Flame photometric detection inside of a capillary gas chromatography column

A novel micro-flame photometric detector (FPD) employing a miniature counter-current flame is described. The micro-FPD flame, encompassing a volume of about 30 nL, is operated inside the end of a capillary gas chromatography column (i.e. on-column) or inside of a quartz capillary after the column (i.e. post-column). Either air or oxygen can support a hydrogen flame in the device, although oxygen is far preferable. The detector can be operated for several hours without any observed degradation in performance or flame stability. The optimal gas flows established for the detection of sulfur and phosphorus are in the range of 4 mL min(-1) of oxygen and 9 to 13 mL min(-1) of hydrogen. The fuel-rich micro-FPD flame generates chemiluminescent blue S2* emission for sulfur and green HPO* emission for phosphorus, similar to a conventional FPD. Sulfur response in the micro-FPD is quadratic over nearly 3 orders of magnitude while that of phosphorus is linear over nearly 5 orders of magnitude. The micro-FPD detection limit for sulfur is 1 x 10(-9) g S s(-1), and that of phosphorus is 2 x 10(-10) g P s(-1). The properties established for the initial prototype of the micro-FPD make this counter-current flame method potentially suitable for integration with on-chip gas chromatography or other micro-analytical devices where flame-based detection methods are desirable.     

Novel flame photometric detector for gas chromatography based on counter-current gas flows

A novel analytical device has been developed for gas chromatography. It is based on optical emission from a counter-current (i.e. counter-flowing) air or oxygen flame, which burns in an opposing stream of hydrogen and column effluent. The flame is typically positioned "upside down" on the upper (air) jet, which faces the lower (hydrogen + effluent) jet. It can also be positioned on the lower jet, be connected to both jets, or be suspended in the gap between them. Excellent stability can be obtained in any of these modes. Overall, this new "counter-current flame photometric detector" (ccFPD) responds to analytes in the manner of a conventional flame photometric detector (FPD); however, it can be operated over a much wider range of gas flows. For instance, the same physical ccFPD burner easily supports stable flames of air flows between 5 and 200 ml/min and corresponding hydrogen flows between 5 and 10,000 ml/min. Visual observation of the counter-current flame, in the presence of sulfur and phosphorus as test analytes, reveals intense, steady luminescence under a wide variety of conditions. Additionally, and in contrast to the commercial FPD, flame conductivity signals can be obtained that are similar in quality to those produced by a conventional flame ionization detector (FID). Thus the ccFPD is a flexible, easily optimized photometric detector. The exceptional flow stability of the ccFPD was used to explore the earlier reported phenomenon of strong signal/noise (S/N) ratios, which had been obtained for hetero-elements of the iron group from a conventional FPD with a small, stoichiometric flame. Results using the ccFPD, which also exhibits this unusual response, indicate that these high S/N ratios are only partly due to the predictable decrease in flame noise with decreasing flame size. Contrary to expectations, the absolute analyte signal often increases as the flame size decreases to the point of extinction. The signal intensity and the magnitude of the observed changes depend to some degree on the flame composition (H2/O2 ratio).     

Improved micro-flame detection method for gas chromatography

A previously developed micro-counter-current flame method is modified to provide both sensitive photometric and ionization detection for gas chromatography (GC). A stainless steel capillary (0.254 mm i.d.) supplying oxygen functions as a burner, which supports a compact flame that burns in a counter-flowing excess of hydrogen. In the “micro-flame photometric detector” (μFPD) response mode, the background emission level is reduced by over an order of magnitude compared to previous experiments using a fused silica capillary burner, resulting in greatly improved detection limits. Chemiluminescent sulfur response in the μFPD is quadratic over 3.5 orders of magnitude, yielding a detection limit of 3 × 10⁻¹¹ gS/s, while that of phosphorus is linear over 5 orders of magnitude down to a minimum detectable limit of 3 × 10⁻¹² gP/s. Tin response is examined for the first time in the μFPD and yields a blue luminescence (ascribed to SnO*) on the surface of the quartz flame enclosure. Although this emission provides a sensitive detection limit near 6 × 10⁻¹⁵ gSn/s, due to the limited surface area within the detector cell it only produces a linear response range of one order of magnitude. Ionization response toward hydrocarbons is also obtained from the hydrogen-rich micro-counter-current flame. A linear response is produced over five orders of magnitude, yielding a detection limit toward carbon of 2 × 10⁻¹⁰ gC/s. Analysis of a simple gasoline sample is used to demonstrate that the device can successfully operate as both a selective and universal GC detector. Results indicate that this micro-counter-current flame method yields comparable performance to conventional flame photometric and flame ionization detectors, making it potentially useful for adaptation to micro-analytical devices and portable GC units.     

