Interference calcium-phosphate

The effect of phosphate on calcium, illustrated in Figure 2.8. is an example of chemical interference. Calcium phosphate is not totally dissociated in an air-acetylene flame consequently. when the phosphate concentration level increases, the absorbance due to the calcium atoms falls. There are two ways of solving this problem. 

Further indirect determinations can be performed by making use of chemical interference. Calcium phosphate interference in flame AAS can be used to determine phosphate by measuring the decrease of the absorption signal for calcium. However, for real samples, indirect techniques should be used very carefully in view of possible systematic errors. 

Transfection is the process of introducing DNA or RNA into eukaryotic ceils. The use of transfection is to study the role and regulation of proteins or to understand the mechanisms of a pathway. Transfection can be transient for rapid analysis or stable , mostly for induction of expression. There are various methods of transfection which include electroporation, viral vectors, DEAE-Dextran, calcium phosphate or Lipofectamine. The choice of transfection depends on the cell type used. The most desirable technique is the one which gives high efficiency of nucleic acid transfection with less interference to the cells physiology and high reproducibility. 

Q. List several ways in which the interference of phosphate on calcium may be minimized ... 

Diluents, although commonly presumed inert, do have the ability to influence the stability or bioavailability of the dosage form. For example, dibasic calcium phosphate (both anhydrous and dihydrate forms) is the most common inorganic salt used as a filler-binder for direct compression. It is particularly useful in vitamin products as a source of both calcium and phosphorous. Milled material is typically used in wet-granulated or roller-compacted formulations. The coarse-grade material is typically used in direct compression formulations. It is insoluble in water, but its surface is alkaline and it is therefore incompatible with drugs sensitive to alkaline pFI. Additionally, it may interfere with the absorption of tetracyclines [7]. 

Interference arises when the intensity of the signal from the required substance is modified by another substance, although the signals of the two substances are adequately resolved. Thus, the presence of phosphate reduces the flame emission of calcium by forming thermally stable calcium phosphate. The instrumental conditions can sometimes be altered to reduce the effect, or the interfering material removed by pretreatment of the sample. Standard solutions are usually chosen to resemble samples as closely as possible in the hope that any interference will occur equally in both. 

Dilution with lanthanum-HCl reduces interference from protein, phosphate, citrate, sulfate, and other anions. Phosphate causes the greatest interference because calcium-phosphate complexes are not dissociated readily by the air-acetylene flame. Lanthanum-HCl dissociates complexes, ensuring that all fractions of calcium (free, protein-bound, and complexed) are measured. Dilution effectively reduces the viscosity, which can also interfere by reducing the aspiration rate and atomization of the specimen. 

Incomplete atomization of the analyte causes so-called chemical interferences. They are due to the fact that atomic absorption can only occur with free atoms. Thus reactions in the flame which lead to the formation of thermally stable species decrease the signals. This fact is responsible for the depression of calcium signals in serum analysis by the proteins present, as well as for the low sensitivities of metals that form thermally stable oxides or carbides (Al, B, V, etc.) in flame AAS. A further example of a chemical interference is the suppression of the absorbance of earth alkali metals as a result of the presence of oxyanions (X) such as aluminates or phosphates. This well-known calcium-phosphate interference is caused by the... 

Allegations have been made that patients suffering from renal failure are susceptible to aluminum toxicity. Anemia (interference with iron transport), softening of the bones (replacement of calcium phosphate by aluminum phosphate), and a form of senile dementia can result. As well, a link to Alzheimer s disease (also a form of senile dementia) has been proposed, with the brains of dementia patients showing characteristic tangles of nervousness and hot-spots ofunusually high A1 concentration. 

The third approach is to eliminate the chemical interference by switching to a higher-temperature flame, if possible. For example, when a nitrous oxide-acetylene flame is used, there is no chemical interference on Ca from phosphate, because the flame has sufficient energy to decompose the calcium phosphate molecules. Therefore, no lanthanum addition is required. 

Among the most common chemical interferences in flame spectrometric methods, is the signal depression of alkaline earth metals in the presence of phosphate. This phenomenon occurs both in absorption and emission measurements. The interference effect is due to the formation of solid alkaline earth metal pyrophosphates which are difficult to vaporize. If calcium and phosphate solutions are simultaneously aspirated into the flame with two different nebulizers, signal depression is not observed. This is an indication that calcium phosphate does not form in the flame, but at an earlier stage of the process. The effect of phosphate can be removed by... 

This is perhaps the most common type of chemical interference. The presence of certain anions may cause refractory compounds to be formed with the analyte. As a consequence, its atomisation is hindered and a decrease in response is observed. A weU-known example is the suppression of the response of Ca with increasing concentrations of phosphate or sulfate. When the anion concentration in the flame is increased while keeping the calcium concentration constant, the absorbance decreases to about half its original value which is attributed to the formation of hardly dissociated calcium phosphate or sulfate. At high anion concentrations, the analyte response again becomes independent of the anion concentration. 

