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This is chemistry element assignment help describes all about Calcium and its applications in various fields of life.  

Calcium

Calcium is the chemical element in the periodic table that has the symbol Ca and atomic number 20. It has an atomic mass of 40.078. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element in the Earth’s crust. It is essential for living organisms, particularly in cell physiology, and is the most common metal in many animals. It may be used as a reducing agent in the extraction of thorium, zirconium and uranium (Dickson and Goyet, 1994).

Isotopes

Calcium has four stable isotopes (40Ca and 42Ca through 44Ca), plus two more isotopes (46Ca and 48Ca) that have such long half-lives that for all practical purposes they can be considered stable. The 20% range in relative mass among naturally occurring calcium isotopes is greater than for any element except hydrogen and helium. Calcium also has a cosmogenic isotope, radioactive 41Ca, which has a half-life of 103,000 years. Unlike cosmogenic isotopes that are produced in the atmosphere, 41Ca is produced by neutron activation of 40Ca. Most of its production is in the upper metre or so of the soil column, where the cosmogenic neutron flux is still sufficiently strong. 41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar-system anomalies. (Explore report of Research on cosmetics)

97% of naturally occurring calcium is in the form of 40Ca. 40Ca is one of the daughter products of 40K decay, along with 40Ar. While K-Ar dating has been used extensively in the geological sciences, the prevalence of 40Ca in nature has impeded its use in dating. Techniques using mass spectrometry and a double spike isotope dilution have been used for K-Ca age dating.

The most abundant isotope, 40Ca, has a nucleus of 20 protons and 20 neutrons. This is the heaviest stable isotope of any element which has equal numbers of protons and neutrons. In supernova explosions, calcium is formed from the reaction of carbon with various numbers of alpha particles (helium nuclei), until the most common calcium isotope (containing 10 helium nuclei) has been synthesized.

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Oxides of calcium

Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic and alkaline crystalline solid at room temperature.

The broadly used term lime connotes calcium-containing inorganic materials, in which carbonates, oxides and hydroxides of calcium, silicon, magnesium, aluminum, & iron predominate, such as limestone. By contrast, quicklime specifically applies to a single chemical compound. {Read about the impact of Antioxidants}

Calcium oxide is usually made by the thermal decomposition of materials such as limestone that contain calcium carbonate (CaCO3; mineral calcite) in a lime kiln. This is accomplished by heating the material to above 825 °C, a process called calcination or lime-burning, to liberate a molecule of carbon dioxide (CO2); leaving quicklime. The quicklime is not stable and, when cooled, will spontaneously react with CO2 from the air until, after enough time, it is completely converted back to calcium carbonate.

Calcium in food

Calcium is found in significant amounts in many foods, including broccoli, kale, dandelion greens, collard greens, almonds, sesame seeds, blackstrap molasses, beans, and fortified beverages such as soy milk and orange juice. The calcium content of most foods can be found in the USDA National Nutrient Database.

Dairy products (such as milk, yogurt and cheese) do contain calcium, however they are not recommended as a dietary source because they contain a significant amount of saturated fat, which can contribute to cardiovascular disease. The calcium content of dairy products is also misleading because most of the calcium is used by the body in the digestion of milk protein (casein). This can lead to calcium deficiency and osteoporosis. However, calcium in dairy products is usually absorbed more easily by the human body than the calcium in other sources such as plant based or dietary supplements.

Calcium in biology

Calcium (Ca2+) plays a pivotal role in the physiology and biochemistry of organisms and the cell. It plays an important role in signal transduction pathways, where it acts as a second messenger, in neurotransmitter release from neurons, contraction of all muscle cell types, and fertilization. Many enzymes require calcium ions as a cofactor, those of the blood-clotting cascade being notable examples. Extracellular calcium is also important for maintaining the potential difference across excitable cell membranes, as well as proper bone formation.

Calcium levels in mammals are tightly regulated, with bone acting as the major mineral storage site. Calcium ions, Ca2+, are released from bone into the bloodstream under controlled conditions. Calcium is transported through the bloodstream as dissolved ions or bound to proteins such as serum albumin. Parathyroid hormone secreted by the parathyroid gland regulates the resorption of Ca2+ from bone, reabsorption in the kidney back into circulation, and increases in the activation of vitamin D3 to Calcitriol. Calcitriol, the active form of vitamin D3, promotes absorption of calcium from the intestines and the mobilization of calcium ions from bone matrix. Calcitonin secreted from the parafollicular cells of the thyroid gland also affects calcium levels by opposing parathyroid hormone; however, its physiological significance in humans is dubious.

