Methanol eluant

Results of lead studies indicate that dissolved lead at 25 ppb is not isolated by the XAD-4 quaternary resin. However, if lead is precipitated in the drinking water sample, the resin acts as a filter, and the precipitated lead compounds collected on the resin can be dissolved by the acid/methanol eluant. Experiments with the presence of humic substances and lead were conducted because humic substances can act as chelating agents for heavy metals. Approximately 85 of the lead was recovered, but lead was removed from water because of the initial precipitation of this element. This phenomenon may not occur in actual field sampling because all lead compounds should be in a dissolved form. 

The columns were then washed with methanol until no trace of triterpenoids were detected. The methanol eluant was evaporated under reduced pressure to give 8.19 g of a residue which was divided in 8 equal portions. Each portion was chromatographed on a silica gel colunm (2.5 X 16 cm) and eluted with chloroform methanoI water (65 35 10). Fractions of 25ml each were collected and examined by TLC. Homogeneous fractions 8-10, 25-30 and 41-45 were combined, evaporated and lyophilized to dryness. The resultant three fractions consisted of pseudoginsenoside-RPi (2) (21 mg, 0.0084%), the major component pseudoginsenoside-RTi (3) (312 mg, 0.125%) and siamenoside (4) (67 mg, 0.027%), respectively. 

In their recent publication. Tucker et al. [73] describe the analysis of iodide in ground water and soil extracts on lonPac ASH using suppressed conductivity detection and a sodium hydroxide/methanol eluant. The soil samples to be analyzed were extracted with a carbonate/bicarbonate mixture and the resulting extracts diluted with de-ionized water after membrane filtration. As expected, the minimum detection limit for iodide with suppressed conductivity detection is in the mid-pg/L range. 

Using this equilibrium relation and the previous set of equations, elution curves by means of methanol eluant from the aaivated carbon column which has adsorbed o-chlorobenzoic acid can be calculated The rate of desorption is also dependent on alcohol content and the amount adsorbed, but as a rough estimation simple treatment of constant... 

Figure 22 Chromatogram of a reference mixture of pyridine compounds. Conditions column, ODS-2 Spherisorb (125 X 4.6 mm, i.d.) mobile phase, gradient elution with 0.1 M KH2PO4, containing 6 mM tetra-n-butylammonium hydrogen sulfate, at pH 5.5 (eluant A), and methanol (eluant B). Initial conditions 96% A and 4% B, increasing stepwise to 10% B in 5 min, 12% B at 10 min, and 30% B from 13 to 15 min, followed by a return to initial conditions (96% A and 4% B) from 19 to 20 min. Flow rate, 1 mL/ min detection wavelength, 254 nm column temperature, ambient. (From Ref 59.)...

The solvents used for liquid chromatography are the commoner ones such as water, acetonitrile, and methanol. For the reasons just stated, it is not possible to put them straight into the ion source without problems arising. On the other hand, the very viscous solvents that qualify as matrix material are of no use in liquid chromatography. Before the low-boiling-point eluant from the LC column is introduced into the ion source, it must be admixed with a high-boiling-point matrix... 

Figure 2. Chromatographic profile of DNA hydrolysate from rat liver 12 h after application of 133 mg/18.5 mCi/kg l l-[2f3- H]-nitrosodipropylamine. Key O, A , CPAf. Conditions included column, 30-cm i rBondapak-C18 eluant, 3% methanol/0.05M ammonium formate (pH 3.5) flow rate, 1 mL/min and sample, 10 mg hydrolyzed DNA containing unlabeled 7-propylguarune (41 fig/mg DNA) and 74sopropylguanine (34 fig/mg DNA), which was injected five times in five...

The submitters report that they currently use two 500-g columns run consecutively. After the first column is used, it is washed with methanol, all traces of solvent flushed through with compressed air, reequilibrated with eluant, then those fractions (from the first column) that contain a mixture of cis- and trans-alkenes are rechromatographed. 

Although a reductase was not actually applied, separation of 26 from (S)/(R)-20 was accomplished by use of reversed-phase silica as the column material and methanol/ water as the eluant. In view of the observed dependence of the g factor on concentration, aggregation in this protic medium was excluded. In the HPLC setup, the mixture was fully separated within less than 1.5 min. By use of the JASCO-CD-1595 instrument in conjunction with a robotic autosampler, it was possible to perform about 700—900 rather exact ee determinations per day (111). 

