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ATOMIC SPECTROSCOPY
LABORATORY
EXPERIMENTAL LIST
1. DETERMINATION OF CALCIUM IN BABY POWDER SAMPLES USING FAAS
2. COMPARISONS OF LEAD LEVEL BETWEEN ORGANIC AND CONVENTIONAL VEGETABLES USING AAS
3. DETERMINATION OF IRON IN SOILS SAMPLES BY AAS
4. HEAVY METALS AND ESSENTIAL MINERALS DETECTION IN FOOD SAMPLE USING ICP-OES
5. MERCURY DETECTION IN VARIOUS SAMPLES USING FIMS
LAB NOTEBOOK
You must have a lab notebook with you at all times when you are doing your lab. Please record all procedures (eg. Instrument parameters, dilutions carried out), data and observations in your lab notebook. The lab notebook is to document the results of an experiment. All entries must be in permanent ink. For each experiment carried out, you should have at least the following in your lab notebook:
1. Title and date of lab. Record the dates for additional work done on different days.
2. Record any changes to the procedures given in the manual.
3. Record all raw data in an organized manner. NEVER use white out for mistakes, just cross out with one or two lines.
4. Record all relevant observations.
5. Include all chemical calculations (eg. For making up standard solutions).
LAB REPORTS (DUE 2 WEEKS AFTER LAB IS CARRIED OUT)
Lab reports must be written with a word processor, single sided only, with numbered pages. You will lose points if you have identical figures, tables or wording with other members of the class.
REPORT FORMAT
1. Title, your name, date
2. General objectives (be brief)
3. Method/ Procedures
a. Summarise any changes to the procedure in the manual.
b. Include examples of relevant calculations in processing the data.
4. Results and discussion
a. Present your data in a well organized manner. Organize this section according to the order that information is requested in the lab directions. There is no need to tabulate data that is already found in plots. Take care to show the proper units and significant figures.
b. When discussing results refer to specific figures or tables. Do not include figures or tables which are not included in the discussion.
5. Answers to questions
EXPERIMENT 1: DETERMINATION OF CALCIUM IN BABY POWDER SAMPLES USING FLAME EMISSION SPECTROMETRY
INTRODUCTION
Flame photometry is an atomic emission method for the routine detection of metal salts, principally Na, K, Li, Ca, and Ba. Quantitative analysis of these species is performed by measuring the flame emission of solutions containing the metal salts. Solutions are aspirated into the flame. The hot flame evaporates the solvent, atomizes the metal, and excites a valence electron to an upper state. Light is emitted at characteristic wavelengths for each metal as the electron returns to the ground state. Optical filters are used to select the emission wavelength monitored for the analyte species. Comparison of emission intensities of unknowns to either that of standard solutions, or to those of an internal standard, allows quantitative analysis of the analyte metal in the sample solution.
Flame photometry is a simple, relatively inexpensive, high sample throughput method used for clinical, biological, and environmental analysis. The low temperature of the natural gas and air flame, compared to other excitation methods such as arcs, sparks and rare gas plasmas, limit the method to easily ionized metals. Since the temperature is not high enough to excite transition metals, the method is selective toward detection of alkali and alkali earth metals. On the other hand, the low temperatures render this method susceptible to certain disadvantages, most of them related to interference and the stability (or lack thereof) of the flame and aspiration conditions. Fuel and oxidant flow rates and purity, aspiration rates, solution viscosity, concomitants in the samples, etc affect these. It is therefore very important to measure the emission of the standard and unknown solutions under conditions that are as nearly identical as possible.
This experiment will serve as an introduction to sodium analysis by flame emission photometry and will demonstrate the effects of cleanliness and solution viscosity on the observed emission intensity readings. The instrument is calibrated with a series of standard solutions that cover the range of concentrations expected of the samples. Standard calibrations are commonly used in instrumental analysis. They are useful when sample concentrations may vary by several orders of magnitude and when the value of the analyte must be known with a high degree of accuracy. This experiment does not produce hazardous waste.
