Titration Alkalinity Research Articles

Alkalinity determination by potentiometry: intercalibration using three different methods

Seawater was sampled from different depths in the North Atlantic Ocean (Canary Islands region) and distributed among three different labs for the determination of titration alkalinity. Analysis was performed by potentiometric methods, involving titration in a closed cell, titration in an open cell and a two end-point acid addition method. The precision, which is the sample reproducibility taken from the mean standard deviation for replicate measurements, was between 0.45 and 0.90 µmol · kg–1 for the individual labs. Accuracy, here taken as the deviation for the values of a lab from the mean of all three, was mostly below 1 µmol · kg–1 and never exceeded 0.1% of the sample value. Mean standard deviation for all labs and all samples was 0.87 µmol · kg–1, once the individual methods were calibrated using certified reference material (CRM). Without CRM calibration, the mean standard deviation would increase to 2.8 µmol · kg–1. The conclusion is that current high precision methods for alkalinity measurements calibrated with CRMs are able to reach similar accuracy as the measurement of total dissolved inorganic carbon by coulometry and therefore allow for the precise determination of the oceanic carbon dioxide system by using the two measured parameters.

Seasonal evolution of hydrographic properties in the Ross Sea, Antarctica, 1996–1997

This paper briefly describes hydrographic and chemical results from four seasonal process cruises in the Joint Global Ocean Flux Study (JGOFS) Antarctic Environment and Southern Ocean Process Study (AESOPS) in the Ross Sea. The data include temperature, salinity, oxygen, nutrients (NO 3 −, NO 2 −, NH 4 +, PO 4 −3, Si(OH) 4), titration alkalinity (TA), and total inorganic CO 2 (TCO 2). In early spring (mid-October to early November 1996) ice cover was near 100%. The water column exhibited only small ranges of potential temperature, salinity, nutrients, TA and TCO 2. These nearly uniform conditions observed during this cruise were used as initial conditions from which to evaluate seasonal changes in biogeochemical properties. Later in the spring (November/December) of the following year (1997), an expanded polynya was present. In the summer (January) 1997, the sea-ice cover was minimal. Meltwater dilution and warming of exposed surface waters were at their maximum. Finally, in early austral autumn (April 1997) rapid cooling and freezing of surface waters and intensified vertical mixing of the water column resulted in a return toward winter conditions, but with significant depletion of nutrients still evident in surface waters. Modified circumpolar deep water (MCDW) was observed at ∼175°E., varying in location zonally with time. Beneath the MCDW, near the eastern end of the section at ∼180°, northward intrusion of ice shelf water (ISW) was persistent though variable. Among the biogeochemical changes observed along this section were: (1) Significant ammonium accretion at about 100 m; (2) appreciable nitrate drawdowns throughout the upper 20–40 m of the water column; (3) silicic acid depletions during the summer in the surface waters, which were largest at the western end of the study area; (4) an increase in TA largely due to the loss of NO 3 −; and (5) decreases in TCO 2 close to expected values for consumption of carbon and nitrogen in “Redfield” proportions. Consistent with previous observations, N, P and Si never approached limiting concentrations during any of the cruises.

Polymorphism of turnip yellow mosaic virus empty shells and evidence for conformational changes occurring after release of the viral RNA

Turnip yellow mosaic virus (TYMV) is a small isometric plant virus which decapsidates by releasing its RNA through a hole in the capsid, leaving behind an empty shell [R. E. F. Matthews and J. Witz, (1985) Virology 144, 318-327]. Similar empty shells (artificial top component, ATC) can be obtained by submitting the virions to various treatments in vitro. We have used differential scanning calorimetry, analytical sedimentation, and electron microscopy to investigate the thermodenaturation of natural empty shells (NTC, natural top component) present in purified virus suspensions, and of several types of ATCs. ATCs divided in two major classes. Those obtained by alkaline titration, by the action of urea or butanol behaved as NTC: their thermograms contained only one peak corresponding to the irreversible dissociation of the shells and the denaturation of the coat protein. The temperature of this unique transition varied significantly with pH, from 71 degrees C at pH 4.5 to 84 degrees C at pH 8.5. The thermograms of ATCs obtained by freezing and thawing, or by the action of high pressure, contained two peaks: shells dissociated first into smaller protein aggregates at 57 degrees C (at pH 5.0) to 61 degrees C (at pH 8.5), which denatured at the temperature of the unique transition of NTC. Shells obtained by heating virions to 55 degrees C at pH 7.6, changed conformation after the release of the viral RNA, as upon continuous heating to 95 degrees C, their thermograms were similar to those of the shells obtained by freezing and thawing, whereas after purification they behaved like NTC. Structural implications of these observations are discussed.

