Deactivation columns

Try another column type (e.g., deactivated column for basic compounds). 

Column. 2.5% SE-30 on 80-100 mesh Chromosorb G (acid-washed and dimethyldichlorosilane-treated), 2 m X 4 mm internal diameter glass column. It is essential that the support is fully deactivated. Column Temperature. Normally between 100° and 300°. As an approximate guide, the temperature to use is the retention index —10. 

The standard method for analyzing paraquat is by ion-exchange cleanup followed by reduction to the radical cation, which is colored and read spect rophotometrically(5). The labor requirements and somewhat limited detectability of this method led us to develop a GC method based upon reduction with sodium borohydride to a mixture of the monoene and diene tertiary amines - both of which are amenable to GC on a deactivated column using an N-selective detector( ). The chromatogram shows both peaks (ratios may vary somewhat) which provides built-in confirmation of paraquat because of this dual response pattern. But the reduction-GC method is still a laborious one with a throughput of perhaps 8-10 samples/day under good conditions. It took nearly one man-year to develop and fully Validate. 

The gas chromatography was carried out at a column temperature of 250°C for morphine base. When decreasing amounts of morphine were.chromatographed on a commercial OV-1 column and on the proposed deactivated column, and graphs showing the relationship between peak hight and amounts of morphine were constructed, it was found that the commercial OV-1 column had a cutoff point at 0.4 ug morphine, whereas the proposed deactivated column had a cut-off point at 0.8 ng. Hence, the proposed column showed an improvement in detection limit of the order of 1000-fold. 

Because of adsorption and degradation problems when using glass capillary columns for the analysis of morphine and codeine, Plotczyk preferred fused silica columns to the analysis of underivatized drugs, i.a. codeine. He used cold on-column injection and cross-linked poly-si loxane deactivated columns and obtained linear quantitation from 1 to 100 ng with precisions of 0.1-2 % for some of the drugs analyzed. 

By means of chloroform - methanol - ethyl acetate - acetic acid (60 20 50 3), reasonable results were achieved. Water-deactivated columns in combination with chloroform - methanol were also used with good results. 

A limited number of experiments were conducted to evaluate the last two possibilities. First, the take-up solvent for two test solutes, anthracene and naphthalene, was cyclopentane (with solution concentrations still about 1 mg/mL and injection aliquots still about 0.3 - 0.5 pL into a 20vL loop) instead of 2-methoxy-ethanol. The distortion persisted even when a gentle stream of air was used after aliquot deposition in the sampling loop to blow off the take-up solvent. Furthermore, the onset of the distortion for naphthalene occurred at a lower carbon dioxide density than for anthracene. When the column was changed to a partially chemically deactivated column, Hypersll SAS, where short alkyl chains are bonded to active sites, onsets of peak distortion for anthracene and for naphthalene were shifted to lower carbon dioxide densities (and still different from each other) than for the fully active Hypersll SIL adsorption column. Only slight peak distortion was observed for a Hypersll ODS column at even lower column midpoint densities (0.33 g/mL with the back pressure at 1170 psig, the FLOW setting at 1.90 mL/min, and 40 C distortion was observed for only anthracene and not naphthalene). 

Bogusz, M. Erkens, M. Maier, R.D. Schroder, I. Applicability of reversed-phase base-deactivated columns for systematic toxicological analysis. J.Liq.Chromatogr., 1992,15,127-150 [simultaneousbral-lobarbital, diphenhydramine, fluphenazine, imipramine, pentobarbital, salicylamide, secobarbital, thiopental, thioridazine]... 

Rutledge, D.R. Abadi, A.H. Lopez, L.M. Liquid chromatographic determination of celiprolol, diltiazem, desmethyidiltiazem and deacetyldiltiazem in plasma using a short alkyl chain silanol deactivated column. J.Pharm.Biomed.Anal., 1994, 12, 135-140 [extracted metabolites, celiprolol LOD 3 ng/mL] Sigusch, H. Henschel, L. Kraul, H. Merkel, U. Hoffmann, A. Lack of effect of grapefruit juice on diltiazem bioavailability in normal subjects. Pharmazie, 1994, 49, 675-679 [pharmacokinetics SPE extracted metabolites flurazepam (IS)]... 

Surface modification reactions used to improve the wettability of glasses by the stationary phase and to deionize some glasses result in an increase in the activity of the glass surface. Without subsequent deactivation, columns coated with low-polarity... 

Capable of producing the most inert deactivated column... 

Most pharmacopoeias specify that ethambutol hydrochloride contains not less than 98.0% and not more than 100.5% of C10H24N2O2 2HCI, calculated on the dried basis. Pharmaceutical products such as tablets must contain not less than 95.0% and not more than 105.0% of the labeled amount.As for pyrazinamide, the main pharmacopoeia assay method for ethambutol is a titration method. However, an HPLC method is used for the assay of ethambutol HCl in tablets.This method requires that a liquid chromatograph equipped with a 200-nm detector and a 4.6 mm X 15 cm base-deactivated column that contains 5 p,m porous silica particles, 3-10 p,m in diameter, with chemically bonded nitrile groups (CN, LIO) is used. The mobile phase is a mixture of 1.0 ml of triethylamine and 1 L of water, adjusted with phosphoric acid to a pH of 7.0. The flow rate is about 1.0 ml/min. Separately inject equal volumes (about 50 p.1) of standard preparations and the assay preparations into the chromatograph, record the chromatograms, and measure the responses for the major peaks and calculate the quantity, in mg, of ethambutol hydrochloride present in the tablets from the peak responses obtained from the assay preparation and the standard preparation, respectively. The tailing factor must not be more than 2.0, and the relative standard deviation for replicate injections not more than 2.0%. 

Despite their structural similarity, atropine ( hyoscyamine) and homatropine cannot be assayed in the same way as hyoscine (6,7-epoxyatropine) as the former compounds are very strongly retained on unmodified silica. Reversed-phase methods usually suffer from analyte peak tailing and, although some success with base deactivated columns has been achieved, it has not proved possible to develop... 

Carbowax 20M has also been successfully used to deactivate column surfaces (84,85). After coating a thin film of Carbowax 20M, for example, on the column wall, the column is heated to 280°C, then exhaustively extracted with... 

Carbowax 20M has also been used successfully to deactivate column surfaces (50,51). After coating a thin film of Carbowax 20M, for example, on the column wall, the column is heated to 280°C, then extracted exhaustively with solvent, leaving a nonextractable film of Carbowax 20M on the surface. Both apolar and polar stationary phases, including Carbowax, can then be coated on capillaries subjected to this pretreatment (52). Dandeneau and Zerenner used this procedure to deactivate their first fused-silica columns (4). Other polyethylene glycols used for deactivating purposes have been Carbowax 400 (53), Carbowax 1000 (54),... 

Amounts of sulphide of up to 2 mg S —/liter are said not to interfere with this method although the repeated analysis of such water will deactivate columns by the production of cadmium sulphide. 

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