Calcium is one of the most abundant element that can be found in the Earth crust. Calcium carbonate is a dietary supplement used when the amount of calcium taken in the diet is not enough. Calcium is needed by the body for healthy bones, muscles, nervous system, and heart. Calcium carbonate also is used as an antacid to relieve heartburn, acid indigestion, and upset stomach. It is available with or without a prescription. Commonly known as: limestone, marble, calcite. It is an inorganic compound that is neutral, substantially insoluble in water, and soluble in hydrochloric acid.
Talc is a clay mineral, composed of hydrated magnesium silicate with the chemical formula Mg3 Si4O10(OH)2. Although all talc ores are soft, platy, water repellent and chemically inert. Talc is practically insoluble in water and in weak acids and alkalis. It is neither explosive nor flammable. Although it has very little chemical reactivity, talc does have a marked affinity for certain organic chemicals, i.e. it is organophilic. Above 900 °C, talc progressively loses its hydroxyl groups and above 1050 °C, it re-crystallizes into different forms of enstatite (anhydrous magnesium silicate). Talc's melting point is at 1500°C. Talc in powdered form, often combined with corn starch, is used as baby powder. Today it also plays an important role in many cosmetic products, providing the silkiness in blushes, powder compacts and eye shadows, the transparency of foundations and the sheen of beauty creams. In pharmaceuticals, talc is an ideal excipient, used as a glidant, lubricant and diluent. Soap manufacturers also use talc to enhance skin care performance.
Crystal structure of talc
PROCEDURE
Consult your Laboratory Assistant and teaching assistant for operating instructions of the flame photometer. Allow a sufficient warm-up period. Be sure to aspirate deionized- distilled water between samples to clean out the sample tube and aspirator. Calcium is ubiquitous. It is imperative that you use scrupulously cleaned glassware to obtain good results. The calibration curves of standard solution were plotted as absorbance or intensity against concentration in ppm.
STANDARD PREPARATIONS
Prepare calcium chloride standard solutions by volumetric dilution of the stock solution. The following approximate concentrations should be made: 1.0, 2.0, 3.0, 4.0 and 5.0 ppm as Ca. Make sure you use volumetric pipette or micropipette and not graduated pipette (know the difference). You will be given a 1000 ppm Ca solution, so make a 100 ppm solution first. From the 100 ppm, you can prepare your 1.0, 2.0, 3.0, 4.0 and 5.0 ppm. Do not contaminate the 1000 ppm Ca solution. Pour some into a beaker for your own use, estimate how much you need. If there is any left, throw it away. DO NOT PUT IT BACK INTO ORIGINAL STOCK SOLUTION.
ACID DIGESTION
The acid digestion procedure performed in this study was adopted from a study reported by Ang and Lee in year 2005. Each of the samples is weight of 0.5 g in 50 mL beaker. A 9 mL of aqua regia acid of HNO3 :HCl is added with the ratio of 1:3 into the beaker. The samples is put into the water bath for boiled at 95 °C for 4 to 5 hours or completely dissolved. During the digestion, deionized-distilled water is added to wash the inner wall. After the digestion is completed, the samples is filtered with filter papers (WHATMAN, qualitative filters paper, 125 mm diameters) and transferred into 50 mL conical flask. After that, the solution is diluted with deionized-distilled water until the mark.
INSTRUMENTAL ANALYSIS
In this study, there are two instruments from analytical laboratory were used to determine the amount Fe in the studied samples. The two instruments were Perkin Elmer AAnalysist 400 Flame Atomic Absorption Spectrometer (FAAS). The operating condition for FAAS is shown in Table 1.
REMAINING SAMPLE
Keep the remaining sample for Experiment 5.
RESULTS
Record your reading. Discuss the results obtained.
REFERENCES
1. Rudenko, Pavlo; Bandyopadhyay, Amit (2013). "Talc as friction reducing additive to lubricating oil". Applied Surface Science. 276: 383–389.