Dried milled leaves (200g) of Salvia divinorum, collected at Huautla, Oaxaca in November 1980, were extracted with boiling chloroform. Evaporation of the solvent gave a green residue (27g) which was purified by chromatography on "Tonsil" (200g) with chloroform as eluant. Thirteen fractions of 50.0 ml were collected, the sixth and seventh of which contained compound [A] as ascertained by t.l.c. (45% ethyl acetate in hexane as developer Rf 0.7). Crystallization from the methanol yielded salvinorin [A] as colorless crystals, m.p. 238 -- 240 C... 

Note 10) with 2.5% methanol/methylene chloride as the eluant yielding 5.25-5.81 g (38.6-42.7%) of 2-methyl-4H-pyran-4-one (Note 11). 

What would have been the order of elution of these compounds if examined by an HPLC column containing a phase of type RP-18 with a binary mixture of acetonitrile/methanol (80/20) as eluant ... 

Saturated HCl/methanol Measure the volume of eluant and analyze spectrophotometrically for humic substances. 

Many classes of organic compounds adsorbed by this resin can be desorbed by solvents such as ether (or acidic methanol and ether). The acidic solvents can be concentrated to remove inorganic acid, but some residual inorganic acid always remained in the concentrated eluants. Residual acid, or possible trace of water in the concentrated eluants, caused analytical variances when methylation was attempted. Therefore, quinaldic acid, trimesic acid, and 5-chlorouracil were analyzed by HPLC rather than by GC-FID. 

Humic substances were concentrated more than 50-fold on the XAD-4 quaternary resin, but a saturated HCl/methanol solution was required for the desorption. This eluant was not concentrated further because the concentration of humic substances could be measured directly with a spectrophotometer. Total recovery of humic substances was higher in the bench-scale experiments than in the pilot plant studies. On the basis of the pilot plant results (see summary of experiment 3), it appears that the adsorption of humic substances was affected by the higher velocity or the loading capacity because 458 was recovered in the effluent water. The higher velocity in the pilot plant studies did not have a similar effect on other compounds such as quinaldic acid, for example, which was recovered at almost 100. It is believed that caffeine, which was concentrated during bench-scale studies, was also affected by the higher velocity in the pilot plant studies. 

The XAD-4 quaternary resin was cleaned by Soxhlet extraction and kept wet under water to minimize artifacts from the resin. An oily, yellow residue observed during concentration of the acidic eluants required an additional cleanup step. On the basis of the results of the resin blank experiments, it was necessary to clean the XAD-4 quaternary resin by batch process with saturated HCl/methanol prior to Soxhlet cleaning with solvents. Artifacts such as benzoic acid were found in the resin blank experiments, but, in general, the mass of each artifact (per dry weight of resin) was negligible. 

To a solution of 2-(trimethylsilyl)ethyl 3-O-allyl-6-0-benzyl-2-phthalimido-2-deoxy-p-D-glucopyranoside (250 mg, 0.49 mmol) and 18 p,L of 1M MeOTf solution in 0.5 mL of dry dichloromethane was added dropwise 18.8 mg (0.07 mmol) of 3-methoxy-2-pyridyl p-L-fucopyranoside in 0.5 mL of solvent over 15 min. The mixture was stirred at room temperature for 30 min, and processed as described in the foregoing. The residue was purified by flash chromatography on silica gel column using EtOAc-hexane, (2 1) as eluant to recover the excess of acceptor. Elution of the column with EtOAc-hexane, (1 1) containing 10% methanol gave 20 mg of the title product in 43% yield as a syrup. 

Willi improved means to separate the compounds of these two elements, future research will yield more details of specific hafnium compounds. The methods of separation used effectively include ion exchange techniques, a particularly effective one using u column of silica gel. w ith a solution of the tetrachlorides in methanol as feed and a 1.9 N HCI solution as eluant for zirconium. Separations also have heen accomplished through the distillation of the phosphorus oxychloride addition products. 

---