Acid Dichromate Research Articles

Use of poly(ethylene terephthalate) plastic bottles for the sampling, transportation and storage of potable water prior to mercury determination

Comparisons were carried out between the use of poly(ethylene terephthalate)(PET) plastic bottles and clear glass bottles for the storage of potable water samples for up to 10 days, prior to mercury determination. The PET bottles were found to be as suitable as glass bottles for the above purpose, while also offering significant cost saving and safety advantages. Two chemical preservatives were also compared. The recovery of mercury was significantly enhanced for both bottle types by the pre-addition of either hydrochloric acid or an acid dichromate preservative solution. The latter was preferred on safety grounds owing to its obvious colour. Long-term storage was not tested as this laboratory has a maximum five working day turnaround time for this determinand. The concentration range of interest was 0.05–1.5 µg l–1 of mercury.

Comparative study of diffracted-to-scattered intensity ratio before and after printout effect in bleached holograms

An experimental study has been made of the diffracted-to-scattered intensity ratio before and after the printout effect, in bleached holograms recorded on AGFA-Gevaert 10E75 NAH plates. Use has been made of nine known conventional and four known reversal bleach processes and different type of developers and developer compositions. High diffracted-to-scattered intensity ratio is achieved by using potassium iodide and iodine bleach process with CW-Cl developer without any perceptible change in diffracted-to-scattered intensity ratio after the printout effect. In case of reversal bleaches, minimum change in diffracted-to-scattered intensity ratio is achieved by using potassium dichromate plus concentrated sulphuric acid bleach with CW-C2 developer.

Evaluation of oxidant media for the determination of lead in food slurries by hydride generation atomic absorption spectrometry

Several oxidant media were evaluated for the generation of lead hydride from slurry samples and their application to the determination of lead in vegetables and fish by hydride generation atomic absorption spectrometry. Three oxidant - acid media were compared: hydrogen peroxide - nitric acid, ammonium persulphate - nitric acid and potassium dichromate - lactic acid. The powdered samples were suspended in Triton X-100 and shaken with 10.0 g of blown zirconia spheres until a slurry was formed. The potassium dichromate - lactic acid medium was the most satisfactory for the determination of lead in fish and vegetables, providing the lowest detection limits as a result of its high sensitivity and low blank values. The ammonium persulphate - nitric acid medium gave good accuracy, precision and selectivity for vegetables (1-2 p.p.m. of lead); however, with fish (0.1-1 p.p.m. of lead) it was only a semi-quantitative medium for the determination of lead owing to its lack of sensitivity and selectivity. The hydrogen peroxide - nitric acid medium was unsatisfactory for the generation of lead hydride from slurry samples because of decomposition of hydrogen peroxide by the organic matter in the sample.

ChemInform Abstract: Photooxidation of 2‐Phenylbenzotriazoles.

AbstractUV irradiation of (I) under aerobic conditions yields (III) (isolated as diester (V)), presumably via the known quinone (II) (independently prepared from (I) and acidic dichromate; yield 8%).

Methods for determination of carbon loss from fungal propagules incubated in soil

Losses of C from fungal propagules exposed in soil were determined by incubating 14C-labelled fungal propagules enclosed in membrane filter envelopes in 4 g soil in planchets in a closed chamber. 14CO 2 evolved was recovered daily by passing air through the headspace and collecting CO 2 in ethanolamine scintillation cocktail. Dissolved 14CO 2 in soil was recovered by bubbling air through an acidified aqueous soil suspension and collecting the CO 2 evolved. Residual 14C in soil was determined, after removal of membrane filters containing conidia, by oxidizing the soil with acid dichromate and collecting the CO 2, evolved. The amount of dissolved 14CO 2 was negligible (0.1 to 0.2% of total label). The amount of residual 14C, as percentage of total label, was 20.6% from conidia of Cochliobolus sativus after 18 days in soil and 2.3% from sclerotia of Sclerotium rolfsii after 26 days in soil. 14CO 2 evolved from the soil with added conidia during 18 days was 31.2%, and with added sclerotia during 26 days was 16.4%. The relative contribution of fungal respiration to total 14CO 2 evolved from soil was estimated to be 57–60% for conidia and 65–72% for sclerotia. Propagule respiration may play a greater role in 14C loss from fungal propagules in soil than assumed previously.

