Aim Report Example
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The aim of this experiment is to investigate the reason of poisoning in a patient whether from mineral bottled water and a saline drip by using ICP-MS and ICP-OES.
A patient was found suffered from excessive Sodium levels in his body. A recently given saline drip was assumed to be a reason, so two saline drips have been investigated. Another reason for this toxicity is that the patients may have consumed it through bottled mineral water. To solve the problem, it is necessary to measure the Sodium levels in saline drips. The evaluation of toxic metal is required to check in the water bottle to check whether it has been a source of poisoning. This assessment of sodium and metal components will be conducted against water SRM using ICP-OES and ICP-MS, respectively.
For the determination of metals and several nonmetals in a solution “Inductively coupled plasma-mass spectrometry,” (ICP-MS) and “Inductively coupled plasma-optical emission spectroscopy,” (ICP-OES) technology is used. Other application fields of ICP are varied research sections in life, environment, earth and forensic sciences as well as food, chemical and material industries. It is helpful in the analysis of acidic aqueous solutions for instance waste water or acidified drinking water (Martin, 1992).
The concept of this technology is based on the potential of inductively coupled plasma as an ideal atomizer and element ionizer for mass spectrometry that provide an atmosphere of high ion density and high temperature for any type of sample. On scattering these ions spatially get separated according to their mass and charge. ICP uses a high linear dynamic range for elemental determination and performs an extremely sensitive analytics. This technology illustrates exceptional properties, for example, comparative salt tolerance, high sensitivity and utmost quantitation accurateness. These features make ICP-MS and ICP-OES unbeatable and outstanding approaches for the accurate detection, identification and quantification of trace elements (Beaty & Kerber, 1978).
ICP-MS has been more advantageous in comparison of other analytical approaches that includes optical emission spectrometer, atomic absorption as well as ICP-AES (Atomic Emission Spectroscopy). Its key advantageous are:
• Shows better detection and has higher throughput in comparison to others (Graphite Furnace Atomic Absorption Spectroscopy (GFAAS).
• It has the capability of handling both types of matrices (simple and complex) with least matrix interferences that are due to high-temperature of its source.
• It has superfine detection competence with the equal sample amount consumption as in IPC-AES.
• ICP-MS can retrieve isotopic information (Beaty & Kerber, 1978).
Though it is not a spectroscopic technique, spectral interference is not observed. ICP-OES is spectroscopic technique so the chances of spectral interference increase. Interferences from mass overlaps exist due to the presence of isotopes and other polyatomic species. Spectral interferences observed in ICP-OES are classified into four categories.
Sloping background shift: The sloping background shift occurs when an extremely intense emission line gets widened due to the high concentration of the element present in the sample. It can be formed when electric fields are present in the plasma that incidence is called Stark broadening.Simple background shift: This is the most ordinary type of interference is simple background shift. Simple background shift is described as a constant shift in the surroundings in a specified range on any side of the analyte line. For instance, this range could be 0.5 nm and this shift happens towards up or down.Direct spectral overlap: This interference occurs due to overlapping of the wings of two close atomic or molecular spectral lines or can be said that the close neighbors cause background correction errors. The two different elements do not show the same ionic or atomic emission line that illustrates the exact similarity with any other element. Each spectral line owns a limited spectral width and the existing measurement systems are not perfect to evaluate with accuracy. Complex background shift: A complex background shift represents a complex shift in the background intensity with a variable characteristic on each side of the analyte line.
The main reason for this interference is numerous intense, close and dense emission lines that cause overlapping the analyte (Boss & Fredeen, 1999). These interferences demonstrate different causes and patterns.Various ICP-MS instruments are available on the market and each owns varied strength and limitations. The basic machinery is similar for all that includes plasma torch, spray chamber, detector, interface, and nebulizer but mass spectrometer designing is considerably different (Beaty & Kerber, 1978).
Generation of ions in the plasma
The principle of technology is based on the usage of high-temperature plasma discharge to produce positive ions. In this process a liquid sample in introduced into a device that consists of nebulizer and spray chamber (Figure 1). In the form of aerosol, it reaches the plasma base through injector get dried, atomized and ionized due to high-temperature ones of the plasma torch. Finally at the analytical plasma zone, at around 6000–7000 K, it stays as excited atoms and ions. The excited outer electron of a ground-state atom releases the wavelength-specific photons that are the principles atomic emission. However, plasma can remove an electron from its orbital to produce an ion. Production, transportation and identification positively charged ions in a big amount make ICP-MS outstanding (Thomas, 2001).
