Impurity profile retention

FIGURE 7 (a) Impurity profile of Intermediate produced by the new process. Peaks after 8 min were impurities that were not previously observed when the Intermediate was produced via the old process, (b) Chromatogram of the drug substance made from intermediate of poor quality. Peak at 22 min retention time is the drug substance Impurity at 36 min retention time was a new impurity and failed specifications. 

This study evaluated the impurity profile of untreated water from a textile plant in Portugal [35]. The organic material was concentrated by extraction from 11 of water into dichloromethane and HPLC-NMR and HPLC-MS experiments were carried out using a reverse-phase separation with an acetonitrile/ D2O gradient elution with H NMR spectroscopic observation at 600 MHz. For the HPLC-NMR studies, the samples were further fractionated into two pools according to their HPLC retention times. The HPLC-NMR studies were carried out in the stop-flow mode and the combination of NMR and MS results yielded the identification or tentative identification of 14 compounds, comprising mainly surfactants, anthraquinone dyes and nonylphenol-related molecules. 

The use of UV spectroscopy, mostly using a photodiode array, allows quantification of drug impurities that have a different retention time from that of the active substance. An example is use of UPLC-U V for determination of the impurity profile... 

The separation selectivity of a mixture of acidic, basic, and neutral compounds can be altered with the addition of chaotropic mobile-phase additives (Figure 4-62). The retention of the basic compounds can be increased by addition of chaotropic counterions in the mobile phase, while the retention of neutral and acidic compounds is generally unaffected. This is particularly useful during the development of impurity profile methods in the pharmaceutical industry where the retention of a polar protonated basic impurity may be adjusted such that adequate separation selectivity is obtained when union-izable, acidic, or basic (in neutral form) impurities in the drug substance are present. In Figure 4-62 the retention of protonated basic compounds, metoprolol and labetalol, increase while the retention of phenol (in its neutral state) remains constant. 

For development of a weight percent assay, a short isocratic method can be implemented based on observations from the gradient method used for the impurity profile. One can use a shorter column such as a 5-cm column and keep retention of the solute of interest to around a capacity factor of 3 as long as it is still resolved from impurities observed in the impurity prohle. Additionally, the elution of more hydrophobic species should not co-elute with the drug substance in later injections. During the method development of an isocratic method, the compound should be injected and then a suitable number... 

Nicolas and Scholz [69] described another use of MS-MS in impurity profiling. In the routine monitoring of dmg impurities by means of LC, variation in retention time can lead to uncertainty with respect to the identity of a particular component. The use of the precursor m/z and at least three product ion m/z are used either as MS-MS fingerprint or as diagnostic ions to trace and confirm related substances. 

Retention time matching can be validated to establish identity, but is insufficiently specific for general use. Retention times are not necessarily unique for chemically distinct species even isomers may or may not co-elute. A change in synthetic process may introduce a different impurity profile any of these new process impurities has a non-zero chance of co-elution with... 

A rationale for the inclusion or exclusion of impurities in a specification should be presented. The rationale should include a discussion of the impurity profiles observed in the safety and clinical development batches, together with a consideration of the impurity profile of batches manufactured by the proposed commercial process. Specified, identified impurities should be included along with specified, unidentified impurities estimated to be present at a level greater than the identification threshold given. For impurities known to be tmu-sually potent or that produce toxic or unexpected pharmacological effects, the quantification/detection limit of the analytical procedures should be commensurate with the level at which the impurities should be controlled. For unidentified impurities, the procedure used and assumptions made in establishing the level of the impurity should be clearly stated. Specified, unidentified impurities should be referred to by an appropriate qualitative analytical descriptive label (e.g., "unidentified A," "unidentified with relative retention of 0.9"). A general acceptance criterion of not more than the identification threshold for any unspecified impurity and an acceptance criterion for total impurities should be included. 

