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1.
Jian Ma  Dongxing Yuan  Ying Liang   《Marine Chemistry》2008,111(3-4):151-159
A cartridge of solid phase extraction (SPE), hydrophilic–lipophilic balance (HLB), has been used to enrich phosphomolybdenum blue (PMB) from water samples without any other additives. Based on this, the previous on-line SPE method established for the determination of nanomolar soluble reactive phosphorus (SRP) in seawater has been greatly improved. Cetyltrimethylammonium bromide (CTAB), the cationic surfactant needed for the formation of the PMB-CTAB paired compound that could be extracted on a Sep-Pak C18 cartridge using the previous method [Liang, Y., Yuan, D.X., Li, Q.L., Lin, Q.M., 2007. Flow injection analysis of nanomolar level orthophosphate in seawater with solid phase enrichment and colorimetric detection. Marine Chemistry 103, 122–130.], was not necessary. Thus the longer time and higher temperature required for the complete formation of the PMB-CTAB compound were no longer needed. In addition, with application of the sequential injection analysis technique the proposed method showed the advantages of being much faster, simpler, sample and reagent saving, as well as more convenient in operation. The PMB compound formed under room temperature was efficiently extracted on an in-line HLB cartridge, rapidly eluted by 0.15 mol/L NaOH solution, and finally determined with a laboratory-made spectrophotometer at 740 nm. Experimental parameters, including the volume of reagents added, sample loading flow rate, and eluting flow rate, were optimized. Time and temperature for the PMB reaction, and salinity effect were also studied, and these were found to have no severe effect on the detection. With variation of sample loading time at a fixed flow rate, a broadened determination range of 3.4 to 1134 nmol/L phosphate could be obtained. The recovery and the method detection limit of the proposed method were found to be 94.4% and 1.4 nmol/L, respectively. The relative standard deviation (n = 7) was 2.50% for the sample at a concentration of 31 nmol/L phosphate. Two typical seawater samples were analyzed with both the proposed method and the magnesium hydroxide-induced coprecipitation method and, using the t-test, the results of the two methods showed no significant difference.  相似文献   

2.
《Marine Chemistry》2007,103(1-2):122-130
Phosphomolybdenum blue (PMB) paired with cetyltrimethylammonium bromide (CTAB) can be extracted using a solid phase extraction technique on C18 sorbent. Based on this, a novel on-line solid phase extraction method coupled with flow injection (FI) analysis and colorimetric detection has been established to determine nanomolar level orthophosphate in seawater. A stopped flow technique was employed to assure the complete formation of the PMB–CTAB compound, which was sequentially extracted on an in-line Sep-Pak C18 cartridge. The adsorbed PMB–CTAB can be rapidly eluted by 0.56 mol/L H2SO4 in ethanol, and determined with a spectrophotometer at 700 nm. Experimental parameters, including reaction temperature, sample loading flow rate, stopped time and eluting flow rate, were optimized throughout the experiments based on univariate experimental design. The results show that reaction temperature and stopped time were the major factors affecting the formation of PMB–CTAB. Silicate concentration up to 5000 times higher than that of orthophosphate would not interfere with the determination of orthophosphate. Using artificial seawater with salinity of 35 as a matrix under the optimized conditions, the standard curve shows a linear range between 3.2 and 48.5 nmol/L, and the recovery and the detection limit of the proposed method are 96.4% and 1.57 nmol/L, respectively. The relative standard deviation (RSD) (n = 8), which was determined daily for 8 days, was 4.52% for the artificial seawater at a concentration of 32.4 nmol/L orthophosphate. Two typical seawater samples were analyzed using both the proposed method and the MAGnesium hydroxide-Induced Coprecipitation (MAGIC) method. The results of the two methods show no significant difference using the t test. Compared to the MAGIC method, the proposed method has the advantage of being more sensitive, faster, sample saving and easy for on-line analysis.  相似文献   

