Peter N. Keliher

Some hydride generation inter-element interference studies utilizing atomic absorption and inductively coupled plasma emission spectrometry

Abstract Three commercially available hydride generation devices have been used in conjunction with atomic absorption spectrometry and inductively coupled plasma emission spectrometry to study the possible inter-element interferences from fifty elements. Nineteen of these elements caused signal reductions of at least 10%. These interferences were reduced (drastically in some cases) by an appropriate choice of hydride generation system and by manipulation of the acid strength.

Some atomic absorption hydride generation inter-element interference reduction studies utilizing ion exchange resins

Abstract Ion exchange resins were used to reduce interelement interferences during the hydride generation flame atomic absorption determination of arsenic and selenium. Commercially available resins provided a means to significantly reduce the interferent to analyte ratio for several of the interfering elements. The procedure was successfully applied to highly polluted environmental samples.

Study of organic interferences in the spectrophotometric determination of nitrite using composite diazotisation-coupling reagents

A study was made of organic interferences in the spectrophotometric determination of nitrite by the diazotisation-coupling technique using three composite reagents [sulphanilamide and N-(1-naphthyl)ethylenediamine (NED); sulphanilic acid and NED; and 4-nitroaniline and NED]. Many organic substances interfere, usually causing low results. The interference is usually less with the 4-nitroaniline-NED and sulphanilamide-NED methods than with the sulphanilic acid-NED method. The interferents tested included aliphatic amines (primary, secondary and tertiary), aromatic amines (primary, secondary and tertiary), various phenolic compounds and miscellaneous organic compounds (sucrose, dextrose, lactic acid, succinic acid, acetamide, acetanilide, ethylenediamine tetraacetate, cholesterol, rennin, dodecyl sodium sulphate, acetophenone, urea, citric acid, caffeine, saccharin, morpholine, L-asparagine, gelatin, benzoic acid, formaldehyde, cinchonine, nicotinic acid, trypsin, creatine, starch, albumin, gum tragacanth, casein, formic acid, sorbic acid, ascorbic acid and acetaldehyde). The effect of detergents and soap was also examined. Large amounts of water-miscible solvents (methanol, ethanol, acetone and glycerin) can be tolerated. Water-immiscible solvents do not affect the colour.

Inorganic interferences in the 2,4-xylenol spectro-photometric method for nitrate and their elimination

Abstract A study of inorganic interferences with the 2,4-xylenol spectrophotometric method for nitrate and their elimination is reported. Fifty-three substances do not interfere with the original method. Nitrite interferes somewhat by producing a faint yellow color. Certain reducing agents (Fe 2+ , S 2- , S 2 O 3 2- , and SCN - ) cause low results by reducing the nitrate in the strong sulfuric acid solution, while some oxidizing agents (Mn 7+ , Cr 6+ , V 5+ , and ClO 3 - ) cause low results by inactivating or destroying the 2,4-xylenol. Persulfate and small amounts of H 2 O 2 produce a slight deepening of the color; larger amounts of H 2 O 2 ; cause low results, as do Cl - , Br - , I - , and metals. The recommended maximum permissible limits (mg per 10-ml aliquot) for the original method are NO 2 - -N, Fe 2+ , S 2- , SCN - , V 5+ , ClO 3 - , Cl - , I - , 0.2; Mn 7+ , Cr 6+ , S 2 O 8 2- , 5; H 2 O 2 , 0.02; S 2 O 3 2- , Br - , 0.1; metals, none. Procedures for the elimination of most of the interferences are described. Nitrite is destroyed with sulfamic acid. The interferences of reductants (Fe 2+ , S 2- , S 2 O 3 2- , and SCN - ) and oxidants (Mn 7+ and Cr 6+ ) are eliminated with hydrogen peroxide, the excess of which (and S 2 O 8 2- ) is destroyed by boiling in the presence of Fe 3+ . The interference of Cl - , Br - , and I - is eliminated by precipitation with silver sulfate. An alternative to the sulfamic acid procedure is to oxidize nitrite to nitrate with peroxide and deduct NO 2 - -N from the total NO 3 - -N. After elimination of interferences, a 10-ml aliquot of sample solution is treated with 17.0 ml of sulfuric acid and 2,4-xylenol, the 6-nitro-2,4-xylenol is steam-distilled into an ammonia—water—isopropanol mixture, and the yellow color is measured.

Study of the behaviour of various phenolic compounds in the 4-aminoantipyrine and ultraviolet-ratio spectrophotometric methods without and with distillation.

It is customary in industrial analysis in the determination of phenols by the 4-aminoantipyrine (4-AAP) and ultraviolet-ratio spectrophotometric methods to report the total of phenolic compounds as phenol. A study was therefore made of the behaviour of 36 representative phenolic compounds in the 4-AAP and UV-ratio methods, with and without distillation, to ascertain the apparent recoveries relative to that for phenol. The Fisher phenol analyser was used for the UV-ratio method, which depends upon the bathochromic shift (from about 270 to about 290 nm) usually obtained when the solution of the phenol is made alkaline. The apparent recoveries by the 4-AAP method both with and without distillation varied from 0 to 100%. The apparent recoveries by the UV-ratio method without distillation varied from 0 to 148%, and those with distillation varied from 0 to 110%. Sixteen of the compounds tested without distillation gave less than 10% recovery by the 4-AAP method and eleven gave less than 10% recovery by the UV-ratio method. The results after distillation indicated that several of the compounds did not distil completely.

