Isocratic separations acids

Trathnigg, B., Rappel, C., Rami, R., Gorbunov, A. (2002b). Liquid exclusion-adsorption chromatography a new technique for isocratic separation of non-ionic surfactants V. Two-dimensional separation of fatty acid polyglycol ethers. J. Chromatogr. A 953(1-2), 89-99. 

Gundersen T.E. and Blomhoff R., 1999. Online solid-phase extraction and isocratic separation of retinoic acid isomers in microbore column switching system. Meth Enzymol 299 430. 

The selectivity of different stationary phase materials can be applied using columns in sequence to provide high-speed isocratic separations instead of gradient elution. An example for amino acids analysis is shown later in Figure 4.15, where the same eluent was used for all of the separations and the fraction containing the sample components of interest was switched from one column to another. 

FIGURE 14.3 Isocratic separation of morpholine, alkali, and alkaline earth metals on lonPac CS12A column. Eluent lOmM sulfuric acid. Detection suppressed conductivity. Peaks 1, lithium (0.5mg/L) 2, sodium (2mg/L) 3, ammonium (2.5mg/L) 4, potassium (5mg/L) 5, morpholine (25mg/L) 6, magnesium (2.5mg/L) 7, calcium (5mg/L). (From Rey, M.A. and Pohl, C.A., J. Chromatogr. A, 739, 87, 1996. Copyright 1996. With permission from Elsevier.)... 

Hupka et al. [29] developed a method for the determination of morphine and its phase II metabolites, morphine-3-beta-D-glucuronide and morphine-6-beta-D-glucuronide in the blood of heroin victims. The method is based on immunoaffinity SPE, RP-HPLC isocratic separation (mobile phase 90% lOmmol KH2PO4, 2mmol 1-heptanesulfonic acid, adjusted to pH 2.5 with H3PO4 and 10% acetonitrile flow rate 1.5 mL/min), and laser-induced native fluorescence detection. 

In the liquid chromatographic methods, separation of nitrofurans is generally carried out on nonpolar reversed-phase columns, the preferred sorbent being octadecyl bonded silica (Tabic 29.5). Polar columns containing cyanopropyl-based sorbents (164, 165) have also been used for die isocratic separation of nitrofuran residues isolated from edible animal products. A literature survey shows that there exists a clear preference for acidic mobile phases containing acetonitrile as the organic modifier (Fig. 29.5.1). 

Refractive-index detection is seldom used for many of the same reasons just mentioned for the spectroscopic detection of amino acids in their native forms. In fact, these problems are even more severe. Refractive-index detection has almost no selectivity whatsoever. Nearly every sample component passing the detector will register a signal. Also, this makes refractive index entirely incompatible with gradient elution. Even for isocratic separation, and detection of only a select few amino acids, refractive index can be very troublesome because of the detector s tendency to drift due to temperature changes in the laboratory (perhaps newer models have fixed this problem ). Finally, detection limits tend to be very poor for refractive-index detection. 

Figure 18.1 Isocratic separation of 17 amino acids, the early appearing ones being insufficiently resolved and the last one not eluted (reproduced by permission of A. Serban, Isotope Department, Weizmann Institute of Science, Rehovot). Conditions sample, 50 ixl containing 5 nmol of each amino acid column, 15 cm x 4 mm i.d. stationary phase. Amino Pac Na-2 (cation exchanger) 7 im mobile phase, 0.4 ml min sodium citrate 0.2 N pH 3.15-sodium phosphate 1 N pH 7.4 (1 1) temperature, BB C VIS detector 520nm after derivatization with ninhydrine.

ICSep AN2 lonPac ASH Isocratic. separation of anions and organic acids and solvent compatible... 

Free toxins C8 (50 x 2.1 mm) separation by gradient elution with acetonitrile containing 5 mM ammonium acetate (pH 6.8) (Stobo et al., 2005). C8 (50 x 2.1 mm) isocratic separation with 50% acetonitrile containing 2 mM ammonium formate and 50 mM formic acid (Stobo et al., 2005). C8 (50 X 2 mm) isocratic separation with 87% acetonitrile containing 0.05% acetic acid (Vale, 2006a). We employ the following conditions in a multitoxin screen (McNabb et al., 2005) ... 

