Organic constituents, detection

Of the more-or-less pure organic constituents detectable in water as analytical methods improve, the insecticides, fungicides, and weedkillers probably have received the most attention. Although inland surface waters have been monitored for about a decade, essentially nothing is known about pesticide levels in the ocean, and existing information comes from indicator organisms. Even current quantitative data from water analyses stretch the limits of accuracy and confirmation of identity (23). 

Formic acid was identified as a constituent in a variety of composted organic wastes. Detectable concentrations were reported in 16 of 21 composts extracted with water. Concentrations ranged from 0.02 mmoFkg in a sawdust + dairy cattle manure to 30.65 mmoFkg in fresh dairy manure. The overall average concentration was 9.64 mmoEkg (Baziramakenga and Simard, 1998). 

By 1974, the need to revise the 1968 standards became apparent because of stimulus by events such as the discovery of chloroform and other THMs in chlorinated drinking water. The detection of various organic constituents at low concentrations made possible by improvements in analytical methodology provided additional impetus. 

Many of the organic constituents of FDR are explosive or explosive-related compounds and much of the work already done on the detection of explosive residues can be extended to include FDR. Explosives and their residues are usually analyzed using chromatographic techniques. Chromatography is the general name given to the methods by which two or more compounds in a mixture physically separate by distributing themselves between two phases (a) a stationary phase, which can be a solid or a liquid supported on a solid, and (b) a mobile phase, either a gas or a liquid which flows continuously around the stationary phase. The separation of individual components results primarily from differences in their affinity for the stationary phase. 

I. Jane, P. G. Brookes, J. M. F. Douse, K. A. O Callaghan, Detection of Gunshot Residue via Analysis of Their Organic Constituents, Proceedings of the International Symposium on the Analysis and Detection of Explosives, FBI Academy, Quantico (1983), 475. 

M. H. Mach, A. Pallos, and P. F. Jones, Feasibility of Gunshot Residue Detection via Its Organic Constituents. Part 1. Analysis of Smokeless Powders by Combined Gas Chromatography-Chemical Ionisation Mass Spectrometry, Journal of Forensic Sciences 23, no. 3 (1978) 433. 

The detection and identification of the organic constituents in FDR has the potential to be used either as a screening technique or, much more likely, as a complementary technique to the particle analysis method. The particle analysis method has proved very satisfactory and has been well tried and tested in casework and court. The objective is to devise an efficient system for organic firearm residue detection that is entirely compatible with the particle analysis method. As a suspect may need to be examined for both firearm and explosive residue the method must also be compatible with organic explosive residue detection techniques. 

The ability to detect organic constituents in FDR from ammunition with single-based propellant was the ultimate goal. If this proved impossible, the investigation would at least clarify the situation and improve the detection method for NG, which could serve as a useful complementary technique to SEM/EDX. If particles in the indicative category were accompanied by NG, it would substantially raise the significance level of such particles. 

Organic FDR detection is a useful additional technique, despite the fact that single-based propellant constituents cannot be reliably detected. The current system uses GC/TEA as a rapid screening technique for NG and 2,4-DNT, and only positive samples need to be subjected to the SPE cleanup/ concentration procedure. The method is flexible in that the extract can be analyzed by a range of analytical instrumentation. There does not appear to be good correlation between the detection of organic and inorganic FDR which emphasizes the need for combined instrumentation, that is, GC/TEA, GC/MS, and SEM/EDX. Details of the method devised are as follows. 

Sreenivasan, A. and Venkataraman, R. (1959) Chromatographic detection of the organic constituents of Corikapuli (Carcinia cambogia Desr.) used in pickling fish. Current Science 28, 151-152. 

Oil Shale Retort Offgases. Analysis of the retort offgas for organic constituents before the offgas burner showed mostly hydrocarbons. Saturated hydrocarbons, alkenes, alkynes, cyclic alkanes, and cychc alkenes were found. Aromatic compounds, mostly alkyl-substituted benzenes, were detected. No heterocyclics were identified in the offgas. 

It is usually more convenient to add an indicator to the solution and visually detect a color change. An indicator for an acid-base titration is a weak acid or weak base that is highly colored. The color of the ionized form is markedly different from that of the nonionized form. One form may be colorless, but the other must be colored. These substances are usually composed of highly conjugated organic constituents that give rise to the color (see Chapter 16). 

Giger, W., Reinhard, M., Schaffner, C. and Ziircher, F., 1976. Analyses of organic constituents in water by high-resolution gas chromatography in combination with specific detection and computer-assisted mass spectrometry. In L.H. Keith (Editor), Identification and Analysis of Organic Pollutants in Water. Ann Arbor Science, Ann Arbor, Mich., pp. 433—452. 

Currently NIR spectrometry is most commonly used to predict or monitor macroconstituents, i.e. >0.1-1% of the sample weight. Common constituents are carbohydrates, cellulose and hemicellulose, proteins and lipids (Osborne Feam, 1986 Davies Williams, 1996). Constituents other than those containing organic, hydrogen bonds have also been monitored by NIR, e.g. heavy metals (Malley et al., 1996). Such NIR applications are based on indirect or correlative modelling, i.e. the concentration of the constituent of interest (e.g. a heavy metal) correlates with some organic constituent occurring at levels detectable by NIR. 

To overcome the problem of false positives it is now more usual, whenever possible, to use a scanning electron microscope to detect the metals, such as barium, associated with discharging of a firearm while the organic constituents of smokeless powder are preferably analyzed as for explosive residues above, i.e., by using LC followed by MS confirmation, GC-MS, etc. 

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