2. Uddin AH, Khalid RS, Alaama M, Abdualkader AM, Kasmuri A, Abbas SA. Comparative study of three digestion methods for elemental analysis in traditional medicine products using atomic absorption spectrometry. J Anal Sci Technol. 2016;7(1). doi:10.1186/s40543-016-0085-6.
3. NUR ANISHA BINTI AZMAN, 2020; “Determination Of IRON (Fe) in soils samples By atomic absorption spectrometry and inductively coupled plasma-optical emission Spectrometry” ; Thesis B.Sc. (Hons.) USM, Supervisor: Lim Gin Keat.
EXPERIMENT 2: COMPARISONS OF LEAD LEVEL BETWEEN ORGANIC AND CONVENTIONAL VEGETABLES USING AAS
INTRODUCTION
Organic is defined as a product that has been produced through acceptable methods that assimilate mechanical practices that encourage cycling of resources, conserve biodiversity and promote ecological balance. There are three different classifications of organics: 100% organic, organic, and made with organic ingredients. 100% organic can only contain organic ingredients, meaning no antibiotics, hormones, genetic engineering, radiation or fertilizers can be used. Organic must contain 95% organic ingredients, with the balance coming from ingredients on the approved National List. The USDA organic logo can be displayed on both 100% organic and organic products. Products made with organic ingredients must be made with at least 70% organic ingredients, three of which must be listed on the package, and the balance must be on the National List. Products made with organic ingredients are not allowed to display the USDA organic logo.
Organic agriculture emphasizes farming based on management of the surrounding ecosystem, integrated cropping and livestock systems, diversity of products, dependence on natural pest and disease control without the use of chemical inputs. The principal objectives of organic agriculture are to produce healthy and sustainable food only using biological and ecological processes. Globally, the organic industry is estimated to exceed $40 billion. While sales in the United States totaled $26.6 billion in 2010. There are more than 100 countries growing organic foods and producing organic products. Ninety of these countries are developing countries with perfect climatic conditions to produce the best organic product.
The debate about the differences in nutritional properties between organic and conventional food interested largely researchers, as shown by the consistent number of papers and reviews published in few years. All the reviews existing about this topic reported different results. Some of these, concluded that organic foods have higher content of such constituent instead others underlined the absence of differences in nutritional values between the two alternatives. The opposite outcomes were principally ascribed to the lack of coherence in study design and implementation. In fact, frequently, inaccurate comparisons led to assert the superior quality of organic respect to conventional foods.
EXPERIMENTAL
SAMPLES COLLECTION AND HANDLING
TWO portions of vegetables which consist of organically and conventionally farmed is purchased from a hypermarket in Penang. The vegetable can be spinach, luffa, Chinese broccoli, spinach or kangkung.
SAMPLES PREPARATION
Weigh 1-2 g of both dried (in oven) vegetables and transfer into separate long neck Kjeldahl flask. In each of the flask, add 20 mL of concentrated HNO3 acid, and carefully and gently shake the flask so that all parts of the sample becomes thoroughly wet. Heat up the flasks gently at low temperature in the beginning; follows by heating the flasks at higher temperature in a electrical heating mantle until the volume of the acid is reduced to 5 mL. DO NOT LET THE SAMPLES TO BECOME DRY!
Notes:
a) NO2 will be released therefore the setup must be done inside the fume hood.
b) The samples may ignite and burn if it is heated too strongly at the beginning of digestion.
c) Generally, the heating should be done for about 30 mins. The longer the heating (at the same temperature), the better will be the result.
Cool the Kjehldahl flasks and filter their contents using deionized glass wool into separate 50-mL volumetric flasks. In each Kjeldahl flasks, add 5-10 mL deionised distilled water into the empty flasks, boil the flasks and filter as like before. Rinse the filter funnels and Kjeldahl flasks with distilled water into their volumetric flasks before top up distilled water up to the mark.
