. At pH 5.5, 1.2– 15.2 times of OH were generated from the reduction of Na-nontronite-2 (Na-NAu-2) compared with other clay minerals in the presence of ascorbic acid (AA) at 144 h. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) analyses indicated that Fe(III) was reduced to Fe(II) by AA during OH formation. Meanwhile, chemical probe tests coupled with quenching experiments confirmed the generation of H2O2 and superoxide radical (O2–), which participated in the formation of OH. The produced OH/O2– can transform 68.4%, 86.4%, and 50.1% of phenol, p-nitrophenol, and 2,4-dichlorophenol within 168 h in AA-Na-NAu-2 suspension, respectively. This work provides valuable insights into OH production in the mutual interaction between organic acids and iron-bearing clays, which is helpful for the development of a new method for removing organic pollutants from contaminated water and soil environments.

Accelerated alkalinity regulation and long-term dry-wet aging durability for bauxite residue remediated with biomass pyrolysis

Biomass fermentation provides a potential route toward the ecological disposal for the bauxite residue (BR) with high alkalinity issues. However, how to accelerate the remediation of the alkaline problem with a long-term durability is still a big challenge. Herein, we investigated the acceleration of the decomposition of straw toward organic acid species via a pyrolysis strategy as well as the pH stability during long-term dry-wet aging for the treated BR. The pH of pyrolytic BR at 300 °C is stabilized at around 8.90 after 70 days’ dry-wet aging. During the aging, the main Ca-contained alkaline minerals of calcite and cancrinite are dissolved and the content of exchangeable Na+ is reduced. This pyrolysis process can decompose straw quickly and produce more organic matters that are easily degraded to fulvic and humic acid as evidenced by 3D fluorescence spectrum analysis. Compared to the fermentation with straw under natural conditions, the alkalinity regulation of BR after pyrolysis is featured with shorter period and lower pH as well as long-term pH stability. Therefore, the synergistic pyrolysis of BR with straw provides an alternative method to address the alkaline issues, which is conducive to promoting the soil formation of BR.

Interactions and Inhibition of Pathogenic Foodborne Bacteria with Individual Dissociated Organic Acid Species: A Review

Interactions and Inhibition of Pathogenic Foodborne Bacteria with Individual Dissociated Organic Acid Species: A Review

Transport of graphene oxide nanoparticles in saturated kaolinite- and goethite-coated sand columns: effects of low-molecular-weight organic acids.

The effects of low-molecular-weight organic acids (LMWOAs) on the transport of graphene oxide nanoparticles in saturated kaolinite- and goethite-coated sand columns were studied. Acetic acid, glycolic acid, malonic acid, and tartaric acid were chosen in the experiments. LMWOAs enhanced the mobility of GO by electrostatic/steric repulsion. In addition, they competed with GO for limited deposition sites on grain surfaces. The effects of organic acids on the transport of GO strongly depended on organic acid species. In general, the transport enhancement effects followed the order of tartaric acid > malonic acid > glycolic acid > acetic acid; this difference may be related to the number and type of functional groups of organic acids. Different LMWOAs enhanced the transport of GO in goethite-coated sand to a larger extent than did in kaolinite-coated sand under the test conditions; this was likely related to the differences of physicochemical characteristics between goethite and kaolinite. Organic acids significantly inhibited the deposition of GO at 0.5 mM Ca2+; this was possible that Ca2+ enhanced adsorption of organic acids by complexing with the surface O-functionalities of both LMWOAs and sand grain. Consequently, more organic acid molecules competed with GO for deposition sites on grain surfaces. Additionally, a two-site transport model was used to fit the transport data. Our findings have important implications for the understanding of the deposition and fate of GO in soil especially in rhizosphere environments where various low-molecular-weight organic acids are active.

