Determination of sulphate in natural waters and industrial effluents by sequential injection analysis

Effects of seawater sulfur starvation and enrichment on Gracilaria gracilis growth and biochemical composition

The genus Gracilaria, largest biomass producer in coastal regions, encompasses a wide range of species including Gracilaria gracilis. Nowadays, there is a spate of interest in its culture in lagoon where the water sulfate concentration is variable. A laboratory culture was carried out to determine the sulfate concentration effect on their growth as well as their biochemical composition, which were 2.5, 27 or 50 mM, referred to as SSS (sulfur starved seawater), SW (seawater) and SES (sulfur enriched seawater).We found that the sulfate content of the surrounding medium is a key parameter influencing both the alga growth and its composition. However, seawater proved to be the most suitable environment to sustain alga growth, proteins, R-phycoerythrin and agar yields, but sulfur enrichment and starvation affects them. The sulfate degree of agar and therefore its quality is related to the medium sulfate concentration. We conclude that sulfur starvation (2.5 mM) for three weeks, led to severe growth retardation, lower agar yield and quality and indicated the limit potential of G. gracilis for mariculture under these conditions. These results demonstrated that the success of G. gracilis culture in the lagoon is feasible if sulfate concentration is closer to that of seawater.

Colorimetric Determination of Sulfate via an Enzyme Cascade for High-Throughput Detection of Sulfatase Activity

High-throughput screening (HTS) methods have become decisive for the discovery and development of new biocatalysts and their application in numerous fields. Sulfatases, a broad class of biocatalysts that hydrolyze sulfate esters, are involved in diverse relevant cellular functions (e.g., signaling and hormonal regulation) and are therefore gaining importance, particularly in the medical field. Additionally, various technical applications have been recently devised. One of the major challenges in the field of enzyme development is the sensitive and high-throughput detection of the actual product of the biocatalyst of interest without the need for chromophore analogues. Addressing this issue, a colorimetric assay for sulfatases was developed and validated for detecting sulfate through a two-step enzymatic cascade, with a linear detection range of 3.3 (limit of detection) up to 250 μM. The procedure is compatible with relevant compounds employed in sulfatase reactions, including cosolvents, cations, and buffers. The assay was optimized and performed as part of a 96-well screening workflow that included bacterial growth, heterologous sulfatase expression, cell lysis, sulfate ester hydrolysis, inactivation of cell lysate, and colorimetric sulfate determination. With this procedure, the activity of an aryl and an alkyl sulfatase could be confirmed and validated. Overall, this assay provides a simple and fast alternative for screening and engineering sulfatases from DNA libraries (e.g., using metagenomics) with medical or synthetic relevance.

An improved procedure for flow-based turbidimetric sulphate determination based on a liquid core waveguide and pulsed flows

An improved flow-based procedure is proposed for turbidimetric sulphate determination in waters. The flow system was designed with solenoid micro-pumps in order to improve mixing conditions and minimize reagent consumption as well as waste generation. Stable baselines were observed in view of the pulsed flow characteristic of the systems designed with solenoid micro-pumps, thus making the use of washing solutions unnecessary. The nucleation process was improved by stopping the flow prior to the measurement, thus avoiding the need of sulphate addition. When a 1-cm optical path flow cell was employed, linear response was achieved within 20-200mgL(-1), described by the equation S=-0.0767+0.00438C (mgL(-1)), r=0.999. The detection limit was estimated as 3mgL(-1) at the 99.7% confidence level and the coefficient of variation was 2.4% (n=20). The sampling rate was estimated as 33 determinations per hour. A long pathlength (100-cm) flow cell based on a liquid core waveguide was exploited to increase sensitivity in turbidimetry. Baseline drifts were avoided by a periodical washing step with EDTA in alkaline medium. Linear response was observed within 7-16mgL(-1), described by the equation S=-0.865+0.132C (mgL(-1)), r=0.999. The detection limit was estimated as 150microgL(-1) at the 99.7% confidence level and the coefficient of variation was 3.0% (n=20). The sampling rate was estimated as 25 determinations per hour. The results obtained for freshwater and rain water samples were in agreement with those achieved by batch turbidimetry at the 95% confidence level.