Keep the solutions for AAS analysis. Calculate the mean Pb concentration using the calibration curve recorded below.
STANDARD CALIBRATION METHOD
From the 1000 ppm stock solution, prepare working solutions that contain 1, 2.5, 5 and 10 µg/mL Pb in 1% HNO3 using 100-mL volumetric flasks and the 5-, 10- and 25-mL pipettes provided. Also prepare a blank solution of 1% HNO3. For the preparation of analytical standards with ±0.1% accuracy, you should always use a transfer pipette with a volume of 5-mL or greater and volumetric flasks with a volume of 25 mL or greater. In this case, prepare first a 100-ppm working standard from the 1000-ppm stock solution and make appropriate dilutions from this to prepare the 10- and 5-ppm standards. The 1- and 2.5-ppm can then be prepared from your 10-ppm standard. Record how you prepared these standards in a table in your report.
For making absorbance measurements, set the integration time to 5 seconds.
Aspirate the blank solution and zero the instrument. Then aspirate each of the standards in turn followed by the prepared unknown sample, making three measurements on each. Aspirate water or blank between each measurement. Occasionally re-zero the instrument with the blank, approximately every ten samples, or more if any drift is observed.
Plot absorbance vs. concentration and determine the concentration of Pb in µg/mL (using linear regression, leave out any standards which do not fall on the linear portion of the plot).
DATA TREATMENT
Compare the results for Pb obtained by the two vegetable samples, including the 95% confidence interval for each. Apply the appropriate t-test to determine if there is statistically significant difference between the two means.
SENSITIVITY AND LIMIT OF DETECTION
SENSITIVITY
Based on your measurements in the preceding section, determine the sensitivity for Pb. Report the value and include a definition of the term you are reporting.
DETECTION LIMITS
Based on your calibration data from the previous section, prepare a Pb standard in 1% nitric acid that will yield an absorbance reading of approximately 0.01. Use this LOD standard to obtain data for the limit of detection. Do not change the integration time setting. The goal here is to determine the LOD for the determination of Pb as you performed it.
Zero the instrument with the 1% nitric acid blank solution and measure the absorbance of the LOD standard ten times, aspirating water or blank between each measurement andre- zero the instrument with the same frequency as you used in the determination of Pb. Obtain the standard deviation for the ten measurements and calculate the limit of detection in µg/mL. Use the expression LOD = nσ/m,where n=2.
REMAINING SAMPLE
Keep the remaining sample for Experiment 5.
REFERENCES
1. Sawyer, Heineman, Beebe, Chemistry Experiments for Instrumental Methods, Wiley, New York, 1984.
2. SITI NURSYAZWANI MOHD ZAMRI, 2017; “Nutrient Comparisons Between Organic and Conventional Vegetables”; Thesis BSc (Hons.) USM, Supervisor: Lim Gin Keat.
3. Woese, K., Lange, D., Boess, C., & Bogl Werner, K. (1997). A Comparison of Organically and Conventionally Grown Foods. J of Sci Food and Agr, 74, 281‐293.
EXPERIMENT 3: DETERMINATION OF IRON IN SOILS SAMPLES BY ATOMIC ABSORPTION SPECTROSCOPY
INTRODUCTION
Iron is the most abundant transition metal in the Earth’s crust, yet it is not commonly reported as a soil or sediment pollutant. Most of the iron comes from Fe(II) bound in the lattice structures of ferro-magnesian silicate minerals and in magnetite, a mixed-valence Fe oxide. An exception is in the rice industry, which increases Fe(II) concentrations under low oxygen conditions, which may lead to Fe toxicity and negatively impact to the rice yields. However, under anaerobic conditions the bioavailability and toxicity of the iron is confined by its very low solubility, as a result, the iron (oxy-hydr) oxide minerals seem to be precipitated and stabilised.