Effects of low-molecular weight organic acids on the transport of graphene oxide nanoparticles in saturated sand columns

The impact of low-molecular weight organic acids (LMWOAs) on the transport of graphene oxide (GO) nanoparticles in saturated quartz sand was investigated. The different LMWOAs such as acetic acid, glycolic acid, malonic acid, and tartaric acid were used in experiments. The effects of LMWOAs on the transport of GO were markedly dependent upon organic acid species. In general, the transport enhancement effects followed the order of tartaric acid > malonic acid > glycolic acid > acetic acid, the regular pattern might be related to amount and type of functional groups of LMWOAs. Additionally, the different enhanced ability of LMWOAs was determined by their molecular weight. In the presence of Na+, the main deposition mechanism was ascribed to steric hindrance and competition between LMWOA and GO for deposition sites on grain surfaces under acidic conditions (i.e., pH 4.0 and 5.0). Batch adsorption experiments indicated the extents of competitive adsorption between LMWOAs and GO on quartz sand. In addition, the DLVO theory was not applicable to describe the transport of GO in the presence of LMWOAs at pH 5.0. Nevertheless, electrostatic and steric repulsion, existing between GO and sand grains, were the most important deposition mechanisms under the neutral condition (i.e., pH 7.0). When Ca2+ was the main cation in the background solution, the transport enhancement effects followed quite similar order to those of Na+, mainly due to different complexing strength of organic acids.

Modifications in Organic Acid Profiles During Fruit Development and Ripening: Correlation or Causation?

The pivotal role of phytohormones during fruit development and ripening is considered established knowledge in plant biology. Perhaps less well-known is the growing body of evidence suggesting that organic acids play a key function in plant development and, in particular, in fruit development, maturation and ripening. Here, we critically review the connection between organic acids and the development of both climacteric and non-climacteric fruits. By analyzing the metabolic content of different fruits during their ontogenetic trajectory, we noticed that the content of organic acids in the early stages of fruit development is directly related to the supply of substrates for respiratory processes. Although different organic acid species can be found during fruit development in general, it appears that citrate and malate play major roles in this process, as they accumulate on a broad range of climacteric and non-climacteric fruits. We further highlight the functional significance of changes in organic acid profile in fruits due to either the manipulation of fruit-specific genes or the use of fruit-specific promoters. Despite the complexity behind the fluctuation in organic acid content during fruit development and ripening, we extend our understanding on the importance of organic acids on fruit metabolism and the need to further boost future research. We suggest that engineering organic acid metabolism could improve both qualitative and quantitative traits of crop fruits.

Effects of Acetic Acid, Tartaric Acid and Pb UPD on Cu Electrodeposition in Sub-Micron Trenches

The effects of acetic acid, tartaric acid, and Pb-mediated underpotential deposition (UPD) on the filling characteristics of copper electrodeposition in sub-micron trenches were studied. In the absence of other electrolyte additives, potentiostatic and galvanostatic depositions from electrolytes containing organic acids were capable of producing dense filling in sub-micron trenches due to higher deposition rates at the trench bottoms compared to the side-walls and adjacent surfaces surrounding the recessed features. The mechanism for dense filling of trenches from depositions in the organic acid containing electrolytes did not appear to match previously identified mechanisms for superfilling associated with surfactant effects. Instead, the differential deposition rates across the trench profile were attributed to textural and/or structural differences in the copper seed layer as the copper deposition rates were enhanced at both the bottom and adjacent surfaces surrounding the trenches, or sidewalls of the trench depending on the organic acid species present in the electrolyte. The organic acids induced conformal and smooth depositions improving with increasing overpotential. Pb mediated UPD yielded smooth, conformal films relative to non-mediated deposition under otherwise identical conditions. The density of the UPD mediated films was best at higher Pb coverage during Cu deposition.