3.
A highly sensitive flow injection analysis (FIA) method for determining the concentration of iron in seawater has been developed. The technique is a modification of the catalytic batch method previously reported by Hirayama and Unohara. By optimising the chemistry for FIA and incorporating in-line preconcentration of the iron from seawater onto a column of resin-immobilised 8-hydroxyquinoline, the detection limit of the method has been reduced to 0.025 nM. The typical precision of the method for a 0.35 nM Fe sample is 2.5% (n = 6). The method has been used at sea in its preconcentration mode to determine iron in open ocean water samples from the equatorial Pacific and the North Atlantic. It has also been used in a direct injection mode for hydrothermal plume samples from around Loihi Seamount in the Central Pacific.  相似文献   

4.
Solid-phase microextraction (SPME) is a simple, sensitive and less destructive method for the determination of dimethylsulfide (DMS) in seawater. Combined with detection by gas chromatography-mass spectrometry (GC-MS), the method had sufficient sensitivity (minimum detectable concentration of DMS was 0.05 nM), and practical levels of reproducibility (relative standard deviation ≤7%) and linearity (r 2 > 0.995) over a wide concentration range (0.5 to 910 nM). The protocol developed was applied to a Sagami Bay water sample to determine concentrations of DMS and DMSP, and in situ DMSP-lyase activity.  相似文献   

5.
Determinations of copper consumption capacity (CuCs.C) and labile copper concentrations in surface coastal seawater, using a copper ion selective electrode (Cu-ISE) potentiometric method under predominantly diffusive conditions, are reported. For evaluation of the copper concentrations, the points of the endpoint contiguity zone of the CuCs.C titration curve were treated by an ISE multiple standard addition technique. The results were compared with those obtained by means of a Chelex-100 (calcic form) ‘batch’ procedure-potentiometric stripping analysis.The labile copper of the sample was determined at concentrations down to 10.70 nM with an average RSD of 12%, independent of the Cu-ISE employed. For adjacent subsamples, the mean CuCs.C values obtained for El Way seawater were equivalent to 81.05 and 48.00 nM copper, with an RSD of 4 and 7%, and for Isla Santa Maria seawater the value was equivalent to 70.27 nM copper, with an RSD of 7%. The theoretical approach of the electrode diffusive mechanism proposed, which would depend, fundamentally, on the adsorptive, complexing and reducing properties of the dissolved organic matter in the seawater sample, allows simultaneous analytical determination of CuCs.C and labile copper concentration in seawater.  相似文献   

6.
Results from laboratory studies indicated that low molecular weight (LMW) carbonyl compounds, especially formaldehyde, acetaldehyde, acetone and glyoxal, can be formed in seawater by photochemical processes. Once formed, these compounds appear to be readily consumed by biota. These results suggest that concentrations of LMW carbonyl compounds should undergo diurnal variations in the illuminated layer of the sea. In support of this, diurnal fluctuations of LMW carbonyl concentrations were observed in humic-rich surface waters off the west coast of Florida over a three day sampling period using a shipboard HPLC system. Fluctuations in acetaldehyde were particularly strong and reproducible, with steady night-time concentrations of 2–3 nM and day-time concentrations reaching a maximum of 20–30 nM in the early afternoon. In contrast, diurnal fluctuations in formaldehyde were less distinct, ranging from 15 to 50 nM.The laboratory and field results are discussed in terms of biotic/abiotic sources and sinks of LMW carbonyl compounds in surface seawater. It is speculated that photooxidative cleavage of biologically refractory dissolved organic matter (DOM) in seawater to yield LMW organic fragments, such as carbonyl compounds, may be important in the breakdown and geochemical cycling of DOM in the ocean.  相似文献   