The addition of Sr or La ions may, for instance, reduce the interference of phosphate in the analysis of calcium by forming a thermally stable compound with phosphate, with the effect that Ca will be released to form free atoms. An opposite approach is used when certain salts such as NH4NO3 are added to remove chloride salts by volatilisation ... 

In some cases a region higher in the flame than normally used provides a region of less interference. In an oxygen-acetylene flame the interference of phosphate on calcium can be minimized by observing the calcium absorption signal 2 or 3 cm above the burner tip in a total-consumption burner. With lower temperature fuel-oxidant combinations there is no area in the flame where the calcium-phosphate interference disappears. Thus a combination of a high-temperature flame and proper choice of flame area can reduce this type of interference to zero or to a very low level. 

The usual way to avoid this interference is to prevent the formation of calcium phosphate during the desolvation of the sample solution in the burner. This can be done by adding another element in excess which binds the phosphate more strongly than calcium. Elements such as strontium, barium, and landianum have been used successfully for that purpose. The other possibility is to add a complexing agent such as EDTA, which forms a complex with calcium and hence prevents the analyte element from reacting with phosphate. 

In water and beverages strontium can be measured directly, but food and biological materials require a pretreatment with hydrochloric acid (3 M) and lanthanum chloride [91]. In urine strontium can be determined after dry-ashing and addition of lanthanum [91] or directly after 1 2 dilution with an acidic lanthanum chloride solution [92], The determination of strontium in bone requires special attention because the bone matrix contains high amounts of calcium and phosphate, which can easily interfere with the determination of strontium. Razmilic described a method to isolate strontium from the calcium phosphate matrix by ion exchange chromatography. The pretreated samples then can be analysed by both emission and absorption spectrophotometry measurements without chemical, ionization, or bulk interferences [93,94]. 

Some effort has also been focused on the determination of other isotope ratios, particularly St/ St with TOF-ICP-MS and LA-TOF-ICP-MS [104].These efforts have not, however, yielded precision and accuracy useful for the characterization of human tooth enamel for population movement studies. Part of the problem probably arises from interferences produced by the calcium phosphate matrix [106], but there also appears to be TOF detector-related fractionation akin to but more extreme than that observed for Pb/ Pb. 

Horstwood et al. [Ill] reported results of experiments to determine strontium isotopes in archaeological tooth enamel using LA-MC-ICP-MS and pointed out the need for careful attention to interferences from the calcium phosphate matrix. In another study, Richards et al. [112] detected evidence of Neanderthal mobility via LA-MC-ICP-MS characterization of strontium isotope ratios in tooth enamel. Enamel values from a Neanderthal molar recovered from a coastal limestone environment in Greece were found to be consistent with... 

Calcification involves the seeding of the calcium apatite crystal and the growth of the crystals. It would be more convenient to review the second of these mechanisms first. This can best be done by assuming for the moment that the bone matrix, connective or cartilaginous, is bathed in a medium supersaturated in calcium phosphate. Intrinsic to the matrix, there is a mechanism that precipitates calcium phosphate in the form of tiny apatite crystals. If there is no interference with the process of calcification, either by deficient absorption of calcium (vitamin D deficiency) or by active dissolution of the calcium crystals (parathormone), most of the process of mineralization can probably be explained by the physicochemical properties of the apatite crystals. Thus, the divalent cations and anions, PO4 and calcium, penetrate the hydration shell reaching the surface of the crystals where they are crystallized, thereby increasing the size of the crystals. As mineralization proceeds, the amount of bound... 

Interference by phosphate ion is an especially common problem. Since the phosphate ion reacts like silica to form a yellow phosphomolybdic acid, its interference must be eliminated. Numerous techniques have been proposed, either for separating the silica and phosphorus before analysis or preferentially reducing silicomolybdic acid to molybdenum blue in the presence of the phosphomolybdic acid (311-313). Snell and Snell (314) summarized the possible procedures (a) precipitating and removing phosphate as the calcium salt. (6) adjusting pH so only silica will form the yellow color, (c) destroying the yellow phosphate complex with citric, oxalic, or tartaric acids, and d) preferentially reducing the silicomolybdic acid to molybdenum blue. 

Calcium phosphate sensors are commonly based on solvents with low permittivities, e.g. DOPP (s = 6.2), whereas neutral carrier types may require highly polar solvents, typically 2-nitrophenyl octylether (2-NPOE), e = 23.6 (28). Another characteristic feature of neutral carrier systems (Table 3.12) is the presence of lipophilic anions, e.g. tetraphenylborate (KTPB) which was first incorporated to reduce the interference by lipophilic sample anions (36) and so dislodge interferents from the membrane phase. Today tetrakis(4-chlorophenyl)borate, KTpClPB, is generally preferred because its water solubility is smaller than that of KTPB by a factor of about 1000, and its... 

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