Bioconversion of ilicic alcohol and derivatives with cultures of filamentous fungi

Aspergillus niger cultures monohydroxylate ilicic alcohol in C-3 in a cis position with respect to the methyl groups at C-4 and C-10, and trans position with respect to the hydroxyl group of C-4. Furthermore, Aspergillus niger cultures reduce ilicic aldehyde to its corresponding alcohol.     

Analytical methodologies for chromium speciation in solid matrices: a survey of literature

The analytical literature about chromium speciation in solid samples has been surveyed. From 451 articles published on the speciation of chromium from 1983 to 1997, the methodologies to do speciation in solids after sample pretreatment are discussed, through consideration of the types of samples and their dissolution, the analytical techniques employed for chromium measurement, and the figures of merit of the 86 papers reported in the Analytical Abstracts data base. Received: 6 February 1998 / Revised: 6 March 1998 / Accepted: 7 March 1998     

Analytical methodologies for chromium speciation in solid matrices: a survey of literature

The analytical literature about chromium speciation in solid samples has been surveyed. From 451 articles published on the speciation of chromium from 1983 to 1997, the methodologies to do speciation in solids after sample pretreatment are discussed, through consideration of the types of samples and their dissolution, the analytical techniques employed for chromium measurement, and the figures of merit of the 86 papers reported in the Analytical Abstracts data base.     

Elemental speciation for chromium in chromium picolinate products

Chromium picolinate products have been examined for different forms of chromium, using chromatographic separation and inductively coupled plasma mass spectrometric detection. The brands we evaluated contained no detectable amount of elemental chromium(VI), the toxic form. Since chromium picolinate might have other chromium forms as impurities, different products may contain different forms of chromium species. Compared with ion-exchange, reversed-phase chromatography showed excellent chromium recovery based on the amount stated on the product label.     

Biosorption of nickel using filamentous fungi

Nickel (Ni) uptake capability from aqueous solutions was studied in a filamentous fungi strains group ofRhizopus sp.,Penicillium sp.Aspergillus sp.,Trichoderma sp.,Byschoclamyss sp., andMucor sp. The metal uptake of aRhizopus sp. strain, which has the highest uptake capacity, was corroborated by electron microscopy; no Ni deposits were observed on the cell wall, but rather a homogeneous accumulation was seen on the cell surface. The influence on the capacity of metal uptake by environmental parameters such as pH, temperature, time, and the interference of other ions in the solution, was also studied. Nickel accumulation by the selected strains is fast, occurring in less than 30 min, and does not require a microorganism’s active metabolism to take place. Sorption isotherms were established for the selected fungi, in order to determine the maximum metal uptake capacity. The sorption isotherms were fixed to the mathematical models of Freundlich and Langmuir, obtaining better performance on the Langmuir model.     

Non-chromatographic speciation analysis of chromium in natural waters

The difference in toxicity between Cr(III) and Cr(VI) species is one of the main reasons for the recent developments in analytical procedures for their differentiate. Non-chromatographic methods offer highly convenient tools for this purpose and can be used as a fast and cheap alternative to the chromatographic processes. The present work overviews and discuss different non-chromatographic procedures for speciation of chromium in natural water samples such as coprecipitation, dialysis, solvent and solid phase extraction. This survey will attempt to cover the state of-the art from 2005 to 2010.     