Disinfectant and Antimicrobial Susceptibility Profiles of the Big Six Non-O157 Shiga Toxin–Producing Escherichia coli Strains from Food Animals and Humans

The disinfectant and antimicrobial susceptibility profiles of 138 non-O157 Shiga toxin-producing Escherichia coli strains (STECs) from food animals and humans were determined. Antimicrobial resistance (AMR) was moderate (39.1% of strains) in response to 15 antimicrobial agents. Animal strains had a lower AMR prevalence (35.6%) than did human strains (43.9%) but a higher prevalence of the resistance profile GEN-KAN-TET. A decreasing prevalence of AMR was found among animal strains from serogroups O45 > O145 > O121 > O111 > O26 > O103 and among human strains from serogroups O145 > O103 > O26 > O111 > O121 > O45. One animal strain from serogroups O121 and O145 and one human strain from serogroup O26 had extensive drug resistance. A high prevalence of AMR in animal O45 and O121 strains and no resistance or a low prevalence of resistance in human strains from these serogroups suggests a source other than food animals for human exposure to these strains. Among the 24 disinfectants evaluated, all strains were susceptible to triclosan. Animal strains had a higher prevalence of resistance to chlorhexidine than did human strains. Both animal and human strains had a similar low prevalence of low-level benzalkonium chloride resistance, and animal and human strains had similar susceptibility profiles for most other disinfectants. Benzyldimethylammonium chlorides and C10AC were the primary active components in disinfectants DC&R and P-128, respectively, against non-O157 STECs. A disinfectant FS512 MIC ≥ 8 μg/ml was more prevalent among animal O121 strains (61.5%) than among human O121 strains (25%), which may also suggest a source of human exposure to STEC O121 other than food animals. Bacterial inhibition was not dependent solely on pH but was correlated with the presence of dissociated organic acid species and some undissociated acids.

The Roles of Organic Acids in C4 Photosynthesis.

Organic acids are involved in numerous metabolic pathways in all plants. The finding that some plants, known as C4 plants, have four-carbon dicarboxylic acids as the first product of carbon fixation showed these organic acids play essential roles as photosynthetic intermediates. Oxaloacetate (OAA), malate, and aspartate (Asp) are substrates for the C4 acid cycle that underpins the CO2 concentrating mechanism of C4 photosynthesis. In this cycle, OAA is the immediate, short-lived, product of the initial CO2 fixation step in C4 leaf mesophyll cells. The malate and Asp, resulting from the rapid conversion of OAA, are the organic acids delivered to the sites of carbon reduction in the bundle-sheath cells of the leaf, where they are decarboxylated, with the released CO2 used to make carbohydrates. The three-carbon organic acids resulting from the decarboxylation reactions are returned to the mesophyll cells where they are used to regenerate the CO2 acceptor pool. NADP-malic enzyme-type, NAD-malic enzyme-type, and phosphoenolpyruvate carboxykinase-type C4 plants were identified, based on the most abundant decarboxylating enzyme in the leaf tissue. The genes encoding these C4 pathway-associated decarboxylases were co-opted from ancestral C3 plant genes during the evolution of C4 photosynthesis. Malate was recognized as the major organic acid transferred in NADP-malic enzyme-type C4 species, while Asp fills this role in NAD-malic enzyme-type and phosphoenolpyruvate carboxykinase-type plants. However, accumulating evidence indicates that many C4 plants use a combination of organic acids and decarboxylases during CO2 fixation, and the C4-type categories are not rigid. The ability to transfer multiple organic acid species and utilize different decarboxylases has been suggested to give C4 plants advantages in changing and stressful environments, as well as during development, by facilitating the balance of energy between the two cell types involved in the C4 pathway of CO2 assimilation. The results of recent empirical and modeling studies support this suggestion and indicate that a combination of transferred organic acids and decarboxylases is beneficial to C4 plants in different light environments.