Steel is an essential raw material used in the manufacturing, machinery and engineering industries, transport equipment (automotive, rail and shipping) as well as a major component of infrastructure projects. It also contributes to the fact that, steel production capacity is seen as a national concern to add value to natural resources, facilitate ready distribution to the manufacturing and construction industry, substitute imports and increase foreign exchange savings.
EXPERIMENTAL
CHEMICAL AND STANDARD
Concentrated HNO3 (65%), dilute HNO3 (1%), HCl (37%) and standard solution of 1000 ppm. All the working standards solution were freshly prepared prior analysis. The deionized water was prepared in the lab and used throughout the whole study in preparation of standard solution and sample digestion.
SAMPLE COLLECTION AND HANDLING
Two soil samples (preferably red soil) are collect in different places in Universiti Sains Malaysia.
ULTRASONIC ACID DIGESTION METHOD
The ultrasonic acid digestion using here is adopted from the study reported by Tasneem G. Kazi in year 2008. Weigh 0.5 g of samples into a 50-mL conical flask. A 9 mL of acid combinations of HNO3 :HCl is added with the ratio of 1:3. Next, allow the samples to stand for 15 min before immerse in ultrasonic water bath for 25 min at 80 ℃ for sonification. After the process, rinse the inner wall with deionized water and sonicate again for another 2 min. Then, transfer the samples into the 100-mL volumetric flasks and top up to the mark. Finally, centrifuge the sample for 10 min at 3000 rpm. Keep the resultant solution in refrigerator for next part.
STANDARD ADDITIONS METHOD
Pipet 10.0 mL of samples into each of the three 50-mL volumetric flasks. Into FIVE of the flasks pipet 2.5, 5.0, 7.5, 10.0 and 12.5 mL of your 10-µg/mL Fe standard, respectively. Dilute each to volume with 1% HNO3.
Zero the instrument with the 1% HNO3 blank solution and measure the absorbance of each of the three solutions. Determine the concentration of copper in the unknown based on these measurements.
INSTRUMENTAL ANALYSIS
Inject your samples into Perkin Elmer AAnalysist 400 Flame Atomic Absorption Spectrometer (FAAS) with the operating condition
|
Parameter |
Conditions for Fe |
|
Wavelength (nm) Slit Width (nm) Lamp Type Lamp Current (mA) Flame Composition |
248.3 1.8 C-HCL 30 Air/C2H2 |
SPECIAL PRECAUTIONS
Before beginning this experiment, please read the following carefully.
1. Never exceed the maximum current rating of the hollow cathode. This rating is checked during the instrument set-up procedure.
2. Always turn the air on first, establish the flow, then turn of the acetylene, establish this flow and ignite the burner. To shut down the burner, reverse this operation. This instrument does this under computer control.
3. If the Mg lamp is in place, assume the burner alignment is correct. If not, do not attempt to move the burner head without first checking with the instructor.
4. If the flame wavers due to drafts in the room, very sporadic data will be obtained. If such a condition exists be sure to block out any drafts and protect the burner form these fluctuations.
5. A clogged burner slot is indicated by an uneven flame. This can be corrected by carefully scraping the burner slot with a spatula or razor blade while running air-only through the burner. Check with your instructor if you suspect that there is a problem like this.
6. Never aspirate a sample with the burner off and always aspirate distilled water after each sample aspiration. When aspirating a variety of samples be sure to rinse the polyethylene tubing between each aspiration with distilled water from a wash bottle and carefully wipe the tubing dry.
PE AAnalyst-100 Instrument Operating Procedures. Please read these instructions completely before operating the instrument or attempting any of the procedures outlined below (the procedures might be different with another version of the operating software).
1. Turn on the instrument, using the Power switch. (This is on the right side next to the power cable input).
2. Turn on the computer and printer. When you have your desktop displayed start the AA program form. the AA WinLab Analyst icon. From the WinLab introduction screen select the “basic system” icon. This will bring you to the “Manual Analysis” window from which you will collect the data for this lab.
