Determination of Total and Free Selenium in Vulcanizates

1936 ◽  
Vol 9 (1) ◽  
pp. 167-171
Author(s):  
E. Cheraskova ◽  
L. Veisbrute
Keyword(s):  
Nitric Acid ◽  
Sodium Sulfite ◽  
Iodometric Titration ◽  
Hydrazine Sulfate ◽  
Sulfurous Acid ◽  
Aqueous Sodium ◽  
Rubber Compounds ◽  
Sulfite Solution ◽  
Total Selenium

Abstract The total selenium in rubber compounds may be determined by disintegrating with nitric acid and then separating the selenium by reducing the nitric acid solution with hydrazine sulfate, or by reducing with sulfurous acid after evaporation of the nitric acid. Free selenium is determined by extracting the rubber with aqueous sodium sulfite, from which selenium is precipitated by formalin. Free sulfur is determined volumetrically by iodometric titration after precipitating selenium from sulfite solution.

DETERMINATION OF TRACE AMOUNTS OF SILVER IN GALENA ORES

1960 ◽  
Vol 38 (9) ◽  
pp. 1488-1494 ◽  
Author(s):  
E. J. Bounsall ◽  
W. A. E. McBryde
Keyword(s):  
Aqueous Solution ◽  
Nitric Acid ◽  
Sodium Chloride ◽  
Hydrochloric Acid ◽  
Chloride Solution ◽  
Sodium Chloride Solution ◽  
Silver Content ◽  
Aqueous Sodium Chloride Solution ◽  
Aqueous Sodium

An analytical method is described for the determination of microgram amounts of silver in galena ores, based on the "reversion" of silver dithizonate. Silver is separated from relatively large amounts of lead by extraction as dithizonate into chloroform from an aqueous 1:99 nitric acid solution. Separation from mercury, which is also extracted under these conditions and would, if present, interfere in the analysis, is achieved by reverting the dithizonate solution with a 5% aqueous sodium chloride solution which is also 0.015 molar in hydrochloric acid. Following dilution of this aqueous solution and adjustment of pH, silver is again extracted into chloroform as the dithizonate, and determined absorptiometrically. Analyses of a number of galena ore samples showed a precision of within 3% for a silver content ranging from 0.03 to 0.4%.Some other methods for isolating silver from these samples, which were tried but found unsatisfactory, are discussed.

scholarly journals A comparison of different methods to remove dissolved oxygen: Application to the electrochemical determination of imidacloprid

2015 ◽  
pp. 149-155 ◽  
Author(s):  
Ana Djurovic ◽  
Zorica Stojanovic ◽  
Snezana Kravic ◽  
Zvonimir Suturovic ◽  
Tanja Brezo ◽  
...  
Keyword(s):  
Glassy Carbon ◽  
Chemical Method ◽  
Sodium Sulfite ◽  
Physical Method ◽  
Electrochemical Determination ◽  
Carbon Electrode ◽  
Nitrogen Stream ◽  
Sulfite Ion ◽  
Sulfite Solution

This study compares different methods for the removal of oxygen from the solution prior to the chronopotentiometric determination of the insecticide imidacloprid on glassy carbon electrode. The research included the application of the chemical method involving addition of sulfite ion, and the physical method of purging the sample with nitrogen stream, as well as their combination. By comparing analytical signals of imidacloprid, chemical method showed almost the same efficiency as conventional physical method, while the best reproducibility was achieved by applying chemical method with addition of the saturated sodium sulfite solution. The method is very simple and can be applied for deoxygenation of the solution prior to the chronopotentiometric analysis. The application of the chemical deoxygenation significantly shortened duration of the chronopotentiometric analysis of imidacloprid from approximately 15 min to 1 min.

Microanalytical Determination of Bromine, Chlorine, and Iodine by Oxygen Flask Combustion

1965 ◽  
Vol 48 (4) ◽  
pp. 709-717
Author(s):  
Al Steyermark
Keyword(s):  
Hydrogen Peroxide ◽  
Organic Compounds ◽  
Iodometric Titration ◽  
Hydrazine Sulfate

Abstract Thirty collaborators participated in a study of the use of oxygen flask combustion for the microdeterminations of bromine, chlorine, and iodine in organic compounds. Generally, there was little difference in the precision of the various methods. Argentometric titration gave better results than did iodometric titration only in the case of bromine. The use of hydrazine sulfate gave better results in the case of iodine than when it was omitted; the same held true for hydrogen peroxide. It is recommended that the study be continued.

Method for the Determination of Total Selenium in a Wide Variety of Foods Using Inductively Coupled Plasma/Mass Spectrometry

2013 ◽  
Vol 96 (4) ◽  
pp. 786-794 ◽  
Author(s):  
Darryl Sullivan ◽  
Richard Zywicki ◽  
Mark Yancey
Keyword(s):  
Nitric Acid ◽  
Infant Formula ◽  
Inductively Coupled Plasma ◽  
Microwave Digestion ◽  
High Volume ◽  
Powdered Infant Formula ◽  
Inductively Coupled ◽  
Plasma Mass Spectrometry ◽  
Total Selenium

Abstract An optimized method for use in a high volume laboratory was developed and validated for the determination of total selenium in a wide variety of food products including infant formula. The method utilizes a single-stage, closed-vessel microwave digestion procedure with nitric acid. Upon completion of digestion, the solution is brought to volume with water. A dilution is prepared for analysis by adding methanol (MeOH) to an aliquot and then brought to volume by nitric acid diluent resulting in a 3% MeOH concentration. The amount of selenium is determined by inductively coupled plasma (ICP)/MS with the capability of removing argon-based polyatomic interferences. Experiments were conducted to validate the method by determining precision, accuracy, linearity, specificity, ruggedness, and robustness. The calculated practical reporting level for this method was 25.0 μg/kg. The method provided an average RSD of 2.03% during analysis of a wheat flour reference material and 2.73% during analysis of a powdered infant formula. The accuracy of the method for these materials was 98.6 and 105%, respectively. The method has also been used successfully on a variety of foods from various categories including fruits, grains, vegetables, protein, and dairy.

