PubMed Health⌕ Search

Biomedical subjects

W Holak

Publications and source records attributed to W Holak.

At least 19 recordsLinked to original sources
PubMed1994

Determination of selenium in food supplements by differential-pulse cathodic stripping voltammetry in the presence of added copper.

Selenium was determined by cathodic stripping voltammetry in a 1 mol l-1 HCl acid solution containing added CuII. In this medium, selenium was preconcentrated on the hanging mercury drop electrode and stripped cathodically in differential-pulse mode. After a deposition period of 1 min, 0.2 ng ml-1 of selenium could be detected. The method was applied to the analysis of food supplements. Total selenium was determined after digestion of the sample with HNO3-HClO4 and reduction to the electroactive SeIV by heating with HCl. Inorganic selenium (i.e., selenite and selenate) was similarly determined after extraction with dilute sodium hydroxide solution and clean-up on activated carbon. Representative over-the-counter preparations have been analysed.

Copper↗
PubMed1983

Atomic absorption spectrophotometric determination of mercury in mercury-containing drugs: collaborative study.

An atomic absorption spectrophotometric (AAS) method applicable to a wide variety of mercury-containing drugs has been developed and subjected to a collaborative study. Samples were digested with a water-HCl-HNO3 (4 + 3 + 1) mixture, and the mercury was determined in solution by AAS. High levels of mercury were measured with a conventional air-acetylene flame, whereas low levels were measured by the flameless technique. Each of 7 collaborators received duplicate synthetic samples of a tincture, an ophthalmic solution, and an antiseptic solution, and duplicate commercial samples of an ointment and an injectable. The overall mean value found by collaborators for mercury in these samples was 100.13%. The corresponding overall repeatability SD (CV, %) and reproducibility SD (CV, %) values were 2.18 (2.18) and 3.38 (3.38), respectively. The proposed AAS method has been adopted official first action.

Mercury↗
PubMed1983

Determination of copper, nickel, and chromium in foods.

A collaboratively studied method for Pb, Cd, As, Se, and Zn that uses a closed system digestion technique has now been extended to include 3 additional elements, Cu, Ni, and Cr. Cu is determined by either atomic absorption spectrophotometry or anodic stripping voltammetry, depending on the concentration. Ni and Cr are determined by differential pulse polarography. Analysis of National Bureau of Standards reference materials by this procedure gives values in close agreement with the accepted values. Recoveries from applesauce and chicken spiked at 0.6-4 micrograms/g are in the 92-101% range. The sensitivity of the multielement procedure is 0.34, 0.14, and 0.24 microgram/g for Cu, Ni, Cr, respectively, at the 90% confidence level.

Chromium↗
PubMed1982

Differential pulse polarographic determination of iodine in thyroid tablets: collaborative study.

A differential pulse polarographic (DPP) method for the determination of iodine in thyroid and thyroid preparations was collaboratively studied by 8 laboratories. The overall concentration of iodine in commercial thyroid tablets containing 1/4, 1,2, and 5 gr. of declared thyroid was 0.196%. The overall repeatability and reproducibility standard deviations were 0.0043 and 0.0067, respectively, and the corresponding coefficients of variation were 2.18 and 3.41%, respectively. The results obtained by the DPP method agreed with those obtained by the U.S. Pharmacopeia XX method at the various concentrations of declared thyroid studied. The DPP method has been adopted official first action.

Iodine↗
PubMed1980

Differential pulse polarographic determination of colchicine.

A differential pulse polarographic method for the analysis of colchicine-containing dosage forms is described. The reduction of the tropolone carbonyl is useful for quantitative analysis in that the relationship of the colchicine concentration to the current is linear over the concentration range of 0 to approximately 50 micrograms/ml, with a slight negative deviation at higher concentration. The procedure involves no preliminary treatment, is simple and specific, and is applicable to the assay of composite tablets, individual tablets, and injectable solutions. Polarography is conduction on a solution of colchicine in pH 1.81 Britton-Robinson buffer with 0.01% alkylphenoxy polyethoxyethanol. The quantitative analysis is achieved using the method of standard addition. A relative standard deviation of 3.2% was obtained for tablets. The results agree with those obtained using the USP XIX method.

Colchicine↗
PubMed1980

Differential pulse polarographic determination of saccharin in foods: collaborative study.

An improved differential pulse polarographic method for the determination of saccharin in foods has been developed. The sample (if solid) is blended with water; an aliquot is acidified with HCl, mixed with Celite, transferred to a chromatographic column, and eluted with chloroform. After chloroform is evaporated with a current of air, the residue is dissolved in 0.1N NaOH, and an aliquot is polarographed in a supporting electrolyte composed of 0.1N HCl, 0.1N KCl, and 0.1% tetrabutylammonium bromide. The method is sensitive, relatively precise, and applicable to a wide variety of foods. A collaborative study has been conducted and the results indicate average recoveries of 101.5, 99.8, 96.9, and 95.3%, respectively, for samples containing saccharin from 0.028 to 1.4%. The method has been adopted as official first action.

Food Analysis↗
PubMed1980

Analysis of foods for lead, cadmium, copper, zinc, arsenic, and selenium, using closed system sample digestion: collaborative study.

