JCE-Ca-AAS Dunnivant 1
Contents
1. also evaluate the affect of adding a releasing agent Sr to your sample and standards You should completely understand why you are adding this before you come to lab v Make a stock solution of Sr NO3 at a concentration that will serve to meet the requirements below Check with me before you make the solutions to ensure that you have the calculations correct v Make a set of solutions containing a known amount of Ca standard your hazardous waste sample and Sr at 1000 mg L in the final solution As a starting point calcium concentrations in the final solutions should be 0 0 5 1 5 10 15 25 and 50 mg Ca L BUT you must determine the exact range of standards Review the standard addition procedure in Skoog Based on your earlier determination of Ca in your sample add an appropriate range of Ca to your samples to yield a plot similar to the one in your textbook For example you should not have to over extrapolate your plot to estimate the concentration of Ca in your sample the positive range of your standards should be of the same scale JCE Ca AAS 9 Dunnivant as the negative extrapolation When you make these solutions I suggest making the samples in 25 50 or 100 mL volumetric flasks For example if a 25 mL volumetric flasks are used add 10 mL of your simulated hazardous waste sample a volume of concentrated nitric acid to yield 1 in the final solution the required volume of Sr solution to obtain 1000 mg Sr L and fill the re2. and compounds can be analyzed by more than one technique Some of these techniques are more direct and simple while others are more involved When samples from industry or the real world are analyzed an additional consideration interferences must be also considered Many samples contain such complicated interferences that the sample is described as a complex matrix It should be no surprise that when a complex matrix is analyzed by a variety of techniques that the measured concentrations do not always agree In these labs you will measure the concentration of Ca in a simulated hazardous waste by flame atomic absorption spectrophotometer FAAS using external standard and standard addition techniques as well as matrix modifiers by EDTA titration an applied review of quantitative analysis and using a Ca ion specific electrode another review of quantitative analysis Although your sample is safe as you handle it consider it as a hazardous waste What steps will you take in the following procedures to protect yourself and your lab partners The order that you do these labs is not important and they will be randomly assigned so that no two groups are doing the same lab at the same time The labs are determination of Ca by flame atomic absorption spectroscopy using external standards without a releasing agent Sr determination of Ca by flame atomic absorption spectroscopy using external standards with a releasing agent Sr determina
3. JCE Ca AAS 1 Dunnivant Lab Documentation Chemicals needed for the following procedures Instructor Information Chemicals One or more carbonated beverages Coca Cola and Pepsi appear to be the most challenging to analyze Other options that have been tried are 7 Up diet and regular and Budweiser beer A reference Ca Atomic Absorption standard 1000 mg L Sr NO3 salt CAS number 10042 76 9 for use as a releasing agent in the FAAS analysis Untra low AAS grade concentrated nitric acid CAS number 7697 37 2 and two empty 2 L acid bottles for dilutions Three liters of standardized NagH EDTA 2H 0 solution FW 372 25 g mol CAS number 6381 92 6 dry at 80 C for 1 hr cool weigh out 0 6 g and dissolve in 400 mL DI Fill to mark in 500 mL vol know the exact weight of EDTA for determining the molarity 50 by wt NaOH CAS number 1310 73 2 Solid hydroxynaphthol blue CAS number 63451 35 4 as an indicator in the EDTA titration Instruments A Ca AAS hollow cathode lamp An AAS unit A Perkin Elmer 1100B was used in these experiments A pre soaked Ca Electrode and ionic strength adjustor Corning Model 34120 70 VWR Scientific Products Catalog Number 34120 706 was used in these experiments Reference electrode for the Ca ISE A millivolt meter JCE Ca AAS 2 Dunnivant Metal Analysis Ca Determination by A Variety of Techniques Student Information The purpose of this series of laboratory exercises is to show that many elements