Spatiotemporal patterns of carbon‐13 in the global surface oceans and the oceanic suess effect

A global synthesis of the 13C/12C ratio of dissolved inorganic carbon (DIC) in the surface ocean is attempted by summarizing high‐precision data obtained from 1978 to 1997 in all major ocean basins. The data, mainly along transects but including three subtropical time series, are accompanied by simultaneous, precise measurements of DIC concentration and titration alkalinity. The reduced isotopic ratio, δ13C, in the surface ocean water is governed by a balance between biological and thermodynamic processes. These processes have strongly opposing tendencies, which result in a complex spatial pattern in δ13C with relatively little variability. The most distinctive feature in the spatial distribution of δ13C seen in our data is a maximum of δ13C near the subantarctic front with sharply falling values to the south. We attribute this feature to a combination of biological uptake of CO2 depleted in 13C (low δ13C) and air‐sea exchange near the front and upwelling further south of waters with low δ13C resulting from the remineralization of organic matter. Additional features are maxima in δ13C downstream of upwelling regions, reflecting biological uptake, and minima in the subtropical gyres caused by strongly temperature dependent thermodynamic isotopic fractionation. At the time series stations, two in the North Atlantic Ocean and one in the North Pacific, distinct seasonal cycles in δ13C are observed, the Pacific data exhibiting only about half the amplitude of the Atlantic. Secular decreases in δ13C caused by the invasion of isotopically light anthropogenic CO2 into the ocean (the 13C Suess effect) have been identified at these time series stations and also in data from repeated transects in the Indian Ocean and the tropical Pacific. A tentative global extrapolation of these secular decreases yields a surface oceanic 13C Suess effect of approximately −0.018‰ yr−1 from 1980 to 1995. This effect is nearly the same as the 13C Suess effect observed globally in the atmosphere over the same period. We attribute this response to a deceleration in the growth rate of anthropogenic CO2 emissions after 1979, which subsequently has reduced the atmospheric 13C Suess effect more than the surface ocean effect.

Interaction of plant and soil phenol with Cu pollution

Vaccinium sp., Rhododendron ferrugineum and mosses are the dominant plant groups present on the moraine soils of Barme I, Barme II and Pierrier in the Arpette valley. The amount of o-diphenols (ODP) available in plants and susceptible to be released each year to the soil surface was determined by HPLC. The quantity of caffeic acid, catechol and protocatechuic acid present in the leaves ranged between 25 and 250 mg/m 2 . The impact caused by Cu pollution on this type of ecosystems was studied by a chemical speciation approach. Potentiometric alkaline titrations were carried out on synthetic phenol solutions containing increasing Cu concentrations. Cu complexation increased with an increasing pH, but in order to have all the Cu in the complexed form a minimum ratio of (4:1) ODP-Cu in the solution was necessary.

The dependence on temperature and salinity of dissolved inorganic carbon in East Atlantic surface waters

