Abstract
The lab exercise adopted the use of unique atomic spectroscopy measures to quantify Zn, Cu, and Se with reference to a Multivitamin. The techniques adopted in this lab test include XRF, Flame atomic absorption (AA), and inductively plasma atomic emission (AE). The main objective of the study was to develop a critical understanding of the application of these techniques. The experiment entails preparation and application of instruments, samples, and analysis of data. The outcome of the experiment highlights advantages and limitations to each technique and instrument applied during the lab exercise.
Analysis of Physiologically-Important Elements in a Multivitamin with Atomic Spectroscopy
Introduction
The analysis of elements in a sample of materials always has many applications especially in the determination of the important elements in a multivitamin. This analysis often involves the use of atomic spectroscopy. The method involves the adoption of such technique like XRF, Flame atomic absorption (AA), and inductively plasma atomic emission (ICP-AE). The determination of LOD/LOQ of the various techniques helps in achieving an accurate result on the component of the multivitamin and the ratio should always be the same. In order to ensure suitable result from the lab, it is important to make use of the autosampler that can always work unattended. Apart from studying the important element in multivitamins, this technique of physiological analysis is applicable in geology, environmental remediation, recycling, and miscellaneous disciplines in comparison to AA and AE that are essential in limited areas. However, this method always has challenges such as the interference related to atomic absorption that an individual would have to apply suppressors. The experiment focuses on studying the various components of Atomic Spectroscopy.
Question 3
Compare your results to those listed on the multivitamin label and discuss any source of error
The regression value related to copper was 0.998 while in the multivitamin label it is slightly lower reading at 0.068. There is a slight different between the values calculated in the lab and those found on the multivitamin label. This occurs as the result of the environmental factors and human errors. It is obvious that the experiment done to get the values for the multivitamin label were in a different environment to that conducted in the lab. The error could have happened because there was not close monitoring of the water bath. There are also high chances that the solutions used could have been cooler or warmer than expected. This would have affected the reaction of copper and zinc in the experiment. The fact that the values were much higher than that on the multivitamin label, show that the temperature might have been slightly lower than the standard temperature required for the system.
Question 4
How do the LOD/LOQ and sensitivity of the flame AA, GFAA, and ICP-AE methods compare? Is this consistent with what we discussed in class?
The values for these are almost the same with the LOD/LOQ ration for GFAA, AA and ICP being approximately 0.30. This is consistent for what learnt in the class since the uniformity in the ratio of LOD/LOQ always implies appropriate analysis of elements present in a sample (Zabicky p.726).
What are the advantages of using ICP-AE flame-based emission?
The presence of the inductively coupled plasma helps in emitting the excited atoms. The advantages of this method in determining the amount of element in a given sample is that they possess the best edge for detection hence allows the user to efficiently determine the level of a certain element in the material (Alloway & Olle p 714). This method also relates to low levels of hindrance from chemicals thereby the users can always use it in presence of any chemical substance. This form of spectroscopy also allows the chance of multi-element ability hence the user can always test as many elements inside the materials without restriction. This reduces on cost and time wasted in looking for other technique.
In two of your three analyses, you employed an autosampler. What are the advantages of such robotic devices versus manual sample introduction?
The use of auto sampler leads to improves efficiency in the analytical performance as compared to the manual sampler that always has low reproducibility in achieving analytical results. The auto sampler does not need the presence of an individual in its operation hence offering unattended operation. The auto sampler also provides an improved quality of sample throughput because of reduced errors by human beings as compared to manual sampler that always involve human inputs.
In ICP-AE, we used an internal standard. In general, what is an internal standard and why is it used?
The internal standard is an already known quantity of a compound but dissimilar to analyte and it is always used in the company of unknown. It helps in determining the amount of present analyte through the comparison of signal from the internal standard and that from the analyte.
Atomic absorption is subject to a number of different interferences. Describe these interferences?
The two interferences, which usually inhibit the concentration of delocalized gas-stage atoms, include ionization and the formation of molecular species. The interference due to ionization occurs because of the ionization in the ground state elements in the flame not permitting the ions to go to the excited state (Zabicky 726). This implies that it does not allow for the absorption of proper wavelength hence leading to ions with low levels of momentum.
With regards to question e, if we were concerned about these interferences in our analysi, what should we have done differently?
The solution to the ionization interference is the addition of ionization suppressant in excess to the material and standards used. Inhibiting the effect of the analyte ionization can occur through addition of an element acting as source of electron in the quest of suppressing the ionization effects (Zabicky 726). The added electrons will serve in shifting the equilibrium of the used analyte from its ionic form to the atomic form. The equation below shows how the suppressor normally reduces the effect of ionization:
Analyte <–> Analyte+ + e–
To reduce the effects of molecular species formation, there is need for vaporizing and atomizing the sample materials at high temperature. This suitable for sample, which are solid, or liquids while a flame may act as a high temperature source.
