Carrier linear flow rate

Mathematical methods for determining the gas holdup tine are based on the linearity of the plot of adjusted retention time against carbon number for a homologous series of compounds. Large errors in this case can arise from the anomalous behavior of early members of the homologous series (deviation from linearity in the above relationship). The accuracy with which the gas holdup time is determined by using only well retained members of a homologous series can be compromised by instability in the column temperature and carrier gas flow rate [353,357]. The most accurate estimates... 

The plate height, and thus the total number of theoretical or effective plates, depends on the average linear carrier gas velocity (van Deemter relationship) and, for a particular carrier gas, the efficiency will maximize at a particular flow rate. Only at the optimum carrier gas flow rate are n, N, and HETP Independent of the column length. The efficiency will also depend on the column diameter (see section 1.7.1) where typical values for n, N, and HETP for different column types can also be found. Values for n, N, and HETP are reasonably independent of temperature but may vary with the substance used for their determination, particularly if the test substance and statioKary phase are not compatible. 

Principles and Characteristics As mentioned already (Section 3.5.2) solid-phase microextraction involves the use of a micro-fibre which is exposed to the analyte(s) for a prespecified time. GC-MS is an ideal detector after SPME extraction/injection for both qualitative and quantitative analysis. For SPME-GC analysis, the fibre is forced into the chromatography capillary injector, where the entire extraction is desorbed. A high linear flow-rate of the carrier gas along the fibre is essential to ensure complete desorption of the analytes. Because no solvent is injected, and the analytes are rapidly desorbed on to the column, minimum detection limits are improved and resolution is maintained. Online coupling of conventional fibre-based SPME coupled with GC is now becoming routine. Automated SPME takes the sample directly from bottle to gas chromatograph. Split/splitless, on-column and PTV injection are compatible with SPME. SPME can also be used very effectively for sample introduction to fast GC systems, provided that a dedicated injector is used for this purpose [69,70],... 

Petty et al. [293] used flow injection sample processing with fluorescence detection for the determination of total primary amines in sea water. The effects of carrier stream flow rate and dispersion tube length on sensitivity and sampling rates were studied. Relative selective responses of several amino acids and other primary amines were determined using two dispersion tube lengths. Linear calibration curves were obtained over the ranges 0-10 6 M and... 

Temperature programmed desorption (TPD) of NH3 was performed in a quartz micro-reactor. 0.10 g of sample was firstly heated in helium at 600°C for 2 h. NH3 was introduced to the sample after it was cooled down to room temperature. To remove the weakly adsorbed NH3, the sample was swept using helium at 100°C for 1 h. The TPD experiments were then carried out with a carrier-gas flow rate of 40 ml/min helium from 100 to 600°C using a linear heating rate of 10°C/min. The desorption of NH3 was detected by Shimadzu GC-8A equipped with a TCD detector. 

The external factors influencing nimodipine concentrations during intravenous administration were studied using GC-electron-capture detection [18]. Nimodipine was extracted from plasma and analyzed using a column (1.8 m x 2 mm) packed with 3% of OV-17 on gas-Chrom Q (50-100 mesh). The column was operated at 255°C with nitrogen as the carrier gas (flow rate of 25 mL/min), and 63 Ni ECD. The calibration graph was linear for upto 1000 ng/mL, and the limit of detection was 0.5 ng/mL. 

Figure 9. Total ion chromatogram for Boscan crude oil obtained by computer summation of ions in the mass range 550—850. Analyses were performed on a 25 m x 0.3 mm i.d. OV-I coated (0.17//m) flexible silica capillary (Hewlett-Packard) using helium carrier gas at a linear flow rate of 50 cm/s. Following on-column injection of ca. 2.5 fig of porpyrins as their (TBDMSO)2Si(IV) derivatives (e.g. see inset, desoxophylloerythroacetioporphyrin derivative, major component of starred peak), the GC oven temperature was programmed ballistically from ambient to 150 °C, then from 150-290 °C at 3°C/min. The retention time scale has been converted to Kovats retention indices by computer interpolation from co-chromatographed n-alkanes..

