Charles J. Fischer

Optimization of performance and minimization of silicate interference in continuous flow phosphate analysis

Specific reaction conditions for automated continuous flow analysis of phosphate are optimized in regard to minimizing coating and silicate interference, while maintaining high sensitivity. Use of Sb in the reagent increases sensitivity and yields absorbances with little temperature dependence. Coating can be minimized by using a final solution at a pH>0.5. At final pH of 0.78 there is maximum interference from silicate in the sample. We recommend therefore as an optimal reaction condition with minimal silicate interference, the use of Sb, a final solution pH of 1.00, room temperature for the reaction and a [H(+)]/[Mo] ratio of 70. An equation is provided to correct silicate interference in high precision phosphate determination.

Potential availability of sedimentary phosphorus to sediment resuspension in Florida Bay

the central bay. The spatial pattern of TSP is consistent with distribution of both seagrass and phytoplankton that are limited by available phosphorus in Florida Bay. Among the five pools, the authigenic carbonate fluorapatite, biogenic apatite and CaCO3-bound phosphorus account for the largest fraction (45%) of TSP, of which inorganic phosphorus is the dominant form, and organic phosphorus accounts for about 30% in the western and north central regions and less than 10% in other areas of Florida Bay. The second largest pools are the refractory organic phosphorus (24% of TSP) and reductant-soluble inorganic phosphorus (19% of TSP). Readily exchangeable phosphorus accounts for 8% of TSP, of which organic phosphorus is 60%. Detrital apatite phosphorus of igneous or metamorphic origin represents the smallest fraction, only 5% of TSP. Spatial distribution of phosphorus and iron in sediments indicates that external sources of these two essential plant nutrients to Florida Bay are spatially separated with phosphorus introduced by west coast waters across the western margin of Florida Bay and iron from freshwater flow into the eastern region. INDEX TERMS: 1030 Geochemistry: Geochemical cycles (0330); 1050 Geochemistry: Marine geochemistry (4835, 4850); 4805 Oceanography: Biological and Chemical: Biogeochemical cycles (1615); 4845 Oceanography: Biological and Chemical: Nutrients and nutrient cycling; KEYWORDS: Florida Bay, phosphorus, sediment

Comparison of Open Tubular Cadmium Reactor and Packed Cadmium Column in Automated Gas-Segmented Continuous Flow Nitrate Analysis

Abstract Detailed procedures are provided for preparing packed cadmium columns to reduce nitrate to nitrite. Experiments demonstrated the importance of conditioning both open tubular cadmium reactor (OTCR) and packed copper-coated cadmium columns to achieve 100% reduction efficiency. The effects of segmentation bubbles in the OTCR upon reduction efficiency and baseline noise in nitrate analysis are investigated using an auto-analyzer. Metal particles derived from segmentation bubbles in OTCR result in interference with continuous flow analyses. Therefore packed columns are recommended for determination of low level nitrate in natural waters.

Nitrogen oxides and ozone production in the North Atlantic marine boundary layer

Measurements of reactive nitrogen gases (NO, NO2, NOy), as well as related chemical (O3, CO, aerosol black carbon, radon, selected nonmethane hydrocarbons) and meteorological parameters were made on board the R/V Malcolm Baldridge prior to and subsequent to the 1992 ASTEX (Atlantic Stratocumulus Transition Experiment) in the North Atlantic Ocean during June and July 1992. Results showed indications of well-defined plumes from North America and Europe from both chemistry and back trajectory data. Elevated ozone concentrations were also observed in airmasses from uninhabited continental regions. Chemical and meteorological data were incorporated into a simple photochemical model in which ozone destruction predominated over

Continuous Flow Analysis of Phosphate in Natural Waters Using Hydrazine as a Reductant

Abstract The use of hydrazine to reduce 12-molybdophosphoric acid to phosphomolybdenum blue in continuous flow analysis of phosphate in natural water samples is characterized. Using hydrazine in gas-segmented continuous flow phosphate analysis minimizes coating and silicate interference in comparison with using ascorbic acid. The addition of Sb to the molybdate reagent increases sensitivity at temperatures greater than 50°C but causes severe additional coating. The degree of coating was found to be a function of pH. Minimal coatings were achieved at a final solution pH of 0.5. Silicate interference was found to increase dramatically with color development temperature. At room temperature no detectable silicate interference was found. We recommend hydrazine in preference to ascorbic acid for gas-segmented continuous flow phosphate analysis with optimal reaction conditions of room temperature color development and a final solution pH of 0.5.

Laboratory glassware as a contaminant in silicate analysis of natural water samples

Abstract When glassware is used for the storage of water samples, reagents and standard solutions, dissolution of silicate from the glass containers can contaminate the samples. Experimental results demonstrate that dissolution from glassware can introduce micromolar silicate within a few hours. The extent of dissolution depends upon contact time, salinity and pH of the solution, and the size and shape of the containers.

An estimate of diapycnal nutrient fluxes to the euphotic zone in the Florida Straits

A recent hydrographic survey of the Florida Current at 27°N revealed an enhanced upward flux of nutrients along the Florida coast. Geostrophic flow of the Gulf Stream through the narrow Florida Straits causes an uplift of the nutricline toward its western edge, shoaling the mixed layers into the base of the euphotic zone. At a nearshore station, nitrate, phosphate, and silicate concentrations reached 19, 1.4, and 10 µM, respectively, at a water depth of 27 m. Furthermore, nutrient vertical gradients below the mixed layer increased with decreasing seafloor depth toward the Florida coast. The estimated vertical eddy diffusive nutrient fluxes across diapycnal surfaces reached 0.40–83.7, 0.03–6.24, and 0.24–45.5 mmol m−2 d−1 for nitrate, phosphate, and silicate, respectively, along the shore. Estimated fluxes span a wide range due to the range of diffusivity measured. The lower end of estimated fluxes are comparable to open ocean values, but higher end of estimates are two orders of magnitude greater than those observed in open ocean. The diapycnal nutrient fluxes declined rapidly offshore as a result of decreasing vertical gradients of nutrient concentration.