ASC115 ass2.docx

ASC115 Assignment 2, CP2404 Group members: Wenhui (244830B), Phoebe (240458M), Nabil (234568P) **[Content]** (Phoebe, Nabil) **Question 1** Identifying the organic compounds in wastewater Page 2-3 1.1 How we identified the organic compounds A and B in the wastewater sample 1.2 Describing the p...

ASC115 Assignment 2, CP2404 Group members: Wenhui (244830B), Phoebe (240458M), Nabil (234568P) **[Content]** (Phoebe, Nabil) **Question 1** Identifying the organic compounds in wastewater Page 2-3 1.1 How we identified the organic compounds A and B in the wastewater sample 1.2 Describing the peak symmetry of compound A 1.3 How we would use the mass spectrum to confirm the identity of compound A (Wenhui) **Question 2** Determining the concentration of heavy metals in wastewater Page 4-5 2.1 The calibration method used to determine the concentration of Cu2+ 2.2 Calculations of standard solutions of Cu2+ 2.3 The calibration curve 2.4 Calculations to determine concentration of Cu2+ in the wastewater sample before dilution 2.5 One suggestion that we can do to improve the quantitative analysis of Cu2+ and reasoning **Reflections** Page 6-7 What we have learnt from GC-MS What we have learnt from ICP-OES **Question 1** **1 Identifying Organic Compounds in Wastewater** ================================================= **1.1 Method for Identifying Compound A and B in Wastewater** ------------------------------------------------------------- The method used for identifying Organic Compounds A and B within the wastewater sample will be done by utilising a gas chromatography mass spectrometry (GC-MS) system. The carrier gas used for this process will be nitrogen (N~2~), which can produce lower sensitivity unless used in low optimal linear velocity. Samples will be prepared to for injection into the column in which it will then elute. After elution, the retention time of each compound within the system during elution will then be presented in a chromatogram against its abundance within the prepared sample. Additionally, the mass spectrum produced from the system can be used to help identify the compounds found within the sample. The peaks identified in the mass spectrum of each component can then be cross-referenced with that of known and pure compounds; this is known as qualitative analysis. \ Appendix A: Chromatogram of wastewater contaminated with Organic Compound A and B The results obtained from testing (as seen above) display the retention time of Organic Compounds A and B against their abundance within the wastewater sample. As observed, there is a lesser abundance of Compound A as compared to B and that Compound A has a lower retention time but a broader peak width, indicating slower elution or poor resolution. **1.2 Description of Peak Symmetry of Compound A Peak** ------------------------------------------------------- The peak symmetry of Compound A is a fronting one; seen as the peak being wider in front half than in the back. This could have been a result of injecting too much sample into the system or poor injection performance by the GC-MS system. **1.3 Mass Spectroscopy for Identification of Compound A** ---------------------------------------------------------- Appendix B: Mass Spectrum of Compound A The mass spectrum obtained after testing (as seen above) presents a molecular ion peak of m/z = 231. As that peak is also the most intense in the system, it is also the base peak of the compound. The m/z value of this peak will be then used to determine the molecular weight of the compound; with m/z = 231 indicating a molecular weight of 231g/mol. From there, we can identify the possible list of compounds that have that same molecular weight. However, the reference of our m/z value for our calculations to properly determine the identity of the compound must be of high resolution as we would need to match at least three out of five decimals from our calculated molecular weight to our obtained m/z value. **\ ** **Question 2** **2 Determining Concentration of Heavy Metal in Wastewater** ============================================================ **2.1 Calibration Method Used** ------------------------------- To determine the concentration of Cu^2+^, external calibration method was used; obeying y = mx rule. **2.2 Calculations of Standard Solutions of Cu^2+^** ---------------------------------------------------- 50ml of 50ppm of Cu^2+^ stock solution Direct dilution 15ppm: \ [*M*~1~*V*~1~ = *M*~2~*V*~2~]{.math.display}\ 10ppm: \ [(50*ppm*)(*V*1) = (10*ppm*)(10*ml*)]{.math.display}\ \ [\$\$V\_{1} = \\frac{\\left( 50ppm \\right)\\left( 10ml \\right)}{\\left( 10ppm \\right)}\$\$]{.math.display}\ V~1~= 2ml 5ppm: \ [(50*ppm*)(*V*1) = (10*ppm*)(10*ml*)]{.math.display}\ \ [\$\$V\_{1} = \\frac{\\left( 50ppm \\right)\\left( 10ml \\right)}{\\left( 5ppm \\right)}\$\$]{.math.display}\ V~1~= 1ml 1ppm:\ **Serial dilution from 10ppm solution** \ [(10*ppm*)(10) = (1*ppm*)(*V*2)]{.math.display}\ \ [\$\$V\_{2} = \\frac{\\left( 10ppm \\right)\\left( 10ml \\right)}{\\left( 1ppm \\right)}\$\$]{.math.display}\ V~2~= 100ml **2.3 Calibration Curve of ICP-OES** ------------------------------------ y-axis: Absorbance in x10^6^ unit x-axis: Concentration in ppm conc. (ppm) Abs(10^6^) ------------- ------------ 1 1.7 5 7.2 10 18.2 15 22.7 Gradient= [\$\\frac{\\left( 26.25 \\times 10\^{6} \\right) - (10 \\times 10\^{6})}{16.25 - 6.25}\$]{.math.inline} = 1.625[×]{.math.inline}10^6^ y= (1.625[×]{.math.inline}10^6^) **2.4 Calculations to determine concentration of Cu^2+^ in the wastewater sample before dilution** -------------------------------------------------------------------------------------------------- Absorbance for Unknown = 20.5 x 10^6^ y= (1.625[×]{.math.inline}10^6^)[*x*]{.math.inline} 20.5 x 10^6^ = (1.625[×]{.math.inline}10^6^)[*x*]{.math.inline} \ [\$\$x = \\frac{20.5\\ x\\ 10\^{6}\\ }{1.625 \\times 10\^{6}}\$\$]{.math.display}\ = 12.61ppm Dilution Factor: 2 Concentration of unknown before dilution = 12.61 x 2 **2.5 Suggestion on Improving Quantitative Analysis of Cu^2+^** --------------------------------------------------------------- To improve quantitative analysis of Cu^2+^, we can focus on the sample preparation method. Factors such as chemical and spectral interference could alter the behaviour of Cu^2+^ during analysis, such as change in volatility. To minimize chemical interference, we can do matrix matching of standards and blank to the sample by using same solvent or same concentrations. **Reflections** =============== [Wenhui] Through GC-MS, I learnt how to identify different compounds based on their molecular weight and separation characteristics. In GC-MS, the choice of column based on their polarity is also important. Even though we did not get to have hands on for gas chromatography, we learnt about the different column characteristics during lecture, and different type of carrier gas that can be used. I also learnt that some compounds requires chemical modification, such as silylation, to improve volatility and detectability. Having chance to observe how an ICP-OES machine is operated, and the sample preparation method, I have a clearer idea of how it is used for quantitative analysis. Compared to other spectroscopy methods, ICP-OES provides the fast results with high throughput. The high temperature plasma also reduces the chemical interference that could affect the atomization of analyte in the flame.  Through lectures, I also learnt that if the absorbance measured is too high, it could be due to spectral interference when substances in the flame absorb same wavelength as the analyte.  [Phoebe ] What I have learnt from GC-MS: How to read and understand the chromatograph and how are they created. Knowing how to identify the components in the wastewater provided. I also learnt to apply my knowledge from the e-lectures into the assignment, reading the graphs and implementing what I recall into my statements. What I have learnt from ICP-OES: I learnt to use an ICP-OES and how it works. I learnt to read the results and how to use them in my calculations. Knowing how to operate an ICP-OES will be useful in the future when i start internship and if my job requires me to operate one. Using my knowledge form the e-lectures, I was prepared to use the ICP-OES with little to no issues as I knew some of the basics to operating one from the videos provided and this allowed me to put the knowledge to the test and observe how it works in real time and see it more closely. [\ ] [Nabil] The usage of GC-MS systems has helped me to apply my knowledge of molecular polarity and composition and its effect on the extraction process of compounds within a sample solution. Depending on the process and intended result, different columns can be applied to assist in the goals of compound separation; such as using non-polar columns to extract and identify non-polar compounds with higher accuracy due to the longer retention time. Additionally, the molecular composition of a compound also affects its retention within the GC-MS; as more complex structures tend to take longer for elution. It was also a great opportunity to learn about the types of carrier gas used in a GC-MS system and its relationship with the mobile phase flow velocity affecting the quality of results, as well as providing insight into how to industry makes financial decisions for lab testing. The ICP-OES system helps to identify components within a sample by using measuring the light emitted from atoms or ions that have been excited by the plasma. The data gathered from the process is presented as fragmentations on a spectrum over wavelengths which can be then used to identify the presence of a compound in a sample based the peaks present. Although I was unable to operate the system due to missing the practical, I got to use the system a lot during my ITE days and reading up on the procedure for carrying out ICP-OES testing helped me to refresh my spectrum reading and analysis of data gathered from the system; helping me to derive the concentration of a target compound within a sample such as the wastewater used in the practical.