Determination of Sulfur in Trace Amounts

Abstract

An absolute method for the determination of trace amounts of sulfur in water and organic matrices is described. The method involves decomposition of organic samples in an oxygen bomb or oxidation of water samples with hydrogen peroxide. The resultant sulfates are reduced and distilled as hydrogen sulfide by the action of stannous phosphate in anhydrous phosphoric acid. The evolved hydrogen sulfide is absorbed in zinc acetate solution, converted to methylene blue and measured spectrophotometrically at 665 mm. The range is from 2 to 40 μg of sulfur using 1 cm cells.     

Methylene blue derivatization then LC–MS analysis for measurement of trace levels of sulfide in aquatic samples

The methylene blue method has been widely used for analysis of sulfide for more than 100 years. Direct measurement of methylene blue at nanomolar concentrations is impossible without a preconcentration step, however. In this study the response of LC–MS with electrospray ionization (ESI) to methylene blue was evaluated. HPLC with simple isocratic elution was followed by ESI-MS quantification, which was compared with traditional UV–visible detection. The limit of detection for sulfide was approximately 50 ng L⁻¹, or 1.5 nmol L⁻¹. Analysis time was substantially reduced by use of isocratic elution. Interfering compounds produced by side reactions can be eliminated by use of the mass filter. A polysulfide sample was also analyzed to determine which products are formed and whether or not polysulfides react stoichiometrically with methylene blue reagent. It seems that polysulfides do not react quantitatively with methylene blue and so cannot be quantified reliably by use of this method.     

Indirect Flow-Injection Analysis of Ascorbic Acid by Photochemical Reduction of Methylene Blue

Abstract

Ascorbic acid was determined indirectly by spectrophotometry at 666 nm based on the photochemical reduction of methylene blue using flow-injection analysis. The carrier stream was 12.7 μgml^?1 methylene blue in phthalate-HCl buffer solution at pH 3.2. The reactor was irradiated with a 500-Watt halogen lamp to facilitate the development of the photochemical reaction. The system allows determination of ascorbic acid in the range 0.18–6.12 μgml^?1 with relative standard deviations of 2.09 and 0.31% for 1.97 and 4.92 μgml^?1 samples, respectively, and a sampling frequency of 50–55 h^?1. The proposed method was applied successfully to the determination of ascorbic acid in vitamin C tablets.     

Isolation of Lipophilic Persistent Organic Pollutants From Human Breast Milk

Background: Lipid removal from biological samples can be achieved by addition of concentrated sulfuric acid. However, certain persistent organic pollutants (POPs) such as chlorophenols are decomposed by sulfuric acid treatment and, thus, a more gentle lipid reduction method is needed for extraction of many environmental contaminants from biological samples. Membrane dialysis extraction (MDE) is a non-disruptive method to extract POPs from biological matrices.

Methods: Human breast milk samples were spiked with radiolabelled p,p′-dichlorodiphenyl trichloroethane ([C-14]-DDT) as a POP proxy and extracted using solid phase extraction (SPE). The extracts obtained were dialyzed by MDE in low-density polyethylene tubings containing a mixture of n-hexane and dichloromethane for 24 h, 48 h, or 72 h.

Results: The lipid content was reduced by 86.2% after one dialysis cycle of 24 h using MDE, and 87.1% recovery of the [C-14]-DDT standard was obtained. The DDT recovery could be further increased up to 96.3% and 98.1% by repeating the dialyses for one or two more cycles, respectively. However, the increased [C-14]-DDT recovery includes a concomitant increase in lipid carryover from 13.8% with one dialysis cycle to 22.1% with three cycles.

Conclusion: An SPE procedure for extracting POPs from breast milk and dialytic conditions for isolation of the extracted POP with minimal lipid carryover was established. The method is nondestructive and acceptable recoveries can be obtained within a single solvent shift as demonstrated by spiking standards. The lipid carryover was minimized, and the method may be considered for lipid removal before HPLC or GC analysis of environmental contaminants.     