3. Select your method from the top menu bar and select the method. You will find most of your parameters set as defaults. This instrument will do an automatic optimization each time the method is closed. Also note that F1 will bring you the appropriate Help for the window that is currently active.
4. Turn on the gas valves, for air and acetylene, on the top of both the tanks.
5. Access the Flame window from the top menu bar. A switch icon in this window will start gas flow and light you burner flame when clicked.
6. Select ‘continuous graphics’ under the tools menu to get a window that shows the lamp signal. Start aspirating your standard. Adjust the absorbance reading to a maximum value by moving the burner assembly up and down and in and out.
INSTRUMENT SHUT-DOWN SEQUENCE
1. Aspirate air when done.
2. Go to the flame window and click off. Turn the main gas tank valves off and bleed the system by hitting the bleed button. Notify the instructor if the acetylene pressure is less than 120 lb/in2 or if the air pressure is less than 1000 lb/in2.
3. Turn the instrument off and shut down the PC.
REMAINING SAMPLE
Keep the remaining sample for Experiment 5.
REFERENCES
4. NUR ANISHA BINTI AZMAN, 2020; “Nutrient Comparisons Between Organic and Conventional Vegetables”; Thesis BSc (Hons.) USM, Supervisor: Lim Gin Keat.
5. Kazi, T.G., Jamali, M.K., Arain, M.B., Afridi, H.I., Jalbani, N., Sarfraz, R.A. and Ansari, R., 2009. Evaluation of an ultrasonic acid digestion procedure for total heavy metals determination in environmental and biological samples. Journal of Hazardous Materials, 161(2-3), pp.1391-1398.
EXPERIMENT 4: HEAVY METALS AND ESSENTIAL MINERALS DETECTION IN FOOD SAMPLES USING ICP-OES
INTRODUCTION
Food is a primary source of nutrients such as minerals. Today, foods are readily contaminated by toxic elements due to the environmental pollution. Thus, public are of increasingly concern about the safety of food consumed daily. In this study, Penang Assam Laksa were collected from a selected stall. The food sample will first be digested using microwave digestion procedure. After that, the content of heavy metals (Cd, Hg, Pb) as well as essential minerals (Fe, Ca, Na, K) in these food samples were detected using ICP-OES (Inductively Coupled Plasma – Optical Emission Spectrometry).
A) SAMPLE COLLECTION AND HANDLING
1. Food sample is purchased from the selected stall, in which solid food and soup are packed into separated leak proof nylon bags.
2. The solid food is soaked into the soup and leaves it for 20 minutes.
3. The soup is filtered and collected for further treatment.
B) MICROWAVE DIGESTION ON FOOD SAMPLES (MODIFIED FROM FDA METHOD)
Method Blank: 1 g of reagent water Step:
1. A 1 g of homogenized samples and 8 mL of HNO3 into digestion vessel
(REMARKS: Add the HNO3 drop by drop to avoid vigorous reaction)
2. Add 1 mL of high purity H2O2
3. Cap and place the vessel into microwave system
4. Start the digestion:
● Ramp power over 25 minutes until temperature of 200 °C is reached
● Maintain the temperature at 200°C for about 15 minutes
5. Cool the vessel to <50 °C and remove the carousel from oven
6. Top up the sample solution with more reagent water to obtain a final volume of 25 mL
REMARKS: The freshly collected food sample will be preceded to digestion procedure on the same day of collection.
Reference
http://www.fda.gov/downloads/Food/FoodborneIllnessContaminants/Metals/UCM27269 3.pdf
C) INSTRUMENTAL ANALYSIS
1. Working standard solutions are prepared accordingly by diluting the standard stock solutions of 1000 ppm.
2. For ICP-OES, 4 levels of standard solutions are prepared for each element in every calibration cycle.
3. Once the calibration curve exhibits the linearity between absorbance intensity and concentration (R2 > 0.99), the analysis of the samples is proceeded.
4. The operating conditions for ICP-OES are shown in the Part F.