Eluents ethylenediamine

FIGURE 14.5 Analysis of rainwater spiked with 0.3 mM H+, Na+, NHJ, K+, Ca +, Mg +. Column DS-coated monolithic stationary phase (Merck Chromolith, 50x4.6mm). Column temperature 35°C. Eluent 2mM ethylenediamine, 0.1 mM Li-DS, pH 6. Flow rate 4.0mL/min. Loop volume lOOpL. (From Xu, Q. et ah, J. Chromatogr. A, 1026, 191, 2004. Copyright 2004. With permission from Elsevier.)... 

A lOOmL three-necked, round-bottomed flask equipped with magnetic stirrer was charged with racemic 1,2-diphenylethylenediamine (1.02 g, 4.8 mmol), triethy-lamine (2mL, 14.3 mmol) and dry tetrahydrofuran (10 mL) followed by dropwise addition of p-toluenesulfonyl chloride (0.91 g, 4.8 mmol) dissolved in 10 mL of dry tetrahydrofuran. The reaction mixture was stirred at ambient temperature for 12 h and a white salt was obtained. The salt was filtered and washed with ether. The combined filtrate was concentrated and purified by flash column chromatography (eluent petroleum ether/ethyl acetate = 1/1) to give 7/-p-toluenesulfony 1-1,2-diphenyl-1,2-ethylenediamine (1.02g, 58.0% yield ). 

Pac AS3 anion exchanger (Fig. 3-49), a mixture of sodium carbonate and sodium dihydrogen borate is used as the eluent. A small quantity of ethylenediamine is also added to the mobile phase to allow for the complexation of traces of heavy metal ions, which could be present in the eluent [56,57], While the detection of these two anions is very easy, the interpretation of experimental results for the investigation of real-world samples is very difficult. These samples normally contain transition and heavy metal ions, in the presence of which sulfide and cyanide are not present or only partly present as free ions. However, only the free ions are detected under the chromatographic conditions listed in Fig. 3-49. 

Fig. 3-49. Separation of sulfide and cyanide. — Separator column IonPac AS3 eluent 0.001 mol/L Na2C03 + 0.01 mol/L NaH2B03 + 0.015 mol/L ethylenediamine flow rate 2.3 mL/min detection amperometry on a Ag working electrode injection volume 50 pL solute concentrations 0.5 ppm sulfide and 1 ppm cyanide.

Fig. 3-50. Separation of sulfide and cyanide in a strongly alkaline solution. — Separator column IonPac AS6 (CarboPac) eluent 0.1 mol/L NaOH + 0.5 mol/L NaOAc + 0.0075 mol/L ethylenediamine flow rate 1 mL/min other chromatographic conditions see Fig. 3-49.

Fig. 3-104. Separation of polyphosphonic acids upon application of phosphorus-specific detection. - Separator column IonPac AS7 eluent 0.17 mol/L KC1 + 0.0032 mol/L EDTA, pH 5.1 flow rate 0.5 mL/min detection photometry at 410 nm after hydrolysis and derivatization with vana-date/molybdate injection 50 pL, l-hydroxyethane-l,l-diphosphonic acid (HEDP), aminotris-(methylenephosphonic acid) (ATMP), ethylenediamine-tetramethylenephosphonic acid (EDTP), l,l-diphosphonopropane-2,3-dicarboxylic acid (DPD), and 2-phosphonobutane-l,2,4-tricarboxylic add (PBTC) (taken from [84]).

Fig. 3-134. Separation of alkaline-earth metals on a silica-based cation exchanger. - Separator column Nucleosil 5 SA eluent 0.0035 mol/L oxalic acid + 0.0025 mol/L ethylenediamine + 50 mL/L acetone, pH 4.0 flow rate 1.5 mL/min detection direct conductivity injection volume 100 pL solute concentrations 2.5 ppm magnesium, 5 ppm calcium, 20 ppm strontium, and 40 ppm barium.

Fig. 3-148. Gradient elution of monovalent and divalent cations. - Separator column Fast-Sep Cation I and II eluent (A) water, (B) 0.04 mol/L HC1 + 0.02 mol/L 2,3-diaminopropionic acid gradient 5 min 7% B isocratically, then linearly to 100% B in 10 min flow rate 1 mL/min detection suppressed conductivity injection volume 50 pL solute concentrations 2 ppm lithium (1), 5 ppm sodium (2), 10 ppm ammonium (3), and potassium (4), 20 ppm tetrabutylammonium (5), 10 ppm magnesium (6) and calcium (7), 20 ppm ethylenediamine (8).

Again, a mixture of hydrochloric acid and DAP was employed as the eluent. Since the concentration of the eluent components is increased by about one order of magnitude during the run, their purity is of essential importance. In the field of cation analysis, the gradient technique is used predominantly for screening purposes. In comparison with isocratic techniques, a significantly better peak shape is observed for strongly retained cations such as ethylenediamine. 

In addition to tartrate, a-hydroxyisobutyrate can be utilized as the complexing anion. It was employed by Cassidy et al. [144] for the separation of lanthanides. In comparison to tartrate, no particular advantages are revealed in the separation of divalent metal ions. Fig. 3-150 shows a separation of the seven heaviest lanthanides with an eluent mixture of ethylenediamine and a-hydroxybutyric acid. The pronounced tailing effects observed under isocratic conditions for late eluting ions are unsatisfactory. 