Sensitive determination of dissolved sulfide in estuarine water by solid-phase extraction and high-performance liquid chromatography of methylene blue

A sensitive method involving solid-phase extraction and HPLC analysis of methylene blue has been developed to measure nanomolar levels of dissolved sulfide in oxic surface waters. The procedure included 1) a preconcentration step, in which methylene blue generated from sulfide reaction with n,n-dimethyl-p-phenylenediamine in acidic conditions in the presence of ferric ion was absorbed onto Waters tC18 cartridge; and 2) a determination step, in which methylene blue was separated by HPLC in a gradient elution to minimize natural organic matter interference and detected by absorbance. The concentrations of the dissolved sulfide, quantified by standard addition, were about 2.1-4.7 nM in oxic surface waters from Galveston Bay, Texas.     

Analysis of Total Non-Volatile Non-Sulfide Reduced Sulfur in Potable and Untreated Surface and Groundwaters

Abstract

An analytical method was developed to measure the total concentration of non-volatile non-sulfide reduced sulfur in treated and untreated surface and groundwater. The method was based on the alkaline reduction by Raney nickel (prepared in situ from Raney alloy) of organic and inorganic sulfur compounds (in oxidation states below +6) to sulfide. Sulfide was swept out of the reflux apparatus under nitrogen into a trap of zinc acetate and determined colorimetrically as ethylene blue. The recoveries obtained from solutions of elemental sulfur, sulfide, sulfite, thiosulfate, tetrathionate, cysteine, cystine, methionine, glutathione, allylthiourea, sulfanilamide and thiocyanate ranged from 84–102% with typical recoveries of approximately 90%. Sulfate was not detectable by the procedure. Chlorine present in potable water samples interfered in the procedure and was removed with sodium borohydride. The relative standard deviation of the method varied from 0.25 to 5.6% and averaged 3%. The detection limit based on a 500 mL sample was 3 mg m^?3.     

New Methylene Blue (NMB) Encapsulated in Mesoporous AlMCM‐41 Material and Its Application for Amperometric Determination of Ascorbic Acid in Real Samples

New methylene blue (NMB) dye incorporated into AlMCM‐41 surfactant‐free and hybrid surfactant‐AlMCM‐41 mesophase. UV‐vis evidence shows that new methylene blue dye protonated in both cases of zeolites. New methylene blue is electroactive in zeolites and their electrochemical activity has been studied by cyclic voltammetry and compared to that of NMB in aqueous solutions. New methylene blue molecules are not released to the solution during CV measurements and are accessible to H₃O⁺ ions. The presence of surfactant affects the kinetics of the redox process through proton ions diffusion. The midpoint potentials (E_m) values show that new methylene blue dye incorporated into AlMCM‐41 can be reduced easily with respect to solution new methylene blue. New methylene blue interacting with surfactant polar heads and residual Br^? ions as a results, it shows a couple of peaks in high potential with respect to new methylene blue solution. The electrode made with methylene blue‐AlMCM‐41 without surfactant was used for the mediated oxidation of ascorbic acid. The anodic peak current observed in cyclic voltammetry was linearly dependent on the ascorbic acid concentration. The calibration plot was linear over the ascorbic acid concentration range 1.0×10^?5 to 5.0×10^?4 M. The detection limit of the method is 1.0×10^?5 M, low enough for trace ascorbic acid determination in various real samples.     

A paper‐based gas sensor for simultaneous noninstrumental colorimetric detection of nitrite and sulfide in waters

The use of paper‐based devices in combination with noninstrumental detection systems is becoming increasingly important in the analytical field due to its simplicity, rapidity, and low cost. However, their use for determination of volatile analyte derivatives is still relatively scarce. The present work reports on the assessment of a paper‐based gas‐sensing approach for the simultaneous noninstrumental colorimetric detection of nitrite and sulfide. Colorimetric systems based on the Griess and methylene blue assays, formation of colored metallic sulfides, and interaction/reaction with in situ generated metallic nanoparticles were preliminary evaluated. Then, the effect of experimental variables affecting the analytical performance of the paper‐based gas sensor was studied with two digitization systems, namely a scanner and a smartphone. Under optimal conditions, the developed system yielded limits of detection of 0.055 and 0.005 mg/L for nitrite and sulfide, respectively. The repeatability, expressed as relative standard deviation, was found to be 5.9 and 6.7% for nitrite and sulfide, respectively. The proposed method was finally applied to the analysis of water samples, showing recoveries in the range of 95–105%.     

