Vanillin-condensed tannin study using flow injection spectrophotometry

Studies involving the kinetic reaction between vanillin and condensed tannins were developed using a flow injection system with spectrophotometric determination. A solution of the monomeric compound (-)-epicatechin was used as the analytical standard. This compound was chosen due to its structure, which is similar to a polymeric unit of the condensed tannin present in plants. The results indicated that the vanillin-condensed tannin reaction is time dependent and affected by the degree of polymerization of the condensed tannin. The flow system allowed (-)-epicatechin to be used without overestimating the content of the tannin present in the forage legume, guandu (Cajanus cajan (L.) Millsp.), studied. A relative standard deviation (R.S.D.) of <1% was found for a 4 h period work and allowed the determination of about 60 samples h(-1) with a detection limit of 1.05 mg l(-1) for condensed tannin. When compared to the manual vanillin procedure, the proposed approach can be used with various advantages.     

Microbial metabolites of harman alkaloids

Several microorganisms showed the ability to transform the harman alkaloids, harmaline (1), harmalol (2) and harman (5). Harmaline (1) and harmalol (2) were converted by Rhodotorula rubra ATCC 20129 into the tryptamines, 2-acetyl-3-(2-acetamidoethyl)-7-methoxyindole (3) and 2-acetyl-3-(2-acetamidoethyl)-7-hydroxyindole (4), respectively. Harman (5) was biotransformed by Cunninghamella echinulata NRRL 3655 into 6-hydroxyharman (6) and harman-2-oxide (7).     

Identification and biological activity of microbial metabolites of xanthohumol

Microbial transformation of xanthohumol using the culture broth of Cunninghamella echinulata NRRL 3655 afforded (2S)-8-[4"-hydroxy-3"-methyl-(2"-Z)-butenyl]-4',7-dihydroxy-5-methoxyflavanone (5) and (2S)-8-[5"-hydroxy-3"-methyl-(2"-E)-butenyl]-4',7-dihydroxy-5-methoxyflavanone (6). Xanthohumol (1) and flavanone 6 as well as (E)-2"-(2"'-hydroxyisopropyl)-dihydrofurano[2",3":4',3']-2',4-dihydroxy-6'-methoxychalcone (2), (2S)-2"-(2"'-hydroxyisopropyl)-dihydrofurano[2",3":7,8]-4'-hydroxy-5-methoxyflavanone (3) obtained with Pichia membranifaciens showed antimalarial activity against Plasmodium falciparum.     

Determination of As(III) and arsenic(V) in natural waters by cathodic stripping voltammetry at a hanging mercury drop electrode

A simple, fast and quantitative method was developed for the determination of As(III) and total inorganic arsenic (As (total)) in natural spring and mineral waters using square wave cathodic stripping voltammetry (SWCSV) at a hanging mercury drop electrode (HMDE). In the determination of As(III), pre-concentration was carried out on the electrode from a solution of 1 mol/l HCl in the presence of 45 ppm of Cu(II) at a potential of −0.39 V versus Ag/AgCl, and the deposited intermetallic compound was reduced at a potential of about −0.82 V versus Ag/AgCl. In the determination of As (total) the pre-concentration was carried out in 1 mol/l HCl in the presence of 400 ppm of Cu(II) at a potential of −0.40 V versus Ag/AgCl, and the intermetallic compound deposited was reduced at a potential of about −0.76 V versus Ag/AgCl. For determination of As(III) the quantification limit was 0.2 ppb for a deposition time of 40 s, and the relative standard deviation (R.S.D.) was calculated to be 6% (n=13) for a solution with 8 ppb of As(III). For As (total), the quantification limit was 2 ppb for a deposition time of 3 min, and the R.S.D. was calculated to be 3% (n=10) for a solution with 8 ppb of As(V). The method was validated by application of recovery and duplicate tests in the measurements of As(III) and As (total) in natural spring and mineral waters. For As (total), the results of the SWCSV method were compared with the results obtained by optical emission spectrometry with ICP coupled to hydride generation (OES-ICP-HG) good correlation being observed.     

Spectrophotometric and derivative spectrophotometric determination of nickel with hydroxynaphthol blue

The reaction of nickel(II) cation with hydroxynaphthol blue (HNB) in aqueous media at pH 5.2–6.0 results in a red complex that is stable for at least 2h. Beer's Law is obeyed up to 3.2 g/ml of nickel(II) with an apparent molar absorptivity of 1.38 × 10⁴l/mol/cm at 563 nm. This paper proposes procedures for nickel determination by ordinary and first-derivative spectrophotometry. The results demonstrate that the linear dynamic range is 0.08–3.20 g/ml with a limit of detection of 23 ng/ml for ordinary spectrophotometry, compared with 21–800 ng/ml and 6 ng/ml, respectively, for first-derivative spectrophotometry. Calcium(II), magnesium(II), barium(II), strontium(II), cadmium(II), lead(II), manganese(II), bismuth(III) and molybdenum(VI) ions do not interfere for at least 1001 mass ratios. The main interferents are cobalt(II), titanium(IV), aluminium(III), mercury(II) and copper(II). The interferences of titanium(IV), aluminium(III), zirconium(IV) and iron(III) can be masked by fluoride and mercury(II) and copper(II) with thiosulfate or thiourea. The derivative method is applied to nickel determination in standard brasses and the results demonstrate that there is no significant difference between the results and certified values at the 95% confidence level.     