Figure 1: Generation of positively charged ions in the plasma (Thomas)
Figure 2: Basic instrumentation of ICP-MS system
The sample is pumped at 1 ml/min into a nebulizer, where it converts into aerosol with Argon gas at 1L/min. The superfine droplets of aerosol represent only 1-2% of the sample which is separated from larger droplets through the spray chamber. Through the exit tube of the spray chamber, it enters the plasma torch. For the identification of elemental ions, it should be transferred from ambient temperature to 7000K and from atm pressure to high vacuum. For accomplishing these step ions are retrieved through apertures. Moreover, ions producing in the plasma also travel through apertures. Their presence produces a high signal in the background on reaching the detector. To lessen this background, a photon-stop is used which is made of the metallic plate located in the center of ion beam. Ion beam keeps the photons away from the detector through reflecting them. Positively charged ions are not blocked by this plate because the positively charged lens directs them in the right direction. The ion beam enters quadrupole mass analyzer where they get separated according to the mass to charge ratio. Each element has specific mass spectrum due to different isotopes and mass characteristics. Now ions hit a specific detector that can be divided into two stages to facilitate the simultaneous measurement of high and low signals. The detection of components and ultra-trace elements simultaneously in a single shot makes ICP-MS a perfect tool for identifying unknown samples. This process has delivered 90 % efficiency in ionizing most of the elements.
Inductively coupled Plasma Optical Emission Spectrometry (ICP-OES) is applied in the labs for metal analysis. Its principle stands for the potential of Atomic emission spectrometer where at high temperature of 8000K sample plasma converts into excited and free ionized ions. The excited atom releases radiation while returning to the ground state and the emitted radiations and intensities are calculated optically through detectors (Beaty & Kerber, 1978; Thomas, 2001).
Figure 3: Basic instrument design ICP-OES system
For the investigation of poison elements, saline bags, and mineral water samples were tested using ICP-OES and ICP-MS respectively. Mineral water was analyzed to check the level of toxic metals in mineral water, such as As, Hg, Cd, Ti and Pb while saline bags were tested to check contamination.
With the help of provided standardized sodium solution (1000 µg/ml), a range of standard solutions is prepared for 0.5, 1, 2, 3 and 4 µg/ml. These aqueous standard samples are analyzed in ICP-OES lab. The emission of each solution sample is calculated for the unknown sample at various wavelengths. A calibration curve is produced by the achieved readings and concentration of Sodium is determined in the saline and water.
Results and discussion
Figure 4: The calibration graph at 330.237nm
The correlation value is acceptable when it is higher than 0.995. The co-relation value under this range is not acceptable. On the basis of the result achieved by Calibration curve of ICP-OES the correlation coefficient (R2) for 330.398nm and 330.237nm wavelengths are below 0.995. This result concludes that lines are not sensitive. Slope of the lines in a calibration graph indicates the association of signal intensity with element’s concentration. The r < 0.995 states the lowest application range indicating the lowest accuracy is the results. This may happen during preparation such as over pipetting of the material could be a reason.
The R2 values or correlation coefficient for the wavelength 589.592nm and 588.995nm has been higher than 0.995. These values illustrate that the line is linear enough with high sensitivity. The sensitivity is demonstrated by the slope of the calibration curve. They are in a linear arrangement except 1-2 points. The reason for this disturbance is might be the over pipetting of the solutions. In the case of 330nm, the sensitivity is poor and some of the signals are below zero (Ebdon & Evans, 1998).
Reference material = 24.7 ug/ml. Evian= 6.5 ug/ml, Volvic = 11.6 ug/ml, Pelligrino = 33.3 ug/ml, pH = 5.2
SRM x 10: Reference material (24.7 ug/ml)
2.5655 x 10 = 25.7
25.7 / 24.7 x 100
Evian tox x 10: Reference value (6.5 ug/ml)
0.6139 x 10 = 6.1
6.1 / 6.5 x 100
Evion x 10: Reference value (6.5 ug/ml)
0.5908 x 10 = 5.9
5.9 / 6.5 x 100
Volvic x10: Reference value (11.6 ug/ml)
1.1576 x 10 = 11.6
11.6 / 11.6 x 100
Pellegrino x 20: Reference value ( 33.3 ug/ml)
1.7122 x 20 = 34.2
34.2 / 33.3 x 100
Bag 1: 2000 fold dilution for Bag 1
23 / 58.5 x 9000 = 3538.5
3538.5 x 2000 = 1.77
3.264 / 1.77 x 100
Bag 2: 2000 fold dilution for Bag 2
23 / 58.5 x 9000 = 3538.5
3538.5 / 2000 = 1.77
3.2803 / 1.77 x 100
Based on the results of percentage recovery it is obvious that bag 2 is the toxic because it contains more Sodium in comparison of another bag 1. Bag 2 has demonstrated higher value. The error against reference material values and dilution error may have generated in the preparation stage. Results confirm that the toxicity present in the bag 2 had poisoned the patient. Theses bags were expected containing similar values as they were acquired from the similar pharmaceutical control. The difference in the values of both bags is not significant, that indicates an error that may have occurred during the preparation of the sample.
