High-throughput reactor for simulating the flame photometric detector.

Quenching of luminescing species by co-eluting hydrocarbons has been widely reported in the flame photometric detector (FPD). This paper describes a novel method of investigating the chemical behavior of both analyte and quencher molecules in the FPD. The method is designed to reproduce the FPD's behaviour on a large scale by using a custom-built reactor. The high-throughput reactor's multi-capillary burner, situated inside a glass housing, is well suited to approximate the low-temperature, fuel-rich conditions of the conventional FPD, and also allows the study of various other flame phenomena. Wide regions of gas composition can be accessed by both diffusion- and premixed-type flames, and products can be easily sampled. Effluent collection demonstrates that 2 to 82% of various organic compounds may survive passage through the diffusion flame and be recovered intact. The recovery of several (unchanged) model hydrocarbons was found to decrease with increasing carbon number. Hetero-atoms such as sulfur, nitrogen, or oxygen greatly decrease the recovery of molecules relative to their pure hydrocarbon analogues. Compared to a diffusion flame, the recoveries of n-alkanes from a premixed flame are much lower and largely independent of carbon number or volatility.

Gas chromatographic determination of primary alcohols as their formylbenzoic esters by gas-phase luminescence detection.

A new and convenient method is described for the derivatization of primary alcohols with p-formylbenzoyl chloride, and the sensitive photometric detection of the resulting formylbenzoic ester derivatives based on their gas-phase luminescence in excited nitrogen. The coupling reaction proceeds rapidly and quantitatively, and the formylbenzoic esters show good GC properties. The minimum detectable amounts of the derivatized alcohols, at a signal three-times the peak-to-peak noise, lie between 10 and 100 pg per injection, and their linear ranges cover approximately three-orders of magnitude.

Analysis of organotin compounds by gas chromatography-reactive-flow detection.

The gas chromatographic (GC) reactive-flow detector (RFD) responds strongly to organotin compounds. The system yields over four orders of linearity with a minimum detectable amount of 8 x 10(-16) g Sn/s (at S/N = 2). The RFD's selectivity towards tin over carbon is approximately 2.5 x 10(5) g C/g Sn. The spectral emission includes a surface luminescence centered at 390 nm and a gas-phase luminescence centered at 470 nm. These findings suggest that the GC-RFD could serve as a sensitive and selective tool for the analysis of organotin compounds.

Triplet-state energies and substituent effects of excited aroyl compounds in the gas phase.

Triplet-state energy values obtained from the gas phase are still scarce. In this study, the triplet-state energies of 58 aroyl compounds, introduced as gas chromatographic peaks at atmospheric pressure and typically 473 K, have been determined from the 0-0 bands of their n --> pi* type phosphorescence spectra in excited nitrogen. Correlations of those gas-phase triplet-state energies with Hammett constants could be observed for substituted acetophenones, benzaldehydes and benzophenones.

Choice of detectors and columns for the analysis of pesticides by GLC.

After introductory remarks about the importance of accuracy in current gas chromatographic methods, this manuscript offers general comments on the choice and proper use of columns and detectors. These are interspersed with illustrative examples provided by the author's own research group.

Quenching and enhancement of aroyl luminescence in excited nitrogen.

This study investigates both decreases and increases of aromatic carbonyl phosphorescence in excited nitrogen, i.e., in a gas-chromatographic device called the aroyl luminescence detector (ALD). The ALD responds, with nigh specificity, to subpicogram amounts of strongly phosphorescing aroyls. Aroyl response may, however, be quenched by coeluting peaks or gaseous impurities. This deleterious effect has been investigated with O2, H2, CH4, and C3H8 as model quenchers. Aroyl phosphorescence is more severely quenched than the nitrogen background, i.e., the so-called second-positive system, N2 (C 3 pi u)-->N2 (B 3 pi g). Oxygen, while being the strongest among the tested quenchers of aroyl phosphorescence, is the weakest quencher of nitrogen emission. The efficiency of various quenchers is similar for aroyl compounds of similar structure. It differs, however--though not by more than a factor of 2--among aroyls of different chemical types. In contrast to these intensity-reducing effects, aroyl phosphorescence is significantly enhanced by the addition of argon to (the carrier and excitation gas) nitrogen. It is proposed that the reaction sequence Ar*(3P0,2) + N2-->N2(C)*-->N2(B)* + hv-->N2(A)* + hv results in an increased yield of the metastable N2(A 3 sigma u+) state (this state being considered responsible for the n-->pi* excitation of aroyl compounds via an efficient triplet-triplet energy-transfer process).

Acoustic flame detector for gas chromatography.

A novel gas chromatography detector is described that uses acoustic signals from a partly premixed hydrogen-air flame burning on top of a capillary. The device, referred to as the acoustic flame detector (AFD), is based on the measurement of the frequency of acoustic transients generated at the burner under a range of operating conditions. The presence of trace amounts of analyte in the flame was found to increase the frequency of these sonic bursts from the baseline level of ∼100 Hz. The response of the AFD for n-dodecane, measured as the shift in frequency, was determined to be linear over ∼3 orders of magnitude, with a minimum detectable level of about 1-5 ng C/s using the current system. The sensitivity correlates roughly with carbon content, except for certain organometallics (Sn, Mn), which gave substantially enhanced signals. Some tailing was observed but became serious only for particular types of organometallics. The noise of the system was predominantly of the 1/f type. The effects of flow conditions, burner geometry, and flame gas constituents were investigated. The oscillations could be followed by acoustic, visual, electrical, and optical means. The AFD mechanism is shown to involve oscillatory chemical kinetics, in which the flame front (the inner cone) temporarily enters a few millimeters into the capillary during each cycle, thereby creating the acoustic signal.