Deep-sea in situ determination of sulfide using a sensitized chemiluminescent terbium complex.

A new chemiluminescence (CL) method based on the chemiluminescent reaction between sulfide and an acidic permanganate solution was used to quantify sulfide in seawater. A terbium-pipemidic acid complex was used as CL enhancer. The method was used to determine sulfide in the concentration range of 1-30 µmol/L in artificial seawater samples. The limit of detection of the method was 21 nmol/L sulfide. The sensitivity of the CL method was eight times higher than that of the CL method reported previously. Br- ions, which are conservative ions, interfered with sulfide. We investigated the effects of salinity, water temperature, and interfering chemicals,such asheavy-metal ions and organic matter, on the performance of the CL method. In addition, sulfite-spiked natural seawater samples were analyzed. The results demonstrate that the CL method can be used to develop a deep-sea sulfide analyzer.

Colorimetric pH Measurement of Pressurized Groundwater Containing CO2.

A gas-tight pH measurement is needed to monitor water chemistry at a CO2 geological storage site. In the CO2 reservoirs, the temperature and pressure are generally more than the critical point of CO2 (31.2°C and 7.38 MPa). In this study, a colorimetric pH measurement method was examined up to 20 MPa for future application to various CO2 reservoirs. A mixture of two color indicators, bromocresol green (BCG) and metacresol purple (mCP), was considered to be a suitable measurement method between pH 3 and 9. The uncertainty up to 20 MPa was less than 0.12 pH units without any correction of pressure effects. We demonstrated a pH measurement of formation water at the Nagaoka CO2 post-injection site. The pH measurement was successfully accomplished under a high-pressure condition (ca. 11 MPa) and without degassing of CO2.

Colorimetric pH measurement for seawater samples using a three light-emitting diodes detector and a calibration method for temperature dependence.

A colorimetric pH measurement of seawater samples using a light source comprising a three light-emitting diodes (TLED) detector and meta-cresol purple (mCP) as an indicator was investigated. The molar absorption ratios (e1, e2, and e3/e2) for mCP using the TLED detector at 25°C were determined to be 0, 1.9994, and 0.1010, respectively. Next, the pH values of 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) and 2-aminopyride (AMP) seawater buffers were determined. Notably, the raw pH of TRIS buffer (∼8.1) agreed with the reference value, while that for the AMP buffer (∼6.8) had an error of +0.004 due to the small absorption ratio (R) and being out of the lower adequate pH range (> 7.2) for mCP. pHT measurements obtained for seawater samples using the present colorimetric method agreed with those obtained using a glass electrode. These results demonstrate that this low-cost TLED detection system with a short cell length, 5 cm, can be used for seawater pHT analysis.

Determination of sulfide with acidic permanganate chemiluminescence for development of deep-sea in-situ analyzers.

A new chemiluminescence method is proposed for the determination of sulfide in seawater based on the chemiluminescence reaction between sulfide and an acidic permanganate solution. 3-Cyclohexylaminopropanesulfonic acid was used as a chemiluminescence enhancer. By use of this method, 1-150 µM of sulfide could be determined in artificial seawater. The limit of detection was 0.17 µM sulfide. We investigated the effects of salinity, water temperature, and interfering chemicals such as heavy-metal ions and organic matter. In addition, natural seawater spiked with sulfide was analyzed. The results showed that the CL method could be applied to a deep-sea sulfide analyzer.

Open-cell titration of seawater for alkalinity measurements by colorimetry using bromophenol blue combined with a non-linear least-squares method.

The open-cell titration of seawater was studied for alkalinity measurements by colorimetry. 1) The colorimetric pH of free hydrogen ion concentration, pH(F(ind)), was calculated from the ratio of the absorbances at 436 and 590 nm (R = (590nm)A/(436nm)A), along with the molar absorption coefficient ratios (e(1), e(2) and e(3)/e(2)) and a tentative acid dissociation constant value (pK(a(2))). 2) The perturbation of hydrogen ion was evaluated from the change in titration mass (Deltam). The total hydrogen ion concentration at m + Deltam, pH(T(at m+Deltam)), was calculated using pH(F(ind)) for a mass m and constants for sulfate (S(T)) and fluoride (F(T)). 3) The alkalinity (A(T)) was computed from the titrant mass (m + Deltam) and the corresponding pH(T(at m+Deltam)) through a non-linear least-squares approach using the pK(a(2)) value as a variable parameter. Seawater sample at 2000 m depth from the West Pacific was analyzed. The resulting A(T) (2420.92 +/- 3.35 micromol kg(-1)) was in good agreement with the A(T) measured by potentiometric electric force (2420.46 +/- 1.54 micromol kg(-1)). The resulting pK(a(2)) was 3.7037, in close proximity to that reported by King et al. (pK(a(2)) = 3.695).