A method for the determination of cadmium, lead, copper, arsenic, selenium, and zinc is presented. This method involves digesting a food sample with nitric acid under pressure and using aliquots of the solution for analysis by suitable techniques. Cadmium, lead, and copper are determined by anodic stripping voltammetry (ASV) after heating with equimolar sodium nitrate/potassium nitrate; arsenic and selenium are determined by atomic absorption spectrophotometry (AAS) after generation of their respective hydrides; zinc is determined by conventional AAS. The combined recoveries and reproducibilities (CVR) of the collaborative study on this multi-element analysis are: Cd, 89.14 (17.65) at 0.10-1.0 microgram/g; Zn, 96,53 (5.59) at 16.7 and 66.7 microgram/g; As, 99.50 (17.02) at 0.5 and 2.0 microgram/g; Se, 95.17 (16.52) at 0.5 and 2.0 microgram/g; Pb, 92.57 (15.22) at 0.3-3.0 microgram/g; Cu, 108.39 (18.30) at 1.0-10.0 microgram/g. The method has been adopted as official first action for cadmium, lead, arsenic, selenium, and zinc.

Arsenic↗
PubMed1979

Differential pulse polarographic analysis of thyroid hormone: determination of iodine, thyroxine, and liothyronine.

A differential pulse polarographic method for the analysis of thyroid and thyroid tablets for total iodine, thyroxine, and liothyronine is described. The procedure for iodine, which is also applicable to individual tablet assay, consists of ashing the sample, coverting iodide to iodate, and analyzing by differential pulse polarography. The procedure for thyroxine and liothyronine involves hydrolysis of the sample with barium hydroxide and isolation and separation of the iodoamino acids using ion exchangers, followed by differential pulse polarographic determination in a supporting electrolyte composed of 0.5 N Na2CO3 in 20% 2-propanol containing 1% tetrabutylammonium bromide. The differential pulse polarographic results for iodine agree with values obtained using the USP XIX procedure, and the quantities of thyroxine and liothyronine found agree with literature values.

Iodine↗
PubMed1977

Temperature-programmable furnace for ashing of foods in trace metal analysis.

The use of programmable furnace in preparing samples for determining cadmium, lead, copper, and zinc by differential pulse anodic stripping voltammetry or atomic absorption spectrophotometry is convenient and time-saving. Recovery data for these 4 metals in various foods (tuna, sardines, and milk) were 93-96% for 0.01-1 ppm cadmium, 96-114% for 0.05-5 ppm lead, 100-108% for 2-10 ppm copper, and 97% for 10 ppm zinc.

Animals↗
PubMed1976

Collaborative study of effect of light on cadmium and lead leaching from ceramic glazes.

A limited interlaboratory study was carried out to determine the effect of lighting conditions on the release of cadmium from ceramic glazes by 4% acetic acid. Cadmium release increased with increased exposure to light. Further interlaboratory study on plates manufactured under controlled conditions showed that if temperature, intensity of illumination, and time of exposure are specified, reproducible results for leaching of both lead and cadmium can be obtained. A modification of the official AOAC method, 25.031-25.034, to increase sensitivity was collaboratively studied by 8 laboratories. Each received 6 solutions of lead in 4% acetic acid (3 sets of blind duplicates at the 0.1, 0.5, and 0.8 mug/ml levels) plus a reagent blank. Average recoveries were 0.1006, 0.5056, and 0.8194 mug/ml, respectively, with coefficients of variation of 11.4, 3.3, and 2.8%, respectively. The proposed modification has been adopted as official first action, and a parameter for exposure to light during extraction has been included in the method.

Cadmium↗
PubMed1976

Drugs. Differential pulse polarography of cacodylate injections.

A method was developed for the analysis of cacodylate injections, using differential pulse polarography for measuring As(III). The cacodylate molecule is decomposed to As(V) by heating with Mg(NO3)2.6H20; As(V) is then chemically reduced to As(III) and polarographed in 1M HCl supporting electrolyte. The method of standard addition is used for quantitation. Recoveries based on the analysis of synthetic cacodylic acid solutions containing approximately 9 mg arsenic/ml ranged from 99.1 to 101.7%.

Arsenic↗
PubMed1975

Collaborative study of the determination of boric acid in caviar by emission spectroscopy.

Caviar samples were spiked at the 0.1 and 0.2% levels and digested with nitric acid in a closed Teflon-lined digestion vessel to prevent volatility losses. The boron was complexed with 2-ethyl-1,3-hexanediol and extracted into methylisobulty ketone. The emission of the boron oxide band was measured in a nitrous oxidehydrogen flame. The mean recoveries at the 0.1 and 0.2% levels for 6 collaborators were 95.7 and 97.1%, respectively.

Boric Acids↗
PubMed1975

Determination of heavy metals in foods by anodic stripping voltammetry after sample decomposition with sodium and potassium nitrate fusion.

A method is described for the simultaneous determination of several heavy metals in foods. The sample is predigested with nitric acid and decomposed completely by heating with a mixture of sodium and potassium nitrates. The resultant melt containing the metals is then dissolved in dilute nitric acid. After the pH is adjusted to an appropriate value, the metals, such as cadmium, copper, lead, and zinc, are determined by anodic stripping voltammetry. The average recoveries of these metals added to 5 commodities were 98, 98,96, and 104%, respectively. The relative standard deviations, based on data from analyses of a commodity containing measurable levels of copper, lead, and zinc, were 12.0, 13.0, and 9.7%, respectively.

Cadmium↗