Chapter 1: Relationship Between Chemical & Instrumental Analysis PDF

Chapter 1 Relationship between the chemical analysis and instrumental analysis  Analytical Chemistry / Pharmaceutical Analysis Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and...

Chapter 1 Relationship between the chemical analysis and instrumental analysis  Analytical Chemistry / Pharmaceutical Analysis Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Pharmaceutical analysis is the application of the knowledge of analytical chemistry to analyze pharmaceutical raw materials or finished products where the principle of analytical chemistry is applied. Types: Qualitative analysis gives an indication of the identity of the chemical species in the sample and Quantitative analysis determines the amount of one or more of these components. The separation of components is often performed prior to analysis.  Analytical Methods Analytical methods can be separated into classical and instrumental. Classical methods use separations such as precipitation, extraction, and distillation and qualitative analysis by color, odor, or melting point. Quantitative analysis is achieved by measurement of weight or volume. Instrumental methods use an apparatus to measure physical quantities of the analyte such as light absorption, fluorescence, or conductivity. The separation of materials is accomplished using chromatography or electrophoresis methods.  Importance To analyze the pharmaceutical raw materials and finished products as a means of controlling their quality. Analytical chemistry has applications also in bioanalysis, clinical analysis, environmental analysis, and materials analysis.  Classical vs Instrumental Techniques In classical analysis, the signal depends on the chemical properties of the sample: a reagent reacts completely with the analyte, and the relationship between the measured signal and the analyte concentration is determined by chemical stoichioimetry. In instrumental analysis, some physical property of the sample is measured, such as the electrical potential difference between two electrodes immersed in a solution of the sample, or the ability of the sample to absorb light. Classical methods are most useful for accurate and precise measurements of analyte concentrations at the 0.1% level or higher. On the other hand, some specialized instrumental techniques are capable of detecting individual atoms or molecules in a sample! Analysis at the ppm (μg/mL) and even ppb (ng/mL) level is routine. The advantages of instrumental methods over classical methods include: 1. The ability to perform trace analysis, as we have mentioned. 2. Generally, large numbers of samples may be analyzed very quickly. 3. Many instrumental methods can be automated. 4. Most instrumental methods are multi-channel techniques (we will discuss these shortly). 5. Less skill and training is usually required to perform instrumental analysis than classical analysis.  Modern Analytical Chemistry Modern analytical chemistry is dominated by instrumental analysis. Many analytical chemists focus on a single type of instrument. Academics tend to either focus on new applications and discoveries or on new methods of analysis. The discovery of a chemical present in blood that increases the risk of cancer would be a discovery that an analytical chemist might be involved in. Many methods, once developed, are kept purposely static so that data can be compared over long periods of time. This is particularly true in industrial quality assurance (QA), forensic and environmental applications. Analytical chemistry plays an increasingly important role in the pharmaceutical industry where, aside from QA, it is used in discovery of new drug candidates and in clinical applications where understanding the interactions between the drug and the patient are critical.  Qualitative analysis A qualitative analysis determines the presence or absence of a particular compound, but not the mass or concentration. That is, it is not related to quantity. Chemical tests There are numerous qualitative chemical tests, for example, the acid test for gold and the Kastle-Meyer test for the presence of blood. Flame test Inorganic qualitative analysis generally refers to a systematic scheme to confirm the presence of certain, usually aqueous, ions or elements by performing a series of reactions that eliminate ranges of possibilities and then confirms suspected ions with a confirming test. Sometimes small carbon containing ions are included in such schemes. With modern instrumentation these tests are rarely used but can be useful for educational purposes and in field work or other situations where access to state-of-the-art instruments are not available or expedient.  Gravimetric analysis. Gravimetric analysis involves determining the amount of material present by weighing the sample before and/or after some transformation. One such example is the determination of the amount of water in a hydrate by heating the sample to remove the water such that the difference in weight is due to the loss of water. Volumetric analysis Titration involves the addition of a reactant to a solution being analyzed until some equivalence point is reached. Often the amount of material in the solution being analyzed may be determined. Most familiar technique of volumetric analysis is the acid-base titration involving a color changing indicator. There are many other types of titrations, for example potentiometric titrations. These titrations may use different types of indicators to reach some equivalence point.  Instrumental methods Spectroscopy Spectroscopy measures the interaction of the molecules with electromagnetic radiation. Spectroscopy consists of many different applications such as atomic absorption spectroscopy, atomic emission spectroscopy, ultraviolet-visible spectroscopy, fluorescence spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy, photoemission spectroscopy and so on. Electrochemical analysis Methods of analysis, in which the analyte participates in a redox reaction or other process. Electroanalytical methods measure the potential (volts) and/or current (amps) in an electrochemical cell containing the analyte. These methods can be categorized according to which aspects of the cell are controlled and which are measured. The three main categories are potentiometry (the difference in electrode potentials is measured), coulometry (the cell's current is measured over time), and voltammetry (the cell's current is measured while actively altering the cell's potential).  Separation Techniques Separation processes are used to decrease the complexity of material mixtures. Chromatography and electrophoresis are representative of this field. Figure: Separation of black ink on a thin layer chromatography plate.  Hybrid techniques of analysis Combinations of the above techniques produce a "hybrid" or "hyphenated" technique. Several examples are in popular use today and new hybrid techniques are under development. For example, gas chromatography-mass spectrometry (GC-MS), gas chromatography-infrared spectroscopy (GC-IR), liquid chromatography-mass spectrometry (LC-MS). Hyphenated separation techniques refers to a combination of two (or more) techniques to detect and separate chemicals from solutions. Most often the other technique is some form of chromatography. Hyphenated techniques are widely used in chemistry and biochemistry. A slash is sometimes used instead of hyphen, especially if the name of one of the methods contains a hyphen itself.  Standards:Standard curve A general method for analysis of concentration involves the creation of a calibration curve. This allows for determination of the amount of a chemical in a material by comparing the results of unknown sample to those of a series of known standards. If the concentration of element or compound in a sample is too high for the detection range of the technique, it can simply be diluted in a pure solvent. If the amount in the sample is below an instrument's range of measurement, the method of addition can be used. In this method a known quantity of the element or compound under study is added, and the difference between the concentration added, and the concentration observed is the amount actually in the sample.  1.2 1 y = 0.02x 0.8 0.6 A 0.4 0.2 0 0.0 20.0 40.0 60.0 concentration (uM)  Internal standards Sometimes an internal standard is added at a known concentration directly to an analytical sample to aid in quantitation. The amount of analyte present is then determined relative to the internal standard as a calibrant. Standard addition The method of standard addition is used in instrumental analysis to determine concentration of a substance (analyte) in an unknown sample by comparison to a set of samples of known concentration, similar to using a calibration curve. Standard addition can be applied to most analytical techniques and is used instead of a calibration curve to solve the matrix effect problem. Signals and noise One of the most important components of analytical chemistry is maximizing the desired signal while minimizing the associated noise. The analytical figure of merit is known as the signal-to-noise ratio (S/N or SNR). Noise can arise from environmental factors as well as from fundamental physical processes.