Recurring latitudinal patterns of the dissolved inorganic carbon (DIC) content and the fugacity of CO2 (fCO2) were observed in East Atlantic surface waters with strong gradients at hydrographic fronts. The dissolved inorganic carbon chemistry clearly displayed the effects of oceanic circulation and of persistent surface water processes. In two cases inorganic carbon components could be used as an indicator of the origin of hydrographic features. Surface water fCO2 below the atmospheric value, low DIC and low salinity north of the equator were ascribed to a combination of high rainfall and low wind speed in the Intertropical Convergence Zone and of biological uptake of CO2. Low surface water DIC and salinity delineated the Congo outflow. Along the cruise tracks calculated titration alkalinity (TA) had an almost linear relationship with salinity, while DIC had an apparent dependence on temperature and salinity. The latter dependence was tested by comparing observed DIC to DIC estimated from fCO2 and a reference value of TA normalised to salinity. Different scenarios of temperature, salinity, fCO2 and nutrient contents were applied. Changes of DIC were found to be indeed related to both temperature and salinity. The latitudinal distribution of DIC could be inferred with an accuracy of 17 μmol kg−1 and a standard deviation of 13 μmol kg−1 from in situ salinity, in situ temperature and the reference values of TA and nutrient contents normalised to in situ salinity (scenario D). The applied technique of estimating DIC from temperature and salinity is a powerful diagnostic tool to evaluate the spatial distribution of DIC.

Solubility and Ion Activity Products of Calcium Phosphate Minerals

AbstractMost phosphate mineral solubility data in use were measured more than 20 yr ago when instrumentation and methods were generally less sophisticated. The objective of this study was to measure calcium phosphate mineral solubilities using modern analytical equipment and techniques. Natural and synthetic Ca phosphate minerals (<50 µm) were equilibrated in water and dilute HCl for 6 mo with continuous agitation. X‐ray diffraction (XRD) was used to identify compositions before and after equilibration. Filtered (<0.2 µm) solution aliquots were analyzed for pH and chemistry. Chemical compositions were determined using inductively‐coupled plasma spectroscopy (ICP). Aqueous carbonates were determined from alkalinity titrations after phosphate alkalinity corrections. The chemical speciation model “Soilchem” was used to calculate free ion concentrations and ionic strengths. Ion activity products (IAPs) were determined from free ion concentrations and single ion activity coefficients. Experimental log IAPs of monetite (CaHPO4) were consistent (−6.60) with published values for brushite (CaHPO4·2H2O) suggesting that the IAPs of these minerals are identical. No change in mineralogy during equilibration was revealed by XRD. Experimental log IAPs of synthetic whitlockite (−30.74, β‐Ca3(PO4)2) indicated somewhat lower solubility than published values. Log IAPs of synthetic hydroxyapatite (−56.02, Ca5(PO4)3OH) were within the range of published values. Natural samples of whitlockite and fluorapatite did not attain equilibrium due to extraneous siderite (FeCO3) and silica phases within the samples. A long equilibration time, modern analytical equipment, and a chemical speciation program can yield more reliable solubility data for phosphates and other minerals.

Improved method for calculating anthropogenic CO2 in the upper layer of the North Pacific Subtropical Gyre along 175°E

Seawater samples were collected in the North Pacific along 175°E during a cruise of the Northwest Pacific Carbon Cycle Study (NOPACCS) program in 1994. Many properties related to the carbonate system were analyzed. By using well-known ratios to correct for chemical changes in seawater, the CO2 concentration at a given depth was back calculated to its initial concentration at the time when the water left the surface in winter. We estimated sea-surface CO2 and titration alkalinity (TA) in present-day winter, from which we evaluated the degree of air-sea CO2 disequilibrium in winter was. Using a correction factor for air-sea CO2 disequilibrium in winter, we reconstructed sea-surface CO2 in pre-industrial times. The difference between the back-calculated initial CO2 and sea-surface CO2 in pre-industrial times should correspond to anthropgenic CO2 input. Although the mixing of different water masses may cause systematic error in the calculation, we found that the nonlinear effect induced by the mixing of different water masses was negligible in the upper layer of the North Pacific subtropical gyre along 175°E. The results of our improved method of assessing the distribution of anthropogenic CO2 in that region show marked differences from those obtained using the previous back-calculation method.

Distribution of total carbonate and related properties in the North Pacific along 30°N

Cross sections of the total carbonate (TC), titration alkalinity (TA), and pH were observed during the WOCE/JGOFS‐P2 cruise (30°N, 130°E –122°W). The increases in TC in the years since 1973 are calculated by the comparison of TC data observed during P2 and those observed during the Geochemical Ocean Section Study. At stations east of 170°W, TC has increased proportionally to the atmospheric increase of CO2 in water shallower than the σθ = 26.20 density surface, while at stations west of 180°E TC had increased proportionally to the atmospheric increase only in water shallower than the σθ = 25.40 density surface. Increase in the column inventory of TC is 143±32 gC/m2 on average and does not significantly differ with longitude.

