Column protection

An HPLC typically includes two columns an analytical column responsible for the separation and a guard column. The guard column is placed before the analytical column, protecting it from contamination. 

Immediately purify the derivative using gel filtration on a Sephadex G-25 column. Protect the solutions from light during the chromatography. 

Orlando and Bonato [73] presented a practical and selective HPLC method for the separation and quantification of omeprazole enantiomers in human plasma. Ci8 solid-phase extraction cartridges were used to extract the enantiomers from plasma samples and the chiral separation was carried out on a Chiralpak AD column protected with a CN guard column, using ethanol-hexane (70 30) as the mobile phase, at a flow-rate of 0.5 ml/min. The detection was carried out at 302 nm. The method is linear in the range of 10-1000 ng/ml for each enantiomer, with a quantification limit of 5 ng/ml. Precision and accuracy, demonstrated by within-day and between-day assays, were lower than 10%. 

Martens-Lobenhoffer et al. [119] used chiral HPLC-atmospheric pressure photoionization tandem mass-spectrometric method for the enantio-selective quantification of omeprazole and its main metabolites in human serum. The method features solid-phase separation, normal phase chiral HPLC separation, and atmospheric pressure photoionization tandem mass spectrometry. The internal standards serve stable isotope labeled omeprazole and 5-hydroxy omeprazole. The HPLC part consists of Agilent 1100 system comprising a binary pump, an autosampler, a thermo-stated column component, and a diode array UV-VIS detector. The enantioselective chromatographic separation took place on a ReproSil Chiral-CA 5 ym 25 cm x 2 mm column, protected by a security guard system, equipped with a 4 mm x 2-mm silica filter insert. The analytes were detected by a Thermo Scientific TSQ Discovery Max triple quadrupole mass spectrometer, equipped with an APPI ion source with a... 

LC-Column InertsilODS-3,50X2.0 mm, 5 pM particle size (Chrompack, Middelborough, Netherlands). An in-line solvent filter frit (5 pM from Upchurch scientific was also implemented for column protection. Mobile Phase ... 

Vertebrate—Includes all animals with a vertebral column protecting the spinal cord such as humans, dogs, birds, lizards, and fish. 

The most common problem associated with analytical columns is column deterioration. Deterioration may appear as poor peak shapes, split peaks, shoulders, loss of resolution, decreased retention times, and high backpressure. These symptoms indicate contaminants that have accumulated on the frit or column inlet, or there are voids, channels, or a depression in the packing bed. Deterioration is more evident in higher efficiency columns. For example, a column with 3-pm packing is more susceptible to plugging than one with 5- or 10-pm packing. Proper column protection and sample preparation are essential to prolong a column s life and obtain its best performance. 

Keeping records of column backpressure and important chromatographic parameters [number of theoretical plates (AO, peak asymmetry factor (As), retention factor k ), resolution factor (Rs)] helps to monitor the required column performance, while storage in the appropriate organic solvent extends column lifetime. Table 8 presents the preventive actions for column protection. 

The present procedure evolved from our previous work on the conversion of allenals, allenones, and allenylcarbinols to furans and 2,5-dihydrofurans with catalytic silver nitrate (AgN03) in acetone.5-10 It has also been shown that allenylcarbinols can be converted to 2,5-dihydrofuran under these conditions.11 0- and y-Alkynyl allylic alcohols can also be isomerized to furans under strongly basic conditions with potassium tert-butoxide in tetrahydrofuran-tert-butyl alcohol-18-crown-6 or hexamethylphosphoramide (KO-t-Bu in THF-t-BuOH-18-crown-6 or HMPA).12 The AgNOa/silica gel method is milder, faster, and more efficient than the previously reported procedures.13 Moreover, it offers the potential advantage of catalyst recovery and possible applicability to a flow system in which a packed column, protected from light, could serve as the reactor.4... 

The best remedy is prevention. Well-design guard columns protect the analytical column quite effectively without a deterioration of column performance. They take care of all colunm contaminants, independent of the source. This way you do not have to sort out exactly what the source of the column problem is. You amply replace the guard column any time the problem is observed, or even better, if the occurrence of the problem is reproducible, just before the problem occurs. 

When properly cared for, a column can last for a long time. Since the major cause for column deterioration is contamination, the protection of the column from contamination is a primary task of colunm care. Column lifetimes of over 10,000 analyses have been achieved with columns protected by guard columns. Under the identical set of conditions, but without this protection, column life was limited to about 2000 injections. 

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