Removal and recovery of chromium and chromium speciation with MINTEQA2

Chromium(III) is commonly found in large quantities in tannery wastewaters. For this reason, the recovery of the chromium content of these wastewaters is necessary for environmental protection and economic reasons. Removal and recovery of chromium were carried out by using ion exchange resins. To this purpose, two weakly acidic exchange resins Amberlite IRC 76 and Amberlite IRC 718 and a strongly acidic exchange resin Amberlite IR 120 were used. Basic chromium sulphate [Cr(4)(SO(4))(5)(OH)(2)] solutions in different concentrations and pH were used in all experiments as tanning baths. The resins were prepared in two different ionic forms as Na(+) and H(+). The effects of concentration, pH, stirring time and resin amount were investigated. The concentration range varied between 5 and 100 mg l(-1), pH range was between 1 and 8, stirring time between 5 and 60, and resin amount was between 50 and 1000 mg. Stirring speed was 2000 rpm during all these experiments. Exchange capacities, moisture contents and optimum conditions of these resins were determined in batch system. The results obtained showed that Amberlite IRC 76 and 718 weakly acidic resins had shown better performance than Amberlite IR 120 strongly acidic resin for removal and recovery of chromium(III) in Na(+) form. Optimum conditions were found as concentration 10 mg l(-1), pH 5, stirring time 20 min, and resin amount 250 mg. Furthermore, chromium(III) speciation was investigated for optimum concentration and pH with MINTEQA2 computer programme. The studied pH range was between 1 and 8 and concentration range was between 5 and 100 mg l(-1). Cr(OH)(2+) species were found to be dominant at pH 5 and 10 mg l(-1) concentration in batch studies. There was a correlation between experimental and computerised results.     

Fast response filter module with plug flow of filtrate for on-line sampling from submerged cultures of filamentous fungi

Automatic and accurate sampling is both convenient and sometimes necessary to obtain detailed information about cell cultures. We developed an autoclavable sampling system in which culture broth was pumped through an ultrafiltration cross-flow module with a novel filtrate collecting principle and a novel regulation of filter back pressure. Filtrate was collected from equal membrane filter areas through holes connected to channels with an even length to the collecting point, resulting in a near plug flow of filtrate and a reduction in the response time to 1 min (98% of full signal of the tracer molecule glucose). Constant pressure difference (0.3 bar) across the membrane filter (30 kDa cutoff value) and prevention of leakage was obtained by squeezing the tubing with culture broth between two flexible spring steel plates fixed at one corner (filtrate flow 1 ml min⁻¹). The large contact area allowed the tubing to open the passage more when pressure increased. Using this design of sampling system, the metabolite profiles of Aspergillus niger wild type and a phosphofructokinase overexpressing strain (three times wild type) were concluded to be indistinguishable by detailed monitoring of fast transients of substrates and products in batch culture and glucose pulse experiments. The combination of the fast response filter module and prevention of high pressure peaks with the flexible resistance to flow enables long-term (>5 days) and automatic monitoring of cultures of filamentous fungi or other microorganisms with fast changes in extracellular concentrations.     

Problems of the speciation of chromium in soil samples

Different separation/detection methods (ion exchange, organic extraction, spectrophotometry) and four extraction media have been compared for the speciation of chromium. Due to the pH dependence of these methods only the spectrophotometric method using the diphenylcarbazide reaction has proved suitable for speciation analyses. If nitric acid is used for the initial extraction stage, problems are often encountered with the other method during subsequent speciation analysis. The reasons for this are discussed.     

Determination of chromium speciation in natural systems using DGT

The techniques of diffusive gradients (DGT) and equilibration (DET) in thin-films have been combined in a single probe that can determine Cr(III) and Cr(VI) simultaneously in solution. The assembly has a layer of polyacrylamide hydrogel overlying a separate layer of resin embedded in gel. Cr(III) species accumulate exclusively and quantitatively in the resin layer, while Cr(VI) species equilibrate with both hydrogel and resin layers. The species are separated by peeling the two layers apart. Chromium is then eluted from each of the two layers. Cr(III) and Cr(VI) were determined quantitatively in standard, mixed solutions by in situ separation with DGT and detection by GF-AAS. With this method, Cr(III) is typically preconcentrated by a factor of 10 over a 24 h deployment, and limits of detection of 8 ng/L Cr(III) and 0.3 micro g/L Cr(VI) were achieved. Due to the inbuilt preconcentration of Cr(III), the technique is particularly good at measuring low concentrations of Cr(III) in the presence of an excess of Cr(VI). Measurements were performed in three soils with various levels of chromium contamination. A concentration of 3 micro g/L of labile Cr(III) was measured reproducibly in the presence of 290 micro g/L of unreactive Cr species and 0.2 micro g/L of labile Cr(III) was measured in the presence of 24 micro g/L of unreactive Cr. The unique feature of the method is that the separation of Cr(III) from Cr(VI) occurs in situ. The Cr species are then stable in the resin and gel prior to analysis, eliminating the artefacts associated with sampling and storage, which are particularly prevalent for redox-sensitive elements. Therefore, it has great potential for assessing Cr(III) and Cr(VI) concentrations in situ in environments near redox boundaries where possible dynamic changes in Cr(III) and Cr(VI) concentrations are occurring.     