Simplified version of the sodium salicylate method for analysis of nitrate in drinking waters

The salicylate method for determination of nitrate in drinking waters has been simplified by using the calibration solutions for 54 days, and therefore, reducing the work time. The results obtained can be considered satisfactory with regard to limit of determination (0.10 mg l⁻¹ nitrate as nitrogen (NO₃⁻-N)), precision (relative standard deviations <4% for five determinations were found) and accuracy (recoveries from 88 to 106% for nitrate in spiked drinking water were obtained).     

n-Hexane hydrogenolysis on bimetallic platinum-palladium catalysts

Alumina supported platinum, palladium and bimetallic platinum-palladium catalysts have been investigated in the hydrogenolysis of n-hexane. Results show that, compared with platinum, the activity of bimetallic catalysts is several times lower while the selectivity to hydrogenolytic products increases from 72 to 100%.

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Detection of preformed type A botulinal toxin in hash brown potatoes by using the mouse bioasssay and a modified ELISA test

A foodborne illness caused by type A toxin-producing Clostridium botulinum was investigated by using the standard mouse bioassay and a rapid invitro test for toxin detection. The patient, who consumed improperly stored hash brown potatoes that contained the preformed toxin, was diagnosed with type A botulism. C. botulinum type A toxin was detected in the hash brown potatoes as well as in the tryptone-peptone-glucose-yeast extract (TPGY) medium subcultures of this food using the mouse bioassay and an amplified ELISA technique. The mouse bioassay revealed preformed toxin at 10,000 minimum lethal dose (MLD)/g uncooked product and the amplified ELISA an equivalent 50,000 MLD/g. The cultural toxin from the uncooked product killed mice at the 10(6) dilution and a modification of the ELISA procedure was positive at the 10(3) dilution. Cooked food obtained from the consumer's waste can contained 100 MLD/g and the ELISA was also positive at the same dilution of the product. The culture of the cooked product obtained from the waste can was lethal for mice at the 10(7) dilution and positive using the modified ELISA at the 10(4) dilution. The unmodified amplified ELISA method indicated a toxin level of approximately 1 ng/mL (equivalent to 5 x 10(5) MLD/mL) in diluted culture fluid from the uncooked food and the culture of cooked food obtained from the waste can. The hash brown potatoes were negative for types B, E, and F preformed and cultural botulinal toxins using both assays.     

Doehlert matrix for optimisation of procedure for determination of nickel in saline oil-refinery effluents by use of flame atomic absorption spectrometry after preconcentration by cloud-point extraction

This paper proposes a preconcentration procedure for determination of nickel in saline aqueous waste samples by flame atomic absorption spectrometry (FAAS). It is based on cloud-point extraction of nickel(II) ions as 2-(5-bromo-2-pyridylazo)-5-diethilaminophenol (Br-PADAP) complexes using octylphenoxypolyethoxyethanol (Triton X-114) as surfactant. The optimisation step was performed using a four-variable Doehlert design, involving the factors centrifugation time (CT) of system after addition of surfactant, solution pH, methanol volume (MV) added at micellar phase, and buffer concentration (BC). The analytical response used was absorbance, after volume correction. Using the established experimental conditions in the optimisation step the procedure enables nickel determination with a detection limit (3 delta/ S) of 0.2 microg L(-1), quantification limit (10 delta/ S) of 0.7 microg L(-1), and precision, calculated as relative standard deviation ( RSD) of 4.7 ( n=8) and 3.5% ( n=8) for nickel concentration of 1 and 5 microg L(-1), respectively. The preconcentration factor, determined from the ratio of the slopes of the analytical curves with and without preconcentration, is 74. The recovery achieved for nickel determination in the presence of several cations demonstrated that this procedure could be applied for analysis of water samples. The robustness was checked by using saturated fractional factorial designs, centred on the established experimental conditions in the optimisation step. The results of these tests demonstrated that the variables centrifugation time and buffer concentration are robust for modification by 10% and that solution pH and methanol volume are robust for 5%. Accuracy was evaluated by using the certified material reference SLEW-3 estuarine water for trace metals. The procedure was used for determination of nickel in saline effluents from oil refinery samples. Recovery results (95-104%) indicate that the procedure has satisfactory accuracy for nickel determination in these samples.     

Cathodic adsorptive stripping voltammetry of nickel complexed with hydroxynaphthol blue at a static mercury drop electrode

A new method is described for the determination of Ni based on the cathodic adsorptive stripping of Ni(II) complexed with hydroxynaphthol blue (HNB) at a static mercury drop electrode. Optimal conditions were found to be: accumulation potential -0.50 V (vs. Ag/AgCl); final potential -1.10 V; accumulation time 50 sec; scan rate 200 mV/sec; linear scan mode; filter 0.1 sec; supporting electrolyte acetic acid/acetate (0.25M, pH = 6.0) and concentration of HNB 3.3 x 10(-5)M. The response of the system was found to be linear in a range of Ni concentrations from 25 ppb to the detection limit. The detection limit was found to be 1.7 nM (0.10 ppb) with 2 mins of accumulation time. The effect of various potential interferences (including a variety of cations, anions and organic surfactants) were also studied. With the exception of Co, at less than equimolar concentrations no significant interferences were observed. Al was found to interfere at high concentrations with respect to Ni, but Al concentrations up to 1000 ppb may be masked by sodium citrate or sodium fluoride. The utility of the method is demonstrated by the recovery of Ni in a doped sample of commercial mineral water.