In light of question e and f, is it possible that there are matrix effects in atomic absorption analysis? If so, how accurate do you think our AA analyse were? If there are significant matrix effects, how should we have modified our procedure to enhance the accuracy of our analysis
Yes, there is possibility of matrix effects on atomic absorption analysis since the presence of ionization and formation of molecular species normally implies the presence impurities in the sample. The presence of ionization interference is always a subject to matrix effect. The AA analyses were not accurate because it did not take into consideration the effect of impurities on the sample. To modify the matrix effect, there is need for addition of standard solution to take care of any impurities that may be present in the sample. The standard solution represents a solution that the user knows its concentration in the analyte.
Question Seven
Does the semi-quantitative data that was obtained make sense in light of the published amounts of metals in each tablet, as well as you AA and AE analysis?
Semi-quantitative data makes sense in light of the published amounts of metals in each tablet, AA, and AE analysis because of the achievement of the standard. The values of the data are within 10 to 20 percent of the actual values. This makes it easy to understand and interpret the data extensively.
Why are there multiple peaks for each element in the XRF spectrum?
There are multiple peaks for each element because of lack of radiation. The essence of irradiated elements within the sample produces multiple or numerous peaks in the XRF spectrum during the experiment.
What is the source of the broad and large hump in the spectrum?
The source of the broad and large hump in the spectrum is known as the broadband power spectra.
What is the purpose of looking at three regions of the XRF spectrum sequentially?
The purpose of looking at the three regions of the XRF spectrum is to obtain accurate results through evaluation of data from the source. Evaluation is executed at each stage or region to enhance accountability or validity thus eliminating elements of error during the experiment (Beckhoff 435).
What role do filters and X-Ray tube parameters play in the 3-step data acquisition?
The X-Ray tube parameters act as the excitation source during the acquisition of data. The tubes also employ a heated tungsten filament that performs the role of inducing the emission with reference to thermionic electrons within the vacuum chamber. Filters within the three-step data collection act towards effective and efficient evaluation of data thus the achievement of reliable and valid data. X-ray tubes determine the nature of the elements to be excited. High power application would ensure lower limit detection hence efficiency of the process. Filters execute background reduction and enhancement of the fluorescence during the experiment. X-ray tubes perform the role of exciting secondary target from the source.
During semi-quantitative analysis, the spectrum fits to a universal calibration stored in the instrument. The sample matrix specification has to match for reasonable analysis of data to be performed (Beckhoff p. 436).
Why the analysis is semi-quantitative and not quantitative?
The analysis is semi-quantitative because it does not provide absolute amount of estimates within the sample. Quantitative analysis has the ability to offer absolute estimates when measuring amount of metals in the sample. The results of the experiment are within the 10 to 20 percent of the real values.
If we wanted to do fully quantitative analysis, rather than semi-quantitative, how would we perform our experiment? To what factors should we pay the most attention to during a quantitative analysis?
In execution of quantitative analysis, it is critical to compare spectral intensities of unknown samples to those of known standards in order to obtain accurate data that relates to the actual values. We should pay attention to dispersion of data, elements of error, accuracy of the source of data, and technique of sampling.
What are the advantages and limitations of XRF versus AA and AE?
One of the main advantages of XRF is its quick execution in comparison to AA and AE. The execution of the XRF in the process of measuring the metal within a sample can take less than an hour thus the quickest means in relation to speed. XRF is applicable in many disciplines thus effective and efficient method for measurement within sample. This includes XRF is applicable in geology, environmental remediation, recycling, and miscellaneous disciplines in comparison to AA and AE that are essential in limited areas. XRF is also cost-effective in operation in comparison to AA and AE. The devices or instruments are easy to use thus requires minimal time for the researcher to obtain the required information in relation to the experiment (Beckhoff p.434).
Some of the limitations of the XRF relate to the object, instruments, or both in the process of executing crucial experiments. High temperature and humidity affects the XRF instruments. This includes limitation to the analyzer and the substrate. The instruments are most efficient in the soil and scrap industry due to density and geometry of the sample. There is also essence of external interference by absorption and scattering or improvement of fluorescence. Detection is also a limitation as it hinders achievement of accurate information in relation to element of interest. The elements of interest are dissimilar in distribution within or on the artifact thus inaccuracy of data during the measurement process (Beckhoff 435).
Works cited
Alloway, Brian J, and Olle Selinus. Essentials of Medical Geology: Impacts of the Natural Environment on Public Health. Amsterdam [u.a.: Elsevier, 2005. Print.
Zabicky, Jacob. The Chemistry of Metal Enolates. Chichester: Wiley & Sons, 2009. Print.
Beckhoff, Burkhard. Handbook of Practical X-Ray Fluorescence Analysis: With 53 Tables. Berlin: Springer, 2006. Print.