Separation of fatty add methyl esters was achieved on an Agilent J W DB-23 fused silica capillary column (60 mxO.251 mm i.d., 0.25 pm Agilent, Santa Clara California, USA). The oven temperature program was initially 120 °C for 5 min, raised to 180 °C at 10 °C min-i, then to 220 °C at 20 °C min-i and finally isothermal at 220 C for 30 min. The injector and detector temperatures were maintained at 220 and 225 °C, respectively. The carrier was high purity helium with a linear flow rate of 1 ml min i and spht ratio 1 50. Fatty add methyl esters were identified using fatty add methyl esters standards (Sigma, St Louis, Mont, USA) by comparison of the retention times of the relative peaks (Nasopwulou et aL, 2011). 

Figure 22-4 Resolution of 22 18-carbon fatty acid methyl esters with 1, 2, or 3 double bonds. Fatty acids shown in Figure 5-3 are labeled (peaks 3, 7, and 14). A Supelco ILIOO ionic liquid wall-coated open tubular gas chromatography column (100 m X 0.25 mm inner diameter with 0.20 xrr film thickness) was operated at 150°C with H2 carrier gas at a linear flow rate of 25 cm/s and flame ionization detection. [From C. Ragonese, P. Q. Tranchida, P. Dugo,...

The peak shape and retention volumes in the non-equilibrium region depend strongly on carrier gas flow rate [161, 220]. The dependence of retention volumes on flow rate at the given temperatures for n-hexa-decane on polystyrene is shown in Figure 5.26 [161]. The linear dependence of retention volume on flow rate extrapolated to zero flow rate yields... 

Combining Eqs. (2-6), including the linear temperature dependency of the carrier gas flow rate, and integrating over the column length the following relation for the retention time in isothermal gas chromatography is obtained [10] ... 

Carrier gas flow rate Each gas type has an optimum linear flow range within which speed can be adjusted. Higher than optimum flow rates are acceptable for productivity increase if critical separations remain compliant. 

An important parameter when considering GC resolution of the sample components is the carrier gas linear velocity (flow rate, F), which can be determined by injecting 5-50 /A of argon or butane and measuring the time from injection to detection by the mass spectrometer. An optimum linear velocity using helium as a carrier gas is approximately 30 cm/sec and... 

Garcia et al. [45] determined penicillamine in pharmaceutical preparations by FIA. Powdered tablets were dissolved in water, and the solution was filtered. Portions (70 pL) of the filtrate were injected into a carrier stream of water that merged with a stream of 1 mM PdCl2 in 1 M HC1 for determination of penicillamine. The mixture was passed though a reaction coil (180 cm long) and the absorbance was measured at 400 nm. Flow rates were 1.2 and 2.2 mL/min for the determination of penicillamine, the calibration graphs were linear for 0.01-0.7 mM, and the relative standard deviation (n = 10) for 0.17 mM analyte was 0.8%. The method was sufficiently selective, and there were no significant differences between the labeled contents and the obtained results. 

The smaller the particle size, the faster the rate of generating theoretical plate (HETP) per unit of time. Figure 14.8 shows a plot of HETP versus linear carrier velocity u for small particles. It indicates that the smaller the particle size, the lower the HETP. It is also important to note that small particles provide nearly the same HETP over a wider range of flow rate.14... 

The carrier gas viscosity is given as r, L the column length, pQ the outlet pressure, P the ratio of inlet pressure to outlet pressure and dc the column diameter. Analysts should take care to be sure that the methods used for determining the flow rate are consistent from in-strument-to-instrument and from method-to-method. Otherwise it will be difficult to compare any data that have the flow rate, gas hold-up time or linear carrier gas velocity as a component. 

However, a direct interface subjects the exit of the column to vacuum conditions. Tire vacuum may lower the inlet pressure required to obtain the desired mass-flow rate of the carrier gas and also changes its linear-velocity profile across the column. These conditions can cause poor retention-time and peak-area precision and can even make the inlet system stop delivering carrier gas to the column. Thus, analysts should use direct interfaces only with long, narrow-bore columns... 

Figure 2.2—Optimum linear velocity and viscosity of carrier gas. The optimal mean linear velocities of the various carrier gases are dependent on the diameter of the column. The use of hydrogen as a carrier gas allows a faster separation than the use of helium while giving some flexibility in terms of the flow rate (which can be calculated or measured). This is why the temperature program mode is used. The significant increase in viscosity with temperature can be seen for gases. In addition, the sensitivity of detection depends on the type of carrier gas used.

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