Evaluation of the performance of various universal and selective detectors for sulfur determination in natural gas

In the present contribution, the performance of a number of commercially available selective and universal detectors that can be used in the analysis of sulfur components in natural gas is evaluated in terms of sensitivity, selectivity, reproducibility, quenching effect, stability, and compound dependence of the sulfur response. Investigated detectors include the sulfur chemiluminescnce, the flame photometric, the electron capture, the mass spectrometric, the thermal conductivity, and the flame ionization detector. The sulfur chemiluminescence detector was found to have the best overall performance, e.g., low picogram amounts of sulfur can be detected accurately and the linear dynamic range is more than five orders of magnitude. After careful optimization, the sulfur response of this detector was found to be almost compound independent. All other detectors, including the flame photometric and the electron capture detector, have more or less compound dependent responses.     

Effects of hydrocarbon quenching in gas chromatography when using the flame photometric detector

Summary The long time retardation of the main hydrocarbon peak in the chimney of the flame photometric detector greatly reduces the responses of later-eluting sulfur compounds. In the absence of hydrocarbons in the flame, the slope (s) of the log I vs. log [S] plot (where I is the sulfur response and [S] is the sulfur concentration in the sample) is of the highest value and is constant for all experimental conditions tested. Flame hydrocarbons cause the s value to decrease, and this is dependent on the oxygen to hydrogen ratio in the flame (O/H) and, under certain conditions, also on the sulfur to carbon ratio (S/C) of the sample. The abnormalities observed in the determination of methyl thiol in natural gas are explained on the basis of the present study.     

Determination of total and speciated sulfur content in petrochemical samples using a pulsed flame photometric detector

The pulsed flame photometric detector (PFPD) has the advantage of being able to measure the concentration of individual sulfur compounds and total sulfur content in a petrochemical sample in a single gas chromatography run. Because it is an equimolar response detector, the PFPD's sulfur response is independent of a compound's molecular structure, and this feature allows quantitation of the total or speciated sulfur content in complex samples using a single calibrant. This paper is a survey describing a variety of applications using the PFPD for sulfur quantitation in petrochemical matrices. Several different approaches to quantitation are described, and simple techniques for circumventing the quenching of the sulfur signal by coeluting hydrocarbon peaks are discussed. Examples from a range of real-world samples are presented.     

Improvements in flame photometric detector design and operation. Determination of organophosphorus pesticide residues at low picogram levels

The molecular emission of heteroelements such as phosphorus and sulfur is the basis of the selective response of the flame photometric detector. The behavior of the FPD towards phosphorus compounds has been studied and design improvements sought with regard to burner configuration and temperature distribution. The possibility of differentiating between compounds containing phosphorus atoms and those containing both phosphorus and sulfur atoms has also been examined. Detection limits and response characteristics have been reported for organophosphorus pesticide residues in samples of natural origin     

Novel on-column and inverted operating modes of a microcounter-current flame ionization detector

Improved operating modes of a microcounter-current flame ionization detector (microFID) are demonstrated. By operating the flame inside the end of a capillary gas chromatography (GC) column, the effective cell volume enclosing the flame is considerably reduced and results in significantly lower gas flows being required to produce optimal sensitivity from the stable flame. For instance, in this mode the tiny counter-current flame is situated "upside down" inside the column on the end of a stainless steel capillary delivering 4mL/min of oxygen and is stabilized by a counter flow of only 10mL/min of hydrogen carrier gas. Under these approximately fourfold reduced gas flow conditions, the microFID carbon response is linear over almost 5 orders of magnitude and yields a detection limit of 6x10(-10)gC/s. These figures agree well with those reported for the original microFID, which also similarly operated under hydrogen-rich conditions. To better simulate the oxygen-rich environment of a conventional FID flame, a novel "inverted" counter-current flow mode was also investigated. In this post-column microFID arrangement, a very lean flame is now situated on the end of a stainless steel capillary delivering 10mL/min of hydrogen, which is opposed by a counter-current flow of only 20mL/min of oxygen. The microFID detection limit obtained in this stable, oxygen-rich counter-current flame mode is 7x10(-11)gC/s with a response that is linear over almost 6 orders of magnitude. These findings are more comparable to those of a conventional FID. Overall, the low-flow sensitive microFID operating modes presented demonstrate that this detector may be potentially useful for adaptation to portable devices and related GC applications.     

