Hydrocarbons trace analysis

In LIF detection systems, excitation power may be increased up to six orders of magnitude compared to CF detection. Most LC-LIF detection concerns under-ivatised polynuclear aromatic hydrocarbons (PAHs) and fluorescing dyes (e.g. polymethines). Because only a limited number of analytes possess native fluorescence, derivatisation of the analyte before detection is normally required in trace analysis of organic solutes by means of LIF detection. LIF detection in HPLC was reviewed... 

Columns lengths of 10-25 m with a 0.32-mm ID and 10-/tm film thickness are available commercially. These phases are ideal for the separation of analytes in aqueous solutions or trace analysis of residual water, because the hydrophobic nature of the polymer allows water to be eluted as a sharp peak. The upper operational temperature of 250°C makes these phases a good choice for the separation of polar light hydrocarbons and alcohols. At subambient temperatures oxygenated gases such as CO and C02 are separated without tailing. 

Strup, P. E., Wilkinson, J. E., and Jones, P. W. Trace Analysis of Polycyclic Aromatic Hydrocarbons in Aqueous Systems Using XAD-2 Resin and Capillary Column Gas Chromatography-Mass Spectrometry Analysis in Carcinogenesis. Vol. Ill, ed. by P. W. Jones and R. I. Freudenthal, Raven Press, New York 1978. 

Lysyj I, Perkins G, Farlow JS. 1980. Trace analysis for aromatic hydrocarbons in natural waters. Environ Int 4 407-416. 

Parameters such as solvent, basic medium and reaction time, affecting the derivatization of alcohols and phenols with benzoyl chloride, were investigated. End analysis was by GC with UVD . a sensitive method proposed for trace determination of phenols in water consists of preconcentration by SPE with a commercial styrene-divinylbenzene copolymer, acylation with pentafluorobenzoyl chloride in the presence of tetrabutylammonium bromide and end analysis by GC with either ECD or ITD-MS. LOD was 3 to 20 ngL for ECD and 10 to 60 ngL for ITD-MS, with 500 mL samples . Acylation with the fluorinated glutaric acid derivative 43 was proposed for determination of urinary phenols, as indicative of exposure to benzene and other aromatic hydrocarbons. End analysis by GC-MS shows strong molecular ions of the derivatives by electron ionization. The proto-nated ions are the base peaks obtained by chemical ionization. LOD was 0.5 mgL and the linearity range 0-100 mg L for phenol . 

Note that direct elution analysis of carbon dioxide even in large samples (25 ml) fails to determine trace hydrocarbons without concentration. The method may be recommended for the trace analysis of other acid gases (e.g., hydrogen sulphide, hydrocyanic acid). A chemical concentration method based on removal of unsaturated gaseous hydrocarbons (main component) for determination of trace amounts of hydrogen and carbon dioxide was developed by Alekseeva and co-workers [56, 57]. For absorption of olefins use was made of a column containing a solution of silver nitrate and mercury salts. 

Trace analysis of polycyclic aromatic hydrocarbons (PAH) in a soil revealed for the trace constituent benzo[a] pyrene the following values (in milhgrams per kilogram dry weight) ... 

Another type of extraction commonly used on liquid samples is based upon the partitioning of an analyte between the hquid in which it is dissolved and a sohd support. Such extractions are typically based upon adsorption of the solute onto the solid. An example of such an extraction is the adsorption of hydrocarbons in aqueous solution onto activated charcoal. This process has long been used in such areas as pollution control (e. g. oil spills in water), and now is beginning to be implemented more in trace analysis procedures as a technique called solid phase micro-extraction. The main disadvantage of extraction techniques is typically the time that is required to recover the majority of the solute. Because of this problem the use of extraction techniques in quantitative analyses is typically performed as a last choice. 

The main hmitation in trace analysis arises from interferences in the SIMS spectra due to detected clusters, hydrocarbons, oxides and hybrides. SIMS is an excellent and powerful analytical destructive technique, but it is based upon processes that are not yet sufficiently understood. 

A distinction is made between organic and inorganic traces. Examples of organic traces are dioxins or furans in waste gases from refuse incineration plants, fliiorochlorohydrocarbons (FCHCs) in the atmosphere, chlorinated hydrocarbons (CHCs) in water, and many others. Inorganic traces are refened to as trace elements, a concept that includes all elements (i.e., metals, semimetals, and nonmetals). Despite the different objects that must be monitored analytically, the methods and instruments in this field have so much in common that a special branch of analysis — trace analysis — has developed [1], [2]. 