Trace sulfide determination in oxic freshwaters

A simplified method for determination of reduced sulfur species in natural waters is presented. Reduced sulfur species were separated from a natural water matrix, using purge-and-trap (PT), after reacting with acid (acid volatile sulfide—AVS) or Cr(II) in acidic medium (chromium reducible sulfur—CRS). Sulfide in the trapping medium (0.05 M NaOH), was analyzed spectrophotometrically after derivatization to form methylene blue (MB). AVS precision for Na₂S and zinc sulfide clusters in synthetic solutions was ≤8.5% RSD at concentrations ranging from 48 to 503 nM. Spike recoveries of zinc sulfide clusters were 75-98% in a variety of freshwaters using the AVS procedure. Spike recoveries of Cu sulfide colloids were 94-109% in the same freshwater samples using the CRS procedure. During the analytical procedure an interfering compound was produced due to the reaction of mixed diamine reagent with itself. Lowering the pH of the reaction mixture minimized the formation of this compound. Minimizing contamination from particulates was necessary to achieve sub-nanomolar detection limits. The detection limit for AVS in a 500 ml sample with a 10 cm spectrophotometer cell was 0.1-0.3 nM (3×S.D. blank). The CRS procedure was calibrated with a synthetic CuS colloid. Interferences to the CRS method included finely divided pyrite, polysulfide, thiosulfate, sulfite and some elemental sulfur. The Cr(II) reagent did not reduce sulfate under our experimental conditions. The degree to which zinc sulfide clusters were adsorbed on membrane filters during filtration was mitigated if the clusters were synthesized in the presence of natural organic matter. Examples of AVS and CRS concentrations determined in oxygenated waters using the PT method were comparable to those reported recently by other methods. This method offers greater simplicity than other methods for trace dissolved sulfide determination in natural waters.     

Determination of nitrite in environmental waters by flow injection catalytic spectrophotometry

ABSTRACT

The flow injection catalytic spectrophotometry is proposed for the determination of nitrite based on the catalytic effect on the redox reaction between methylene blue and potassium bromate in acidic medium. The reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of methylene blue at the maximum absorption wavelength of 664 nm. The method is characterised by low solvent consumption and easy automatic continuous analysis. It has higher sensitivity and lower detection limit. Experimental analysis conditions of the flow injection-catalytic photometry are optimised, and the best analysis conditions are: the concentration of the potassium bromate is 0.068 mol L^?1; the concentration of the phosphoric acid in oxidation liquid is 0.045 mol L^?1; the concentration of the methylene blue in colour-substrate solution is 2.4 mg L^?1, the volume of sample ring is 200 μL; the reaction coil is around 7 m in length; the inject time is 50 s and analysis time is 70 s. Under the optimal conditions, the linear range is from 10 to 500 μg L^?1 and the detection limit is 1 μg L^?1. The nitrate standard solution is continuously determined with a mass concentration of 300 μg L^?1. The RSD is determined to be 1.41% (n = 10). The nitrite in water samples, which were from the Half Acre pond, the Ink River and the Small West lake in a campus, was determined respectively by this method. A satisfactory standard addition recovery of 96.7%–103.9% was obtained.     

Coupling on-line of a dialyser with a flow-continuous system to separate Vitamin B(12) from milk