用毛细管气相色谱脉冲火焰光度检测器测定汽油中的含硫化合物

采用毛细管气相色谱／脉冲火焰光度检测器（GC／PFPD）对催化裂化汽油中大部分硫化物做了定量和定性研究。在此基础上,考察了降硫助剂与平衡剂掺混后的使用性能,并采用GC／PFPI）对产物FCC汽油中硫化合物进行了分析测定,结果表明降硫助剂的加入使FCC汽油硫含量显著下降。     

The fundamental properties of the direct injection method in the analysis of gaseous reduced sulfur by gas chromatography with a pulsed flame photometric detector

In this study, the fundamental aspects of gas chromatography with a pulsed flame photometric detector were investigated through the calibration of gaseous reduced sulfur compounds based on the direct injection method. Gaseous standards of five reduced sulfur compounds (hydrogen sulfide, methane thiol, dimethyl sulfide, carbon disulfide, and dimethyl disulfide) were calibrated as a function of injection volume and concentration level. The results were evaluated by means of two contrasting calibration approaches: fixed standard concentration method (variable volumetric injection of standard gases prepared at a given concentration) and fixed standard volume method (injection of multiple standards with varying concentrations at a given volume). The optimum detection limit values of reduced sulfur compounds, when estimated at 100 μL of injection volume, ranged from 2.37 pg (carbon disulfide) to 4.89 pg (dimethyl sulfide). Although these detection limit values improved gradually with decreasing injection volume, the minimum detectable concentration (e.g., in nmol mol⁻¹ scale) remained constant due to a balance by the sample volume reduction. The linearity property of pulsed flame photometric detector also appeared to vary dynamically with changes in its sensitivity. According to this study, the performance of pulsed flame photometric detector, when tested by direct injection method, is highly reliable to precisely describe the behavior of reduced sulfur compounds above ∼20 nmol mol⁻¹.     

煤热解过程中气态硫及气态烃逸出的同步在线分析

建立了一种简单的在线同时检测煤热解过程中气态硫及烃类选出的方法-TPD-FPD＆FID。检测装置由可实现程序升温的微型热解反应器(TPD)、在线的火焰光度检测器和火焰离子化检测器(FPD)及数据采集系统构成，数据处理方法简单。应用此方法对神木煤进行了分析，得到了其气态硫及烃类选出的动态特征。并通过对比实验验证了此方法的准确性及重复性。     

Determination of the boiling point distribution of sulfur compounds in light cycle oil using GC with a flame photometric detector and pyrolyzer

A method has been developed to determine the boiling point distribution of sulfur compounds in light cycle oils (LCO'S). The method chosen for this analysis was GC with a flame photometric detector (FPD) and pyrolyzer. Tests were carried out to evaluate the recovery efficiency, repeatability, and accuracy of the method. Repeatabilities within 2% were obtained. The recovery of benzothiophenes and dibenzothiophenes was close to 100%; this was important because these are the major sulfur components in LCO's. No hydrocarbon or solvent interferences were observed with the use of the pyrolyzer, even for a 95% solvent level. Comparison with results from other techniques showed that the method accurately determined the levels of sulfur compounds in the LCO boiling point range.     

Mesure par photometrie de flamme du soufre particulaire atmospherique

Flame photometric measurement of atmospheric particulate sulfur. Particles collected on glass fibre filters washed with nitric acid are introduced into headspace vials containing a reducing mixture of hydroiodic acid, sodium hypophosphite and acetic anhydride. The sulfur concentration in the particles is determined by measurement of generated hydrogen sulfide using a flame photometric detector.     

An improved flame photometric detector for gas chromatography

A simple modification in the flame photometric detector is reported. This modification enables liquid sample injections of up to 50 μl without solvent flame out. The signal to noise ratio is also increased, the baseline has increased stability and dynamic working range and linearity are improved. No loss in specificity is reported for either the phosphorus (526 nm) or sulfur (394 nm) modes. Detection of picogram quantities of chromium is possible using this detector and a 520 nm filter. The modification now allows automatic analysis of pesticide extracts and liquid samples without the use of flame autoignitors.     