In situ submicron organic aerosol characterization at a boreal forest research station during HUMPPA-COPEC 2010 using soft and hard ionization mass spectrometry

Abstract. The chemical composition of submicron aerosol during the comprehensive field campaign HUMPPA-COPEC 2010 at Hyytiälä, Finland, is presented. The focus lies on online measurements of organic acids, which were achieved by using atmospheric pressure chemical ionization (APCI) ion trap mass spectrometry (IT-MS). These measurements were accompanied by aerosol mass spectrometry (AMS) measurements and Fourier transform infrared spectroscopy (FTIR) of filter samples, all showing a high degree of correlation. The soft ionization mass spectrometer alternated between gas-phase measurements solely and measuring the sum of gas and particle phase. The AMS measurements of C, H and O elemental composition show that the aerosol during the campaign was highly oxidized, which appears reasonable due to high and prolonged radiation during the boreal summer measurement period as well as the long transport times of some of the aerosol. In order to contrast ambient and laboratory aerosol, an average organic acid pattern, measured by APCI-IT-MS during the campaign, was compared to terpene ozonolysis products in a laboratory reaction chamber. Identification of single organic acid species remains a major challenge due to the complexity of the boreal forest aerosol. Unambiguous online species identification was attempted by the combinatorial approach of identifying unique fragments in the MS2 mode of standards, and then comparing these results with MS2 field spectra. During the campaign, unique fragments of limonene-derived organic acids (limonic acid and ketolimononic acid) and of the biomass burning tracer vanillic acid were detected. Other specific fragments (neutral loss of 28 Da) in the MS2 suggest the occurrence of semialdehydes. Furthermore, an approach to determine the average molecular weight of the aerosol is presented. The campaign average organic molecular weight was determined to be 300 g mol−1. However, a plume of aged biomass burning aerosol, arriving at Hyytiälä from Russia, contained organic compounds up to 800 Da (MWom≈450 g mol−1), showing that the average molecular weight can vary significantly. The high measurement frequency of both AMS and APCI-IT-MS enabled the partitioning of selected organic acids between gas and particle phase as a function of the total particulate mass to be quantified. Surprisingly high fractions of the higher molecular weight organic acids were observed to reside in the gas phase. These observations might be a consequence of large equilibration timescales for semi-solid boreal forest aerosol, as has been recently hypothesized by Shiraiwa and Seinfeld (2012).

Empirical equation of CO2 corrosion with presence of low concentrations of acetic acid under turbulent flow conditions

The presence of organic acid species in formation water of oil and gas reservoirs has long been suspected to contribute to the corrosivity of CO2 corrosion. The effect had been regarded as secondary until new findings in the 1980s and 1990s revealed the increase in corrosion rate in CO2 environment with the presence of acetic acid species. This is potentially detrimental as most of the predictive models used in corrosivity assessment of the field do not incorporate considerations of the effects of acetic acid species. This paper presents experimental corrosion rates of carbon steel in CO2 environments with the presence of low concentrations of acetic acid species under the turbulent flow conditions, based on linear polarisation resistance analysis. The experimental corrosion rates are compared with the corrosion rates predicted by industrial predictive models such as Norsok and Cassandra. Based on the findings, the authors can conclude that acetic acid species increase the corrosion rate of carbon steel in CO2 corrosion and standard predictive models do not capture this effect. An empirical equation is proposed to cater for the presence of low concentrations of acetic acid in CO2 corrosion under turbulent conditions.

Alpha-hydroxybutyrate is an early biomarker of insulin resistance and glucose intolerance in a nondiabetic population.