Rising surface ocean dissolved inorganic carbon at the Hawaii Ocean Time-series site

Abstract Surface ocean dissolved inorganic carbon (DIC) and titration alkalinity have been measured for 7 years as a part of the Hawaii Ocean Time-series (HOT) program. The time-series data set displays an interannual increase in the inventory of surface ocean DIC which we interpret as a response to increasing atmospheric carbon dioxide concentrations. The rate of increase in surface ocean DIC at the open ocean HOT site is approximately 1 μ mol kg −1 yr −1 with a 95% confidence interval of 0.72 to 1.37 μ mol kg −1 yr −1 . This accumulation rate is consistent with the rate of increase predicted from the rise in boundary layer p CO 2 .

Soy hull carbon as adsorbents of crude soy oil components: Effect of carbonization time

AbstractStudies were conducted to evaluate the performance of soy hull carbon adsorbents as affected by carbonization time. Carbonization was done by heating soy hulls to 400°C for up to 30 min. Increased carbonization time resulted in elevated surface pH and titratable alkalinity. The effectiveness of adsorbents in binding minor soy oil components was studied. Free fatty acids content was decreased 70% with adsorbents carbonized for 30 min. Peroxides were adsorbed, but increasing carbonization time did not alter absorption by carbons. A similar trend was observed with the adsorption of total phospholipids. The residual lutein content of crude soy oil was not affected by the adsorbents. X‐ray diffraction studies showed that carbonization at 400°C converted the polysaccharide‐based structure of soy hull to an amorphous, highly disorganized, random structure. Increase in carbonization time resulted in broadening of the diffraction pattern between 5 and 25° 2ϑ. Infrared spectra of soy carbon samples revealed presence of asymmetric C‐H stretch, symmetric C‐H bends, and C=O groups. The intensities of these spectra decreased with time of carbonization.

Rapid, high-precision potentiometric titration of alkalinity in ocean and sediment pore waters

A system for rapid, high precision potentiometric determination of alkalinity in sea water and sediment pore water is presented. Two titration units were used: a 40 ml unit for seawater and a small volume unit for sediment pore water. Titration time was normally less than 10 minutes per sample, including sample exchange. With a 40 ml sample volume, the relative standard deviation of the alkalinity obtained in the laboratory was 0.05% and at sea 0.1 %. The small-volume system (0.5–1.5 ml) gave a precision of 0.07%. Five titration points, in two groups after the second equivalence point, were used to evaluate the equivalence volume. Results from equilibrium calculations and computer simulated alkalinity titrations show that it was possible to use a non-modified Gran function [( V 0 +v) ∗10 ( E Z ) ] and still achieve good accuracy and precision.

Concentrations and isotope ratios of dissolved inorganic carbon in denitrifying environments

We measured the concentration and isotope ratio of dissolved inorganic carbon (DIC) in groundwater associated with denitrification (Corg + NO3−=CO2 + N2) in an agriculturally impacted site in southwestern Michigan. Samples with the lowest nitrate levels also had low dissolved oxygen content and were more depleted in δ13C than background groundwater. All the samples had DIC concentrations in excess of titratable alkalinity. The magnitude of this DIC in excess of alkalinity correlated with a decreasing δ13C attesting to the presence of CO2 derived from organic carbon. Carbon dioxide is one of the by‐products of denitrification. Since the carbon isotope ratio of carbon dioxide produced during denitrification can be expected to be similar to that of the substrate consumed in the process, this can serve as a useful tool in monitoring denitrification. The estimated carbon isotope ratio of source carbon added to the DIC pool via denitrification was close to the value obtained for the organic carbon in the aquifer solids, suggesting that the carbon substrate used in denitrification came from soil organic matter. The results provide support for the hypothesis that the concentration and carbon isotope ratios (δ13C) of dissolved inorganic carbon (DIC) in groundwater might be useful to monitor denitrification.

