Strontium interference

Direct Metal Analyses. Calcium ion can be detected to a lower limit of 10 M hy Aequorea bioluminescence. Strontium interferes to a minor extent (270,271). 

In most cases where strontium interference was evaluated, a positive interference was found, but the degree of correction (of the calcium titre) varied from about -0.38% in several studies to -0.7% and -0.88% in other investigations which claim that all or nearly all strontium is co-titrated. 

Interference effects begin to appear at higher magnesium or strontium molar ratios. Tsunogai et al. [157] found the interference of magnesium to be negative and, for strontium, interference is related to the extraction into the organic layer of the calcium GHA complex. They found a positive interference for strontium at twice the seawater molar ratios. Therefore, the interference of... 

Calcium and strontium interfere when ethylenediamine is used. Gadolium behaves similarly and the other rare earths react in higher concentration. 

Samples of animal bones weighing approximately 3 g are ashed at 600 °C until the entire bone is ash-white. Samples are then crushed in a mortar and pestle. A portion of the sample is digested in HCl and diluted to a known volume. The concentrations of zinc and strontium are determined by atomic absorption. The analysis for strontium illustrates the use of a protecting agent as La(N03)3 is added to prevent an interference due to the formation of refractory strontium phosphate. 

Hardness Calcium, magnesium, barium and strontium salts expressed as CaCOa Chief source of scale in heat exchange equipment, boilers, pipe lines, etc. forms curds with soap interferes wKh dyeing, etc. Softening, distillation, internal boiler water treatment, surface active agents, reverse osmosis, electrodialysis... 

The determination of magnesium in potable water is very straightforward very few interferences are encountered when using an acetylene-air flame. The determination of calcium is however more complicated many chemical interferences are encountered in the acetylene-air flame and the use of releasing agents such as strontium chloride, lanthanum chloride, or EDTA is necessary. Using the hotter acetylene-nitrous oxide flame the only significant interference arises from the ionisation of calcium, and under these conditions an ionisation buffer such as potassium chloride is added to the test solutions. 

Polarography has also been applied to the determination of potassium in seawater [535]. The sample (1 ml) is heated to 70 °C and treated with 0.1 M sodium tetraphenylborate (1 ml). The precipitated potassium tetraphenylborate is filtered off, washed with 1% acetic acid, and dissolved in 5 ml acetone. This solution is treated with 3 ml 0.1 M thallium nitrate and 1.25 ml 2M sodium hydroxide, and the precipitate of thallium tetraphenylborate is filtered off. The filtrate is made up to 25 ml, and after de-aeration with nitrogen, unconsumed thallium is determined polarographically. There is no interference from 60 mg sodium, 0.2 mg calcium or magnesium, 20 pg barium, or 2.5 pg strontium. Standard eviations at concentrations of 375, 750, and 1125 pg potassium per ml were 26.4, 26.9, and 30.5, respectively. Results agreed with those obtained by flame photometry. 

An example is shown in figure 1 of the molecular interferences which must be dealt with around mass 87 if one wishes to use a mass spectrometer for rubidium/strontium measurements in a geological sample [22]. The major elements in this lunar sample all have mass numbers less than 48. Thus, the mass 87 region should be completely free of atomic peaks except for the minor components such as rubidium and strontium. This is clearly not the case and at most mass numbers in the rubidium region there are major interferences from molecules. 

There are a number of interferences that can occur in atomic absorption and other flame spectroscopic methods. Anything that decreases the number of neutral atoms in the flame will decrease the absorption signal. Chemical interference is the most commonly encountered example of depression of the absorption signal. Here, the element of interest reacts with an anion in solution or with a gas in the flame to produce a stable compound in the flame. For example, calcium, in the presence of phosphate, will form the stable pyrophosphate molecule. Refractory elements will combine with 0 or OH radicals in the flame to produce stable monoxides and hydroxides. Fortunately, most of these chemical interferences can be avoided by adding an appropriate reagent or by using a hotter flame. The phosphate interferences, for example, can be eliminated by adding 1 % strontium chloride or lanthanum chloride to the solution. The strontium or lanthanum preferentially combines with the phosphate to prevent its reaction with the calcium. Or, EDTA can be added to complex the calcium and prevent its combination with the phosphate. 

Remedy The addition of an excess of strontium (Sr), or lanthanum (La), or thorium (Th) ion remarkably minimizes the interference of P043 ion in the determination of Mg, and Ca by replacing the analyte in the analyte in the compound formed with the respective interfering species. In short, these ions do combine preferentially with P043 ions. 

The atomic absorption characteristics of technetium have been investigated with a technetium hollow-cathode lamp as a spectral line source. The sensitivity for technetium in aqueous solution is 3.0 /ig/ml in a fuel-rich acetylene-air flame for the unresolved 2614.23-2615.87 A doublet under the optimum operating conditions. Only calcium, strontium, and barium cause severe technetium absorption suppression. Cationic interferences are eliminated by adding aluminum to the test solutions. The atomic absorption spectroscopy can be applied to the determination of technetium in uranium and its alloys and also successfully to the analysis of multicomponent samples. 

Strontium-90, a radioactive strontium isotope with a half-hfe of 29 years, is a dangerous fallout source of radiation from atmospheric nuclear bombs. If a person is exposed to it, it will rapidly accumulate in bone tissue and interfere with the production of new red blood cells... 

Ionisation is an equilibrium and may be shifted to the left by addition of another readily ionised element to the sample which produces electrons. The emission lines from the added metal are unlikely to interfere because AE lines are very narrow, and thus there will be no overlap, e.g. strontium chloride solution is added in order to suppress the ionisation of K in the BP assay of effervescent KCI tablets. 