The use of membranes for on-line separations in flow-through dialyser as a part of a flow system is extremely useful for automated samples preparation. In this paper a method to couple the dialysis and the UV detection on-line of Vitamin B₁₂ from milk is proposed. Firstly, the milk samples were pre-treated with trichloroacetic and centrifuged (to eliminate proteins and fats) and later, using a dialyser coupled a flow-continuous manifold was possible dialyse the Vitamin B₁₂, which was monitored spectrophotometrically at 361 nm. On the other hand, the milk samples were also dialysed on-line but without the acid treatment and the results were compared. The influence of various parameters, including the pump speed for both the donor and acceptor stream, dialysis time, donor and acceptor loop volume on dialysis efficiency was studied. The method was applied to different kinds of milk (skimmed and semi-skimmed milk, evaporated milk, lactose free milk and liquid and powder whole milk). The relative standard deviation (R.S.D.) of the proposed method was of 0.45% and the obtained dialysis percentage was of 5.8%. The proposed method very easy permit a pre-treatment of the sample, quick and on-line with the detection. The dialysis process permitted the pass of vitamin and avoided the pass of other analytes as proteins in the case of the milk samples without acid treatment.     

Flow injection method for sulfide determination by the methylene blue method

Flow injection determination of sodium sulfide and hydrogen sulfide in solution through the methylene blue spectrophotometric procedure is described. The carrier streams are N,N-dimethylaniline sulfate (5.4 mM, HCl solution) and iron(m) ammonium sulfate (14.2 mM, HCl solution) and are merged before injection of sulfide (in 0.01 M NaOH). The sampling rate is 210 per hour. The effect of reagent concentrations and interferents on the determination has been investigated.     

Simultaneous Gas Chromatographic Determination of Nitrobenzene and 2,4-Dinitrophenol in Nitrobenzene Manufacturing Plant Wastewater

Abstract

A simple and rapid gas chromatographic procedure is described for the identification and quantification of pollutants in the nitrobenzene manufacturing plant wastewater. The samples were extracted with methylene chloride and subsequently nitrobenzene and 2,4-dinitrophenol were analysed by GC using FID. The method was found to be precise and accurate and applicable for monitoring the effluent treatment system at ppm levels.     

A Simple and Selective Oxidation of Sulfides to Sulfoxides Using Tetrabutylammonium Peroxydisulfate: A Rebuttal

Abstract

The report that oxidation of sulfides to sulfoxides using tetrabutylammonium peroxydisulfate (2) in methylene chloride was found to be erroneous. We repeated the procedure described in the paper and found that oxidation of sulfide to sulfoxide could not be achieved with the method.     

Sorption properties of activated carbons obtained from corn cobs by chemical and physical activation

The paper presents results of a study on obtaining activated carbon from common corn cobs and on its use as adsorbent for removal of pollution from liquid and gas phases. The crushed precursor was subjected to pyrolysis at 500 and 800?°C in argon atmosphere and next to physical or chemical activation by CO₂ and KOH respectively. The effect of pyrolysis conditions and activation method on the physicochemical properties of the materials obtained was tested. The sorption properties of the carbonaceous adsorbents obtained were characterized by determination of nitrogen dioxide and hydrogen sulphide sorption from gas stream in dry and wet conditions as well as by iodine and methylene blue removal from aqueous solution. The final products were microporous activated carbons of well-developed surface area varying from 337 to 1213 m²/g and showing diverse acid-base character of the surface. The results obtained in our study have proved that a suitable choice of the activation procedure for corn cobs permits production of cheap adsorbents with high sorption capacity toward toxic gases of acidic character as well as different pollutants from liquid phase.     

Direct Determination of Benzo(a)pyrene and Pyrene in Solid Environmental Samples by Jet-Cooled Spectroscopy

Abstract

We report the direct determination of two polycyclic aromatic hydrocarbons (PAH), Benzo(a)Pyrene [B(a)P] and Pyrene (Pyr), in solid environmental samples, i.e. a marine sediment and scrapings from the interior walls of a steel foundry, by the supersonic jet/laser induced fluorescence technique. We have found limits of detection (LOD) for these samples of 900ng (1.8ppm) for B(a)P and 200ng (0.4ppm) for Pyr. The LOD's for prepared solutions were 100 ng for B(a)P and 40 ng for Pyr. In validating the procedure we have also analyzed a standard mixture of PAH. The results of our analyses of the solid environmental samples agree well with those obtained by chromatography in other laboratories. We have found evidence of incomplete recovery of PAH from soil sediments by a prolonged low temperature Soxhlet extraction using methylene chloride.     