Jellyfish Lake, Palau: Regeneration of C, N, Si, and P in anoxic marine lake sediments

Sediment cores from Jellyfish Lake were processed under an inert atmosphere and the pore waters extracted and analyzed for the following parameters: pH, titration alkalinity (TA), Cl−, H4SiO4, PO43−, NH4+, Ca2+, Mg2+, SO42−, and H2S. Additionally, in one set of pore‐water samples (core 10), the δ13C of the ∑CO2 was also determined. The TA, H4SiO4, PO43−, NH4+, and H2S increased with depth in the pore waters above anoxic bottom‐water values. H2S values increased to 3.8 M. In one case, both H4SiO4 and PO43− concentrations increased to a maximum value and then decreased with depth, suggesting removal into solid phases. The H4SiO4 concentrations are equal to or greater than pore‐water value observed in sediments underlying upwelling areas. PO43− concentrations are, in general, lower than pore‐water values from terrigenous nearshore areas but higher than nearshore carbonate pore‐water values from Florida Bay or Bermuda. The Ca2+, Cl−, and Mg2+ : Cl− ratios show slight decreases in the top 15–20 cm, suggesting that authigenic carbonate may be forming. This suggestion is supported by the fact that the pore waters are saturated with respect to CaCO3 due to the very high TAs. The δ13C measurements of the pore‐water ∑CO2 are from a shorter core. These measurements reach their most negative concentration at 72 cm and then become slightly heavier. This change is accompanied by a decrease in TA, suggesting the onset of methanogenesis at this location in this core.

Root Medium Carbon Dioxide and Oxygen Partial Pressures for Container-grown Chrysanthemums

Medium CO2 and O2 partial pressures were measured at three locations [3.8 (top layer), 7.5 (middle layer), and 10.3 (bottom layer) cm below the rim] in 15-cm-tall pots containing flowering chrysanthemums [Dendranthem×grandiflorum (Ramat.) Kitamura] grown in one of three root media. Average ambient medium CO2 and O2 partial pressures were 63 Pa and 21 kPa, respectively, and were similar in the three sampled layers in root media with an average moisture content of 50% to 60% of container capacity. Within 10 minutes after a drip-irrigation application of well water containing a titratable alkalinity to pH 4.5 of 320 mg CaCO3/liter, the partial pressure of medium CO2 increased to ≤1600 Pa and medium O2 decreased to 20.5 kPa in the top and middle layers of the pot. With subirrigation, medium CO2 partial pressures increased to ≤170 Pa and medium O2 remained at 21 kPa. When reverse-osmosis purified water (titratable alkalinity to pH 4.5 of <20 mg CaCO3/liter) was used instead of well water, the large increase in medium CO2 did not occur, indicating that the bicarbonate alkalinity in the irrigation water was the source of CO2. The high medium CO2 partial pressure measured after irrigation was not persistent; within 180 minutes, it returned to levels averaging 45% higher (100 Pa) than that measured before the irrigation. Medium O2 also had returned to ambient levels 180 minutes after the irrigation.

ChemInform Abstract: Synthesis and Reactivity of (NEt4)2(ReBr3(CO)3). Formation and Structural Characterization of the Clusters (NEt4) (Re3(μ3‐OH)(μ‐ OH)3(CO)9) and (NEt4) (Re2(μ‐OH)3(CO)6) by Alkaline Titration.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Combined pH gradient and anion-exchange high-performance liquid chromatographic separation of oligodeoxyribonucleotides

A novel method of elution using a pH gradient to separate small thymidine- and guanosine-containing oligonucleotides on a Pharmacia Mono Q HR anion-exchange column is described. The method is based on the alkaline titration of ring protons of the thymine and guanine base moieties and results in excellent separations of di-, tri- and tetranucleotides that either are not resolved in salt gradients near neutral pH or require long elution times when salt gradient elution is used with strongly alkaline eluents.

