Grob mixture

Guthrie and Harland (4) have commented that the effects of deactivation, the chemistry of the stationary phase and its crosslinking, as weU as the effect of any postprocess treatment all appear in the final version of a column. An example of this situation is the separation of die Grob mixture (Figure 3.26a) performed on... 

FIGURE 3.26 Chromatogram of a comprehensive Grob mixture on a 15-m x 0.32-mm-i.d. Carbowax 20M capillary column (a) after coating and (b) after crosslinking the stationary phase. Column conditions 75-150°C at 2°C/min 28 cm/s He. Designation of solutes appears in Table 3.16. (Reference 7.)... 

Another decarboxylation reaction that employs lead tetraacetate under milder conditions, has been introduced by Grob et alJ In that case A-chlorosuccinimide is used as chlorinating agent and a mixture of A,A-dimethylformamide and acetic acid as solvent. 

A partial solution to the problem of producing sharp peaks at low elution temperatures is to add a small amount of a higher-boiling co-solvent to the main solvent. As suggested by Grob and Muller (23, 24), butoxyethanol can be used as a suitable cosolvent for aqueous mixtures in such cases. 

K. Grob and Z. Li, Intr oduction of water and water-containing solvent mixtures in capillary gas clir omatogr aphy. I. Eailure to produce water-wettable precolumns (retention gaps) , J. Chromatogr. 473 381-390 (1998). 

Gianesello et al. (120) described the determination of the bronchodilator brox-aterol in plasma by on-line LC-GC. After deproteination and extraction, the LC separation was carried out by using a mixture of -pentane and diethyl ether (55 45 (vol/vol) as mobile phase. A small cut of the LC chromatogram (shown in Figure 11.9(a)) was introduced at 85 °C into the GC via so-called concurrent solvent evaporation. Figure 11.9(b) demonstrates that a detection limit of about 0.03 ng/ml was obtained. A fully automated LC-GC instrument was described by Munari and Grob (121) and its applicability was demonstrated by the determination of heroin metabo-... 

Figure 15.11 (a) Total ion clnomatogram of a Grob test mixture obtained on an Rtx-1701 column, and (b) re-injection of the entire clnomatogram on to an Rtx-5 column. Peak identification is as follows a, 2,3-butanediol b, decane c, undecane d, 1-octanol e, nonanal f, 2,6-dimethylphenol g, 2-ethylhexanoic acid h, 2,6-dimethylaniline i, decanoic acid methyl ester ], dicyclohexylamine k, undecanoic acid, methyl ester 1, dodecanoic acid, methyl ester. Adapted from Journal of High Resolution Chromatography, 21, M. J. Tomlinson and C. L. Wilkins, Evaluation of a semi-automated multidimensional gas chromatography-infrared-mass specti ometry system for initant analysis , pp. 347-354, 1998, with permission from Wiley-VCH. 

Figure 5.4-65. Di Ccurves for nitration of reaction mixtures 1 mg sample, sealed crucible, 10 °C/min (adapted from Hoppe and Grob, 1990).

Figura 2.9 Dse of th Grob test Mixture to compare tbe activity of various glass surfaces coated with ov-ioi. Surface types A > Untreated pyrex glass, B pyrex glass deactivated by thermal degradation of Ceurbowax 20M, C < SCOT column, prepared with Silanox 101, D pyrex glass column coated with a layer of barium carbonate and deactivated as in (B), and E - untreated fused silica. Components are identified in Table 2.7 with ac - 2-ethylhexanoic acid. (Reproduced with permission from ref. 152. Copyright Elsevier Scientific Publishing Co.)...

A good way to test the operation of the GC and the GC-MS interface is to run a standard sample. For this purpose the so-called Grob test mixture [226] is suitable. 

Figure 1 highlights the separation of a mixture of different polarity GC standards known as the "Grob mix" commonly used to test the efficiency of columns. Figure 2 shows the linear representation highlighting the closeness of elution time if only a single column had been employed. The identity of the mix chemicals and their retention times are given in Table 3. 

In the course of a feasibility study, sponsored by the European Union, the components of the GC separation efficiency test, according to K. Grob, were tested for their usability as certificated tertiary standards. Seven compounds are now available as a ready-to-use mixture for testing the accuracy of the GC-IRMS measurements, and furthermore simultaneously provide important information about the actual quality status of the GC column system used [53]. 

Qrloff, J- Russ. Phys. Chem. Roc., 1904, 3d, 1311 j also Bosshard and Grob, loc,. cit. For a method of determination of eaoh of the sulphur aoids in a mixture containing sulphide, hydrosulphite, sulphite, thiosulphate and sulphate, see Binz and Sondag, Ber., 1905, 38, 3830. For monographs on the hydrosulphites, see Jellinek, Ahrens Sammlung, 1911 and 1912. 

Figure 15.11 (a) Total ion chromatogram of a Grob test mixture obtained on an Rtx-1701... 

Figure 8.7. Grob test mixture run on 30 m DB-5 OT column. Courtesy of J W Scientific.

It is claimed (Youk et al., 1999) that olive, sunflower and peanut oils contain mainly esterified sterols, while soyabean and sesame oils contain mainly free sterols. This does not appear to have been utilized previously, but could be useful with mixtures of the two classes. Although it is possible to de-sterolize oils, and remove characteristic sterols, this usually forms other sterols that can be detected (Biedermann and Grob, 1996 Lanuzza and Micali, 1997 Mariani and Venturini, 1997). If it is suspected that this has occurred, then the presence of other suspect components should be investigated. 

In olive oil, the main sterol is (l-sitosterol and this dehydrates to a mixture of 2,4- and 3,5-stigmastadienes on heating to high temperatures or in the presence of a bleaching earth (Grob and Bronz, 1994 Cert and Moreda, 1998). 

Belanich, M., Cummings, B., Grob, D., Klein, J., O Konner, A., and Yarosh, D. (1996). Reduction of endotoxin in a protein mixture using strong anion-exchange membrane absorption. Pharm. Technol. 20(3), 142-150. 

The use of HPLC need not be limited to the analysis of nonvolatile flavor components. HPLC can be coupled with GC/MS to form an extremely powerful separation system. The unique separation properties of HPLC can be used to separate complex flavor mixtures to simplify later GC/MS separation and identification. This approach can be somewhat tedious to use in that a separate GC/MS run must be made for each HPLC fraction - but for very complex flavor systems there is often no other choice. Grob et al. (61 ) devised a direct transfer for HPLC fractions into a capillary GC to make this approach more convenient to use. They demonstrated the practical workability of the system by separating and Identifying two components in a toothpaste using both HPLC/GC and HPLC/GC/MS. 

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