Fig. 3-149. Separation of divalent cations with direct conductivity detection. - Separator column surface-sulfonated cation exchanger (Benson Co., Reno, USA) eluent 0.0015 mol/L ethylenediamine + 0.002 mol/L tartaric acid, pH 4.0 flow rate 0.85 mL/min injection volume 100 pL solute concentrations 10.3 ppm Zn2+, 9.1 ppm Co2+, 16 ppm Mn2+, 16.1 ppm Cd2+, 17.1 ppm Ca2+, 16 ppm Pb2+, and 20.3 ppm Sr2+ (taken from [148]).

Alternatively, a strongly conducting eluent may be used. In this case, elution of the solute ions is associated with a negative conductivity change. This indirect detection method is applied to the separation of anions with potassium hydroxide as the eluent [7], A corresponding chromatogram is displayed in Fig. 6-2. This indirect detection method is also utilized in the analysis of mono- and divalent cations, which are eluted by dilute nitric acid or nitric acid/ethylenediamine-mixtures. 

Table 5.8. Comparison of capacity factors (k) of various cations with cationic eluents. (Concentrations HCIO4, 0.250 M NaClOa, 0.100 M all others are 1.0 x 10 M, pH 2.5 t = 0.495 min. EnH j = ethylenediamine eluent PhenH 2 = oj-phenylenediamine eluent.

Sevenich and Fritz found an eluent containing 2.0 x 10 - M ethylenediammonium tartrate to be effective for separating several divalent metal cations [13]. Calculations from ionization constants showed ethylenediamine to be fully protonated (EnH2 ) at pH 5.0 or below. The adjusted retention times for several metal ions were obtained as a function of eluent pH (Table 7.6). The retention times increased in almost every case between pH 5 and 6. Furthermore, some minor extraneous peaks appeared in this pH region. A buffer pH of 4.5 was selected as giving generally the best results. 

FIG. 3. Schematic illustration of the equilibria existing between a solute cation (M ), ethylenediamine (en), and an added ligand (H2L) at the surface of a cation exchanger, (a) Eluent contains only the ligand, (b) Eluent contains both ligand and ethylenediamine. 

FIG. 4. Separation of metal ions when complexing agents are used as eluent components (AU = absorbance units), (a) A Nucleosil SA-10 column was used with 0.5 M tartrate at pH 2.76 as eluent. Detection by postcolumn reaction. (From Ref. 8.) (b) A TSKIC Cation SW column was used with 3.S mM citric acid-10.0 mM ethylenediamine at pH 2.8 as eluent. Detection by conductivity. (From Ref. 9.)... 

Figure 4.40 Separation of aikaiine-earth metals on a sulfonated silica-based cation exchanger. Separator column Nucleosil 5 SA eluent 3.5 mmol/L oxalic acid -I- 2.5 mmol/L ethylenediamine -l-50mL/L acetone, pH 4 ...

In ion chromatography systems with nonsuppressed conductivity detection, mixtures of ethylenediamine and aliphatic dicarboxyhc acids such as tartaric acid or oxalic acid are typically employed as an eluent for the separation of alkaline-earth metals. Those mixtures have a relatively high intrinsic conductance, so that chromatographic signals are registered as negative peaks. 

While both conductivity detection modes are suitable for the detection of alkali and alkaline-earth metals, only nonsuppressed conductivity detection can be used for the analysis of transition metals. The formation of nondissociated metal hydroxides from the suppressor reaction precludes the use of a suppressor system for this type of analysis. Nonsuppressed conductivity detection is also impeded by the presence of complexing agents in the mobile phase these agents are required for separating transition metals. In 1983, Sevenich and Fritz [34] found an eluent mixture suited for nonsuppressed conductivity detection. It was comprised of ethylenediamine and tartaric acid. Ethylenediamine serves as an eluent ion, because it is already fully protonated (EnH ) at pH values < 5. The... 

Typical procedure. Imidazolidinone 1068 [778] A mixture of ethylenediamine (1.2 g, 20 mmol), PhsSbO (1.0 mmol), and P4S10 (2.0 mmol) was autoclaved under a pressure of CO2 (4.9 MPa). Imidazolidinone was isolated by column chromatography (silica gel eluent ethyl acetate/hexane, 1 1, v/v) yield 1.5 g (85%). 

To a stirred mixture of arylaldehyde (1 1.0 mmol) or saUcylaldehyde (1.0 mmol), malononi-trile (or ethyl cyanoacetate 2 1.0 mmol) and triethyl phosphite (or phosphite derivative 3 1.0 mmol) in 5 mL of ethanol (or other alcohol), ethylenediamine diacetate EDDA (0.2 mmol) was added. The resulting mixture was stirred at room temperature until completion of the reaction, as indicated by TLC. The reaction mixture was evaporated under reduced pressure and the crude product was purified by silica gel column chromatography using EtOAc/ -hexane as the eluent to give the desired products (4) in good yields. AU the products were characterized from their detailed spectral studies including IR, NMR, NMR, and El- and HR-MS. 

A possibility of eluent adaptation having a positive effect on the trace metal problem is to add some ethylenediamine tetra-acetate (EDTA) to the eluent in addition to phosphoric acid and to use "demineralized" phases, as illustrated in Table 16. 

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