The Basis of Flame Photometry - Research Proposal Example

Introduction Potassium and sodium are very important element as they perform vital biological functions in human body. They are required by the body for cellular stability, but levels that are out of normal range can result in severe problems with neuromuscular, cardiac and renal function (Peate & Dutton, 2014, 201). Excess consumption of sodium may lead to high blood pressure or may result in a buildup of fluid in the body that leads to cirrhosis, kidney disease and congestive failure. Potassium is important for maintaining blood volume and normal heart function and enables normal function of the nerves and muscles. Excess potassium results in muscles weakness, malaise and palpitations. In extreme cases, it leads to fatal abnormal heart rhythms (arrhythmia) (Grosvenor & Smolin, 2009). Thus it is important that we monitor the intake of salt that include potassium and sodium. In order to do this, food must be tested using one of the test techniques. The simplest method for testing these elements is flame photometry. The basis of flame photometry is similar to simple analysis flame test. It exploits the fact that alkali and alkaline earth metals ions dissociate at high temperature and the atoms produced are excited to a higher energy level. The excited atoms emit radiation as they return to ground energy level (Chawla, 2014; Thomas, 2014). The radiation emitted lies within the visible region of electromagnetic spectrum. Figure 1: Atomization process The different elements emit light with specific wavelength. Potassium has a wavelength of 766nm, while sodium has a wavelength of 589 nm. The intensity of light emitted is proportional to the quantity of the element present in the flame (Chawla, 2014) In this experiment, the solutions of potassium and sodium are aspirated in the flame. The samples absorb heat from the flame and the atoms are excited to electronically to high energy level. As the electrons return to the ground state, energy in form of light is emitted. The atoms have characteristic colours which are related to the energy difference in the electronic states. Flame photometer is shown below. Figure 2: Flame photometer The concentration of the unknown sample is obtained by plotting calibration curve, before measuring the emission of the sample and using the calibration curve to find the concentration of the unknown sample. Objectives a) To create calibration curve using the solutions of potassium and sodium b) To measure the concentration of sodium and potassium in soy sauce using the calibration curve Procedure A series of standard solutions of sodium and potassium were prepared at the concentration of 5, 10, 15, 20 and 25 ppm for sodium and the concentration of 3, 6, 9, 12 and 15 ppm for potassium from the standard concentration of 1000 ppm of each. When the standard solution was ready, the flame photometer was light and stabilized. Then, deionized water was aspirated for 2 minutes in order to clean it and make the unit stable. As the water was being aspirated, the zero knob was set to give a reading of zero units. The most concentrated solution of the standard solution of sodium was then aspirated before setting the scale to read 100 units using the coarse and fine knobs. After setting up the instrument, each of the standard solutions and samples were aspirated in turn and the reading of each solution was recorded, but deionized water was aspirated between each solution to clean the burner. All these steps were repeated to obtain triplicate measurements, before calculating the average. The same process was repeated for potassium solution. Finally, calibration curves were made by plotting the absorption of the solution against the concentration of each. The curves were then used to determine the concentration of the unknown solution. Table 1: Results for the standard solutions Sodium Potasium Conc. (ppm) Reading 1 Reading 2 Reading 3 Average Reading 1 Reading Reading 3 Average 0 0 0 0 0 0 0 0 0 5 63 63 63 63 55 55 60 56.667 10 130 155 140 141.667 130 130 125 128.333 15 170 195 180 181.667 200 200 200 200 20 200 240 240 226.667 250 250 255 251.667 Unknown diluted (1/5000) 35.2 35.2 35.2 35.2 7.2 7.2 7.2 7.2 The graphs obtained by plotting the average readings verses the concentration of the standard solution on the excel sheet are shown below. Figure 3: The curve for concentrations of standard solution of potassium From the table, the average reading of the unknown solution is 7.2. Thus from the graph, the concentration of the unknown solution = 0.75 ppm Figure 4: The curve for concentrations of standard solution of sodium From the table, the average reading of the unknown solution is 35.2. Thus from the graph, the concentration of the unknown solution = 2.3 ppm Calculation The general formula = Volume of solution 1 x Concentration of solution 1= Volume of solution 2 x Concentration of solution 2 Potassium 3 ppm of standard solution of potassium was prepared by diluting 5 ml of 1000ppm potassium standard solution to 1000ml of deionized water. Concentration of the flask solution Sodium Concentration of the flask solution Discussion The results obtained in this experiment for the unknown solution are 0.75 ppm and 2.3 ppm for potassium and sodium respectively. The concentration is relatively low but they are reasonable, especially because of the interferences. The concentration in the flame is reduced by interference which can be chemical or spectral. Spectral interference is due to dispersal of the products and the absorption of molecular species in the flame. Chemical reaction occurs due to reactions that involves the analyte (Gopalan, Venkappayya & Nagarajan, 2010). When the solutions of potassium and sodium are aspirated into the flame, sequence of changes occurs in the flame. The solvent evaporates and leave behind the salt in the flame. Then the salt evaporates and changes into salt vapour, where it dissociates further into atoms. Some of the atoms absorb heat energy form the flame and get excited to high energy level, but because they are not stable at this excited state, they emit energy in from of