Electrolytic Regeneration of Acidic Dichromate used in Oxidation of Alcohols

Electrolytic Regeneration of Acidic Dichromate used in Oxidation of Alcohols

Enhancement of the Atomic Absorption of Iodine in Hydrogen-Entrained Air Flames

Hydrogen-entrained air flames diluted with either argon or nitrogen are used to atomize iodine in aqueous solutions. The iodide ion present in the sample is oxidized to elemental iodine with acidic dichromate before being aspirated into the flame. Sensitivity (concentration I− per 1% absorption) in either flame after preliminary oxidation is about 0.6 ppm with a 10-cm single slot burner. Sensitivity without addition of the acidic dichromate reagent is about 150 ppm. Either hydrogen-entrained air flame yields absorbance value about eight times greater than those obtained with a fuel-rich air-acetylene flame when the iodide is oxidized to elemental iodine.

Sectionalised bubble column: Gas hold‐up and wall side solid—Liquid mass transfer coefficient

AbstractThe effect of gas sparger type, clear liquid height, liquid viscosity and addition of electrolyte on fractional gas hold‐up in a 0.38 m i.d. sectionalised bubble column (SBC) was studied for superficial gas velocities ranging from 0.03 to 0.15 m s−1. A study of the wall side solid–liquid mass transfer coefficient, kSL, has been made by considering the dissolution of copper in acidic dichromate solutions. The variation of kSL with axial distance in a section for different gas velocities has been explained. A comparison between the performance of sectionalised bubble columns and conventional bubble columns has been presented. In some cases, the SBC may prove to be superior to bubble columns in practice.

Hydrodynamics and mass transfer characteristics of co‐current downflow packed tube columns

AbstractHydrodynamics and effective interfacial area in a 25 mm i.d. packed tube column were studied over a wide range of operating conditions for demister pad packings (DPP). Flow maps have been prepared. Values of effective interfacial area as high as 1880 m−1 in the spray flow regime were obtained. Data on pressure drop and effective interfacial area have been correlated for different flow regimes. Values of liquid side volumetric mass transfer coefficient, kL a, were measured by absorption and desorption of oxygen in different packed tube columns containing Pall rings (standard and low height to dia. ratio), multifilament wire gauge packings (MFWGP) and DPP. kL a was found to vary from 0.017 to 0.34 s−1 for DPP.Values of wall side solid‐liquid mass transfer coefficient, kSL, were obtained in a 25 mm i.d. copper tube column packed with MFWGP by the dissolution of copper in acidic dichromate solutions. Values of wall side heat transfer coefficient could be obtained by analogy.

Correlations between indexes of soil nitrogen availability and nitrogen percent in plant, nitrogen uptake, and dry-matter yield of rice grown in the greenhouse

Relationships between available nitrogen determined by two anaerobic incubation methods (30°C for 2 weeks: 40°C for 1 week) and seven chemical indexes (Organic C, total N, ammonium released by acid dichromate, acid permanganate, alkaline permanganate, hydrogen peroxide and dilute sulfuric acid) and nitrogen percent in rice plant, nitrogen uptake and dry-matter yield of IR 26 rice grown under submerged conditions in pots were investigated using 39 Philippine wetland rice soils differing markedly in their capacities to supply nitrogen. It was found that all the availability indexes were best correlated with nitrogen uptake of rice followed by N% in rice plants at 55 days after seeding. Dry-matter yield of rice was also significantly correlated with the available nitrogen status but the correlation coefficients were the lowest. It is concluded that for unfertilized soils, nitrogen uptake provides a better criterion for evaluating the performance of nitrogen availability indexes for wetland rice.