4. centration of 1 nitric acid When you make these solutions I suggest making the samples in 25 50 or 100 mL volumetric flasks For example when preparing a standard in a 25 mL volumetric flask add a volume of standard to yield the desired final concentration of Ca a volume of concentrated nitric acid to yield 1 in the final solution the required volume of Sr solution to obtain 1000 mg Sr L in the final solution and fill the remainder with distilled water For a sample in a 25 mL volumetirc add an exact and known volume of sample as much as possible since this will improve your detection limit concentrated HNO to yield 1 in the final solution a volume of SrNO solution that will give you 1000 mg Sr L in the final solution and fill the flask with distilled water to the mark Remember to make 5 replicate solutions of your sample v Setup the AAS as instructed 20 minutes before you are finished making your solutions You should already know the lamp current wavelength slit width and fuel and air flow rates v Analyze the standards and samples on the AAS v Make sure that the data set is linear If it is not consult me before you throw away your solutions v Plot the data approximate the linear portion of the data and if the unknown sample signal is in the linear range estimate the concentration of Ca You will have to re do this more accurately for your JCE Ca AAS 7 Dunnivant article If the signal of the sample is too high mak
5. e the appropriate dilution of the sample in 1 HNO and reanalyze all five replicates JCE Ca AAS 8 Dunnivant Determination of Ca using Atomic Absorption Spectroscopy using the Standard Addition Technique with and without Sr Student Procedures Purpose 1 refine your ability to make reference standards Ca 2 learn to use the atomic absorption spectroscopy system 3 learn the standard addition technique 4 learn one technique for overcoming interferences 5 determine the concentration of Ca in a simulated hazardous waste sample Plan ahead and completely understand the standard addition procedure before you come to lab Reading for the AAS is in chapters 8 and 9 Skoog while information on releasing agents and standard addition can be found on pages 221 and 15 18 respectively With respect to the standard addition method I will show you a better way of doing this DO ALL CALCULATIONS FOR DILUTIONS AND PREPARING SOLUTIONS BEFORE YOU COME TO LAB OR YOU WILL BE VERY LATE LEAVING TODAY Exercises Prepare all solutions first When you are approximately 20 minutes from finishing making your solution turn on the AAS unit adjust the lamp current and allow it to warm up about 20 minutes Standard addition calibration method with the Sr releasing agent Here we are concerned with overcoming viscosity effects from the sample matrix We ignored this in the external standard method but it may have been present We will
6. elength slit width and fuel and air flow rates before you arrive in lab e Analyze the standards and unknown samples on the AAS e Plot the data approximate the linear portion of the data and if the unknown sample signal is in the linear range estimate the concentration of Ca You will have to re do this more accurately for you JCE Ca AAS 6 Dunnivant report If the signal of the sample is too high make the appropriate dilution of the sample in 1 HNOs and reanalyze all five replicates of your sample External standard calibration method with the Sr matrix modifier We will also evaluate the affect of adding a releasing agent Sr You should completely understand why you are adding this before you come to lab Again I suggest analyzing your standards from low to high concentration and making a blank measurement between each standard Repeat this entire process twice This will give you 15 to 20 blank measurements which you will need to determine the signal to noise ratio v Make a stock solution of Sr NO3 at a concentration that will serve to meet the requirements below Check with me before you make the solutions to ensure that you have completed the calculations correctly v Make a set of standards and samples containing Sr at a final concentration of 1000 mg L Calcium concentrations in the final standards should be 0 0 5 1 5 10 15 25 and 50 mg Ca L Also make sure that each standard and sample contains a final con
