Temperature isothermal column

Alternatively, the retention index of an analyte at an isothermal column temperature can be calculated from the following equation ... 

Isothermal operation of a chromatographic column has a number of drawbacks, as illustrated in the scenario depicted for the separation of lime oil in Figure 3.62. If the selected isothermal column temperature is too low, the early-eluting peaks will... 

A log (k) versus IIT plot very nicely demonstrates that we can predict accurate peak retention factors as a function of isothermal column temperature. However, the separation of those peaks is of more interest for optimization. We can observe from the plot that the naphthalene and dodecane peaks will merge between 100 and 110°C, but it is difficult to imagine at what temperatme or temperatures all of the peaks exhibit maximum separation. In order to better visualize these relationships, Laub and Purnell (9,10) described a window diagram plot of the peak s separation factors (a), which can be constructed from retention factor data such as presented in Figure 4.9 according to... 

FIGURE 4.8 The influence of isothermal column temperature on separation. Column temperature as shown. Sample 0.1 p.L direct injections of a 2 p.g/mL 1-propanol solution of A = n-nonane B = n-decane C = 1-octanol D = n-undecane E = 2, 6-DMP F = 2, 4-DMA G = naphthalene H = n-dodecane. Column 30-m x 0.53-mm i.d. X 3-p.m 5%-diphenyl-95%-dimethylpolysiloxane stationary phase. Helium carrier at constant 12 mL/min flow. [Reprinted from LC/GC Magazine with permission of Advanstar Publications (8).]... 

Earlier Method Isothermal Column Temperature Programmed Column... 

Programmed Temperature Injectors The programmed temperature injector is held near the boiling point of the solvent after injection of the sample, it is temperature programmed rapidly until it reaches the desired maximum temperature, which is normally higher than that of an isothermal (constant temperature) injector. As the sample components vaporize, they are transferred onto the head of the GC column. This technique is a varia-... 

Due to existence of an isothermal region, temperature of both entrance and outlet was rather lower than that of intermediate section. Where temperature was high, the reaction was sever and fast. So, at site 200-300 mm away from entrance, the temperature was highest, the scale layer was thickest and the whisker column was longest there. The reaction route in this zone could be described as phase reaction homogeneous nucleation — coagulation. When... 

We also vary the sample size (from 1 to 2 y ) between runs at a given P and T. This allows extrapolation of peak areas to zero sample size as shown in Figure 4. The flow rate within the column must be constant for an isotherm. We record the following parameters ambient pressure and temperature, inlet pressure, outlet pressure, column temperature, retention time for both air and water, water peak area, ambient flow rate, regulator pressure, sample sizes, detector current and temperature, injector temperature, and attenuation. 

Ee was determined by gas chromatography (GC) on a Supelco Beta-DEX 120 column (fused-sihca capillary column, 30 m, 0.25 mm inner diameter, 0.25 mm film thickness Supelco, Buchs, Switzerland) with spht injection (20 1) and an isothermal oven temperature profile at 90 °C for separation of styrene oxide enantiomers. 

The feed gas flow rate was monitored and controlled by mass flow controllers. Product gases were fed through heated stainless steel lines to a sample loop in an automated gas chromatograph. The GC analysis was performed using two isothermal columns (80°C) in series, a Porapak T and a Molecular Sieve 5A column. When necessary, a second GC analysis using a temperature programmed Hayesep R column was used to separate and detect small hydnx arbons (such as ethylene and ethane) and H2O. 

Figure 24-10 Comparison of (a) isothermal (constant temperature) and ( >) programmed temperature chromatography. Each sample contains linear alkanes run on a 1.6-mm-diameter x 6-m-long packed column containing 3% Apiezon L (liquid phase) on 100/120 mesh WarAport 30 solid support with He flow rate of 10 mL/min. Detector sensitivity is 16 times greater in panel a than in panel b. [From H. M McNair and E. J. Bonelli, Basic Gas Chromatography (Palo Alto. CA Varian Instrument Division. 1968).]...

The introduction of forced air circulation in an oven allowed the control up to 300 - 400°C and the air bath is the main type of column oven available today for laboratory gas chromatographs. Several types of temperature controllers are used to control the temperature of these ovens. They basically differ in terms of cost, accuracy, and flexibility. They are usually advertised as isothermal or temperature-programming controllers but all, in general, use the following basic types of control ... 

Figure 6.18. Comparison of isothermal and temperature-programmed chromatograms. Sample of Cg to C2o normal paraffins on 15 foot x 1/8 inch column packed with 10% OV-1 on Chromosorb W.

Cimbura and Kofoed (50),mentioned earlier, used GLC to separate amphetamine and methamphetamine after acetylation with acetic anhydride in methanol. Derivatives were extracted using diethyl ether and chromatographed op columns of either 3% OV-17, OV-1, or SE-30. Column temperature was 160°C. They also reported the chromatographic determination of acetylated morphine on 3% SE-30, OV-1, or OV-17 at temperatures of 220°C. Cruickshank et al.(21) separated 21 amino acids as their trifluoroacetylated methyl esters. The column was 5% neopentyl glycol succinate on Gas Chrom P. Column temperatures were both isothermal and programmed 65°C for 20 min at 1.5°C/min then 2°C/min until 42.5 min then 4°C/min until 60 min then isothermal until about 75 min (see Figure 12.2). Chang et al. (19), used BSA/pyridine to form the TMS derivatives of levodopa, methyldopa, tyrosine. 

Samples of the reaction products were withdrawn out of the reactor at regular time intervals and analysed Dy gas chromatography. The conditions for the GC measurements were as follows a packed column (4m- 1/8") with 0V 210 10 % + XE 60 5 % on Chromosorb WHP 80/100 and column temperature isothermal at 110°C - Dodecane was used as a standard. 

According to eqn.(5.4), if the result of a programmed temperature scanning experiment in GC is a bunch of peaks eluted around a column temperature of 195 °C, then a chromatogram in which all the peaks appear with roughly optimal capacity factors may be expected to result from an isothermal experiment at 150 °C. 

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