Calcium storages are intracellular organelles that constantly accumulate Ca2+ ions and release them during certain cellular events. Intracellular Ca2+ storages include mitochondria and the endoplasmic reticulum.

In vertebrates, calcium ions are of such vital importance to many physiological processes that its concentration is maintained within specific limits to ensure adequate homeostasis. This is evidenced by human plasma calcium, which is one of the most closely regulated physiological variables in the human body. Normal plasma levels vary between 1 and 2% over any given time. Approximately half of all ionized calcium circulates in its unbound form, with the other half being complexed with plasma proteins such as albumin, as well as anions including bicarbonate, citrate, phosphate, and sulfate.

Different tissues contain calcium in different concentrations. For instance, Ca2+ (mostly calcium phosphate and some calcium sulfate) is the most important (and specific) element of bone and calcified cartilage. According to Human Bio Sciences, in humans, the total body content of calcium is present mostly in the form of bone mineral (roughly 99%). In this state, it is largely unavailable for exchange/bioavailability. The way to overcome this is through the process of bone resorption, in which calcium is liberated into the bloodstream through the action of bone osteoclasts. The remainder of calcium is present within the extracellular and intracellular fluids.

Within a typical cell, the intracellular concentration of ionized calcium is roughly 100 nM, but is subject to increases of 10– to 100-fold during various cellular functions. The intracellular calcium level is kept relatively low with respect to the extracellular fluid, by an approximate magnitude of 12,000-fold. This gradient is maintained through various plasma membrane calcium pumps that utilize ATP for energy, as well as a sizable storage within intracellular compartments.

Ca2+ ions are an essential component of plant cell walls and cell membranes, and are used as cations to balance organic anions in the plant vacuole. The Ca2+ concentration of the vacuole may reach millimolar levels. The most striking use of Ca2+ ions as a structural element in plants occurs in the marine coccolithophores, which use Ca2+ to form the calcium carbonate plates, with which they are covered.

Calcium is needed to stabilize the permeability of cell mebranes. Without calcium, the cell walls are unable to stabilize and hold their contents. This is particularly important in developing fruits. Without calcium, the cell walls are weak and unable to hold the contents of the fruit.

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Some plants accumulate Ca in their tissues, thus making them more firm. Calcium is stored as Ca-oxalate crystals in plastids.

Calcium in geology

Calcium metal is never found as the free metal in nature. Calcium is fifth in abundance in the earth’s crust, of which it forms more than 3%. It occurs as limestone (CaCO3), gypsum (CaSO4.2H2O), and fluorite (CaF2). Apatite is calcium fluorophosphate or chlorophosphate.

Values for abundances are difficult to determine with certainty, so all values should be treated with some caution, especially so for the less common elements. Local concentrations of any element can vary from values in various literature sources.

Calcium in the environment

Calcium is the fifth element and the third most abundant metal in the earth’s crust. The calcium compounds account for 3.64% of the earth’s crust. The distribution of calcium is very wide; it is found in almost every terrestrial area in the world. This element is essential for the life of plants and animals, for it is present in the animal’s skeleton, in tooth, in the egg’s shell, in the coral and in many soils. Seawater contains 0.15% of calcium chloride.

Calcium cannot be found alone in nature. Calcium is found mostly as limestone, gypsum and fluorite. Stalagmites and stalactites contain calcium carbonate.

Calcium is always present in every plant, as it is essential for its growth. It is contained in the soft tissue, in fluids within the tissue and in the structure of every animal’s skeleton. The vertebrate’s bones contain calcium in the form of calcium fluoride, calcium carbonate and calcium phosphate.

Hazards and toxicity

Compared to other metals, the calcium ion and most calcium compounds have low toxicity. This is not surprising given the very high natural abundance of calcium compounds in the environment and in organisms. Calcium poses few, if any, serious environmental problems. Acute calcium poisoning is rare, and difficult to achieve unless calcium compounds are administered intravenously. For example, the oral median lethal dose (LD50) for rats for calcium carbonate and calcium chloride are 6.45 and 1.4 g/kg, respectively (Lewis, 1996).