Determination of lead by continuous-flow hydride generation and atomic absorption spectrometry: Comparison of malic acid—dichromate, nitric acid—hydrogen peroxide and nitric acid—peroxodisulfate reaction matrices in combination with sodium tetrahydroborate

A continuous-flow hydride generator is combined with a heated quartz tube atomizeratomic absorption spectrometer system for the trace determination of lead. Malic acid K 2Cr 2O 7, HNO 3—H 2O 2 and HNO 3—(NH 4) 2S 2O 3 are all effective for plumbane generation by means of sodium tetrahydroborate. The relative merits of these systems are investigated in terms of sensitivity, efficiency of plumbane generation and interferences. The sensitivities (0.0044 absorbance) obtained under the recommended conditions for the three systems are 3.2, 1.7 and 1.1 ng Pb ml -1, respectively, whereas plumbane generation efficiencies are 33%, 47% and >80%, respectively, for 1 μg Pb ml -1. Silver, Au, Cu and Cd interfere seriously in all reaction systems. A dithizone extraction and back-extraction method is utilized to eliminate interfering ions, followed by reduction of the resulting solution in the peroxodisulphate system. The proposed method is applied to water samples and NBS 1566 oyster tissue.

The oxidation of secondary alcohols with Cr(VI): A kinetic investigation of steric strain

A titrimetric method for the determination of the rate of acid dichromate oxidation of a series of secondary alcohols; using and excess of the alcohol substrate, pseudo first-order rate constants can be calculated from which estimates of the relative steric strain within these molecules may be obtained.

The determination of chemical oxygen demand in waste-waters with dichromate by flow injection analysis

A simple method is described for the continuous determination of chemical oxygen demand (COD) in wastewater samples by flow injection analysis. Samples are injected into a water stream which merges with an acidic dichromate carrier solution. After reaction in a PTFE coil at 120°C, absorbances are measured at 445 nm. D-Glucose is satisfactory as a standard substance for COD in a variety of wastewaters. A sampling rate of 15 samples per hour can be achieved, and the detection limit and precision are 5 mg l -1 as COD and 0.4%, respectively. Chloride concentrations of ⩾ 100 mg l -1 interfere slightly unless silver and/or mercury salts are added. COD values for various wastewater samples correlate well with those obtained by standard methods using dichromate or permanganate.

Determination of content of anti-icing additives by indicator liquid chromatography

The content of anti-icing additive (AIA) in jet fuels is determined either refractometrically (according to the change in refractive index of water after it has extracted the additive from the fuel) or by a dichromate method (according to the change in color of an aqueous extract from the fuel after a solution of potassium dichromate and sulfuric acid is added). Points out that the first of these methods is not suitable for the analysis of fuels under field conditions, and the second is not suitable for use in the winter. Uses indicator liquid chromatography as a basis for the development of a rapid method for the determination of the content of AIA in jet fuels under any conditions, including wintertime operations at airports and temporary landing fields. Finds that the chromatographic method gives better precision indexes over a wide range of temperatures; it requires less fuel for analysis; and there is no need for complex apparatus, nor for the water and aqueous solutions of potassium dichromate and concentrated sulfuric acid, items that make it difficult to determine the AIA content at subfreezing temperatures.

Simple modification of the Walkley-Black method for simultaneous determination of organic carbon and potentially mineralizable nitrogen in tropical rice soils

A modified version of the Walkley — Black method of organic C determination is described, which allows simultaneous determination of organic C and potentially mineralizable N in soils. As usual the organic matter of the soil is oxidized by acid dichromate reagent by heat of dilution. The excess of chromate left after C oxidation is titrated with standard ferrous sulfate solution instead of ferrous ammonium sulfate to avoid contamination due to NH4 +. The NH4 + released due to oxidative action of acid dichromate is determined by distilling a suitable aliquot from the known volume with 50% of NaOH solution. The ammonium released by this method with 15 surface soils showed highly positive correlations with organic C (r=0.969**), total N (r=0.976**) and the NH4 + produced under waterlogged conditions (r=0.985**). The modification is very simple and is easily adaptable for estimation of potentially mineralizable N in soils alongwith organic C determination.