7. he concentration of Ca in a simulated hazardous waste sample analyze your sample at least 5 times Plan ahead have your calculations make for your solutions and completely understand this procedure before you come to lab Reading for the AAS is in Chapters 8 and 9 Skoog Exercises Prepare all solutions first When you are approximately 20 minutes from finishing making your solution turn on the AAS unit adjust the lamp current and allow it to warm up about 20 minutes External standard calibration method without the Sr matrix modifier This is the normal way of using a calibration curve you make a set of standards measure the instruments response to the standards and unknowns make a plot and use the instrument response to estimate the concentration I suggest analyzing your standards from low to high concentration and making a blank measurement between each standard Repeat this entire process twice This will give you 15 to 20 blank measurements which you will need to determine the signal to noise ratio e Make a set of Ca standards in 1 HNO3 Concentrations as Ca should range from 0 1 to 50 mg L Evenly divide up the concentrations into 10 standards Note that some of these standards will be below the detection limit while others may be above the limit of quantitation LOQ e Make 5 replicate solutions of your simulated hazardous waste sample e Setup the AAS as instructed you should already know the lamp current wav
8. mainder with distilled water i e to each volumetric flask add 1 an exact and equal volume of sample to each flask as much as possible 2 concentrated HNO to yield 1 3 a volume of SrNO solution that will give you 1000 mg Sr L and 4 fill the flask with distilled water to the mark v Setup the AAS as instructed 20 minutes before you are finished making your solutions You should already know the lamp current wavelength slit width and fuel and air flow rates v Analyze the solutions on the AAS unit v Make sure that the data set is linear If it is not consult me before you throw away your solutions v Plot the data determine the linear portion of the data and if the unknown sample signal is in the linear range determine the concentration of Ca You will have to re do all of this using your spreadsheet If the signal of the sample is too high make the appropriate dilution of the sample in 1 HNOs and reanalyze all five replicates Standard addition calibration method without the Sr matrix modifier Repeat the procedure given above but do not add Sr to your solutions JCE Ca AAS 10 Dunnivant AAS Questions for the Students In the four AAS procedures we are evaluating one physical and one chemical interference The physical interference can be evaluated by comparing the difference in the detection limit and slope of your calibration curves for each procedure The chemical interference will be distinguishable with the
9. tion of Ca by flame atomic absorption spectroscopy using standard addition without a releasing agent Sr determination of Ca by flame atomic absorption spectroscopy using standard addition with a releasing agent Sr determination of Ca by EDTA titration determination of Ca by ion specific electrode JCE Ca AAS 3 Dunnivant At the beginning of the first lab you will have to remove the carbonation in your sample by placing it in a vacuum system for at least 1 hour FOR EACH TECHNIQUE except the standard addition ANALYZE THE UNKNOWN SAMPLE FIVE TIMES What do you turn in One of the goals of the chemistry department is not only to teach you proper methods for analyzing samples but to also teach you to how to analyze the data and to effectively disseminate your results and conclusions One dissemination method is your lab notebooks and lab reports that you will complete for the other labs but for this lab you will do something a little different After completion of all experiments you are to compile the methods and results and write a journal article suitable for publication in the Journal of Analytical Chemistry The theme of your article will be comparing analytical techniques for Ca analysis of complex aqueous samples You are upper level students about to impart on the real world so I will treat you as such You must obtain the Instructions to Authors for the Journal from the library or Internet and follow proper scientific
10. unders College Publishing 1998 Before beginning any experiments that use the AAS you are expected to learn about the instrument and analytical methods by reading the relevant sections in your textbook Also some reading will be made available from the instrument manuals There are also guidelines for each instrument for startup and shutdown Follow these closely FIVE CARDINAL RULES TO BE FOLLOWED WHEN OPERATING THE INSTRUMENT 1 ALWAYS wear safety glasses when in the vicinity of the instrument 2 NEVER leave the flame unattended Shut it off when you leave the room even for a few seconds 3 CONSERVE acetylene shut off the burner when not doing analyses it burns C 2H at the rate of over 4 L min 4 DO NOT operate the instrument until you have been checked out by me 5 Regarding the air and acetylene when using older instruments ALWAYS TURN THE C H ON LAST AND OFF FIRST TO DO OTHERWISE INVITES A POSSIBLE EXPLOSIVE FLASHBACK 6 Before you use the AAS CHECK and make sure the drain tube loop contains water 7 CHECK to make sure the waste container is not full JCE Ca AAS 5 Dunnivant Determination of Ca using Atomic Absorption Spectroscopy using External Standard Addition with and without Sr Student Procedures Purpose 1 refine your ability to make reference standards Ca 2 learn to use the flame atomic absorption spectroscopy system 3 determine the linear range for the instrument and 4 determine t