Calcium metal is hazardous because of its sometimes violent reactions with water and acids. Calcium metal is found in some drain cleaners, where it functions to generate heat and calcium hydroxide that saponifies the fats and liquefies the proteins (e.g., hair) that block drains. When swallowed calcium metal has the same effect on the mouth, esophagus and stomach, and can be fatal.

Excessive consumption of calcium carbonate antacids/dietary supplements (such as Tums) over a period of weeks or months can cause milk-alkali syndrome, with symptoms ranging from hypercalcemia to potentially fatal renal failure. What constitutes “excessive” consumption is not well known and probably varies a great deal from person to person. Persons who consume more than 10 grams/day of CaCO3 (=4 g Ca) are at risk of developing milk-alkali syndrome, but the condition has been reported in at least one person consuming only 2.5 grams/day of CaCO3 (=1 g Ca), an amount usually considered moderate and safe (Picolos and Orlander, 2005).

Sampling

It is well known that the principal disadvantage of any method for the determination of calcium involving precipitation as calcium oxalate lies in washing the precipitate. The solubility of the precipitate in water or in dilute ammonium hydroxide is appreciable and, in centrifuging, a small amount of calcium oxalate tends to float on the surface of the liquid and is lost in decanting. The satisfactory results obtained by the oxalate method are due largely to the compensation of errors, the loss of the precipitate of calcium oxalate being balanced by incomplete removal of ammonium oxalate in the washings. It is apparent that a washing fluid which would remove the excess of oxalate solution with no appreciable solution of the precipitate and which prevents any of the precipitate from floating on the surface of the liquid would increase the accuracy of the method (Wang, 1935).

Review of methods for analysis of calcium

Field-effect calcium sensor

Urinary stone formation has been identified as a disease widespread over last years.  The main causes of these stones are crystals of calcium oxalate found in human kidney. The risk of urinary stone formation among potential patients is determined by the “Bonn-Risk-Index” method which involves potentiometric determination of Ca2+ ion concentration. The technique optically determines the crystallized calcium oxalate present in urine before processing.

The review of the research paper highlights the development of miniaturized capacitive field-effect EMIS (electrolyte-membrane-insulator-semiconductor) sensors for the determination of Ca2+ ions in human urine (Beginga et al, 2008). The obtained results proved that the use of EMIS sensors for the measurement of Ca2+ in human urine sample is very much possible. Detection of urinary stone formation risk is now possible this technique, although the technique is costly for laboratory research. Another disadvantage of the technique is the big size of the ISEs, which frequently need to be carefully cleaned and calibrated. The cost-intensive solutions and the lowlife-time in urine are certain other limitations of this technique for implementation in medical practices. Recently silicon technology has been used in capacitive EMIS sensors, which provides easy and cost-effective fabrication without the need of any complicated encapsulation or photolithographic processes, and provides a small and simple layout.

Six months of testing was done to develop the long-term stability of the sensors. Sensitivity values of Ca2+ and the drift behavior were periodically tested.  For the tested sensors, an average sensitivity of (27±2) mV/pCa in was achieved, which were comparable to those that were previously obtained using ion-sensitive field-effect transistors (28 mV/pCa) and light-addressable potentiometric sensors (25–27mV/pCa).

Recent developments have been done in the capacitive field-effect EMIS sensors technique, combining them with an ETH 1001-containing PVS-based membrane, and the possibility of its future applications in the determination of urinary stone formation has been realized. The developed EMIS sensors have been systematically characterized by impedance spectroscopy, capacitance–voltage and constant–capacitance methods in both CaCl2 solution of different concentrations and human native urine. The experimental method uses Nyquist plot for determination of geometric capacitance and resistance of the Ca2+ deposited on the PVC membrane. Stability of the sensors was established by comparing results obtained from calibrated solutions to the real urine samples. Furthermore, the Ca2+ concentration values obtained were in good agreement with those obtained with a commercial macro-ISE. In future, focus needs to be on establishing sensor’s behavior in urine samples with high concentrations of lithogenic substances and varied composition with respect to molecular fractions. Experiments should be done in developing the calcium sensors in terms of long-term stability and life-term under clinical conditions.