A low-cost light-scattering detector for the flow-injection nephelometric determination of sulfate

A simple low-cost flow-through light-scattering detector was developed for determining the particle mass concentration in colloidal suspensions. Employing a laser pointer as a light source and a photodiode IC as a light sensor, the detector was shown to have good sensitivity, yet was small and battery operated. The detector was demonstrated to be effective for the flow-injection nephelometric determination of sulfate by precipitation as barium sulfate.

Use of a single air segment to minimise dispersion and improve mixing in sequential injection: turbidimetric determination of sulphate in waters

In this work, we propose the use of an air segment in a sequential injection system to simultaneously improve the overlapping of the stacked zones and minimise dispersion. This strategy was developed for the determination of sulphate in natural and wastewaters. Barium chloride was used as a precipitating agent and the turbidity of the suspension formed was measured at 420 nm. Analysis was performed without sample pre-treatment and the system was able to monitor sulphate concentration at a rate of at least 20 determinations per hour. Slightly different analytical sequences were developed for natural and wastewaters in order to minimise specific interferences. Direct determination of sulphate was possible within a concentration range of 10-100 and 16-100 mg SO(4)(2-) L(-1) for natural and wastewaters, respectively. Results obtained were comparable with those of the reference method with relative deviations lower than 5%. Relative standard deviations between 1.6% and 3.3% were found.

Rationally designed fluorescently labeled sulfate-binding protein mutants: evaluation in the development of a sensing system for sulfate

Periplasmic binding proteins from E. coli undergo large conformational changes upon binding their respective ligands. By attaching a fluorescent probe at rationally selected unique sites on the protein, these conformational changes in the protein can be monitored by measuring the changes in fluorescence intensity of the probe which allow the development of reagentless sensing systems for their corresponding ligands. In this work, we evaluated several sites on bacterial periplasmic sulfate-binding protein (SBP) for attachment of a fluorescent probe and rationally designed a reagentless sensing system for sulfate. Eight different mutants of SBP were prepared by employing the polymerase chain reaction (PCR) to introduce a unique cysteine residue at a specific location on the protein. The sites Gly55, Ser90, Ser129, Ala140, Leu145, Ser171, Val181, and Gly186 were chosen for mutagenesis by studying the three-dimensional X-ray crystal structure of SBP. An environment-sensitive fluorescent probe (MDCC) was then attached site-specifically to the protein through the sulfhydryl group of the unique cysteine residue introduced. Each fluorescent probe-conjugated SBP mutant was characterized in terms of its fluorescence properties and Ser171 was determined to be the best site for the attachment of the fluorescent probe that would allow for the development of a reagentless sensing system for sulfate. Three different environment-sensitive fluorescent probes (1,5-IAEDANS, MDCC, and acylodan) were studied with the SBP171 mutant protein. A calibration curve for sulfate was constructed using the labeled protein and relating the change in the fluorescence intensity with the amount of sulfate present in the sample. The detection limit for sulfate was found to be in the submicromolar range using this system. The selectivity of the sensing system was demonstrated by evaluating its response to other anions. A fast and selective sensing system with detection limits for sulfate in the submicromolar range was developed.

A fast and simple turbidimetric method for the determination of sulfate in sulfate-reducing bacterial cultures

A standard turbidimetric assay for the determination of sulfate in water was modified with the objective of achieving a quick and simple method for monitoring the decrease of sulfate in cultures of sulfate-reducing bacteria. The effects of sulfate concentration, mixing time and the ratio of sample to conditioning reagent were optimized using a central composite face-centered response surface model design. The results suggested that a mixing time of 30 s resulted in smaller absorbance variance, the variance in absorbance measurements tended to increase with concentration of sulfate and that the ratio between the amount of conditioning reagent and sample had no significant influence on the absorbance variance. The modified assay thus developed is simple and quick, and covers a comparatively large sulfate concentration range (0-5 mM) compared to the standard turbidimetric assay.