ALOT columns

Fig. 1>5. Chromatogram of separation of hydrogen (1), oxygen (2) and nitrogen (3) on ALOT column with molecular sieve SA [20].

Fig. 1-6. Chromatogram of hydrocarbons on ALOT column with porous polymer adsorbent [21].

The present book discusses open adsorption columns (mainly ALOT columns) (see Fig. 1-8) and compares their characteristics and analytical features. 

Comparison of adsorbent layer open tubular and traditional packed columns shows the advantages of ALOT columns. 

ALOT column 10 m x 0.5 mm, adsorbent Molsieve 13X, temperature 150 °C, then 10 7min to 400 °C, carrier gas hydrogen, split injection, detector FID. 

Using molecular sieve 13X it is possible to separate paraffinic and naphthenic hydrocarbons according to carbon number (22]. However, the retention of high boiling hydrocarbons was very high. For example, the time required for the elution of hydrocarbons up to Cii in a typical naphtha sample on a packed column is 1.5 h (see Fig. 2-3a [21]). With 10 m X 0.5 mm stainless steel ALOT column with 0.3 p.m porous layer, Cii hydrocarbons elute at 400 °C (see Fig. 2-3b [21]). ALOT column permits to decrease the maximal separation temperature (400 °C instead of 500 °C). 

Rapid analysis is a very important direction in gas chromatography [23-28]. ALOT columns can be used for fast gas analysis [23]. According to Tijssen and co-workers [23] the minimum analysis time can be determined with the following equation ... 

Fig. 2-4 Fast separation of some alkanes on ALOT columns with silica layer [23].

Fused-silica aluminum oxide ALOT column 30 m x 0.32 mm oven temperature 60 °C detector FID split ratio, split injection 1 25 of 20 nl gas mixture of Ci - 64 hydrocarbons water equalizer. 

Therefore, using ALOT columns with small column diameter for high-speed analysis is very promising. ALOT columns can eilso allow faster chromatographic separations in routine analysis. For example, Fig. 2-5 shows the separation of 16 hydrocarbons C1-C4 within 300 seconds using ALOT column with alumina [29]. As can be seen from... 

The utility of ALOT columns for high-speed analysis of some volatile aromatic compounds was also investigated by Peters and Saks [30]. Methane, benzene, toluene, o- and p-xylene are separated on capillary columns with alumina. 

There are some artifacts associated with the use of ALOT columns as compared to traditional forms of stationary phases for open tubular columns. An important example is the irreversible adsorption of water and other polar molecules on alumina... 

Column 30 m X 0.32 mm, fused-silica alumina ALOT column, oven temperature 60°C, detector FID. 

Fig. 2-1 Ob Separation of hydrocarbons on ALOT column for water pressure 2.310-3 bar HjO 1291,...

Jacobsson and Falk [56] suggested determination of low (ng/ml) concentrations of hydrogen sulfide in aqueous solutions with ALOT column (PoraPLOT Q). The detection limit is about 1 ng/ml (see Fig. 2-11 [56]). If greater sensitivity is needed stripping analysis in combination with a cryogenic focusing device should be used. A prerequisite of such a method, however, is that water has to be removed prior to the trap (for example, by calcium chloride [57]) in order to prevent plugging of the cold trap. Thus, ALOT columns can be recommended for trace analysis of polar compounds. 

This chapter Fundamentals of gas-solid chromatography comprises four sections 3.1. Retention in gas-solid chromatography 3.2. Chromatographic zone broadening in ALOT columns 3.3. Dependence of column efficiency on sample size and 3.4. Resolution of analyzed compounds. From a theoretical point of view, these topics are mainly of interest for capillary gas-solid chromatography. 

Data in agreement with Golay s equation for ALOT columns [41]. 

De Nijs [7] showed experimentally the possibility of using ALOT column with aluminum oxide for trace determination (see, for example, Fig. 3-5, note splitless injection). 

For low k veilues resolution increases very rapidly with increasing k. At large k values the term C 1 and a further k increase will not improve resolution. Thus, the optimum veilues of k lie in the range 1 < k < 10. The minimum analysis time for open tubular columns is achieved under the conditions where k is about 1-2. As a rule, capacity is not a critical parameter in ALOT columns. 

The ALOT column with molecular sieve 13X was suggested by Soulages and Brieva [130]. For the analysis shown in Fig. 5-39 [130] temperature programming started at 100 C and increased slowly... 

Fig. 5-39 Chromatogram of dearomatized naphtha on ALOT column with molecular sieve 13X [130].

Fig. 5-40 shows the results of a rapid analysis of the same sample. This analysis is recommended for routine determinations of paraffins and naphthenes. Thus the use of a molecular sieve 13X ALOT column permits determination of paraffins and naphthenes in dearomatized naphthas with boiling points up to 200 °C. Souleges and Brieva [130] established the practical possibilities and of this type of ALOT column, in which a porous layer adheres to the inner walls of the tube by natural cohesive forces only. The column was used for more then 100 analyses at different times and no sign of deterioration was observed. ALOT columns... 

Usually ALOT columns can be prepared using dynamic or static coating techniques (classical methods, see, for example, [13, 14]). Static coating places considerable demands on adsorbent sus-... 

Main factors influencing preparation of ALOT columns... 

The layer thickness may be controlled via the solid concentration in the suspension. It is also possible to vary the radius of the uncoated capillary, since the column diameter influences the loading capacity. Mohnke and Heybey [22] deduced a formula for the estimation of solid adsorbent concentration in the suspension for ALOT columns. 

ALOT Columns with Graphitized Carbon Black... 

Van Deemter plots for ALOT columns with Cartmpack B + SP-1000... 

Many investigators, and especially Italian scientists, have studied ALOT columns with internal walls modified by a thin layer of graphitized carbon black and stationary liquid phase (see, for example, [24, 28, 29, 37-43]). As a rule these researchers studied mainly columns of 200-500 pm i.d., with the exception of some promising work [39] perfomed on columns of less than 200 pm i.d. 

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