chm4130

chm4130 - INTRODUCTION A common challenge faced by an...

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1 INTRODUCTION A common challenge faced by an analytical chemist is the determination of target species in complex samples Complex sample: sample with numerous species. Example of complex samples: physiological fluids (blood, urine, saliva), environmental samples (air, water, soil), etc. Target species is the species of interest. It is also called analyte. Example: benzo[ a ]pyrene in soil sample, PSA (prostate specific antigen) in physiological fluid, etc. Some possibilities: Analyte: Other species = concomitants: Analyte is the main component in the sample with only two types of species Analyte is not the main component in the sample bu t sample contains only two types of species Analyte is not the main component in the sample and sample contains several types of species
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2 Sample Collection Sample = Matrix Sample Preparation: Clean-up and/or Pre-concentration Analytical Sample Qualitative and Quantitative Analysis Statistical Analysis of Data General Scheme
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3 Quantitative and Qualitative Analysis Classical and instrumental methods Classical methods = wet-chemical methods Analyte separation: precipitation, extraction or distillation Qualitative analysis: chemical reactions yielding products of characteristic colors boiling or melting points solubility in a series of solvents odors, optical activities or refractive indexes Quantitative analysis: Gravimetric or volumetric analysis Main disadvantages of classical methods: Time consuming Numerous manual steps, which make them prone to indeterminate (random) errors
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4 Instrumental Methods Most instrumental methods require a source of excitation to stimulate a measurable response from the analyte. See Figure 1-1. The first six entries in Table 1-1 involve interactions of the analyte with electromagnetic radiation. The first characteristic response involves radiant energy produced by the analyte. The next five properties involve changes in electromagnetic radiation brought about by its interaction with the sample. Four electrical properties and miscellaneous properties follow. The name of the corresponding instrumental method is given in the second column of Table 1-1.
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Evaluation of Analytical Data (Appendix One) 6 Analytical chemists may be presented with two types of problems 1) Provide a qualitative answer Example: Does this distilled water contain any Boron? Is this soil sample contaminated with polycyclic aromatic hydrocarbons (PAH)? 2) Provide a quantitative answer Example: How much lead is in this water sample? This steel sample contains traces of chromium, tungsten and manganese; how much of each one? Often, both types of questions are answered with quantitative methods Example: B, Pb, Cr, W, Mn in H2O: AAS or AES PAH in H2O: HPLC In cases where a positive answer is obtained, the analyst will give the answer in terms of analyte concentration Example: This water sample contain 1 μ g/mL of B Most certainly, if the analyst repeats the experiment with the same sample using the same method he/she will find a different result Why? Because of inherent experimental errors
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chm4130 - INTRODUCTION A common challenge faced by an...

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