Spectrometric Detection Methods

One of the most important applications of UV/Vis detection is photometric determination after derivatization of the column effluent First of all, this includes the determination of transition metals after reaction with 4-(2-pyridylazo)-resorcinol (PAR). 

When alkaline-earth metal ions, M +, are added to this system, zinc ions are released from the Zn-EDTA and subsequently form the chelate complex Zn(PAR)2 with PAR  

Reagent delivery is improved significantly upon application of a membrane reactor. This contains a semipermeable membrane which is permeable to certain reagents. The operation of a membrane reactor requires a pressurized container, from which the reagent solution reaches the membrane reactor pulsation-free. 

A post-column derivatization with subsequent photometric detection has also been developed for the determination of aluminum. Using a mixture of ammonium sulfate and sulfuric acid, aluminum is separated as AISO/ ion on a cation exchanger. It forms a stable complex with the disodium salt of 4,5-dihydroxy-l,3-benzenedisulfonic acid (Tiron) at pH 6.2 which can be detected at 313 nm. 

At this pH value Tiron only reacts with aluminum and iron(III), hence this method for aliuninum determination is very selective. The only disadvantage is the comparatively low extinction coefficient, s = 6000 L/(mol cm), of the resulting complex at 310 nm. A corresponding standard chromatogram of the separation of almninum is illustrated in Fig. 4-59 (see Section 4.5.3). 

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Chemical methods apply to the separation and purification of radioactive substances in the same way they apply to stable substances. A radiochemical separation is judged in terms of both the yield and the purity of the separated material this is particularly important when analyte concentrations are low or contaminant levels are high. Purity and fractional recovery are often evaluated with the tracer technique. Radiochemical and mass spectrometric detection methods are quite sensitive, and it is possible to work with trace amoimts of analyte. However, radiochemical procedures involving the presence of an isotopic carrier (which can also function as a tracer) are often simpler to design than are carrier-free procedures losses from adsorption on vessel walls or suspended particles may negatively affect the recovery of the analyte in a tracer-level sample. 

Andrle C. M., Jakubowski N. and Broekaert j. a. C. (1997) Speciation of chromium using reversed phase-high performance liquid chromatography coupled to different spectrometric detection methods, Spectrochim. Acta, Part B 52 189-200. 

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