Acetonitrile from water

FIGURE 2 Spectrum of anthracene solution (l(lg/mL in acetonitrile) from Waters 996 PDA detector showing the annotations of The inset shows an expanded view of the 340-nm band. 

Figure 2-8. Typical excess adsorption isotherm of acetonitrile from water on the surface of reversed-phase silica.

Thiourea [62-56-6] M 76.1, m 179 , pK -1.19 (aq H2SO4). Crystd from absolute EtOH, MeOH, acetonitrile or water. Dried under vacuum over H2SO4 at room temperature. 

Lithium perchlorate [7791-03-9] M 106.4, pK -2.4 to -3.1 (for HCIO4). Crystd from water or 50% aq MeOH. Rendered anhydrous by heating the trihydrate at 170-180° in an air oven. It can then be recrystd twice from acetonitrile and again dried under vacuum [Mohammad and Kosower J Am Chem Soc 93 2713 19711... 

Sodium thiocyanate has also been recrystd from water, acetonitrile or from MeOH using Et20 for washing, then dried at 130°, or dried under vacuum at 60° for 2 days. [Strasser et al. J Am Chem Soc 107 789 1985 Szezygiel et al. J Am Chem Soc 91 1252 1987.] (The latter purification removes material reacting with iodine.) Sodium thiocyanate solns can be freed from traces of iron by repeated batch extractions with Et20. 

The basic polymer appears to be a hydroxylated polyether to which octadecyl chains have been bonded and so it behaves as a reverse phase exhibiting dispersive interactions with the solutes. An example of the separation of a series of peptides is shown in figure 15. The column was 3.5 cm long, 4.6 mm i.d. The solutes shown were (1) oc-endorphin, (2) bombesin, (3) y-endorphin, (4) angiotensin, (5) somatostatin and (6) calcitonon. The separation was carried out with a 10 min linear program from water containing 0.2% trifluoroacetic acid to 80% acetonitrile. 

The newcomer to chromatography, faced with a hitherto unknown sample, would do well to start with a C8 silica based reverse phase and an acetonitrile water mixture as a mobile phase and carry out a gradient elution from 100% water to 100% acetonitrile. From the results, the nature and the complexity of the sample can be evaluated and a more optimum phase system can be inferred. 

The separation was carried out on a column 25 cm long, 4.6 mm in diameter and packed with a Cl8 reversed phase. The mobile phase was programmed from a 93% acetonitrile 7% water to 99% acetonitrile 1% water over a period of 30 minutes. The gradient was linear and the flow... 

A biphasic solvent system composed of tert-butyl methyl ether, -butanol, acetonitrile, and water (2 2 1 5) acidified with triflnoroacetic acid has been applied to fractionate anthocyanins. The npper (organic) phase acts as the stationary phase and the lower (aqneons) as the mobile phase. HSCCC has been applied to obtain several anthocyanin fractions from wine, red cabbage, black cnrrants, chokeber-ries, " bilberries (Vaccinium myrtillus) acylated anthocyanins, and also isolate individnal anthocyanins from wine. ... 

Many industrial laboratories conducting significant amounts of additive analyses have developed a universal HPLC method which may be used to separate most of the additives of interest. Thomas [417] has reported a method that can separate over 20 common primary and secondary stabilisers. Verdurmen et al. [197] employ a gradient ranging from 60 % acetonitrile/40 % water to 100% acetonitrile subsequently, all components are eluted off the column in isocratic mode. Irganox 1063 is used as a suitable internal standard since this compound is not frequently encountered in commercial polymers, elutes without overlap to other additives and shows good UV absorbency. In order... 

Fig. 3-2. Semipreparative RP-HPLC profile of cyclo(Arg-Lys-X-Pro-X-Ala). The crude sublibrary (160 mol) was dissolved in 0.1 % (v/v) TFA and applied to a Whatman Partisil 10 jam ODS-2 (1 x 50 cm) column. The peaks were eluted using a 40-min linear gradient of 0-25 % acetonitrile in water at a flowrate of 7 mL min-1. Fractions were collected every 2 min and pooled in three fractions as indicated by arrows 130 jimol of peptides was recovered (yield 81 %). (Reprinted with permission from ref. [75]. Copyright 1998, American Chemical Society.)...

