Ricardo D. Riso

Rapid and simultaneous analysis of trace metals (Cu, Pb and Cd) in seawater by potentiometric stripping analysis

Abstract A potentiometric stripping method for a simultaneous measurement of copper, lead and cadmium in oceanic waters using a TraceLab PSU22 unit has been developed. Compared to the earlier TraceLab PSU20 unit, the PSU22 has a sampling rate of the potential during the stripping step that is three times lower. This results in the decrease of the detection limit by about four times. The detection limits obtained with a pre-electrolysis time of 15 min were 44 ng l−1 (0.7 nM), 3 ng l−1 (14 pM) and 1 ng l−1 (9 pM) for Cu, Pb and Cd, respectively. The precision, accuracy and reproducibility of the method agree well with those obtained by other techniques for trace metals analysis in seawater. Vertical profiles of Cd in the Mediterranean waters obtained by AA and PSA were concordant.

Speciation of dissolved copper within an active hydrothermal edifice on the Lucky Strike vent field (MAR, 37°N)

The objective of this study was to determine the concentrations of different fractions of dissolved copper (after filtration at 0.45 microm) along the cold part of the hydrothermal fluid-seawater mixing zone on the Tour Eiffel edifice (MAR). Dissolved copper was analyzed by stripping chronopotentiometry (SCP) after chromatographic C(18) extraction. Levels of total dissolved copper (0.03 to 5.15 microM) are much higher than those reported for deep-sea oceanic waters but in accordance with data previously obtained in this area. Speciation measurements show that the hydrophobic organic fraction (C(18)Cu) is very low (2+/-1%). Dissolved copper is present mainly as inorganic and hydrophilic organic complexes (nonC(18)Cu). The distribution of copper along the pH gradient shows the same pattern for each fraction. Copper concentrations increase from pH 5.6 to 6.5 and then remain relatively constant at pH>6.5. Concentrations of oxygen and total sulphides demonstrate that the copper anomaly corresponds to the transition between suboxic and oxic waters. The increase of dissolved copper should correspond to the oxidative redissolution of copper sulphide particles formed in the vicinity of the fluid exit. The presence of such a secondary dissolved copper source, associated with the accumulation of metal sulphide particles, could play a significant role in the distribution of fauna in the different habitats available at vents.

Measurements of trace concentrations of mercury in sea water by stripping chronopotentiometry with gold disk electrode: influence of copper

A stripping chronopotentiometric method, using a rotating gold disk electrode for mercury measurements in sea water is described. Compared with a same method using a stationary gold film electrode, this method has a eight times higher sensitivity and a detection limit of 5 ng l 1 after 10 min deposition time. Moreover, the time needed for gold plating is eliminated. Compared with other electrochemical methods capable of measuring mercury at low concentrations, the present method is more simplified with no degassing step and no need to use a medium-exchange procedure before the stripping step. These characteristics render the method easily practicable on board oceanographic vessels for ‘in situ’ measurements.

Measurement of Copper in Sea-water by Constant Current Stripping Analysis (CCSA) With a Rotating Gold Disk Electrode

A chronopotentiometric stripping method [constant current stripping analysis (CCSA)] using a rotating gold disk electrode for measurements of copper in sea-water is described. Compared with a CCSA method using a stationary gold film electrode, the new method has a sensitivity 2.5 times higher and a detection limit of 11 ng l–1 after a 5 min deposition time, and eliminates from the analysis the time needed for gold plating. The precision and accuracy of this method agree well with those obtained by other techniques. Vertical profiles of copper obtained by two different chronopotentiometric stripping methods, CCSA and potentiometric stripping analysis (PSA) in west Brittany coastal waters show that the measurement of copper by CCSA coupled with a gold disk electrode appears to be less affected by organic matter than those made by PSA with a mercury electrode.

Structural and functional properties of hemocyanin from Cyanagraea praedator, a deep-sea hydrothermal vent crab.

Cyanagraea praedator (Crustacea: Decapoda: Brachyura) is an endemic species of the East Pacific Rise hydrothermal vents, living in the upper part of black smoker chimneys. Because we were seeking species that have made respiratory adaptations to the hydrothermal environment, we looked at Cyanograea hemocyanin (Hc) and determined its quaternary structure and the oxygen‐binding properties in relation to temperature, pH, and lactate. C. praedator Hc is composed of dodecamers and hexamers, with dodecamers formed by the perpendicular association of two hexamers. The composition of these polymers was determined by electrophoresis and, for the first time, by electrospray mass spectrometry. Dodecamers and hexamers are composed of six subunits common to the two forms, with molecular mass ranging from 75,008 Da to 75,534 Da. In addition, we found two dodecamer‐specific subunits, at 75,419 Da and 75,629 Da. The native hemocyanin possesses a high oxygen affinity (P50 varies between 4 and 10 Torr at pH 7.5, 15°C) and a large Bohr coefficient (Δ log P50/ΔpH ∼ −1.8). Oxygen affinity is not affected by lactate or, surprisingly, temperature between 5°C and 35°C (ΔH = 1.16 kJ/mol1 5–35°C). Dialysis of native hemolymph elicited a significant increase in Hc‐O2 affinity (ΔP50 = 2.5 Torr at pH 7.5), an effect opposite the usual trend observed for crustacean hemocyanins. In this article these functional properties are interpreted in relation to characteristics of the environment. Proteins 2001;45:351–359.

Simple and simultaneous determination of glutathione, thioacetamide and refractory organic matter in natural waters by DP-CSV.