Figure 4 Typicai gas chromatographic impurity profiies of different MDMA sampies. The big peak at retention time 12.2 min (after peak no. 12) corresponds to MDMA. Peaks 7, 3,4-meth-ylenedioxy-A/-melhyibenzyiamine 10, 3,4-methyienedioxyphenyi-2-propanone 12, 3,4-methyienedioxy-phenyi-2-propanoi 16, /V-ethyl-3,4-methyienedioxyamphetamine 17, A/,A/-dimethyi-3,4-methylenedioxyamphetamine 18, 1-(1,2-dimethyi-1-azacyciop-ropyl)methyl-3,4-methylenedioxybenzene 21, caffeine 24, palmitic acid 28, stearic acid. (Reproduced with permission from Palhol F, Boyer S, Naulet N, and Chabrillat M (2002) Impurity profiling of seized MDMA tablets by capillary gas chromatography. Analytical and Bioanalytical Chemistry 374 274-281 Springer-Verlag.)...

In addition to the precautions already mentioned, the time of column equilibration between each run should be about the same. Ideally the profile of one of the two peptides (native or synthetic) should give a symmetrical absorbance as well as show the presence of a small amount of an impurity. Under such circumstances, the coelution run should show a symmetrical absorbance of the size of that of the synthetic and native molecules. In addition, the absorbance of the impurity should now be half the size of that seen in the chromatogram of the contaminated peptide. All other absorbances such as injection artifacts should be identical in all runs 2-6. CAUTION Two peptides that show the same retention times after being run separately under the same conditions cannot be said to have coeluted ... 

The success of the analysis is dependent on the selection of a suitable internal standard. Some important criteria for such selection are as follows (a) that it is not chemically reactive towards any of the components of the mixture (b) that it has a retention time which gives a base line separation from the other components, including any impurities (c) that the retention time is comparable with that of the components of the mixture (d) that the peak profile is symmetrical and therefore does not exhibit either fronting or tailing and (e) that the detector response to the internal standard is such that neither an excessive, nor a minute, weight of standard compared to the weight of mixture needs to be used. 

Figure 8.2 shows the decision scheme for establishing the purity profile of an active substance. First, the impurities are separated using chromatographic or electrophoretic methods, in at least three distribution systems. The retention times are compared with the retention times of standards, and the eluents quantified. Next, spectroscopic methods (UV, FT-IR, MS) combined with chromatographic/electro-phoretic methods are used to establish the structures of unknown impurities. If this... 

Figure 12.8 Profiles of trace components of the feed in displacement chromatography. Amounts impurities, 0.1 mg main components, 50, 50, and 100 mg. Injection concentrations impurities, 0.02 mg/mL main components 10,10,20 mg/mL displacer, 125 mg/mL. tp = 5.1 min void fraction, 0.8 L = 50 cm Fj, = 1 mL/min to = 6.65 min. (a, c) Profiles of the main components and displacer retention factors, /Cq, 5, 7, 9, and 13.5 b = 0.0159, 0.0171 0.0187 0.02 mg/mL. (a, c, insets) Profile of impurity with an isotherm below the operating line, k o = 2. (b, d) Profiles of the impurities eluting between the main component bands, retention factors, 6, 8, 11 respectively, (b, d, insets) Profile of impurity imder elution conditions, kg - 6 injection concentration, 0.2mg/mL, tp = 0.51min.

When the displacer contains impurities, multicomponent frontal analysis of the displacer solution takes place. The impiuities that are less retained than the displacer have a breakthrough curve which appears earlier and interferes with the component bands [18]. Depending on the relative retention of the feed components and the displacer impiuities, various types of breakthrough profiles can be observed for these impurities. Those which are less retained than all the components are eluted as a very sharp initial peak, or staff, in the front of the first band,... 

Experimental restdts (Figure 12.11b) are in agreement with the band profiles calculated using the equilibrium-dispersive model [18]. This demonstrates that displacer impurities with lower retention than the displacer will pollute the pu-... 

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