吹扫捕集-气相色谱联用测定城市河流中的挥发性硫化物

建立了一种吹扫捕集 气相色谱联用测定城市河流中挥发性硫化物的方法。二甲基硫、甲基乙基硫、二甲基二硫最低检测质量浓度分别为80,80和100ng/L,水样加标回收率在91%～101%之间。方法操作简单,灵敏度高,成功应用于城市河流中水样中挥发性硫化物的测定。     

柱后切换及程序升温气相色谱法测定六氟化硫气体中痕量一氧十氟化二硫

本工作提供了用柱后切换和程序升温技术测定纯六氟化硫气体中痕量有毒杂质Ｓ２Ｆ１０Ｏ含量的气相色谱方法。用火焰光度检测器检测，进样量为 １ｍＬ时，Ｓ２Ｆ１０Ｏ最小检测浓度为５×１０－７（ｍｏｌ／ ｍｏｌ）。     

Evaluation and comparison of selective gas chromatographic detectors for the analysis of pesticide residues

Summary A series of studies is described on the evaluation and comparison of some selective gas chromatographic detectors used in pesticide residue analysis. A detailed study of the optimization and response characteristics of the CsBr and RbCl three-electrode alkali flame ionization detector for N and P compounds, the Coulson electrolytic conductivity detector in the nitrogen, sulphur and pyrolytic modes of operation and the sulphur phosphorus emission detector, a type of flame photometric detector, was carried out to obtain maximum sensitivity and reliability for the analysis of pesticide residues in various biological substrates. It was observed that the alkali flame and electrolytic conductivity detector responses to nitrogen compounds were of the same order, while the electrolytic conductivity detector was more sensitive than the flame photometric detector to sulphur compounds. Also, attempts were made to correlate the responses from these different detector systems using the insecticide chlorpyrifos which contains P, S, Cl and N atoms. The use of chlorpyrifos as an evaluation standard in verifying the acceptable performance of these types of detectors is recommended.Chemistry and Biology Research Institute Contribution No 901     

煤热解过程中气态硫逸出特性的在线分析

建立了一种简单的在线检测煤热解过程中气态硫选出的方法-程序升温热解-火焰光度检测法(TPD-FPD)，该方法适用于煤的连续热处理过程。检测装置由可实现程序升温的微型热解反应器(TPD)、在线的火焰光度检测器(FPD)及数据采集系统构成。应用此方法分别对神木煤、依兰煤进行了分析，得到了其气态硫选出的动态特征谱图。并通过对比实验验证了此方法的准确性及重复性。结果表明：TPD-FPD是一种研究热解过程中煤中硫向气态迁移的有效的在线分析手段。     

汽油中有机硫化物的酸富集和结构分析

石油中发现的硫化物已超过250种，其中约有1／4存在于汽油中。由于汽油中每种硫化物的含量都很低，又有十分复杂的烃组分和含氮组分的干扰，单纯使用仪器方法对汽油中的有机硫化物进行结构分析是十分困难的。通常的做法是对汽油样品进行预处理，使硫化物从混合烃体系中分离出来，再通过仪器和相应标样进行类型分析或结构鉴定。目前研究者在此方面做了很多工作，花瑞香等用29种硫化物标样，采取GC／SCD辅以选择性化学反应对汽油馏分的硫化物形态分布研究。     

Simultaneous Measurement of Hydrocarbons and Sulfur Compounds using Flame Ionization and Sulfur Chemiluminescence Detection for Sulfur Simulated Distillation

A gas chromatographic system for the simultaneous acquisition of hydrocarbon and sulfur chromatograms was developed. Detection of sulfur compounds is achieved using a sulfur chemiluminescence detector (SCD) mounted in series with a flame ionization detector (FID). A constant fraction of the effluent of the FID is transferred to the SCD by means of a fixed restrictor. Unlike previous versions of this approach, the FID is not used to generate the chemiluminescent sulfur species. Rather, the FID is operated under optimum conditions for hydrocarbon analysis and a furnace is used to generate the chemiluminescent sulfur species. The system permits dual acquisition of the hydrocarbon and sulfur signals in a single analysis with a single column, since the detectors are operated in a serial fashion. The application of sulfur simulated distillation using this approach was examined, since this requires simultaneous universal and sulfur selective detection. Precision of absolute response of both the FID and SCD was typically less than 2% RSD for a standard reference material.