In this experiment, a specific interference is observed that a peak indicates Simple background shift in the case of 589.952 nm wavelength. A continuous peak is observed in the graph of 588.995nm wavelength with a background slope, so it is showing sloping background shift.
Figure 7: Subarray plot for Na5889 – Na 588.995
An intense ionic or atomic emission line results in a sloping background shift that widens due to the high concentration or due to the electric field. Sometimes the presence of molecular emission bands ICP discharge can also cause such interference. This condition appears when plasma is not protected from the ambient atmosphere (Boss & Fredeen, 1999). Since the slope is constant and is downward. Two correction points can be selected on each side of the peak to correct the interference.
There are many ways to correct or control the spectral interference. Through preparing standards with similar concentrations of interfering elements can reduce the interference. Many ICP experts use standard additions method for interference correction. It is a time taking process that requires efforts so has limited use in ICP. Determination of multiple emission lines is a good idea to solve the problems linked to spectral interferences. High-resolution system can reduce the spectral interference such as overlaps (Boss & Fredeen, 1999).
Figure 8: Subarray plot for Na5895 – Na 589.952
The R2 or correlation coefficient is acceptable when R2 > 0.995. Below this range it is unacceptable. The results obtained from ICP-MS calibration curves the value of R2 are greater than 0.995, which demonstrate the lines are sensitive.
The difference between ICP-OES and ICP-MS is in the calibration technique where ICP-MS used on the basis of an internal standard while not in ICP-OES. ICP-MS is considered more effective because it uses the ratio method of analyte/Rh signal. This ratio is applied while plotting the calibration graph. The possible errors during the preparation and dilution process are considered in this method. The Correlation values obtained from both methods have shown a significant difference. ICP-MS delivered the values under the acceptable range, on contrary ICP-OES results presented an unacceptable value range below the 0.995. The lack of internal standard implementations in ICP-OES makes this method weaker. The variation in the temperature plasma plays a dominant role in internal standard method. The calculation of emission is temperature dependent which considers the temperature variations during the process. These temperature fluctuations take place due to the ion generation from alkaline metals that reduce the temperature, which in turn influence the emission (Ebdon & Evans, 1998).
The acceptable value of percentage recovery lies between the ranges of 95-100%. The calculation involves the division of actual value with reference material multiplied by 100.
Figure 9: Ref x 9.7
Recovery Calculations for the internal Standards
Recovery% = 206pb value/0.97(dilution)/5.2(reference) x 100=outcome%
= [(4.467/0.97)/5.2] x 100 = 88.6%
Recovery% = 207pb value/0.97(dilution)/5.2(reference) x 100=outcome%
= (4.915/0.97)/5.2] x 100 = 97.4%
Recovery% = 208pb value/0.97(dilution)/5.2(reference) x 100=outcome%
= (5.116/0.97)/5.2] x 100 = 101.4%
In this experiment, the ICP-OES and ICP-MS demonstrated outstanding performance and facilitate the multielement evaluation process delivering results with high sensitivity, speed, and precision. ICP-OES and ICP-MS have several pros and cons. The ICP methods are applied to detect the elemental toxicity and it has potential to deal with sample and complicated matrices with minimal interference. The high temperature of Plasma of ICP provides it an ability to acquire isotopic information. The temperature and humidity are observed playing a noteworthy role that can impact the performance of ICP. The other influencing factors are ions affected by matrix composition, fluctuation in the plasma ionization efficacy and unstable concentrations of components of the matrix. Acid or bulk elements present in the samples can restrain the matrix.
This experiment is based on the investigation of how a patient got poisoned, either by Sodium present in saline water or toxic element from mineral water through applying ICP-OES and ICP-MS. The result of this experiment concludes that the patient was poisoned by the excessive sodium present in saline bag number two.
Beaty, R. D., & Kerber, J. D. 1978. Concepts, instrumentation and techniques in atomic absorption spectrophotometry (p. 27). USA: Perkin-Elmer.
Boss, C. B., & Fredeen, K. J. 1999. Concepts, instrumentation and techniques in inductively coupled plasma optical emission spectrometry. Norwalk: Perkin Elmer.
Ebdon, L., & Evans, E. H. (Eds.). 1998. An introduction to analytical atomic spectrometry. John Wiley & Sons.
Martin, T. D., Brockhoff, C. A., Creed, J. T., & Long, S. E. 1992. Determination of metals and trace elements in water and wastes by inductively coupled plasma-atomic emission spectrometry. In Methods for Determination of Metals (pp. 33-91).
Thomas, R. 2001. A beginner’s guide to ICP-MS. Spectroscopy, 16(4), 38.
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