11. use of Sr in your samples and standards Not all simulated hazardous waste samples will have both interferences If these are observed for your sample use them as a point of discuss in your article In each of the AAS procedures you may have diluted your simulated hazardous sample for analysis with Sr HNOs etc How will you account for this dilution when calculating the concentration of Ca in your original sample Exactly what type of Ca does the FAAS technique measure What special handling procedures did you develop for dermal contact with the sample volatile toxins that may be in the sample JCE Ca AAS 11 Dunnivant Determination of Ca using the EDTA Titration Student Procedures Purpose 1 develop your ability to perform titrations of complex samples 2 review learn the details of the EDTA titration and 3 determine the concentration of Ca in a simulated hazardous waste sample Plan ahead and completely outline a procedure before you come to lab Reading for the EDTA titration can be found in Harris 1988 Chapter 13 in Quantitative Chemical Analysis 5 edition W H Freeman and Company NY A guideline for your experiment can be found in experiment 29 9 page 853 In procedure 29 9 you will not need to complete the Mg determination steps 2 and 3 or need the pH 10 buffer or Eriochrome black T indicator A solution of reference EDTA will be provided to you Consider the following when preparing for your laboratory e
12. writing guidelines refer to the ACS Style Guide in room 307 Remember that in your lab reports you are to write down meticulous lab methods and show calibration curves but you will not be able to do this in your journal article if you did the article would be 50 pages long You must decide the fine line between too little and too much information The best way to do this is to review several articles in the Journal perhaps 2 or 3 on AAS 2 or 3 on titration techniques and 2 or 3 on ion specific electrodes Note that you MUST also do a literature search on your topic and include these results in your introduction Your article should be no longer than 25 typed double spaced pages including text figures tables and references In your discussion and conclusions section defend which method is the most accurate for determining the Ca concentration in your sample JCE Ca AAS 4 Dunnivant Atomic Absorption Spectroscopy Student Information Useful References Van Loon J C Analytical Atomic Absorption Spectroscopy QD96 A2V36 Selected Methods Ebdon et al An Introduction to Analytical Spectrometry QD96 A8 158 1998 J Chem Ed Index Search an online searchable database of articles in the Journal of Chemical Education http jchemed chem wise edu Journal Search index html Harris Daniel C Quantitative Chemical Analysis Fifth Edition 1998 W H Freeman Skoog Holler amp Nieman Principals of Instrumental Analysis Fifth Edition Sa
13. xercise What is the color change for the Eriochrome black T indicator What problems might a sample with strong color pose in your titration How could you overcome this problem while maintaining a low detection limit Exactly what type of Ca does the FAAS technique measure JCE Ca AAS 12 Dunnivant Determination of Ca using a Ion Specific Electrodes Student Procedures Purpose 1 refine your ability to make reference standards Ca and dilutions 2 review learn the details of ion specific electrodes 3 determine the concentration of Ca in a beverage sample Plan ahead and completely outline a procedure before you come to lab Reading on electrodes can be found in Harris 1988 Chapter 15 in Quantitative Chemical Analysis 5 edition W H Freeman and Company NY This should be a review from Quantitative Analysis although you may not have specifically used a Ca electrode you should know the basic technique Consult the user manual operation for operation of the Ca electrode provided in lab Exercises Follow the instructions in the electrode manual but make an external calibration curve to check the slope of the calibration line If it is within the acceptable range analyze your sample five times Estimate the Ca concentration using the linear least squares LLS analysis Exactly what type of Ca does the FAAS technique measure
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