BackgroundInsulin resistance is a risk factor for type 2 diabetes and cardiovascular disease progression. Current diagnostic tests, such as glycemic indicators, have limitations in the early detection of insulin resistant individuals. We searched for novel biomarkers identifying these at-risk subjects.MethodsUsing mass spectrometry, non-targeted biochemical profiling was conducted in a cohort of 399 nondiabetic subjects representing a broad spectrum of insulin sensitivity and glucose tolerance (based on the hyperinsulinemic euglycemic clamp and oral glucose tolerance testing, respectively).ResultsRandom forest statistical analysis selected α-hydroxybutyrate (α–HB) as the top-ranked biochemical for separating insulin resistant (lower third of the clamp-derived MFFM = 33 [12] µmol·min−1·kgFFM −1, median [interquartile range], n = 140) from insulin sensitive subjects (MFFM = 66 [23] µmol·min−1·kgFFM −1) with a 76% accuracy. By targeted isotope dilution assay, plasma α–HB concentrations were reciprocally related to MFFM; and by partition analysis, an α–HB value of 5 µg/ml was found to best separate insulin resistant from insulin sensitive subjects. α–HB also separated subjects with normal glucose tolerance from those with impaired fasting glycemia or impaired glucose tolerance independently of, and in an additive fashion to, insulin resistance. These associations were also independent of sex, age and BMI. Other metabolites from this global analysis that significantly correlated to insulin sensitivity included certain organic acid, amino acid, lysophospholipid, acylcarnitine and fatty acid species. Several metabolites are intermediates related to α-HB metabolism and biosynthesis.Conclusionsα–hydroxybutyrate is an early marker for both insulin resistance and impaired glucose regulation. The underlying biochemical mechanisms may involve increased lipid oxidation and oxidative stress.

Chemical characteristics of precipitation at metropolitan Newark in the US East Coast

To investigate the chemical characteristics of precipitation in the polluted coastal atmosphere, a total of 46 event-based precipitation samples were collected using a wet-only automatic precipitation collector from September 2006 to October 2007 at metropolitan Newark, New Jersey in the US East Coast. Samples were analyzed by ion chromatography for the concentrations of major inorganic ions (Cl −, NO 3 −, SO 4 2−, F −, NH 4 +, Ca 2+, Mg 2+, Na +, K +) and organic acid species (CH 3COO −, HCOO −, CH 2(COO) 2 2−, C 2O 4 2−). Selected trace metals (Sb, Pb, Al, V, Fe, Cr, Co, Ni, Cu, Zn, Cd) in samples were determined by ICPMS. Mass concentration results show that SO 4 2− was the most dominant anion accounting for 51% of the total anions, controlling the acidity of the precipitation. NH 4 + accounted for 48.6% of the total cations, dominating the precipitation neutralization. CH 3COO − and HCOO − were the two dominant water-soluble organic acid species, accounting for 42% and 40% of the total organic acids analyzed, respectively. Al, Zn and Fe were the three major trace metals in precipitation, accounting for 34%, 27%, and 25% of the total mass of metals analyzed. The pH values in precipitation ranged from 4.4 to 4.9, indicating an acidic nature. Enrichment Factor (EF) Analysis showed that Na +, Cl −, Mg 2+ and K + in the precipitation were primarily of marine origin, while most of the Fe, Co and Al were from crust sources. Pb, V, Cr, Ni were moderately enriched with EFs ranging 43–410, while Zn, Sb, Cu, Cd and F − were highly enriched with EFs > 700, indicating significant anthropogenic influences. Factor analysis suggests 6 major sources contributing to the observed composition of precipitation at this location: (1) nitrogen-enriched soil, (2) secondary pollution processes, (3) marine sources, (4) incinerations, (5) oil combustions, and (6) malonate–vanadium enriched sources. To further explore the source–precipitation event relationships and seasonality, cluster analysis was performed for all precipitation events. Results show that about half of the precipitation events were characterized by mixed sources. Significant influences of nitrogen-enriched soil and marine sources were associated with precipitation events in spring and autumn, while secondary pollution processes, incineration and oil combustion contributed greatly in summer.