Interference of ascorbic and isoascorbic acids in the spectrophotometric determination of nitrite by the diazotisation - coupling technique

The problem of the interference of ascorbic and isoascorbic acids in the spectrophotometric determination of nitrite by the diazotisation-coupling technique is important because these substances are frequently added to cured meats containing nitrite. The chemistry of the reaction of ascorbic and isoascorbic acids with nitrite is discussed. The effect of pH on the reaction at room temperature and on digestion at 80 °C was investigated. Two composite diazotisation-coupling reagents [sulphanilamide and N-(1-naphthyl)ethylenediamine; 4-nitroaniline and N-(1-naphthyl)ethylenediamine] were used in this investigation. At room temperature 1 mg of ascorbic or isoascorbic acid (per 50 ml) interfered only slightly or moderately at pH 10 and 12 but interfered very significantly at pH 8 and below. When solutions at pH 8, 10 and 12 were heated at 80 °C for 1 h, satisfactory recovery was obtained in the presence of 2.5 mg of ascorbic or isoascorbic acid (per 50 ml). A study of the stability of pure nitrite solutions indicated that solutions at pH 6.5, 8, 10 and 12 show no decomposition after standing at room temperature for 24 h. The solutions at pH 8, 10 and 12 showed no significant decomposition on heating at 80 °C for 2 h. A tentative method is proposed for the determination of nitrite in cured meats containing ascorbic or isoascorbic acid, whereby a slurry of 5 g of the sample in 0.01 M sodium hydroxide is digested at 80 °C for 90 min, zinc sulphate is added as a clarifying agent, the volume is made up to 250 ml, the solution is filtered and nitrite in an aliquot of the filtrate is determined.

Effect of acidity and alkalinity on the distillation of phenol: interferences of aromatic amines and formaldehyde with the 4-aminoantipyrine spectro-photometric method for phenol

Abstract As determined by the 4-aminoantipyrine (4-AAP) spectrophotometric method, the distillation of phenol is quantitative over the range from about pH 6 to very strongly acidic solutions. Recovery from alkaline solutions decreases with increasing alkalinity. Aromatic amines can interfere with the 4-AAP method by producing colors. The extent of the interference varies markedly with different aromatic amines and is much greater for the extraction method than the direct method. The interference can be considerably reduced by distillation from a strongly acidic solution (10 ml of concentrated sulfuric acid per 500 ml); for large amounts of aromatic amines, double distillation may be necessary. Formaldehyde can interfere by reacting with phenol and repressing the color development. This interference can be eliminated by treatment with ammonium sulfate and sodium hydroxide to form hexamethylenetetramine, followed by acidification and distillation.

Spectral Line Profile Measurements from Calcium, Silver, and Aluminum Hollow Cathode Lamps

There has recently been a great deal of interest in the direct measurement of atomic spectral line profiles from sources which are commonly used in atomic absorption (AAS) and atomic fluorescence spectrometry (AFS), e.g., hollow cathode lamps (HCLs), electrodeless discharge lamps (EDLs), and vapor discharge lamps (VDLs). Knowledge of spectral line profiles is of great importance in theoretical AAS and AFS studies.

Observations on arsenic and selenium determinations using hydride generation atomic absorption and/or plasma emission spectrometry

Abstract Regulatory and environmental concerns have made the determination of trace amounts of arsenic and selenium extremely important. Selenium is an essential trace nutrient while arsenic is a cumulative poison. Unlike synthetic organic chemicals, these “heavy metals,” of course, are not man-made. Environmental pollution problems associated with these elements, therefore, are the result of redistribution of naturally occurring elements by agricultural and industrial processes.

Organic interferences and their elimination in the 2,4-xylenol spectrophotometric method for nitrate

Abstract The 2,4-xylenol spectrophotometric method for nitrate involves formation of 6-nitro-2,4-xylenol, which is steam-distilled into an ammonia—water—isopropanol mixture. The yellow color of the ammonium salt of 6-nitro-2,4-xylenol is measured at 455 nm. A detailed study of the possible interferences from 123 representative organic compounds is described; 61 compounds interfered (when present in amounts of 0.1 g in the original sample). The interfering compounds can be classified according to their mode of interference: (1) compounds that are readily nitrated or oxidized by nitrate in the sulfuric acid medium used cause low results; (2) compounds containing the ONO 2 group that hydrolyze to nitrate cause high results; (3) compounds that steam-distil to produce colored solutions; (4) compounds that steam-distil to produce turbid solutions; (5) compounds that hydrolyze, either in water or sulfuric acid solution, to produce inorganic ions or compounds (e.g. Cl - , S 2- , and H 2 O 2 ) that repress the color development. Three procedures are described for the elimination of the interferences: (1) oxidation of the organic compound with permanganate, reduction of the excess of permanganate with hydrogen peroxide, and destruction of the peroxide by boiling in the presence of Fe(III) catalyst (this is unsuitable for organic compounds containing nitrogen, as there is invariably some oxidation to nitrate); (2) extraction of interfering organic compounds with methyl isobutyl ketone; (3) precipitation—adsorption method involving treatment with zinc sulfate and sufficient sodium hydroxide to precipitate most of the zinc as zinc hydroxide, addition of 3 g of activated carbon, digestion at 55–65°C for 20 min. cooling, dilution, and filtration. Method (3) is applicable to all organic compounds tested except formaldehyde. The amount of organic compound used to test the methods was normally 0.25 g in the solution being treated.