Time-of-flight secondary ion mass spectrometry

The paper reviewed focuses on the experimental study of human calculi by time-of-flight secondary ion mass spectrometry, and comparison of the obtained results with commercially available urinary minerals. Identification of calcium phosphate compounds in the phase was done by measuring the relative ion abundances of [Ca2O]R and [CaPO2]R (Ghumman et al, 2009).

Human calculi are composed of a variety of organic and inorganic substances, including calcium oxalate and calcium phosphate constituting 80%. Other substances are struvite (10%), uric acid (9%), and the rest of cysteine and other compounds. More accurate information is needed on the chemical content of the calculi, for a better understanding of the formation, promotion and inhibition of the calculi and the physiochemical principles behind them. Precise chemical analysis is important in determining the right treatment and eventually plan ways to stop reoccurrence. Several analytical methods have been devised for accurate determination of calculi composition. The most common and simplest and simultaneously, the most inaccurate of them is wet chemical analysis.  Use of X-ray diffraction was also realized and later, discarded to its inefficient analysis of amorphous substances. Another technique mentioned in literature is infrared spectroscopy, which is reliable but suffers from multiple interferences from biomaterials with unknown substances resulting in complex spectra. Thermal decomposition analysis has also been used for determination of calculi, but the use is only limited to a few types of kidney calculi such as struvite. A recent development has brought out the use of synchrotron radiation (X-ray absorption near-edge spectroscopy), which has reportedly been already applied to accurate calculi analysis.

SIMS (secondary ion mass spectrometry) is another technique used in material characterization, and has been popular since its introduction long ago. The technique is used and preferred by most for the study of metal and semiconductors. The implementation has recently been extended to oxides and other non-conductive samples, and the potential for its use on biological samples is being explored. The introduction of time-of-flight SIMS (TOF-SIMS) has provided the possibility of working over unlimited mass range and very high mass resolution. Also, the technique only uses a small dose of primary ions in order to generate chemical spectra. Therefore, the technique is being increasingly used in elemental and molecular determination of composition of a variety of industrial materials.  TOF-SIMS can also be applied in the characterization of biomaterials, and the use has been evident from a recent biological study for structural investigations and cellular distribution of calcium. The technique, as such, has almost established itself for use in biomaterial investigations. However, there have been no references on its use in analysis of human calculi.

The paper reviewed tries to expand the use of TOF-SIMS to determination of organic and inorganic substances in human calculi. The process involved a simple sample preparation and sensitive detection of fragment ions, making TOF-SIMS applicable not only for analysis, but also towards speciation, profiling and imaging of trace elements in the sample. The spectra obtained from TOF-SIMS were compared with those acquired from the reference chemicals found in human calculi. Results were qualitatively presented and quantification was done by comparison with known mixtures. The presence of trace elements establishes low detection limits of the technique, and evidently supports the applicability of the technique to more than just identification of main components. TOF-SIMS also provides a reliable way to achieve determination of trace elements more accurately than wet analysis, by facilitating measurement of both, positive and negative ion spectra.

Atomic absorption spectrometry

The reviewed research focuses on developing response surface methodology (RSM) as a procedure for determination of calcium in synthesized samples, using flame atomic absorption spectrometry (FAAS). Response surface study was used in designing the optimal conditions for the procedure. The concentration response of calcium ions was optimized using three variables; time, HNO3 volume and HF volume Surface composition of the sample was determined through the use of XPS. Before measurement, the sample was mounted in a cup and pressed manually. The biomorphic powder obtained was homogenized in an agate mortar. The obtained XPS spectrum helped in evaluating the synthesized performance of ceramics up to error limits of 10% (Rojas, Ojeda and Pavon, 2009). {Read more about psychoactive drugs}

A fundamental step in any analytical method is sample preparation, and involves steps from simple dilution to partial or total dissolution. The samples are decomposed using thermal, ultrasonic or radiant energy. Microwave assisted energy sources have been widely applied for sample preparation in studies of decomposition of inorganic or organic materials. The process uses electromagnetic radiation to dissolve samples and the rate of digestion depends on the coupling efficiency of microwaves with digestion acids. The technique is safe, provides an easily programmable interface and can be simultaneously used for a large number of samples. When compared to the conventional acid digestion methods, the microwave technology uses convective heating for precision and recovery. Also, the sample is decomposed within a short time through direct heating of reagents. The microwave digestion method also helps in reducing contamination problems and volatile losses of elements. The amount of reagents used is also relatively less, thereby, decreasing the possibilities of blank signals during analysis.