Effects of pH Adjustment and Sodium Ions on Sour Taste Intensity of Organic Acids

Protonated organic acid species have been shown to be the primary stimuli responsible for sour taste of organic acids. However, we have observed that sour taste may be modulated when the pH of acid solutions is raised using sodium hydroxide. Objectives were to evaluate the effect of pH adjustment on sour taste of equimolar protonated organic acid solutions and to investigate the potential roles of organic anions and sodium ions on sour taste perception. Despite equal concentrations of protonated acid species, sour taste intensity decreased significantly with increased pH for acetic, lactic, malic, and citric acids (P < 0.05). Total organic anion concentration did not explain the suppression of sour taste in solutions containing a blend of 3 organic acids with constant concentration of protonated organic acid species and hydrogen ions and variable organic anion concentrations (R(2)= 0.480, P = 0.12). Sour taste suppression in these solutions seemed to be more closely related to sodium ions added in the form of NaOH (R(2)= 0.861, P = 0.007). Addition of 20 mM NaCl to acid solutions resulted in significant suppression of sour taste (P = 0.016). However, sour taste did not decrease with further addition of NaCl up to 80 mM. Presence of sodium ions was clearly shown to decrease sour taste of organic acid solutions. Nonetheless, suppression of sour taste in pH adjusted single acid solutions was greater than what would be expected based on the sodium ion concentration alone, indicating an additional suppression mechanism may be involved.

Aluminium induces changes in organic acids metabolism in Coffea arabica suspension cells with differential Al-tolerance

The primary Al-tolerance mechanism in plants involves exudation and/or accumulation of specific organic acid species, which form non-phytotoxic complexes with Al 3+ under physiological conditions. An evaluation was done of the role of organic acids in the tolerance mechanism of a cell suspension line of coffee Coffea arabica that exhibits Al-tolerance (LAMt) but for which the metabolic tolerance mechanism remains unknown. Significant differences existed in malate dehydrogenase and citrate synthase activities (key enzymes in organic acids metabolism) between protein extracts (day 7 of culture cycle) of the L2 (Al-sensitive) and LAMt (Al-tolerant) cells when cell suspensions were treated with 100 μM AlCl 3. HPLC analysis showed that the suspension cells of both lines exudate malate when incubated in a minimal solution but that exudation was not enhanced by treatment with AlCl 3 (100 μM). This is the first study demonstrating that plant Al-tolerance may be associated with down-regulation of malate dehydrogenase and citrate synthase activities.

A Chemical Basis for Sour Taste Perception of Acid Solutions and Fresh‐Pack Dill Pickles

Sour taste is influenced by pH and acids present in foods. It is not currently possible, however, to accurately predict and modify sour taste intensity in foods containing organic acids. The objective of this study was to investigate the roles of protonated (undissociated) organic acid species and hydrogen ions in evoking sour taste. Sour taste intensity increased linearly with hydrogen ion concentration (R(2)= 0.995), and with the concentration of protonated organic acid species at pH 3.5 (R(2)= 0.884), 4.0 (R(2)= 0.929), and 4.5 (R(2)= 0.975). The structures of organic acid molecules did not affect sour taste after adjusting for the effects of protonated organic acid species and hydrogen ions. Sour taste intensity was also linearly related to the total concentration of protonated organic acid species in fresh-pack dill pickles (R(2)= 0.957). This study showed that the sour taste of organic acids was directly related to the number of molecules with at least 1 protonated carboxyl group plus the hydrogen ions in solution. Conclusions from these results are that all protonated organic acids are equally sour on a molar basis, that all protonated species of a given organic acid are equally sour, and that hydrogen ions and protonated organic acids are approximately equal in sour taste on a molar basis. This study provides a new understanding of the chemical species that are able to elicit sour taste and reveals a basis for predicting sour taste intensity in the formulation of acidified foods.