Determination of Free Sulfur in Hard Rubber

1955 ◽  
Vol 28 (4) ◽  
pp. 1221-1225 ◽  
Author(s):  
C. Wynne-Evans
Keyword(s):  
Sodium Sulfite ◽  
Volumetric Method ◽  
Aqueous Sodium ◽  
Free Sulfur

Abstract The volumetric method for the determination of sulfur by means of aqueous sodium sulfite has been adapted for the determination of free sulfur present in hard-rubber vulcanizates. This work was carried out because there was not a speedy free sulfur method applicable to hard rubbers, and the investigation has shown that, by the use of aqueous sodium sulfite, it is possible to obtain reliable and extremely accurate free sulfur results in a little over three hours, against the usual three to four days by other methods which are discussed.

Photolysis of p-benzoquinone and p-chloranil in aqueous sodium sulfite solution

2011 ◽  
Vol 45 (3) ◽  
pp. 210-213 ◽  
Author(s):  
V. L. Ivanov ◽  
S. Yu. Lyashkevich
Keyword(s):  
Sodium Sulfite ◽  
Aqueous Sodium ◽  
Sulfite Solution

Determination of Free Sulfur in Stocks Cured with Sulfur Containing Accelerators

1962 ◽  
Vol 35 (2) ◽  
pp. 498-500
Author(s):  
E. P. Khehaskova ◽  
N. A. Okhapkina ◽  
V. N. Provorov
Keyword(s):  
Sodium Sulfite ◽  
Sodium Stearate ◽  
Cadmium Acetate ◽  
Strontium Nitrate ◽  
Vulcanized Rubber ◽  
Normal Method ◽  
Sulfur Containing ◽  
Sulfite Solution ◽  
Free Sulfur

Abstract For the determination of free sulfur in vulcanized rubber the normal method is the sulfite method, consisting of the heating of a sample of rubber with a solution of sodium sulfite. The free sulfur reacts with the sulfite, forming thiosulfate, which is determined by iodometric titration. The unreacted excess of sulfite is removed with formalin. The method gives good results in the analysis of stocks which do not contain sulfur-containing accelerators. In the presence of these accelerators the results are high: in some cases the method is quite inapplicable, as it is impossible to establish the endpoint of titration accurately. This may be explained by the circumstance that the accelerators and the products of their decomposition during vulcanization can pass into the solution of sodium sulfite and react further with the iodine. The method of determination of free sulfur proposed by Hardmann, consisting of the acetone extraction of the rubber in the presence of copper gauze, is protracted and complicated. A certain improvement in the sulfite method of Bolotnikov and Gurova was introduced in the ASTM method (1952). Sodium stearate is added to the sodium sulfite solution for better wetting of the rubber, and a certain amount of paraffin to prevent the formation of foam. After termination of heating the solution the stearic acid is precipitated with strontium nitrate and certain accelerators with cadmium acetate. For the majority of stocks this method gives correct results, but in a number of cases it is difficult to establish the end of titration at all.

scholarly journals Determination of Selenium in Urine by Hydride Generation Atomic Absorption Spectrometry

1996 ◽  
Vol 79 (3) ◽  
pp. 773-776 ◽  
Author(s):  
Miguel Navarro ◽  
Herminia Lopez ◽  
Maria C Lopez ◽  
Vidal Perez
Keyword(s):  
Nitric Acid ◽  
Atomic Absorption Spectrometry ◽  
Atomic Absorption ◽  
Hydride Generation ◽  
Absorption Spectrometry ◽  
Acid Mixture ◽  
Acid Digestion ◽  
Daily Diet ◽  
Total Selenium

Abstract A procedure has been developed for determination of total selenium in urine by hydride generation atomic absorption spectrometry. Mineralization was performed with a nitric acid–perchloric acid mixture on a thermostated digestion block. The method was validated by comparison with the method involving mineralization in a microwave acid digestion bomb containing nitric acid and small amounts of vanadium pentoxide. Se(VI) was reduced to Se(IV) by dissolution in 7N HCI. Sample recoveries, precision studies, and analyses of a certified reference material demonstrated the reliability and accuracy of this technique. Urine samples had selenium concentrations ranging from 4.6 to 50.3 μg/L. These values correspond to an average of 54.9 μg per person per day total ingested and bioavailable Se in the daily diet.

Differential Pulse Polarographic Determination of Total Iodine in Milk

1982 ◽  
Vol 65 (1) ◽  
pp. 20-23
Author(s):  
A Ralph Curtis ◽  
Percy Hamming
Keyword(s):  
Standard Deviation ◽  
Sodium Sulfite ◽  
Differential Pulse ◽  
Differential Pulse Polarography ◽  
Polarographic Method ◽  
Total Iodine ◽  
Pulse Polarography ◽  
Sulfite Solution ◽  
Different Levels

Abstract A differential pulse polarographic method for total iodine in milk is presented. Samples are ashed, sodium hypochlorite is added to oxidize iodide to iodate, and the product is mixed with sodium sulfite solution and measured by differential pulse polarography at μ90 V against SCE. The standard deviation for 53 duplicate samples was 0.011. Average recovery for 10 or more samples at different levels was 98.6% with a standard deviation of 2.9%.

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