Capillary electrophoresis speciation of chromium in leather tanning liquor

We present a method for the speciation of chromium by capillary electrophoresis. Cr(III) was complexed with diethylenetriaminepentaacetic acid (DTPA) to form a negatively charged complex. Using 20 mM phosphate buffer of pH 8 containing 0.5 mM tetradecyltrimethylammonium hydroxide (TTAOH) at a separation voltage of -15 kV, both forms of chromium CrDTPA(2-) and CrO(4) (2-) were separated in less than 6 min. Direct UV detection at 214 nm was used. The effect of the presence of interfering ions was investigated. The application of the developed method to speciation of chromium in tanning liquor is demonstrated. The obtained results have shown a good correlation with those of flame atomic absorbance spectrometry (FAAS), inductively coupled plasma-mass spectrometry (ICP-MS) and UV/VIS spectrophotometry.     

Field sampling technique for speciation of inorganic chromium in rivers

A simple and robust field sampling technique has been developed for the determination of chromium (III) and chromium (VI) in rivers. Water samples, on collection, were immediately passed through microcolumns of activated alumina to isolate and retain the desired species. Microcolumns were then returned to the laboratory and inserted into a FI-ICP-ES system for elution/ quantitation. Field sampling performed at 2 stations in S. Yorkshire over a 1 month period yielded elevated concentrations of chromium (III) (8–20g/1) and chromium (VI) (1.1–4.5 g/1) and, for each data set, the sum of the two fractions matched the total chromium concentration.     

Chemical speciation of chromium in sea water: Part 3. The determination of chromium species

A method for the determination of chromium(III), chromium(VI) and organicallybound chromium in sea water is reported. It is confirmed that sea water contains about 9 × 10^-9 M dissolved chromium. This is shown to be divided as ca. 15% inorganic Cr(III), ca. 25% inorganic Cr(VI) and ca. 60% organically-bound chromium. It is suggested that the inconsistency of earlier results on the dominant chromium species and its concentration in sea water is largely due to the fact that organically bound chromium species were not considered.     

Analytical artefacts in the speciation of arsenic in clinical samples

Urine and blood samples of cancer patients, treated with high doses of arsenic trioxide were analysed for arsenic species using HPLC-HGAFS and, in some cases, HPLC-ICPMS. Total arsenic was determined with either flow injection-HGAFS in urine or radiochemical neutron activation analysis in blood fractions (in serum/plasma, blood cells). The total arsenic concentrations (during prolonged, daily/weekly arsenic trioxide therapy) were in the μg mL⁻¹ range for urine and in the ng g⁻¹ range for blood fractions. The main arsenic species found in urine were As(III), MA and DMA and in blood As(V), MA and DMA.With proper sample preparation and storage of urine (no preservation agents/storage in liquid nitrogen) no analytical artefacts were observed and absence of significant amounts of alleged trivalent metabolites was proven. On the contrary, in blood samples a certain amount of arsenic can get lost in the speciation procedure what was especially noticeable for the blood cells although also plasma/serum gave rise to some disappearance of arsenic. The latter losses may be attributed to precipitation of As(III)-containing proteins/peptides during the methanol/water extraction procedure whereas the former losses were due to loss of specific As(III)-complexing proteins/peptides (e.g. cysteine, metallothionein, reduced GSH, ferritin) on the column (Hamilton PRP-X100) during the separation procedure. Contemporary analytical protocols are not able to completely avoid artefacts due to losses from the sampling to the detection stage so that it is recommended to be careful with the explanation of results, particularly regarding metabolic and pharmacokinetic interpretations, and always aim to compare the sum of species with the total arsenic concentration determined independently.     