light radiation and return back to lower ground state. The radiated light intensity is directly proportional to the number of atoms in the excited from. This is turn is directly related to the number of atoms in the flame or concentration of the solution flowing to the flame. Thus, the concentration of the solution is directly proportional to the light radiation emitted. The concentration of the solution is then determined by measuring the intensity of radiation using a suitable detector. Different metals emit radiations at their respective wavelengths and they are filtered as required (Gadag, 2010). The series of changes that takes place in the flame when the solution is aspirated can be summarized as shown below. The intensity of light emitted as measured but the detector is related as follows Where h is the Planks constant, v is the frequency of radiation, E is the energy of the radiation emitted, c is the velocity of the electron and λ is the wavelength In flame atomization, analyte solution in converted to a mist (nebulized) and carried by the fuel into the flame. The gaseous medium produces emission and absorption spectra. In the nebulizer, the analyte is sucked by a high pressure gas stream flowing at the tip of the tube. After the solution is converted to mist by the nebulizer and fed to the flame. It then passes through a series of baffles that remove the fine mist droplets. The rest of the sample is collected at the bottom of the mixing chamber before being exhausted out. The atomized part passes through a flame with approximate length of 5 – 10 cm in the burner. The colour of the flame tells the type of element present in the sample which is qualitative analysis, and the radiation intensity shows the conctration of the element present (quantitative analysis) (Bhangwan, 2005). The flame is composed of the primary combustion zone, inter-zonal region and the secondary combustion region like as shown below. When the nebulized sample flow through the flame, it evaporates in the primary combustion zone, and the solid particles obtained flow through the hottest region of the flame (interzonal region) where they turn into atom gases and ions. The ions and atoms are may be oxidized in the secondary combustion zone. The atoms of the elements are excited in the interzonal region. The flame determines the relative number of excited (Na+ + e-) and unexcited (Na) atoms in the flame. In the ineterzonal region, an equilibrium of is established. The rise in temperature leads to an increase in the number of ions in the flame. The loss of atoms because of ionization causes imbalance of the atoms in the interzonal region. The results obtained were affected by errors. One of the main areas of concern was fluctuation of photometer. The error was minimized by aspirating deionized water between each solution to clean the burner and to reduce ‘memory effect’. However, there was still some instability in the readout of the unit. Thus, there is no way if the flushing was enough. Another source of error was the age of the apparatus. It is likely that due to inadequate cleaning previously may have left some residue in the photometer which may have contaminated the solution and influence the change in results. Although the flame photometer was calibrated to zero using deionized water at the beginning of the experiment, after the measurement was taken, and the flame photometer was flushed again, the read out was 0.5. this shows that either the flushing was not sufficient or the digital read out was inaccurate. Significance of flame photometry This method is applied in different fields to determine the amount of elements in substances. For example it is used to quantify the metal and alkali earth metals presence in food sample such as fruit drinks and other types of food. It can also be used to quantify the elements found in blood. This technique is less expensive has been used for many generations to quantify the amount of metals ions like sodium, lithium, calcium and potassium. It is also sensitive, quick, convenient and selective (Bhagwan, 2005, 279 -288). Disadvantages The main disadvantages for this technique include the following. Although the technique allows determination of that amount of metal present in a sample, it does not quantify the amount of metal present in the original sample. It cannot be used in direct detection or for determining inert gases. In many cases, the sample used are prepared through many steps The technique is not used to determine all metal atoms directly, as it can be used to analyze some metals only. Non-radiating elements like halides, hydrogen and carbon cannot be detected using this technique, unless under very special circumstances (Bhagwan, 2005, 279 -288). Recommendations Special attention should be given to cleaning the glass chimney, burner head and nebulizer. At the end of each run, the fluid that are used to clean it like deionized water should be aspirated for atleast two minutes. Since the instrument has a very small bore, they can easily be blocked. This can be avoided by centrifuging and inspecting using plasma to make sure there are no particles before aspirating. Zero drift may result due to accumulation of materials that emit light on the burner, changes in temperature of the electronic parts of the instrument. This effect can be assessed sampling water at regularly (Chawla, 2014, 283). References Bhagwan P., (2005). A Handbook of Chemical Analysis, Mittal Publications Chawla, R. (2014). Practical clinical biochemistry: Methods and interpretations, New Delhi: Jaypee Brothers Medical Publishers (P) Ltd Gadag R. V., (2010) Engineering Chemistry, I. K. International Pvt Ltd Grosvenor, M. B., & Smolin, L. A. (2009). Visualizing nutrition. Hoboken, N.J: Wiley. Gopalan, R., Venkappayya, D., & Nagarajan, S. (2010). Textbook of engineering chemistry. New Delhi: Vikas Publishing House Pvt. Ltd. Peate I., & Dutton H., 2014. Acute Nursing Care: Recognising and Responding to Medical Emergencies, Routledge Thomas, D. E. (2014). The lupus encyclopedia: A comprehensive guide for patients and families, Baltimore: Johns Hopkins University Press. Read More