Fluorometry is used to determine elements such as boron, silicon, aluminum, beryllium, and zirconium [7], [129], [130], as well as organic compounds [131] (e.g., vitamins [132]). An important application in the field of trace analysis is the determination of aromatic hydrocarbons in wastewater [133], Here, the limits of detection can be improved considerably [64] if fluorescence is excited by a laser (LIF). This is very important for the measurement of polycyclic aromatic hydrocarbons [134],... 

Septum bleed can become a serious problem during trace analysis, as the leached compounds elute in the middle of the GC run with high intensity. Persistent bleed causes low sensitivity and poor quantification. Once a septum is punctured, a small amount of silicon can be transferred into the injector with each injection. This is quickly transferred to the top of the column, and if the column is at a low temperature, focused here. Once the column is heated, the bleed components elute. The longer the column is held at a low temperature, the more intense the presence of bleed peaks in the chromatogram. The major component of septum bleed is a series of siloxanes with increasing molecular weight (see Table 3.16 and Figure 3.168). Other observed bleed components are phthalates and also hydrocarbons (Warden, 2007). 

Limitations Adjustment of the combustion gases important for reproducibility and selectivity. In sulfur mode, quenching effect is possible because of too high hydrocarbon matrix (double flame necessary). Sensitivity in sulfur mode is not always sufficient for trace analysis. 

For a possible application for trace analysis and speciation of tetraalkyllead and trialkyl-lead compounds in CH2CI2 solution, see [17]. The determination of trace amounts of Pb(C2H5)4 and Pb(CH3)4 in gasoline after appropriate separation of hydrocarbons by means of a sensing electrode of a galvanic cell is patented [6]. 

Density or specific gravity, total sulfur, aniline point, total nitrogen, viscosity, cloud point, pour point, trace metals (Fe, Ni, V), and carbon residue would normally be determined on this fraction. If the fraction is to be used as catalytic cracker feedstock, asphaltenes would also be determined by precipitation with normal-heptane (ASTM Test Method D3279, Heptane Insolubles). Wax content determination by solvent reflux [24] might be included in a lube stock evaluation. Hydrocarbon-type analysis by mass spectrometry or other means is an important part of lube stock evaluation, but this is beyond the scope of this chapter. 

Dialysis and electrodialysis are techniques which are applicable to the separation of smaller ions and molecules, including ionic surfactants, from larger species. These methods have been used to separate sodium dodecylsulfate from biochemical media (106). Such separations must normally be run at surfactant concentrations below the critical micelle concentration, since the micelles are too large to pass through the dialysis membrane. A general difficulty in application to trace analysis is the loss of surfactant due to adsorption on the surface of the apparatus. Most often, the object of the experiment is the purification of a protein solution, rather than isolation of a pure solution of the surfactant. Dialysis has been used for the removal of hydrocarbon oil solvent from lubricating oil surfactants in micellar form. In this case, n-heptane was used as solvent at reflux temperature (107). 

Because of the lack of specificity, polarographic techniques are only useful for analysis of real world samples if they are coupled with separation procedures. For example, one team has demonstrated that the BIAS procedure for trace analysis of nonionics can be improved by using an electrochemical procedure for surfactant determination after first precipitating and isolating the potassium iodobismuthate-nonionic complex from the sample (18,26). They prevent interference of hydrocarbons by washing the precipitate with isooctane (27). 

Analytical Procedures. Standard methods for analysis of food-grade adipic acid are described ia the Food Chemicals Codex (see Refs, ia Table 8). Classical methods are used for assay (titration), trace metals (As, heavy metals as Pb), and total ash. Water is determined by Kad-Fisher titration of a methanol solution of the acid. Determination of color ia methanol solution (APHA, Hazen equivalent, max. 10), as well as iron and other metals, are also described elsewhere (175). Other analyses frequendy are required for resia-grade acid. For example, hydrolyzable nitrogen (NH, amides, nitriles, etc) is determined by distillation of ammonia from an alkaline solution. Reducible nitrogen (nitrates and nitroorganics) may then be determined by adding DeVarda s alloy and continuing the distillation. Hydrocarbon oil contaminants may be determined by ir analysis of halocarbon extracts of alkaline solutions of the acid. 

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