There is also substantial stabilization of [4+] by electron delocalization from the cyclic a-vinyl group. This is shown by a comparison of the thermodynamic driving force (p Tr lies between —7.8 and —8.5) and absolute rate constant (ks = 1 -6 x 107 s 1) for the reaction of [4+] in 25% acetonitrile in water with the corresponding parameters for reaction of the resonance-stabilized l-(4-methoxyphenyl)ethyl carbocation in water (p Tr = — 9.4and s= 1 x 108 s Table 5). 

The Aspen NRTL-SAC solvent database was identified from the list of solvents presented in the pharmaceutical based International Committee on Harmonization s guidelines for residual solvents in API [28], Hexane, Acetonitrile and Water were selected as the basis for the X, Y and Z segments respectively, the binary interaction parameters for the segments together with molecular descriptors in terms of X,Y and Z segments were then regressed from experimental vapour-liquid and liquid-liquid equilibrium data from the Dechema database. The list of solvent parameters that were used in the case study are given in Table 13. 

Fig. 16. Separation of cytochrome c (1), myoglobin (2), and chicken egg albumin (3) by re-versed-phase chromatography on a monolithic poly(styrene-co-divinylbenzene) column at flow rates of a 5 ml/min b 25 ml/min. (Reprinted with permission from [53]. Copyright 1996 American Chemical Society). Conditions column 50 mmx8 mm i.d., mobile phase linear gradient from 20 to 60% acetonitrile in water... 

Fig. 17. Rapid reversed-phase separation of proteins at a flow-rate of 10 ml/min (Reprinted with permission from [127]. Copyright 1999 Elsevier). Conditions Column, 50x4.6 mm i.d. poly(styrene-co-divinylbenzene) monolith,mobile phase gradient 42% to 90% acetonitrile in water with 0.15% trifluoroacetic acid in 0.35 min, UV detection at 280 nm. Peaks ribonucle-ase (1), cytochrome c (2), bovine serum albumin (3), carbonic anhydrase (4), chicken egg albumin (5)...

Fig. 2.55. Gradient reversed-phase HPLC analysis of flavonoids in white onions (a) and celery (b). ODS column of 150 X 3.9mm i.d particle size 5pm. Mobile phase 20min gradient of 15-35 per cent acetonitrile in water adjusted to pH 2.5 with TFA. Fowrate lml/min. Upper and lower traces represent samples before and after hydrolysis, respectively. Detection wavelength 365 nm. IS = internal standard Qc = quercetin Ap = apigenin Lt = luteolin. Reprinted with permission from A. Crozier et al. [159],...

Figure 4.4 Effect of TFA concentration on peptide retention. A series of five synthetic peptides containing 0, 1,2, 4, or 6 basic residues were separated on an octadecyl reversed-phase column using a 1%/min linear gradient from water to acetonitrile. Both solvents contained TFA at the indicated concentrations. (Reproduced from D. Guo, C.T. Mant, and R.S. Hodges, J. Chromatogr., 386 205 [1987]. With permission from Elsevier Science.)...

Figure 4.13 Separation of the tryptic peptides from recombinant HGH using a 120-min linear gradient at 60°C from water + 0.1% TFA to 40 60 water acetonitrile + 0.1% TFA. Column Zorbax SB-C8, 4.6 X 150 mm, 30-nm pore, 5- tm particle size. (Reprinted from W.S. Hancock, R.C. Chloupek, J.J. Kirkland, and L.R. Snyder, J. Chromatogr. A, 686 31 [1994]. With permission from Elsevier Science.)...

Flush buffers from system with water (or 10% acetonitrile in water) before switching to organic mobile phase. 

Relaxivities were measured either as a function of the applied field or in titration experiments at 20 MHz in anhydrous acetonitrile solutions of Gd(C104)3, i.e., in the simplest possible conditions with no competition from water or coordinating anions for the complexation of the metal ions. 

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