Although reduced sulphur substances, such as thiol compounds, contain extremely reactive functional groups in the cell, and influence metal speciation and solubility, very few techniques have been developed to quantify such substances in natural waters. In this paper we present a novel method that allows for the simultaneous identification and quantification of glutathione (GSH), thioacetamide-like compounds (TA), and refractory organic matter (ROM) by differential pulse cathodic stripping voltammetry (DP-CSV). Organic compounds are initially deposited on a mercury drop electrode at 0.000 V, pH 1.95, in the presence of ~200 nmol L(-1) Mo(VI), and then stripped, creating reduction peak currents at specific potentials. Using a 60-s deposition time, limits of detection (LODs) are 1 nmol L(-1), 81 nmol L(-1) and 14 μg C L(-1) for GSH, TA and ROM, respectively. By increasing the deposition time to 300 s, LOD is decreased to 0.2 nmol L(-1), 22 nmol L(-1) and 2 μg C L(-1), respectively. This method has a number of advantages in terms of its rapidity, low cost, and relative simplicity (due to the lack of derivatization and pre-concentration steps) and is also an effective method for simultaneously analysing GSH, TA and ROM in water. When not mixed in solution, GSH, L-cysteine and N-acetyl-L-cysteine, as well as TA-like compounds and thiourea, can be detected and identified by measuring their peak potential and standard addition, due to the acidic pH, which also allows for a longer preservation of the filtered sample. The new method described in this paper was tested along an entire river-seawater gradient of the Aulne Estuary (Brittany, France) to assess its capability in terms of determining these natural organic compounds in various surface waters.

Dynamics and sources of reduced sulfur, humic substances and dissolved organic carbon in a temperate river system affected by agricultural practices

Although reduced organic sulfur substances (RSS) as well as humic substances (HS) are widely suspected to play a role in, for example, metal speciation or used as a model of dissolved organic carbon (DOC) in laboratory studies, reports of their quantification in natural waters are scarce. We have examined the dynamics and sources of reduced sulfur, HS and DOC over an annual cycle in a river system affected by agricultural practices. The new differential pulse cathodic stripping voltammetry was successfully applied to measure glutathione-like compounds (GSHs), thioacetamide-like compounds (TAs) and the liquid chromatography coupled to organic detector to analyze HS and DOC at high frequency in the Penzé River (NW France). The streamflow-concentration patterns, principal components analysis and flux analysis allowed discrimination of the source of each organic compound type. Surprisingly, the two RSS and HS detected in all samples, displayed different behavior. As previously shown, manuring practice is the main source of DOC and HS in this watershed where agricultural activity is predominant. The HS were then transferred to the river systems via runoff, particularly during the spring and autumn floods, which are responsible of >60% of the annual flux. TAs had a clear groundwater source and may be formed underground, whereas GSHs displayed two sources: one aquagenic in spring and summer probably linked to the primary productivity and a second, which may be related to bacterial degradation. High sampling frequency allowed a more accurate assessment of the flux values which were 280 tC y(-1) for DOC representing 20 kg C ha(-1) y(-1). HS, TAs and GSHs fluxes represented 60, 13, and 4% of the total annual DOC export, respectively.

Sulfide determination in hydrothermal seawater samples using a vibrating gold micro-wire electrode in conjunction with stripping chronopotentiometry.

A rapid electrochemical stripping chronopotentiometric procedure to determined sulfide in unaltered hydrothermal seawater samples is presented. Sulfide is deposited at -0.25 V (vs Ag/AgCl, KCl 3M) at a vibrating gold microwire and then stripped through the application of a reductive constant current (typically -2 μA). The hydrodynamic conditions are modulated by vibration allowing a short deposition step, which is shown here to be necessary to minimize H(2)S volatilization. The limit of detection (LOD) is 30 nM after a deposition step of 7s. This LOD is in the same range as the most sensitive cathodic voltammetric technique using a mercury drop electrode and is well below those reported previously for other electrodes capable of being implemented in situ.

The removal of colloidal lead during estuarine mixing: seasonal variations and importance of iron oxides and humic substances

In the present study, seven colloidal fractions of lead (Pb) were analysed along the mixing zone of the Penze estuary over the Year 2009, with the aim to provide some insight into the mechanism that removes the metal from the 300 kDa) and was removed in the salinity range 0-10 from all of the size fractions where it was significantly found. Because the colloidal fractionation of Pb was strongly linked to that of iron (Fe) and humic substances (HS), the removal of Pb in the mixing area must occur under flocculation of organomineral complexes. A key period corresponding to the first strong autumnal precipitations was also revealed in the present work. At this time of the year, the mobilisation of Pb (and Fe) from catchment soils is enhanced by the mobilisation of HS and the metal is associated with smaller colloids (30-300 kDa).

Vertical distribution of cadmium, copper and lead in the eastern Alboran Sea: enrichment of metals in surface waters

The vertical distribution of cadmium, copper and lead was studied in the 0–500 m layer of the Eastern Alboran Sea. The concentrations measured compare favourably with recent data for the neighbouring area (53 pM < Cd < 124 pM; 1.4 nM< Cu < 2.8 nM, and 90 pM < Pb < 310 pM). The analysis of six profiles showed the presence of a sub-surface water mass, the northwestern Mediterranean Water (NWMW, 75-30 m), with high concentration of trace metals. Metal-salinity relationships, typified by cadmium, showed that the Atlantic surface waters (ASW) with low metal concentrations before entering the Mediterranean Sea become enriched with metals from some as yet not clearly understood source near the Straits of Gibraltar. The salinity-Cd relationship, taken together with flux rates of salt and Cd, however, shows that the Modified Atlantic water (MAW) gains its high metal concentrations during its transit in the Alboran Sea principally from a mixing with the underlying metal-rich NWMW.