7.
A chemiluminescent analysis technique for the determination of nanomolar quantities of nitrate, nitrate plus nitrite or nitrite alone in seawater is described. The method depends on the selective reduction of these species to nitric oxide which is then determined by its chemiluminescent reaction with ozone, using a commercial nitrogen oxides analyzer. The necessary equipment is compact and sufficiently sturdy to allow shipboard use. A precision of ±2 nM is claimed with analytical rates of 10–12 samples h?1, and modifications are discussed to allow doubling the analytical rate.  相似文献   

8.
A sensitive method for iron determination in seawater has been adapted on a submersible chemical analyser for in situ measurements. The technique is based on flow injection analysis (FIA) coupled with spectrophotometric detection. When direct injection of seawater was used, the detection limit was 1.6 nM, and the precision 7%, for a triplicate injection of a 4 nM standard. At low iron concentrations, on line preconcentration using a column filled with 8-hydroxyquinoline (8HQ) resin was used. The detection limit was 0.15 nM (time of preconcentration = 240 s), and the precision 6%, for a triplicate determination of a 1 nM standard, allowing the determination of Fe in most of the oceanic regimes, except the most depleted surface waters. The effect of temperature, pressure, salinity, copper, manganese, and iron speciation on the response of the analyser was investigated. The slope of the calibration curves followed a linear relation as a function of pressure (Cp = 2.8 × 10− 5P + 3.4 × 10− 2 s nmol− 1, R2 = 0.997, for Θ = 13 °C) and an exponential relation as a function of temperature (CΘ = 0.009e0.103Θ, R2 = 0.832, for P = 3 bar). No statistical difference at 95% confidence level was observed for samples of different salinities (S = 0, 20, 35). Only very high concentration of copper (1000 × [Fe]) produced a detectable interference. The chemical analyser was deployed in the coastal environment of the Bay of Brest to investigate the effect of iron speciation on the response of the analyser. Direct injection was used and seawater samples were acidified on line for 80 s. Dissolved iron (DFe, filtered seawater (0.4 μm), acidified and stored at pH 1.8) corresponded to 29 ± 4% of Fea (unfiltered seawater, acidified in line at pH 1.8 for 80 s). Most of Fea (71 ± 4%) was probably a fraction of total dissolvable iron (TDFe, unfiltered seawater, acidified and stored at pH 1.8).  相似文献   

9.
The method of Parsonset al. (1984) for measuring dissolved free amino acids (DFAA) in coastal seawater was modified. We found considerable interference in DFAA determination from ammonia dissolved in coastal seawater, although the interference of urea could be ignored. For DFAA analysis for coastal seawater samples, ammonia determinations for the same sample are needed to correct DFAA values. For coastal surface seawater samples from all over the Seto Inland Sea, Japan, values of DFAA ranged from undetectable to 1.87 μg-at N/l when corrected for ammonia, while uncorrected values ranged from undetectable to 2.61 μg-at N/l. DFAA, urea, nitrate+nitrite, ammonia and DON concentrations in surface seawater collected in the Seto Inland Sea were analyzed simultaneously. DFAA at four seasons constituted from 1.4 to 10.1% of DON, with a mean value of 6.5%. The concentration of urea was similar to that of DFAA and often higher than that of ammonium, although generally lower than that of nitrate.  相似文献   

10.
The metal complexing ability of surface water of the Irish Sea has been measured by the MnO2 adsorption method. In all samples strong copper-chelating compounds are present at concentrations of 60–150 nM, with conditional stability constants (log values) of 10.0–10.4. The concentrations of Cu, Pb and Cd in the samples are 16–39 nM, 1–7 nM and 0.1–2 nM, respectively; much less than the ligand concentrations. The organic compounds form complexes with 94–98% of dissolved copper, and therefore constitute the major form of copper in surface water of the Irish Sea. Recalculation of speciation of the inorganic fraction of copper in seawater reveals that the major complex ion is that of CuCO30 (60%), followed by CuOH+ (16%) and Cu(OH)20 (16%). Complexes with borate ions form a small and rather insignificant fraction of 1%.  相似文献   

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