The optimization method reviewed generates new possibilities towards a better understanding of effects that were not adequately explained by previous traditional methods. It helps in explaining the analytical responses of the multimodal functions of independent variables and helps understand the interaction between these variables. The use of microwave-assisted digestion in the design helps in faster pretreatment of sample and improves the accuracy and precision of obtained results. The technique however, does not result in achieving low detection limits and rapid data acquisition for determination of elements, for which ICP-MS is generally considered as a more suitable technique.

X-ray fluorescence

The paper reviewed presented the analysis of a bee honey sample for the determination of calcium. The technique used was dry ashing (DA) method for XRF with Mo-secondary target (Mo-XRF) as the excitation source. It was observed that the sensitivity in the measurements using the dry ashing method had significantly improved over those obtained using wet ashing (WA) and direct methods. Detection limits achieved by DA (0.007 μg/g) were a magnitude lower than those of WA method (0.120 μg/g) and direct (0.270 μg/g) methods. The sensitivity values obtained by DA-XRF were further improved by the use of copper secondary target for excitation of calcium. It was also observed that incomplete destruction of charcoal remains in the honey sample led to decrease in sensitivity measurements. This improved method was then applied to the determination of calcium in Syrian be honey samples. The results obtained were in good agreement with those acquired by atomic spectrometry method (Khuder, Ahmad, Hasan and Saour, 2009).

During recent years, the determination of trace elements in biological, medicinal, environmental, and food samples has become increasingly important. For this purpose various techniques have been used and improvements have been made over the years. Some of the commonly used analytical methods for analytical studies of trace elements are neutron activation analysis (NAA), atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission or mass spectrometry (ICP-AES, ICP-MS), particle-induced X-ray emission (PIXE) and total reflection X-ray fluorescence (TXRF). Combinations of energy dispersive X-ray fluorescence (ED-XRF) with different radionuclide sources have grown into some reliable methods in trace determination of elements in blood, plant and honey samples. A common feature of these analytical methods is the sampling procedure which requires pre-concentration, in order to achieve high sensitivity and applicability in determination of trace elements. Different methods have been developed for pre-concentration procedure, including the dry ashing method for biological materials. Dry ashing provides mass reduction and the effectiveness of this method depends on the composition of the residual ash. A major disadvantage of this procedure is loss of analyte from the sample when it is subjected to dry ashing. However, the results obtained suggest that the detection limits achieved in the analysis of trace elements using DA method were lower than those of other methods including PTFE and microwave oven.

Plasma-atomic emission spectrometry

The primary challenge in bio-medical analysis is the insufficient quantity of sample available for investigation. Therefore, it is extremely important to formulate a technique capable of analyzing small amount of samples. The paper reviewed demonstrates the possibility of using two-jet plasma atomic emission spectrometry for determination of calcium levels in blood samples. The technique was successfully applied to analysis of freeze-dried blood and was further extended to calcium determination in blood of living experimental rats and mice (Zaksas, Gerasimov and Nevinsky, 2009).

There are many techniques available for blood sampling, such as inductively coupled plasma (ICP) atomic emission spectrometry (AES), ICP mass spectrometry (ICP-MS), and total reflection X-ray fluorescence, which decompose the organic matrix by digesting it in wet acid. Techniques such as electrothermal atomization atomic absorption spectrometry have been used for direct determination of single elemental levels in blood samples. For analysis of multiple elements, ICP-MS has been implemented over the years. However, in order to prevent blood clotting and lysing of blood cells, the techniques required pre-treatment of the blood sample, either by sample dilution or by using additional reagents. Generally, these techniques require 1mL of blood which is not experimentally convenient for analysis of living animals. Therefore, the reviewed work focuses on two-jet plasma (TJP)-AES for determination of small quantity of samples. During recent years, ICP has replaced dc plasmas as a source of excitation in analysis studies. However, when compared to ICP or dc plasma, a TJP can be used for high-powered simultaneous analysis of multiple elements present in powdered samples. The technique has already been applied to geological and mineral samples for quite a while. The results obtained were found to be in good agreement with those acquired after wet acid digestion and carbonization of the samples. The sample preparation was relatively easier and no reagents aside from a spectroscopic buffer were used.