The influence of organic matter diagenesis on CaCO 3 dissolution at the deep-sea floor

In situ benthic flux chamber measurements were performed at seafloor locations in the Atlantic and Pacific oceans where the bottomwaters were supersaturated, approximately saturated, and undersaturated with respect to calcite. There was no evidence of significant dissolution at or above the saturation horizon. Below the saturation horizon, however, significant benthic fluxes of titration alkalinity and calcium out of the sediments were observed indicating appreciable dissolution. Where observed, the rate of dissolution is consistent with a rate expression of reaction order 4.5 and a rate constant in the range of 0.05 to 0.5% per day. A numerical simulation was constructed to represent organic matter and CaCO 3 diagenesis at the seafloor. At the supersaturated and near-saturation sites, the model over-predicts the influence of metabolically produced CO 2 on the extent of CaCO 3 dissolution. It is possible that these results can be reconciled by a better understanding and parameterization of organic matter mineralization and porewater transport processes in surface sediments. The primary factors to be considered include ( 1 ) the oxidation state of the carbon being oxidized, (2) the vertical distribution of oxidation rates including the role of DOC in sediment remineralization, (3) the influence of nondiffusive transport of near-surface porewaters, and (4) the influence of episodic depositional events on organic and inorganic carbon cycling.

Air‐sea carbon dioxide exchange in the North Pacific Subtropical Gyre: Implications for the Global Carbon Budget

The role of the ocean as a sink for anthropogenic carbon dioxide is a subject of intensive investigation and debate. Interest in this process is driven by the need to predict the rate of future increase of atmospheric carbon dioxide and subsequent global climatic change. Although estimates of the magnitude of the oceanic sink for carbon dioxide appear to be converging on a value of ∼2 (Gt) C yr−1 for the 1980s, a detailed understanding of the temporal and spatial variability in the rate of exchange of carbon dioxide between the ocean and the atmosphere is not available. For example, recent modeling work and direct measurements of air‐sea carbon dioxide flux produce very different estimates of the air‐sea flux in the northern hemisphere. As a consequence, it has been suggested that a large unidentified oceanic carbon dioxide sink may exist in the North Pacific. As a part of our time series observations in the North Pacific Subtropical Gyre, we have measured dissolved inorganic carbon and titration alkalinity over a four‐year period. These measurements constitute the most extensive set of observations of carbon system parameters in the surface waters of the central Pacific Ocean. Our results show that the ocean in the vicinity of the time series site is a sink for atmospheric carbon dioxide. On the basis of these observations, we present a mechanism by which the North Pacific Subtropical Gyre can be a potential sink for ∼0.2 Gt C yr−1 of atmospheric carbon dioxide. Although our observations indicate that the North Pacific Subtropical Gyre is a sink for atmospheric carbon dioxide, the magnitude of this oceanic sink is relatively small. Our data and interpretations are therefore consistent with the argument for a relatively large sink during the 1980s in northern hemisphere terrestrial biomass. Another possibility is that the net release of carbon dioxide to the atmosphere owing to land use activities in tropical regions has been overestimated.

Porewater geochemistry and solute flux from bottom sediments, Devils Lake, North Dakota

Sediment cores were collected for pore-water analysis from the eastern end of Devils Lake, located in northeastern North Dakota, to determine diagenetic reactions occurring in surficial bottom sediments and to evaluate the impact of these reactions on chemical concentrations in the overlying lake water. Sediment pore waters are enriched in major ions and nutrients relative to lake water. The principal sources of major ions to pore water are saline sediments located in the upper 1 m of bottom sediment. The principal source of titration alkalinity and nutrients to pore water is microbial decomposition of sedimentary organic matter by sulfate reduction. Sediment pore waters in the eastern part of Devils Lake have higher major-ion concentrations and solute-flux rates than the sediment pore waters in the central part of the lake. In contrast, sediment pore waters in the central part of Devils Lake have significantly higher nutrient concentrations and solute-flux rates. Major-ion concentrations and solute-flux rates in sediment pore water increase from west to east. These trends indicate that bottom-sediment diagenetic processes are, in part, responsible for the observed concentration gradient in the lake. The higher nutrient concentrations and the higher nutrient diffusional-flux rates in Main Bay are the result of more labile sedimentary organic matter and the occurrence of sulfate reduction. Environmentally-reactive trace-metal concentrations (Cu, Pb, Zn, and Fe) in bottom sediments decrease from west to east with distance from the surface-water sources and with increasing surface-water salinity.