Analytical Chemistry I CHEM247. Introduction Lecture. Mehmet U. Garip Office : AS 348 Tel:

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1 Mehmet U. Garip Office : AS 348 Tel: mehmet.garip@emu.edu.tr FALL Monday Tuesday Wednesday Thursday Friday CMS213 CMS213 ASA ASA OFFICE HOUR OFFICE HOUR Analytical Chemistry I CHEM OFFICE HOUR CHEM545/01 ASG01 CMS212 CMS212 Introduction Lecture CHEM545/01 ASG01 OFFICE HOUR CMS CHEM545/01 ASG01 Definitions Analysis separation of a whole into its component parts the identification or separation of ingredients of a substance a statement of the constituents of a mixture Analyte a chemical substance that is the subject of a chemical analysis A specific component of a whole that is being analysed/analyzed A specific component of a whole that is to be determined Analytical Chemistry I Definitions Qualitative Analysis Determining the identity of elements or compounds in a sample Quantitative Analysis Determining the quantity/amount of a substance (element or compound) in a sample Elemental Analysis Usually reserved for organic chemistry where elemental composition is determined quantitatively Sample a representative part or a single item from a larger whole or group especially when presented for inspection or shown as evidence of quality :specimen Structural Analysis Determining the molecular/crystalline structure of the compound a finite part of a statistical population whose properties are studied to gain information about the whole

2 Definitions CLASSICAL or WET CHEMICAL METHODS OF ANALYSIS Gravimetric Methods of Analysis Based on measuring mass of precipitated substance containing the analyte. Titrimetric Methods of Analysis Based on titrating the analyte in the sample. Definitions Non-destructive method of analysis Sample is not consumed during the analysis and can be recovered completely and in tact. Destructive method of analysis Sample is destroyed during the analysis and can not be recovered. INSTRUMENTAL METHODS Electrochemical Methods of Analysis Based on measuring voltage or electric currents through electrochemical cells. Spectrochemical Methods of Analysis Determining the molecular/crystalline structure of the compound Separation Methods Methods based on separating components in a sample by precipitation, extraction, distillation or chromatography. Thermal Methods of Analysis Measuring heat-temperature properties Areas of Chemical Analysis and Questions They Answer Quantitation: How much of substance X is in the sample? Detection: Does the sample contain substance X? Identification: What is the identity of the substance in the sample? Separation: How can the species of interest be separated from the sample matrix for better quantitation and identification? Scheme of a general quantitative analysis select a method, acquire and process the sample, dissolve the sample in a suitable solvent, measure a property of the analyte, calculate the results, and estimate the reliability of the results.

3 An analysis involves several steps and operations which depend on: the particular problem your expertise the apparatus or equipment available. The analyst should be involved in every step. Different methods provide a range of precision, sensitivity, selectivity, and speed capabilities. Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Steps in an analysis The sample size dictates what measurement techniques can be used. Deer Kill Case Study : Deer Kill Problem: Dead whitetail deer near pond in the Land Between the Lakes State Park in south central Kentucky. Chemist state veterinary diagnostic laboratory helped find the cause Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)

4 Site Investigation Careful visual observation of a two acre area around the site: Observation: grass around nearby powerpoles was wilted and discolored. Speculation: Herbicide used on grass. Ingredient: Arsenic in a variety of forms CH 3 AsO(OH) 2 very soluble in water. Select Method Association of Official Analytical Chemists (AOAC) Distillation of arsenic as arsine which is then determined by colorimetric measurements. Representative Sample Dissect both deer. Removed kidneys for analysis. Laboratory Sample. Preparation Cut kidney into pieces and blend in a high speed blender to homogenize the sample. Defining Replicate Samples Three 10-g samples of the homogenized tissue were placed in porcelain curcibles and dry ashed. Dry ashing serves to free the analyte from organic material and convert the arsenic present to As 2 O 5. Samples of the discolored grass were treated in a similar manner.

5 Dissolving the Samples The dry solid in each of the sample crucibles was dissolved in dilute HCl, which converted the As 2 O 5 to soluble H 3 AsO 4. Eliminating Interferences Reactions to Eliminate Interferences: H 3 AsO 4 + SnCl 2 + 2HCl --> H 3 AsO 3 + SnCl 2 + H 2 O H 3 AsO 3 + 3Zn + 6HCl --> AsH 3(g) + 3ZnCl 2 + 3H 2 O Bubble gas into collectors with silver diethyldithiocarbamate to form a colored complex compound shown below. Measuring the Amount of Analyte Spectrophotometer: Highly colored complex of arsenic was found to absorb light at a wavelength of 535 nm. Conc. ppm Absorbance deer deer A b s o r b a n c e Absorbance vs Concentration y = x R 2 = Conc., ppm

6 Calculating the Concentration ppm = (Absorbance -.005)/ Deer 1: ( )/ = 22 ppm Deer 2: ( )/ = 15 ppm Arsenic in the kidney tissue of animals is toxic at levels above about 10 ppm. Grass Samples showed about 600 ppm arsenic. Reliability of the Data The data from these experiments could be analyzed using the statistical methods we will describe in Section 3. Where Do We Begin? Review of Basic Tools and Operations of Analytical Chemistry The Laboratory Notebook Analytical Balances, Volumetric Glassware Laboratory Safety Error Analysis Concepts Terminology Evaluation of Data Experimental Design Review of Solution Chemistry Units Concentration Calculations Stoichiometry Balanced Chemical Reactions