Cation simultaneous analysis

Ohta and Tanaka reported a method for the simultaneous analysis of several inorganic anions and the cations Mg + and Ca + in water by ion-exchange chromatography. The mobile phase includes 1,2,4-benzenetricarboxylate, which absorbs strongly at 270 nm. Indirect detection of the analytes is possible because their presence in the detector leads to a decrease in absorbance. Unfortunately, Ca + and Mg +, which are present at high concentrations in many environmental waters, form stable complexes with 1,2,4-benzenetricarboxylate that interfere with the analysis. 

Kato, M., Onda, Y., Sakai-Kato, K., and Toyo oka, T. (2006). Simultaneous analysis of cationic, anionic, and neutral compounds using monolithic CEC columns. Anal. Bioanal. Chem. 386, 572-577. 

Ion chromatography is not restricted to the separate analysis of only anions or cations, and, with the proper selection of the eluent and separator columns, the technique can be used for the simultaneous analysis of both anions and cations. 

Simultaneous analysis of both anions and cations indicates that water samples from various localities contain many of the same ions but in differing amounts. Fig. 2.24 illustrates typical chromatograms of tap water and rain water. 

Couchman et al. developed a method for simultaneous analysis of amisulpride, metamphetamine, and amphetamine in plasma by HPLC-MS/MS. To the sample (200 pi), ISTDs solution and NaOH solution were added to the extraction solvent (butyl acetate-butanol, 9 1). HPLC separation was performed by strong cation-exchange. The use of methanol as eluent improved sensitivity for analytes due to more efficient in-source desolvation when compared with aqueous eluents [99],... 

In the investigations of the systems so far mentioned, only the kinetics of the long-wavelength absorbing radical anions could be monitored spectroscopically. Simultaneous analysis of both transient species was performed using p -chloranil (9) as the acceptor and 2-methoxy-l,l-diphenylethene (10) as the donor [33, 36]. Both the radical anion 9 and the radical cation 10+ decay within the same halflife of ca. 1 ps, as expected for back electron transfer as the major process (Fig. 6). Utilizing the special salt effect (addition of lithium perchlorate) increases the lifetime of both intermediates by a factor of ten. 

The separator column introduced as the Fast-Sep-Cation has similar physical properties. This column was developed primarily for the fast separation of alkali or alkaline-earth metals. In combination with a column switching technique, it is also suitable for the simultaneous analysis of the most important cations of both compound classes (see... 

The simultaneous analysis of the most important alkali and alkaline-earth metals was once impossible due to their markedly different retention behavior. However, the inorganic chemists have finally realized their dream this analytical problem no longer poses a problem. One of the two possible solutions is the novel silica-based cation exchanger modified with poly(butadiene-maleic acid), introduced in Section 3.4.I.3. As shown in Fig. 3-135, the most important alkali and alkaline-earth metals and ammonium can be analyzed in a single run via direct conductivity detection using tartaric acid as the eluent. The extremely short time required for such a separation is quite impressive. 

Fig. 3-146. Simultaneous analysis of alkali and alkaline-earth metals by means of column switching. - Separator column Fast-Sep Cation I and II switching time 0.5 min eluent 0.02 mol/ L HC1 + 0.0002 moI/L 2,3-diaminopropionic acid flow rate 2 mL/min detection suppressed conductivity injection volume 50 pL solute concentrations 1 ppm lithium (1), 4 ppm sodium (2), 8 ppm ammonium (3), 4 ppm potassium (4), 4 ppm magnesium (5), and 20 ppm calcium (6).

A simultaneous analysis of alkali and alkaline-earth metals - either via column switching or by using a special cation exchanger — is only possible, however, if the components exist in comparable concentrations. Otherwise, a separate analysis of both classes of compounds is indispensible. 

The solid curves in Fig. 3 were calculated by simultaneous non-linear least-squares regression of reaction-rate data at all alkali-metal cation concentrations (20 kobs values using three different cations) to the complex rate constant in eq 15. The calculation was performed subject to the stipulation that aU three curves converge to a single k value. (Convergence to a single kobs value, k, at infinite dilution is implicit to derivation ofeq 15.) Simultaneous analysis of the three curves (one for each of the cations, Li, Na and K ) provides unique values for rate and equilibrium constants, kMi and Kmi, i.e., for kui, knai, kxi, Kbii, KnbI and Kki. 

A basic characteristic of ITP is the limitation of its use to ionogenic substances. In a single run either anions or cations are analyzed however, electrolyte systems that enable simultaneous analysis of both groups can be found and so called bi-directional ITP employing two detectors can be performed. Non-ionogenic substances that often form the bulk of a sample do not interfere with the analysis. Advantages of ITP include its independence of derivatization and deproteination of the sample and this feature can be very effectively evaluated when ITP is used as a preseparation method. ITP is mostly carried out in aqueous solutions or in aqueous mixtures with solvents and therefore it is most useful for substances that are water-soluble or can be included into water-soluble complexes, e.g., with micelles of surfactants. 

Simultaneous analysis of alkali and alkaline earth metals can only be performed with weak acid cation exchangers, using carboxylic groups as ion-exchange functionality group and usually with methanesulfonic acid as the eluent. 

These types of polymer resins are widely used as substrate materials for the manufacture of cation exchangers. Simultaneous analysis of mono- and divalent cations is not possible with surface-sulfonated cation exchangers thus, they are used for sequential analysis of alkali and alkaline earth metals. The ion-exchange capacity is determined by the degree of PS-DVB sulfonation. The characteristic structural and technical properties of... 

A quality feature of all cation exchangers suitable for simultaneous analysis of mono- and divalent cations is the maximal concentration ratio between sodium and ammonium that allows a separation of both components. Under isocratic conditions with lOmmol/L methanesulfonic acid at 2mL/min, lonPac CS12... 

Cation exchangers based on PBDMA-coated silica are offered by a number of companies. Metrohm (Herisau, Switzerland), for example, offers two columns under the trade names Metrosep Cl and C4. The 5 pm Metrosep Cl is considered to be the high-performance column for the simultaneous analysis of mono-and divalent cations with an analysis time of less than 20 min. It can also be used for the separation of various amines, which are typically eluted with a nitric acid eluent. Figure 4.41 shows an example chromatogram obtained under standard chromatographic conditions with an eluent mixture of tartaric acid and pyridine-2,6-dicarboxyiic acid (PDCA) (dipicohnic acid). Under these chromatographic conditions, calcium elutes ahead of magnesium, followed by strontium and barium. This unusual retention behavior can be attributed to the complex-ing properties of pyridine-2,6-dicarboxylic acid. With a pure tartaric acid eluent. 

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