Analytical protocol for investigation of zinc speciation in plant tissue

A specific procedure is proposed for investigating the chemical speciation of zinc (Zn) in plant tissues, viz., the extraction of Zn compounds from Plantago lanceolata L. followed by the chromatographic separation and inductively coupled plasma mass spectrometry (ICP-MS) identification of these compounds. In order to separate the Zn compounds, both size-exclusion (SEC) and ionexchange liquid chromatography (IC) were used in direct sequential and reverse sequential modes. In the direct sequential mode, the entire extract undergoes SEC separation and then the individual fractions are injected onto the ion-exchange column. The molecular size distribution is evaluated by SEC coupled on-line to the UV detector. In the reverse sequential mode, the entire extract undergoes the ion-exchange chromatographic separation and then the individual fractions are injected onto the size-exclusion column. The identification of Zn incorporated into the compounds is further performed using ICP-MS. This procedure is particularly useful in speciation studies when identification of the individual components of the element is problematic due to the lack of suitable standard substances, as is the case for Zn compounds. The proposed procedure facilitates assignment of the signals to the individual components of the fractions for both types of chromatography, thus rendering the chemical speciation of Zn possible when the lack of suitable standard substances impedes the identification of individual components.     

Mass spectrometry in the study of extracellular enzymes produced by filamentous fungi

The use of MALDI-TOF and other types of mass spectrometry for the identification and investigation of extracellular enzymes (carbohydrases, proteinases, esterases, etc.) produced by filamentous fungi belonging to the genera Aspergillus, Trichoderma, Penicilium, Chrysosporium, etc. is discussed. The method of mass spectrometric peptide fingerprinting combined with the use of Internet software for on line data analysis (MASCOT, Aldente, FindPept, FindMod, GlycoMod) allows the fast and reliable identification of both individual enzymes and the components of crude multienzyme preparations without their fractionation. The method was also applied to the discrimination of the fungal genes encoding enzymes with similar substrate specificity. Other enzyme-based applications of mass spectrometry, such as the revelation of the presence or absence of structural domains in the molecules of carbohydrases, the detection of posttranslational and artificial modifications in the enzymes, and the use of tandem mass spectrometry for de novo peptide sequencing are described.     

Analytical methodology for speciation of arsenic in environmental and biological samples

A literature search on the speciation of arsenic in environmental and biological samples shows an increasing interest of many researchers in the subject. Because of the low level of arsenic species in real samples, many problems related with its speciation remain unresolved: species instability during sampling, storage and sample treatment, incomplete recovery of all species, matrix interferences, lack of appropriate certified reference materials and of sensitive analytical methods, etc. These aspects are underlined in this paper. The continued development of new analytical procedures pretending to solve some of these problems claim for an up-to-date knowledge of the recent publications. Therefore, this paper pretends to review the latest publications on the chemical speciation of arsenic, emphasizing the increasing activity in the development of accurate and precise analytical methods. In most of the cases, separation and preconcentration is necessary, followed by element-specific detection for sensitivity improvement. Hydride generation following separation procedures (e.g., ion-exchange or high performance liquid chromatography) coupled to atomic absorption or atomic emission detectors proved to have sufficient sensitivity to monitor arsenic exposure, although restricts the analysis to hydride-forming species. Modified procedures including some kind of heating in the presence of highly oxidizing agents have proved successful to completely decompose the arsenic containing compounds to arsenate and so to extend the range of compounds which can be determined by these methods. On-line arrangements have the additional advantage of avoiding excessive sample handling, although some of them involve numerous steps and others are too costly to be recommended for routine use. The analytical figures of merits, specially detection limits are given for most of the methods in order to afford comparison and judge possible applicability. These studies, which have been approached in many different ways, would lead to knowledge that are determinant in the understanding of the cycle of this element in environment and of its physiological and toxicological behavior in the living organisms.     