Table 1: Results for the standard solutions Sodium Potasium Conc. (ppm) Reading 1 Reading 2 Reading 3 Average Reading 1 Reading Reading 3 Average 0 0 0 0 0 0 0 0 0 5 63 63 63 63 55 55 60 56.667 10 130 155 140 141.667 130 130 125 128.333 15 170 195 180 181.667 200 200 200 200 20 200 240 240 226.667 250 250 255 251.667 Unknown diluted (1/5000) 35.2 35.2 35.2 35.2 7.2 7.2 7.2 7.2 The graphs obtained by plotting the average readings verses the concentration of the standard solution on the excel sheet are shown below.

Figure 3: The curve for concentrations of standard solution of potassium From the table, the average reading of the unknown solution is 7.2. Thus from the graph, the concentration of the unknown solution = 0.75 ppm Figure 4: The curve for concentrations of standard solution of sodium From the table, the average reading of the unknown solution is 35.2. Thus from the graph, the concentration of the unknown solution = 2.3 ppm Calculation The general formula = Volume of solution 1 x Concentration of solution 1= Volume of solution 2 x Concentration of solution 2 Potassium 3 ppm of standard solution of potassium was prepared by diluting 5 ml of 1000ppm potassium standard solution to 1000ml of deionized water.

Concentration of the flask solution Sodium Concentration of the flask solution Discussion The results obtained in this experiment for the unknown solution are 0.75 ppm and 2.3 ppm for potassium and sodium respectively. The concentration is relatively low but they are reasonable, especially because of the interferences. The concentration in the flame is reduced by interference which can be chemical or spectral. Spectral interference is due to dispersal of the products and the absorption of molecular species in the flame.

Chemical reaction occurs due to reactions that involves the analyte (Gopalan, Venkappayya & Nagarajan, 2010). When the solutions of potassium and sodium are aspirated into the flame, sequence of changes occurs in the flame. The solvent evaporates and leave behind the salt in the flame. Then the salt evaporates and changes into salt vapour, where it dissociates further into atoms. Some of the atoms absorb heat energy form the flame and get excited to high energy level, but because they are not stable at this excited state, they emit energy in from of light radiation and return back to lower ground state.

The radiated light intensity is directly proportional to the number of atoms in the excited from. This is turn is directly related to the number of atoms in the flame or concentration of the solution flowing to the flame. Thus, the concentration of the solution is directly proportional to the light radiation emitted. The concentration of the solution is then determined by measuring the intensity of radiation using a suitable detector. Different metals emit radiations at their respective wavelengths and they are filtered as required (Gadag, 2010).

The series of changes that takes place in the flame when the solution is aspirated can be summarized as shown below. The intensity of light emitted as measured but the detector is related as follows Where h is the Planks constant, v is the frequency of radiation, E is the energy of the radiation emitted, c is the velocity of the electron and λ is the wavelength In flame atomization, analyte solution in converted to a mist (nebulized) and carried by the fuel into the flame.

The gaseous medium produces emission and absorption spectra. In the nebulizer, the analyte is sucked by a high pressure gas stream flowing at the tip of the tube. After the solution is converted to mist by the nebulizer and fed to the flame. It then passes through a series of baffles that remove the fine mist droplets. The rest of the sample is collected at the bottom of the mixing chamber before being exhausted out. The atomized part passes through a flame with approximate length of 5 – 10 cm in the burner.

The colour of the flame tells the type of element present in the sample which is qualitative analysis, and the radiation intensity shows the conctration of the element present (quantitative analysis) (Bhangwan, 2005).

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