Flame-based detector

The flame ionization detector Is the most popular of the flame-based detectors. Apart from a reduction in sensitivity compared to expectations based on gas chromatographic response factors [138] and incompatibility with the high flow rates of conventional bore columns (4-5 mm I. 0.), the flame ionization detector is every bit as easy to use in SFC as it is in gas chromatography [148,149]. It shows virtually no response to carbon dioxide, nitrous oxide and sulfur hexafluoride mobile phases but is generally incompatible with other mobile phases and mixed mobile phases containing organic modifiers except for water and formic acid, other gas chromatographic detectors that have been used in SFC include the thermionic ionization detector (148,150], ... 

A nonselective detector more sensitive than the RID and easier to use with a small contribution to band broadening is thus desirable in HPLC. The mass spectrometer would be a good solution if it were not so complex [10] and expensive. The electron-capture detector (BCD) [11] and flame-based detectors have been suggested [12]. Both are very sensitive and could be made with very small volumes. Unfortunately, the... 

BCD can be used only with volatile analytes and it is very selective. Both BCD and flame-based detectors are very sensitive to the solvent flow rate, and noisy signals are often produced. The adaptability of these detectors to packed columns is thus difficult. This probably explains why the BCD has been all but abandoned. 

Detectors such as laser fluorometry, FT-IR, mass spectrometer and flame-based detectors can be used to obtain desired selectivity and resolution. A phosphorus-selective detector for HPLC can provide ultrahlgh resolution. In the phosphorus-selective chromatogram, the analyte peak is well resolved from neighboring peaks and the slgnal-to-nolse ratio Is also much higher than for the RI detector (13). 

The driving forces for the rapid development and growth In mlcrobore column HPLC are (1) savings In solvent consumption a total saving of up to 99.9% can be achieved when narrow-bore microparticle packed columns or open—tubular micro-capillary columns are used (2) the high separation power using long column and small particles (e.g., 3 nm) (3) the compatibility of the column eluent flow rates with a mass spectrometer and flame based detectors and (4) opportunities In new detector development,... 

Direct interfacing of mlcrocaplllary packed column LC to a GC flame-based detector (flame photometric detector and ionic detector) was demonstrated by McGuffln and Novotny ... 

The flame-based detector was reported to accept in excess of 20 ui/mln of 10-25Z aqueous methanol without extinction of the flame Optimum response was obtained at flow rates below 5 iii/min. Compatible solvent systems were aqueous methanol (up to 50%), acetone and ethanol (up to 40%) The minimum detectable quantity (at 5 times noise) measured for the FPD was 2 pg P. The dual-flame TSD can also be directly Interfaced with mlcrocaplllary packed columns The TSD was reported to be compatible with 75 to 100% aqueous methanol The utilization of microbore column LC-TSD for the analyls of nitrogen, phosphorous, and halogen containing compounds is particularly Important in studies of biomolecules, and drugs and their metabolites in physiological fluids ... 

The type and purity of the mobile phase used for SFC depends largely on the application and the detection system in use [7]. Flame-based detectors can be used only with fluids such as SFg, NH3, CO2 or N2O which have a low background signal. Consequently, the purity of these fluids must be carefully controlled to ensure that they are not contaminated. In addition, a high-pressure 2-/im inlet filter is usually placed in-line before the pump inlet to prevent particulate matter entering the pump. 

Open-cell, flame-based detectors typically have response times of a few milliseconds or less if the capillary separation column is passed through the burner tip and positioned just below the base of the flame. Thus, At is small, and from the detector usually is negligible relative to other extracolumn sources of band broadening. While many HSGC studies have used the FID, few data are... 

---