Total reflection X-ray fluorescence spectrometry

Research is being done for exploring new ways of using X-ray spectrometry for analytical measurements. The technique can be simultaneously used for analysis of multiple elements over a wide concentration range. Furthermore, the processing of operations in the technique is fast and low detection limits are achieved in the results, making it suitable for a variety of environmental, biological and toxicological studies. Irrespective of the research method, the quality of results greatly depends on the subsequent steps of the process, such as, calibrations, sample preparation and spectra evaluation. In environmental and biological studies related to analysis of trace elements, up to low detection levels; the benefits of using total reflection X-ray fluorescence spectrometry (TXRF) are being realized.

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The reviewed paper aims at evaluating the concentration of calcium in the roots of water hyacinth from the Lerma River; a Mexican water body known for its high pollution content such that only highly resistant organisms are able to reproduce in it. During the experimental process, samples were collected from five different sites in the river and analyzed using TXRF spectrometer. The results obtained for the concentration of calcium were found to be in good agreement with the reference values. Percentage of recovery after the acid digestion process was used as the quantitative benchmark for accuracy. Recovery was achieved, reportedly, at values higher than 97% and the percentage relative error was found to be between 1-9%. The relative standard deviation for all elements was lower than 10%. The results obtained prove that TXRF can be suitably applied to biomonitoring studies because it offers reliable information about a wide range of elements (with atomic number between 18 and 82), and over a wide range of concentrations including trace presence (Tejeda et al, 2009).

Conclusion

Review of various methods was done in comparing different techniques used applicable to determination and analysis of calcium present in biological, medical and environmental samples. The EMIS method used small sensors, was easy to use and involved cost effective fabrication technology. The time-of-flight SIMS method increased the applicability of the spectroscopy technique by allowing experimentation over an unlimited mass range and resolution. Another recent development in precise measurement of calcium traces was done in the field of emission spectroscopy. The laser ablation ICP-MS technique overcomes the shortcomings of sample preparation and allows rapid analysis of solid-state samples at high spatial resolutions. However, the technique has poor precision and is quantitatively unreliable due to its dynamic scan approach. On the other hand, ICP-OES equipped with a Charge Coupled Device (CCD) detector has the advantage of simultaneously determining different analytical wavelengths.  The errors originating from signal fluctuations induced by the instability of the ICP source are also eliminated. Therefore, the technique gives highly precise results than ICP-MS. The ICP-OES technique also employs less expensive instrument with minimal sample preparation, and has multiple advantages over ICP-MS and TIMS technologies, thus making it the technique of choice for calcium determination in a variety of samples.

References

Beginga, S.  Mlyneka, D.  Hataihimakula, S.  Poghossiana, A. Baldsiefenc, G. Buschc, H. Laubed, N.  Kleinene, L.  and Schoninga, M. J. 2008. Field-effect calcium sensor for the determination of the risk of urinary stone formation. Sensors and Actuators. 144 (2010), pp. 374–379

Deng, W. Liu, Y. Wei, G. Li, X. Tu, X. Xie, L. Zhang, H. and Sun, W. 2009. High-precision analysis of Sr/Ca and Mg/Ca ratios in corals by laser ablation inductively couples plasma optical emission spectrometry. Journal of Analytical Atomic Spectrometry. 25, pp. 84-87.

Dickson, A.G. and Goyet, C. 1994. Handbook of method for the analysis of the various parameters of the carbon dioxide system in sea water. [online] Available at: http://cdiac.esd.ornl.gov/ftp/cdiac74/chapter5.pdf ]Accessed 04 March 2011]

Ghumman, C. Carreira, O. Moutinho, A. Tolstogouzov, A. Vassilenko, V. and Teodoro, O. 2009. Identification of human calculi with time-of-flight secondary ion mass spectrometry. Rapid Commun. Mass Spectrom.; 24, pp. 185–190

Khuder, A. Ahmad, M. Hasan, R. and Saour, G. 2009. Improvement of X-ray fluorescence sensitivity by dry ashing method for elemental analysis of bee honey. Microchemical Journal. 95. Pp. 152-157.

Lewis, R. J. 1996. Sax’s Dangerous Properties of Industrial Materials. NY: Van Nostrand Reinhold. pp. 635.

Picolos, M. K. and Orlander P. R. 2005. Calcium carbonate toxicity: The updated milk-alkali syndrome; report of 3 cases and review of the literature. Endocrine Practice 4 (11), pp. 272–80.

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