Eluents phthalate

Acid Eluent Phthalate buffer Gluconate/ Hydroxide Benzoate... 

Figure 12.10 Microcolumn SEC-LC analysis of an acrylonitrile-butadiene-styrene (ABS) teipolymer sample (a) SEC ti ace (b) EC ti ace. SEC conditions fused-silica column (30 cm X 250 mm i.d.) packed with PL-GEL (50 A pore size, 5 mm particle diameter) eluent, THE at a flow rate of 2.0 mL/min injection size, 200 nL UV detection at 254 nm x represents the polymer additive fraction (6 p-L) tr ansferred to EC system. EC conditions NovaPak CIS Column (15 cm X 4.6 mm i.d.) eluent, acetonitrile-water (60 40) to (95 5) in 15 min gradient flow rate of 1.5 mL/min detection at 214 nm. Peaks identification is follows 1, styrene-acrylonitrile 2, styrene 3, benzylbutyl phthalate 4, nonylphenol isomers 5, Vanox 2246 6, Topanol 7, unknown 8, Tinuvin 328 9, Irganox 1076 10, unknown. Reprinted with permission from Ref. (14).

Figure 3 Gradient separation of anions using suppressed conductivity detection. Column 0.4 x 15 cm AS5A, 5 p latex-coated resin (Dionex). Eluent 750 pM NaOH, 0-5 min., then to 85 mM NaOH in 30 min. Flow 1 ml/min. 1 fluoride, 2 a-hydrox-ybutyrate, 3 acetate, 4 glycolate, 5 butyrate, 6 gluconate, 7 a-hydroxyvalerate, 8 formate, 9 valerate, 10 pyruvate, 11 monochloroacetate, 12 bromate, 13 chloride, 14 galacturonate, 15 nitrite, 16 glucuronate, 17 dichloroacetate, 18 trifluoroacetate, 19 phosphite, 20 selenite, 21 bromide, 22 nitrate, 23 sulfate, 24 oxalate, 25 selenate, 26 a-ketoglutarate, 27 fumarate, 28 phthalate, 29 oxalacetate, 30 phosphate, 31 arsenate, 32 chromate, 33 citrate, 34 isocitrate, 35 ds-aconitate, 36 trans-aconitate. (Reproduced with permission of Elsevier Science from Rocklin, R. D., Pohl, C. A., and Schibler, J. A., /. Chromatogr., 411, 107, 1987.)...

Figure 5.2 Normal phase separation of phthalates. Column, Yanapak CN, 25 cm x 2 mm i.d. eluent, n-hexane-n-butanol (200 1) flow rate, 0.25 ml min-1 pressure, 3 MPa. Peaks 1, lauryl phthalate 2, heptyl phthalate 3, butyl phthalate 4, propyl phthalate 5, ethyl phthalate and 6, methyl phthalate.

For ions that are UV transparent, detection is possible through the use of indirect detection. A wide variety of different eluent systems have been described in the literature. Eluents commonly used for indirect UV detection are similar to those used in non-suppressed conductivity detection phthalate and p-hydroxybenzoic acid along with other... 

The direct mode is employed with eluents with significantly lower equivalent conductance than the analyte ion. Increase in sensitivity is obtained as the degree of the ionization of the eluent decreases, that is, with more weakly dissociated eluents, and non suppressed conductivity methods have been extensively developed using benzoate, phthalate [246], oxalate [53] or other partially ionized species as mobile phases. A key factor in the success of this technique is the use of an ion exchanger of low-exchange capacity, which in turn permits the use of a very dilute eluent. 

Indirect detection exploits the absorbance of the eluent ion (e.g., NOj , phthalate, benzoate, meth-ylbenzylamine) that should absorb more than the analyte. The eluting analyte exhibits a negative peak. Nevertheless, this mode of detection has limited utilization since the detection limits are often inadequate. 

Figure 2. Ion chromatographic separation of a series of anions on polymer-based column with adsorbed decyl-2.2.2 using gradient capacity from sodium hydroxide to lithium hydroxide aqueous eluent. Anions 1) fluoride 2) acetate 3) chloride 4) nitrite 5) bromide 6) nitrate 7) sulfate 8) oxalate 9) chromate 10) iodide 11) phosphate 12) phthalate 13) citrate 14) thiocyanate (from refs. 13,14)...

The adoption of an eluent having a very low conductivity, which can be passed directly through the conductometric detector. Typical eluents used are benzoate, phthalate, or other aromatic acid salts, with low limiting equivalent conductances (leading to direct detection) or potassium hydroxide eluent, with high conduc-... 