Chemiluminescence from singlet oxygen that was detected at two wavelengths and effects of biomolecules on it.

We developed the detection apparatus that equipped with the two-photomultiplier tubes for chemiluminescence from singlet oxygen. Singlet oxygen was generated with reaction between sodium hypochlorite and hydrogen peroxide. The chemiluminescence from singlet oxygen, the dimol light emission (ca. 634 nm) and the monomol light emission (ca. 1270 nm), was observed simultaneously for the same reaction cell. The effects of sodium azide as an antioxidant, human serum albumin, and alpha-amino acids on the chemiluminescence based on the both emissions were examined; the observed chemiluminescence could provide direct information with regard to the reaction between singlet oxygen and antioxidant/biomolecules. The apparent rate constants for quenching singlet oxygen in the presence of human serum albumin were calculated to be ca. 3.3 x 10(9) and ca. 8.8 x 10(8)M(-1)s(-1) for the dimol and monomol light emissions, respectively, under the present conditions. The chemiluminescence intensities of the dimol emission decreased in the presence of His, Asp, Phe, Ser, and Tyr, and that of the monomol decreased in the presence of Cys and Trp. The chemiluminescence observed in the presence of biomolcules was discussed together with the reactivities of sodium hypochlorite and hydrogen peroxide to biomolecules.

Ultraviolet radiation (UV-C): a potential tool for the control of biofouling on marine optical instruments.

In an effort to develop a tool for controlling biofouling of marine optical instruments, the efficiency of ultraviolet radiation (UVR - 254 nm) in preventing biofouling was evaluated by conducting in situ experiments at different intensities (14.7, 9.6, 7.3 Wm(-2)) and exposure times (continuous, on for 30, 15, 5, 1 min h(-1)) using glass as test coupons. Although there was significant seasonal variation in environmental conditions and phytoplankton composition among each experiment, the amount of biofilm relative to the internal control demonstrated consistent trends. The efficiency of UVR in preventing biofouling increased significantly with increase in intensity and exposure time. UVR was effective even in reducing the population of microfoulers from already developed biofilms. UVR exposure for 30 min h(-1) at all intensities as well as for 5 and 15 min h(-1) at the highest intensity was found to be most effective. It was observed that UVR dose is not the sole determinant of UVR effectiveness. The reduction in transmission level of the UVR treated coupons was < 5% irrespective of exposure time except for 1 min h(-1). These results reveal that UV-C radiation can be used as a potential biofouling control tool for optical instruments.

Achieving high time-resolution with a new flow-through type analyzer for total inorganic carbon in seawater.

A fully automated, continuous-flow-through type analyzer was developed to observe rapid changes in the concentration of total inorganic carbon (CT) in coastal zones. Seawater and an H3PO4 solution were fed into the analyzer's mixing coil by two high-precision valveless piston pumps. The CO2 was stripped from the seawater and moved into a carrier gas, using a newly developed continuous-flow-through CO2 extractor. A mass flow controller was used to assure a precise flow rate of the carrier gas. The CO2 concentration was then determined with a nondispersive infrared gas analyzer. This analyzer achieved a time-resolution of as good as 1 min. In field experiments on a shallow reef flat of Shiraho (Ishigaki Island, Southwest Japan), the analyzer detected short-term, yet extreme, variations in CT which manual sampling missed. Analytical values obtained by the analyzer on the boat were compared with those determined by potentiometric titration with a closed cell in a laboratory: CT(flow-through) = 0.980 x CT(titration) + 38.8 with r2 = 0.995 (n = 34; September 1998).