Resonance-ionization mass-spectrometry is still in the development stage in terms of its application to cosmochemistry. The Charisma instrument, which is operated by Argonne National Laboratories, uses multiple lasers to resonantly ionize only the elements of interest, which are then analyzed with a time-of-flight mass spectrometer. The Charisma instrument has made isotopic measurements of molybdenum, zirconium, strontium, ruthenium, barium and other elements in presolar grains. These measurements are made possible by the high ionization efficiency of the RIMS technique and its ability to completely eliminate isobaric interferences. Work is now underway to build a RIMS instrument that can be operated by an individual investigator in a university laboratory. If this succeeds, RIMS will play an increasing role in analysis of extraterrestrial materials. 

A stock solution of calcium ions was prepared by dissolving 0.1834g of CaCl2.2H20 in 100 ml of distilled water and then further diluting by a factor of 10. From this new solution, three standard solutions were prepared by further dilutions of five, 10 and 20 times, respectively. The unknown sample is itself diluted 25 times. Sufficient strontium chloride was then introduced to eliminate any interference due to phosphate ions. An analytical blank containing the same concentration of strontium was the first solution to be examined by the air/acetylene flame. The results were as follows ... 

The method of standard addition (Section 5-3) compensates for many types of interference by adding known quantities of analyte to the unknown in its complex matrix. For example, Figure 21-27 shows the analysis of strontium in aquarium water by standard addition. 

The increasing threat of international terrorism was one motivation for development of ISE for the determination of Cs+ in environmental samples [80]. In an event such as a Chernobyl-type disaster or the explosion of a dirty bomb , cesium is one of the most important reaction products and is expected to be the most significant threat to public health [81]. With a detection limit of 10 8M, the developed electrode is sensitive enough for this application and the successful detection of cesium activities in spiked water samples has been demonstrated (see Procedure 2 in CD accompanying this book). In addition, the electrode shows excellent selectivity to cesium in the presence of high levels of strontium, an important interferent originating from nuclear explosions. 

It is noteworthy to mention that under normal conditions, cesium is not considered a major contaminant of natural and ground waters since it preferentially adheres to soils, thereby showing relatively low mobility. Therefore, a cesuim-selective electrode for the successful determination of cesium in natural waters that exhibits negligible interference by strontium was characterised and developed utilising UIC as the ion exchanger. 

The most sensitive flame spectrometric procedure for the determination of strontium is FES, the emission intensity at 460.7 nm being measured from a nitrous oxide-acetylene flame. A detection limit of 1 ng ml-1 or better is generally readily attainable, although the element has a low ionization potential and addition of potassium or caesium at a final concentration of 2-5 mg ml 1 is essential as an ionization buffer. Chemical interference from phosphate, silicate and aluminium is reduced dramatically in this flame. 

Strontium may also be determined at the same wavelength by AAS, using a nitrous oxide-acetylene flame and ionization buffer to minimize the risk of interference. Although slightly poorer by AAS than by AES on most instruments, the detection limit is still as low as a few ng ml-1. 

Strontium. Strontium like Rb and Pd was included in anticipation of a standard. Strontium may be subject to more ionization and chemical interferences than other alkaline earths. Thorough studies of interfernces from mineral acids, HC1, HNO, and l SO are reported (3) as well as from Al, Si, and other ionization enhancement elements. Sr is strongly ionized, 84%, in nitrous oxide/acetylene the addition of 1000 ppm Cs is very important in suppressing Al, Si, and other interferences that cause enhancement. The 460.7 nm line is significant for AAS analysis of Sr. 

This is by far the most frequently encountered interference in AAS. Basically, a chemical interference can be defined as anything that prevents or suppresses the formation of ground state atoms in the flame. A common example is the interference produced by aluminium, silicon and phosphorus in the determination of magnesium, calcium, strontium, barium and many other metals. This is due to the formation of aluminates, silicates and phosphates which, in many instances, are refractory in the analytical flame being used. 

For strontium determinations samples, standards and blanks are made to 1% (m/v) in lanthanum to prevent the formation of refractory compounds. Analyses for strontium also suffer from ionisation interferences which are discussed later. 

There are alternative ways of modifying the matrix to remove the interference. Organic compounds have been shown to be effective. Regan and Warren [41] studied potential interferences on lead determinations in water. 100 mg l-1 of calcium, magnesium, strontium and barium were added to lead solutions in hydrochloric acid and nitric acid. The most severe interferences... 

Metal salts may be used in the treatment of wool. Flame methods for the determination of aluminium [185], barium, chromium, copper, mercury, strontium, tin, zinc [186] and zirconium [187] in wool have been published. Standard additions to wool cleaned by soaking and washing it with disodium EDTA (800 ml of 0.5 M for 30g wool with soaking for 3 days and double washing) was used as the calibration technique. This compensated for interferences from hydrochloric acid and amino-acids. The samples were equilibrated to a constant humidity for 24 h and then 0.3 g sealed with 5 ml of constant boiling point hydrochloric acid in a glass tube. The tubes were placed in an oven at 110UC for 20 h. The nitrous oxide/acetylene flame was used for the determination of aluminium and zirconium. Sulphate, phosphate, citrate and silicate have been found to interfere in the determination of titanium and zirconium in fire-proofed wool [188], These flame... 

In the presence of ammonium chloride the test is more sensitive. In this case potassium is replaced by ammonium ions in the precipitate. The test can be used to distinguish calcium from strontium barium and magnesium ions however interfere. 

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