Analysis of Phenoxycarboxylic Acids and Other Acidic Compounds in Tap,Ground, Surface and Sewage Water at the Low ng/1 Level

Abstract

Solid-phase extraction with RP-C18 phase has been successfully applied for the determination of more than 30 acidic herbicides and related compounds from environmental water samples. Detection of these contaminants was performed after pentafluorobenzylation at the low ng per liter level using gas chromatography/mass spectrometry. With multiple-component SIM programming simultaneous detection of all compounds in one single gas chromatographic run was possible.

Increased reliability of acidic herbicide analysis from water samples with high matrix content was achieved by using a surrogate as well as an internal standard. 2-(4-chlorophenoxy) butyric acid, being a structural isomer of clofibric acid and mecoprop, was chosen as surrogate standard because cloflbric acid was found to be a widespread contaminant in environmental water samples from the Berlin area. Mecoprop, dichlorprop and 1-naphthylacetic acid were also found in field studies of some of these samples. A few examples of positive findings in tap, ground, surface and sewage water samples are presented.     

An Improved Gas-Liquid Chromatographic Method for the Analysis Of 1,1,1-Trichloro-2,2-BIS(p-Chlorophenyl) Ethane(p,p′-DDT) and Its Metabolites in Milk

Abstract

A rapid method has been developed, in which p,p′-DDT residues are extracted from milk samples with n-hexane, following treatment of the milk with concentrated sulfuric acid. The extract, containing p,p′-DDT residues is then cleaned up on a silica gel column. Electron capture gas chromatography was used to measure the efficiency of the extraction and cleanup procedure. An overall average recovery of 97% was obtained on samples at concentration levels of 0.05 to 1.00 ppm.     

High-Performance Liquid Chromatography of Domoic Acid,a Marine Neurotoxin,with Application to Shellfish and Plankton

Abstract

A recent outbreak of poisoning resulting from the consumption of cultured blue mussels (Mytilus edulis L.) from a localized area in Eastern Canada has been attributed to the presence of domoic acid (1), a relatively rare neurotoxic amino acid, previously found only in some algae of the family Rhodomelaceae. Studies on aqueous extracts of shellfish tissue indicated that the toxin and several of its isomers could be separated (and isolated in sufficient amounts for subsequent structural identification) by reversed-phase high-performance liquid chromatography (HPLC) with ultraviolet (UV) diode array detection (DAD). Aqueous acetonitrile containing 0.1% v/v trifluoroacetic acid was used as mobile phase. As the retention time and characteristic UV absorption spectrum of 1 (λ_max = 242 nm) permit unequivocal identification, the HPLC-DAD procedure was refined with a microbore column to provide a rapid (5 min), sensitive (0.3 ng detection limit) and reproducible assay method for the determination of 1 in shellfish tissue. Extraction was accomplished by boiling homogenized shellfish tissue for 5 min with distilled water. Extracts were taken through an octadecylsilica solid phase extraction clean-up prior to HPLC. This method has been applied to a variety of shellfish and phytoplankton samples.

BRIEF

Reversed-phase HPLC with ultraviolet diode array detection was used to analyze shellfish tissue and phytoplankton extracts for domoic acid. A rapid (5 min) and sensitive (0.3 ng detection limit) assay is presented.     

Exploiting Sulphide Generation and Gas Diffusion Separation in a Flow System for Indirect Sulphite Determination in Wines and Fruit Juices

A flow system for sulphite determination in wines and fruit juice samples has been developed exploiting H₂S generation and gas diffusion separation. The composed sandwich gas diffusion cell was coupled in the flow manifold to permit sulphite reduction to H₂S and H₂S diffusion through a microporous PTFE membrane to produce methylene blue resulting from the reaction with N,N-dimethylphenylene diamine (DMPD) and Fe³⁺. The flow parameters were optimized, and the best results were obtained by using NaOH solution for H₂S collection. Interferences of H₂S, CO₂ and ascorbic acid were evaluated. Limits of detection (3σ) for the free and total sulfite were calculated at 0.12 and 0.25 mg L⁻¹, respectively. The results obtained by the proposed process were in agreement with the reference methods for a 95% confidence level.