Assay of nitrogen supplying capacity of tropical rice soils

The nitrogen supplying capacity of 39 wetland rice soils evaluated by two anaerobic incubation methods and six chemical methods was compared with N uptake of IR 26 rice grown on these soils under flooded conditions in a greenhouse pot study. The uptake of N by rice correlated highly with the N supplying capacity determined by anaerobic incubation methods involving incubation of soils at 30°C for 2 weeks (r=0.84**) or at 40°C for 1 week (r=0.82**) as well as with the organic carbon (r=0.82**) and total N (r=0.84**) contents of soils. Among the chemical indexes, available N determined by the oxidative release of soil N by alkaline permanganate, acid permanganate, acid dichromate and hydrogen peroxide also provided good index of soil N availability to rice. According to these results soil organic carbon and total N contents seem to be good indexes of available nitrogen in tropical wetland rice soils.

Evaluation of some chemical indexes for predicting mineralizable nitrogen in tropical rice soils

Abstract Five chemical indexes were evaluated for predicting mineralizable nitrogen in 39 rice soils from the Philippines having a wide range in texture, pH and organic matter. The indexes evaluated were based on oxidative release of soil ammonium‐N by alkaline permanganate, acid permanganate, acid dichromate, hydrogen peroxide and dilute sulfuric acid. The amounts of mineralizable N obtained by the chemical indexes were correlated to varying degrees with those determined by anaerobic incubation methods. The basis of good agreement for mineralizable N determined by chemical arid biological indexes appears to be due to the fact that both derive the mineral N from the pool of organic nitrogen in soils. The support for this conclusion was obtained by highly significant correlations between mineralizable N determined by chemical and biological indexes with soil organic C and total N contents of soils. These results alongwith other evidence suggest that the chemical indexes may be useful for predicting pools o...

Alcohol determination in the clinical laboratory.

Four methods for blood-alcohol analysis--gas chromatography, enzymatic oxidation with alcohol dehydrogenase, chemical oxidation with acid dichromate, and osmometry--are briefly reviewed from the point of view of the clinical laboratory. Advantages and limitations of these methods are discussed, and their key features are tabulated. The correlation of the results of blood-alcohol analyses with stages of alcoholic influence and their corresponding signs and symptoms is presented in tabular form.

Automatic method for the determination of total mercury in fresh and saline waters and sediments

Acid—dichromate and ultraviolet digestion are used sequentially in an automated system to extract mercury from particulate matter and oxidize organomercurials in briny waters and sediments. Mercury is then determined by reduction with tin(II) and cold-vapor atomic absorption spectrometry. The flow-through system is completely automatic and can accommodate samples with particulate solids up to 1 g l -1. The detection limit is 0.02 μg Hg l -1 in water or 20 μg Hg kg -1 in sediments. Both waters and sediments with high chloride levels can be analysed without interference at a rate of 30 samples per hour.

Reference Materials for Ultraviolet Spectrophotometry: Further Comments

Abstract The influence of temperature variations and uncorrect positioning of the cuvette in its holder on the accuracy of absorbance measurements was thoroughly discussed in the case of potassium dichromate and nicotinic acid solutions to be used as reference materials for the periodic control of spectrophotometers. Results showed that temperature control to within ± 0.5 °C is sufficient. On the other hand, the error connected with cell positioning was found to be negligible under the usual working conditions. Finally, the effect of the purity degree on the absorbance values of the above substances was investigated.