Fig. 11.2.11. Isocratic separation of PTH-amino adds. Chromatographic conditions column, Ultrasphere ODS (250 X 4.6 mm I.D.) mobile phase, 0.01 M sodium acetate (pH 4.9)-acetonitrile (62.2 37.8) flow rate, 1 ml/min temperature, ambient. Peak identity corresponding to the single letter code for amino acids D, aspartic acid E, glutamic acid N, asparagine Q, glutamine T, threonine G, glycine A, alanine Y, tyrosine M, methionine V, valine P, proline W, tryptophan F, phenylalanine K, lysine I, isoleucine L, leucine S, serine. Reproduced from Noyes (1983), with...

Liquid chromatography Separation and quantitative analysis of flavanols and polyphenols may be conducted by Cig reversed-phase LC methods, using either isocratic or gradient modes. In one example of the isocratic separation method, the solvent system used consists of acetic acid-methanol-dimethylform-amide-water (1 2 40 157 v/v/v/v). Eluting peaks are monitored by UV absorption at 254 nm. 

Figure 1 Separations on silica IDA columns with different elution protocols. (A) Isocratic separation of four metal ions on a 100mmX4mm column packed with 5pm IDA silica. Eluent, lOmmoll nitric acid. Detection, PAR postcolumn reaction at 510nm. (Unpublished work, Nesterenko PN and Jones P.) (B) Isocratic separation of five metal ions on a 250 mm x 4 mm column packed with 5 pm IDA silica. Eluent, 0.5 mol I KCI, 20mmoll picolinic acid, and 12.5mmoll" nitric acid. Detection, PAR postcolumn reaction at 510 nm. (Unpublished work, Nesterenko PN and Jones P.) (C) Step gradient separation of Mn(ll), Cd(ll), Co(ll), Zn(ll), and Pb(ll). Eluent conditions 0.1 mol r NaCI (pH 2.6) switched to 0.1 mol 1 NaCI (pH 1.6) at time = 3 min prior to standard injection. Column, 250mm X 4 mm, packed with 8 pm silica IDA. Detection, PAR postcolumn reaction at 495 nm. (Reprinted with permission from Bashir W and Pauli B (2002) Ionic strength, pH and temperature effects upon selectivity for transition and heavy metal ions when using chelation ion chromatography with an iminodiacetic acid bonded silica get column and simple eluents. Journal of Chromatography 942 73-82 Elsevier.)...

Figure 11 Isocratic separation of Bi(lll), U(VI), and Zr(IV) in GBW07311 sediment sample at pH 0 on the 15cm PLRP-S column dynamically modified with 0.1 mmoll dipicolinic acid. Injection volume used was 500 pi with detection at 654 nm with Arsenazo III postcolumn reaction. (Reproduced with permission from the Ph.D. dissertation of James Cowan (2002) The development and study of chelating substrates for the separation of metal ions in complex sample matrices. University of Plymouth, Figure 5.15, p. 218.)...

Figure 7 Ion exclusion isocratic separation of organic acids. Peaks 1 chloride, 2 oxalate, 3 pyruvate, 4 tartrate, 5 malonate, 6 lactate, 7 malate, 8 acetate, 9 isocitrate, 10 citrate, 11 p-hydroxy-n-butyrate, 12 succinate, 13 proprionate. (Reproduced with permission from Dionex Product Selection Guide 1991.)...

P. N. Nesterenk and P. Jones, Isocratic separation of lanthanides and yttrium by high performance chelation ion chromatography on iminodiacetic acid bonded to silica,/. Chromatogr. A, 804, 223,1998. 

Not only do organic solvents influence the selectivity for carbon-containing anions but they can also reduce significantly the retention of polarizable anions, which are retained by ion-exchange and adsorptive interactions. Figure 3.41 shows an isocratic separation of iodide, thiocyanate, and thiosulfate together with the five most important mineral acids, which can be achieved with a... 

Figure 4.14 Isocratic separation of alkali metals, alkaline-earth metals, and amino alcohols on lonPacCS14. Eluent 10 mmol/L trifluoro-acetic acid -F15 m L/L MeCN flow rate ...

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