Determination of the speciation of chromium from a bicycle factory discharge

The discharge from a bicycle factory in Dar-es-Salaam was analysed for dissolved trace metals so as to monitor what was being introduced onto the environment. An X-ray Fluorescence Spectrophotometer with a Si (Li) detector connected to a multichannel analyser Canberra 40 series was used for the analysis. Computation of the peaks and results was done by a Professional Deck 350 computer. The elements contained in the discharge were Ca (596 ppm), Ti (369 ppm), Cr (11 ppm), Zn (0.98%) and Sr (73.5 ppm). Further analysis of the speciation of chromium revealed that there was Cr(III) (9 ppm) and Cr(VI) 2 ppm. The level of Cr(VI) was considered too high considering its toxicity.     

Specific extraction of chromium as tetrabutylammonium-chromate and spectrophotometric determination by diphenylcarbazide: speciation of chromium in effluent streams.

A very specific, selective, simple, and inexpensive procedure was developed for the speciation of CrVI and CrIII. This method is based on the quantitative extraction of chromate and CrIII (previously oxidized to CrVI) as a tetrabutylammonium-chromate ion-pair in methyl isobutyl ketone (MIBK), and then back extraction and preconcentration with an acidic diphenylcarbazide (DPC) solution. Back extraction was applied to achieve further preconcentration by a final factor of 20. The CrVI-DPC complex was determined in back-extract by a spectrophotometer at 548 nm. Under these extraction conditions, most of the probable concomitant cations and anions remained in the first inorganic phase. The calibration curve was linear up to 0.14 microg L(-1) of CrVI with a detection limit of 2.22 ng L(-1). The developed procedure was found to be suitable for the determination of the CrVI and CrIII species in various natural water samples with a relative standard deviation of better than 1.6%. The method was successfully applied to the speciation of chromium in spiked natural water samples, and also samples of effluent from a leather treatment plant.     

A new cation-exchange method for accurate field speciation of hexavalent chromium

A new method for field speciation of Cr(VI) has been developed to meet present stringent regulatory standards and to overcome the limitations of existing methods. The method consists of passing a water sample through strong acid cation-exchange resin at the field site, where Cr(III) is retained while Cr(VI) passes into the effluent and is preserved for later determination. The method is simple, rapid, portable, and accurate, and makes use of readily available, inexpensive materials. Cr(VI) concentrations are determined later in the laboratory using any elemental analysis instrument sufficiently sensitive to measure the Cr(VI) concentrations of interest. The new method allows measurement of Cr(VI) concentrations as low as 0.05 μg l⁻¹, storage of samples for at least several weeks prior to analysis, and use of readily available analytical instrumentation. Cr(VI) can be separated from Cr(III) between pH 2 and 11 at Cr(III)/Cr(VI) concentration ratios as high as 1000. The new method has demonstrated excellent comparability with two commonly used methods, the Hach Company direct colorimetric method and USEPA method 218.6. The new method is superior to the Hach direct colorimetric method owing to its relative sensitivity and simplicity. The new method is superior to USEPA method 218.6 in the presence of Fe(II) concentrations up to 1 mg l⁻¹ and Fe(III) concentrations up to 10 mg l⁻¹. Time stability of preserved samples is a significant advantage over the 24-h time constraint specified for USEPA method 218.6.