On the Source of Organic Acid Aerosol Layers above Clouds

During the July 2005 Marine Stratus/Stratocumulus Experiment (MASE) and the August-September 2006 Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS), the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter probed aerosols and cumulus clouds in the eastern Pacific Ocean off the coast of northern California and in southeastern Texas, respectively. An on-board particle-into-liquid sampler (PILS) quantified inorganic and organic acid species with < or = 5-min time resolution. Ubiquitous organic aerosol layers above cloud with enhanced organic acid levels were observed in both locations. The data suggest that aqueous-phase reactions to produce organic acids, mainly oxalic acid, followed by droplet evaporation is a source of elevated organic acid aerosol levels above cloud. Oxalic acid is observed to be produced more efficiently relative to sulfate as the cloud liquid water content increases, corresponding to larger and less acidic droplets. As derived from large eddy simulations of stratocumulus underthe conditions of MASE, both Lagrangian trajectory analysis and diurnal cloudtop evolution provide evidence that a significant fraction of the aerosol mass concentration above cloud can be accounted for by evaporated droplet residual particles. Methanesulfonate data suggest that entrainment of free tropospheric aerosol can also be a source of organic acids above boundary layer clouds.

Photo-induced chemical vapour generation with formic acid: novel interface for high performance liquid chromatography-atomic fluorescence spectrometry hyphenated system and application in speciation of mercury

Based on a novel photo-induced chemical vapour generation (CVG) with formic acid instead of the conventional K2S2O8/KBH4 system, an on-line coupled HPLC and atomic fluorescence spectrometry procedure was developed for the speciation of inorganic mercury, methylmercury (MeHg), ethylmercury (EtHg) and phenylmecury (PhHg). Under UV irradiation, the decomposition of organic mercury species and the reduction of Hg2+ could be completed in one step with this proposed photo-induced CVG system. The novel CVG system used formic acid only, which simplified the flow system and avoided the possibility of contamination originating from additional chemicals. A number of operating parameters including organic acid species, concentration of formic acid, pH, flow rate of formic acid and flow rate of carrier gas were optimized, and comparable method sensitivities with the conventional K2S2O8/KBH4 system were obtained. The limits of detection at the optimized conditions were 0.81, 0.20 and 0.87 μg L−1 for MeHg, EtHg and PhHg, respectively. The developed method was validated by determination of certified reference material DORM-2 and was further applied in determination of seafood samples. The new CVG system is simple, environmentally benign, and inexpensive for the speciation analysis of mercury. It is expected to have similar applications in other analytical atomic spectrometric techniques as well as speciation of other organic metal compounds.

A Hypothesis for the Chemical Basis for Perception of Sour Taste

Sour taste has been considered the simplest of the basic tastes because it is elicited only by hydrogen ions. However, there is not a sufficiently clear understanding of that relationship to allow sour taste intensity to be predicted and rationally modified in foods. On the basis of analysis of sensory data from our laboratory and reanalysis of previously published data, we propose a new hypothesis for the chemical basis for sour taste perception: The intensity of sour taste perception in acid solutions or acidified foods is linearly related to the molar concentration of all organic acid species with at least 1 protonated carboxyl group plus the molar concentration of free hydrogen ions. This hypothesis implies that, on a molar basis, different organic acids will be equally sour, provided at least 1 carboxyl group is protonated. The major effect of pH on sour taste will be to determine the degree of protonation of organic acids. If this hypothesis is confirmed, it will provide a new understanding of the chemical basis for this basic taste perception and have broad usefulness in the formulation of products in which sour taste is an important component of flavor.

Preparation and Crystal Structure of the Silver(I) p-Toluenesulfonate−p-Aminobenzoic Acid Complex Polymer Adduct, the First Reported Example of a Silver(I) Complex Involving Two Different Organic Acid Species

The silver(I) complex adduct with p-toluenesulfonate and p-aminobenzoic acid, catena-(μ-4-aminobenzoic acid)(μ-4-toluenesulfonato-O,O‘,O‘‘)silver(I), has been prepared and its structure determined by X-ray diffraction. This compound represents the first structurally characterized example of a complex of silver(I) involving two different organic acid species. The complex network polymer is based on a distorted tetrahedral AgO3N center with silver bonded to oxygens from sulfonate residues of three independent p-toluenesulfonate molecules [Ag−O = 2.309−2.518(3) Å] and the amine nitrogen of a p-aminobenzoic acid adduct molecule [Ag−N = 2.223(3) Å].