1a.Explain the specific functions of an internal standard in i) HPLC ii) AES b. Define the...

1a.Explain the specific functions of an internal standard in i) HPLC ii) AES

b. Define the following terms in atomic spectroscopy. Give two examples for each of them.
i) releasing agents
ii) protective agents
iii) ionization suppressors

Expert Solution

1. a. An internal standard is a known concentration of a substance that is present in every sample that is analyzed by any of these techniques. They can be used with either the calibration curve or standard addition methods, although the former is probably more common.
The purpose of the internal standard is to behave similarly to the analyte but to provide a signal that can be distinguished from that of the analyte. Ideally, any factor that affects the analyte signal, such as those related with a chromatographic run or with the atomization process in AES, will also affect the signal of the internal standard to the same degree. Thus, the ratio of the two signals will exhibit less variability than the analyte signal.
Internal standards are often used in chromatography, mass spectroscopy and atomic emission spectroscopy. They can also be used to correct for variability due to analyte loss in sample storage and treatment.

b. Releasing agent: It is a species that reacts with interferent/s, releasing the analyte during atomization, therefore decreasing the interference. For example, adding Sr²⁺ or La³⁺ to solutions of Ca²⁺, minimizes the effect of PO₄^3– and Al³⁺ by reacting in place of the analyte. Another example is the releasing effect of Fe(III) on the Ni interference on As and Se determinations.

Protective agent: Chelating agents the react with the analyte to form a stable volatile complex. Examples of this are EDTA and 8-Hydroxyquinolone in Ca determinations.

Ionization supressor: A species that ionizes more easily than the analyte. If the concentration of the ionization suppressor is sufficient, then the increased concentration of electrons in the flame pushes the ionization equilibrium of the analyte to the left, preventing its ionization. Potassium and cesium are frequently used as an ionization suppressor because of their low ionization energy.

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