Fig. 3-24. Gradient elution of inorganic and organic anions on IonPac AS5A. - Eluent (A) 0.00075 mol/L NaOH, (B) 0.1 mol/L NaOH gradient 100% A isocratically for 5 min, then linearly to 30% B in 15 min, then linearly to 86% B in 15 min flow rate 1 mL/min detection suppressed conductivity injection volume 50 pL solute concentrations 1.5 ppm fluoride (1), 10 ppm a-hydroxybutyrate (2), acetate (3), glycolate (4), butyrate (5), gluconate (6), a-hydroxyvalerate (7), 5 ppm formate (8), 10 ppm valerate (9), pyruvate (10), monochloroacetate (11), bromate (12), 3 ppm chloride (13), 10 ppm galacturonate (14), 5 ppm nitrite (15), 10 ppm glucoronate (16), dichloroacet-ate (17), trifluoroacetate (18), phosphite (19), selenite (20), bromide (21), nitrate (22), sulfate (23), oxalate (24), selenate (25), a-ketoglutarate (26), fumarate (27), phthalate (28), oxalacetate (29), phosphate (30), arsenate (31), chromate (32), citrate (33), isodtrate (34), eis-aconitate (35), and frons-aconitate (36).

The silica ion exchanger manufactured by Wescan is based on a macroporous substrate with a pore width of 300 A. The big differences in the retention behavior of monovalent and divalent anions are characteristic for the respective chromatogram depicted in Fig. 3-28. The negative signal appearing at about 20 minutes is the system peak (see Section 3.3.4.3), which is inevitable upon employing phthalates as eluents. 

Fig. 3-70. pH dependence of the retention of various inorganic anions with a phthalate eluent of the concentration c = 0.004 mol/L (taken from [70]). 

According to the above definition, direct detection is feasible when using carefully selected eluents such as phthalate [5] or benzoate [6], which exhibit a low equivalent ionic conductance (see Table 6-1). This results in a conductivity increase when a solute ion passes the conductivity cell. 

Fig. 6-16. Indirect photometric detection of various inorganic anions. - Separator column 250 mm x 4 mm I.D. SAR-40-0.6 eluent 0.001 mol/L sodium phthalate (pH 7 to 8) flow rate 2 mL/min detection UV (285 nm, indirect) injection volume 20 pL solute concentrations 106 ppm chloride, 138 ppm nitrite, 400 ppm bromide, 310 ppm nitrate, and 480 ppm sulfate (taken from [29]).

Electronic suppression is possible if the eluent is properly chosen for extra-low conductivity which is e.g. the case with phthalate buffers. The detector must be able to compensate for the background conductivity by its electronics. Such a set-up gives good calibration linearity over a wide range but its detection limit is rather poor. For historical reasons it is also termed single-column ion chromatography. 

Most of the monovalent anions exhibit only small changes in their relative retention on resins containing one, two, or three hydroxyethyl groups, compared to the tri-methylamine resins (Table 3.1). However, when a stronger eluent was used (phthalate,... 

The data in Table 3.2 show that MDEA considerably lowers the relative retention of nitrate, chlorate, iodide and thiocyanate compared to the TMA resin. It also shows that with the phthalate eluent the tributyl resin (TBA) has longer retention times for nitrate and much longer for iodide, but shorter for sulfate and thiosulfate, all compared to the TMA material. 

Table 3.5. Relative retention times (min) of selected anions on columns prepared from trimethylamine (TMA), tributylamine (TBA) and tributylphosphine (TBP). Eluent 2.2 mM sodium phthalate at pH 6.0.

Table 3.9. Adjusted retention times for anions relative to chloride. Capacity of trimethylamine XAD-1 was 0.027 mequiv/g theoretical capacity of cetylpyridinium coated resins was 0.050 mcquiv/g. Eluent was 0.2 raM tetrabutylammonium phthalate, pH 6.5. Conductivity detection.

Figure 6.9. Separation of standard solutions of sulfate (2.75-13.75 ppm) from chloride and nitrate. Resin XAD-1, 44-57 pm 0.04 mequiv/g eluent, 5,0 X 10 M potassium phthalate, pH 6.2.

The benzoate salt is one of the two most useful carboxylic acid salts for eluents. The other is phthalate. Benzoate salts are useful for separation of acetate, bicarbonate, fluoride, chloride, nitrite, nitrate, and other early-eluting anions. Divalent anion and other late-eluting anions such as thiocyanate and perchlorate are not eluted effectively by benzoate. The concentration of a benzoate eluent that should be used depends on the type and capacity of anion-exchange resin used, but is typically 0.5 to... 

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