Artifacts formation

The concentrations of nitrosamines were reduced to undetectable levels by ultraviolet treatment of the amine solutions and were not increased by addition of 2 ppm NaN02> indicating that the nitrosamines were present originally in the amines and were not formed in the GC injection port. Similar concentrations were found when the amine samples were analyzed using the column extraction method. Direct injection is appropriate for analysis of relatively simple mixtures, if adequate precautions are taken ( ), but can result in significant artifact formation in more complex systems (42). 

Bioom ns, Colman JA, and Barber L 1997) Artifact formation of methyl mercury during aqueous distillation and alternative techniques for the extraction of methylmercury from environmental samples. Fresenius J Anal Chem 358 371-377. 

Quevauviller Ph (1998) Requirements for production and use of certified reference materials for speciation analysis a European Commission perspective. Spectrodiim Acta 536 1261-1279. Quevauviller Ph, and Horvat M (1999) Artifact formation of methylmercury in sediments. Anal Chem, Letter to the Editor 7i i55A-i56A. 

In certain areas, particularly the rapidly developing area of organo-metalhc spedation, concern has been expressed that artifacts may lead to false results. One example are the doubts about the accuracy and suspicion of possible artifact formation of methyhner-cury (MeHg) duriri analytical procedures, mainly distillation and alkaline dissolution, which were expressed for the first time at the Conference Mercury as a Global Pollu-tanf in 1996 (Hintelmann and Evans 1997 Hintelmann et al.1997). 

Quevauviiler Ph and Horvat M (1999) Artifact formation of methylmercury in sediments. Letter to the Editor. Anal Chem 7i i55A-i56A. 

The relative instability of bromocriptine makes it very difficult to avoid artifact formation in test solutions or during spotting on the plate. Therefore, bromocriptine mesi-late, usually dissolved in chloroform/methanol 1 1, has to be spotted on the plate very rapidly and with the exclusion of light. The separation being terminated, the mobile phase is removed by means of high vacuum for 30 minutes. 

Modification of the conditions used for thermal desorption, including a change of adsorbent, were unable to fully resolve the problems of artifact formation and either adsorptive or catalytic loss of thermo-labile species at trace levels. 

The compatibility of the chromatographic system with aqueous biological fluids (urine, serum), and the direct analysis of highly polar compounds with no need for hydrolysis and derivatization allow to reduce sample manipulation and the probability of artifact formation/analyte degrada-tion/contamination. In addition, the possibility of carrying out separate LC and MS experiments accounts for rapid and cost-effective method development. These features are highly considered in the forensic field where often the analyst is requested to deal with the setup of a method for an unusual analyte or substrate. 

The filter material of choice is a thin teflon membrane since it minimizes artifact formation and maximizes analytical sensitivity by X-ray fluorescence analysis. Although X-ray fluorescence (XRF) may not be the only analytical technique used, it is generally accepted as being the most cost effective analysis for source apportionment. ( 2) Its background and therefore, analytical sensitivity, is dependent on the filters surface density. The analytical sensitivity of XRF for aerosols deposited on a stretched teflon membrane with a density of about 0.3 to 0.4 mg/cm, for example, is about three times greater than an aerosol deposited on a cellulose based filter with a surface density of about 4 mg/cm. This difference can be translated into either more information for the same analytical costs or the same information for a lower analysis cost. 

Angeles, R. M. Keefer, L. K. Roller, P. P. Uhm, S. J. Chemical models for possible nitrosamine artifact formation in environmental analysis. In Walker, E. A. Castegnaro, M. Griciute, L. Lyle, R. E., Eds. "Environmental Aspects of N-Nitroso Compounds" lARC Scientific Publication No. 

The production of NO has also been observed in this heterogeneous N02-H20 reaction (Sakamaki et al., 1983 Pitts et al., 1984a Svensson et al., 1987). In addition, recent studies show the formation of N20 at longer times, both in the absence of S02 (e.g., Wiesen et al., 1995) and in its presence (e.g., Eriksson and Johansson, 1991 Pires et al., 1996 Pires and Rossi, 1995, 1997). While the mechanism of formation of N20 is not clear, it is thought to involve secondary reactions of HONO (e.g., Kleffmann et al., 1994 see later). Indeed, this heterogeneous hydrolysis of N02 to HONO occurs in exhaust from combustion systems and is responsible for the artifact formation of N20 reported in such samples (e.g., Muzio and Kramlich, 1988 Muzio et al, 1989). 

Coutant, R. W L. Brown, J. C. Chuang, R. M. Riggin, and R. G. Lewis, Phase Distribution and Artifact Formation in Ambient Air Sampling for Polynuclear Aromatic Hydrocarbons, Atmos. Environ., 22, 403-409 (1988). 

The major problem with LIF measurements in the past has been what might be called the atmospheric uncertainty principle i.e., in the act of carrying out the measurement, the system is perturbed and artifact formation of OH can occur (e.g., see Smith and Crosley, 1990 and Hard et al., 1992b). This is primarily due to the photolysis of 03 to generate O( D), which in the presence of water vapor forms OH ... 

Rounbehler, D.P. Reisch, J.W. Coombs, J.R. and Fine, D.H., "Nitrosamine Air Sampling Sorbents Compared for Quantitative Collection and Artifact Formation" Anal. Chem. 1980, 52, 273-276. 

The use of solvent extraction also represents a potentially feasible process. Solvent extraction is an engineering unit operation that is adapted effectively to continuous processing. It has been used with success for the isolation of nonpolar compounds of bp >100 °C (58). Solvent extraction (continuous liquid-liquid extraction) may represent a useful process for routinely concentrating 50-100 L of water. The major problem with solvent extraction is the evaporation and recovery for reuse of large volumes of the organic solvent. Other problem areas that must be considered are purification of sufficient solvent and minimization of artifact formation by heat. 

Active sampling has always been preferred in traditional air pollution studies because a substance can be concentrated on a particular substrate and because continuous measurements can be taken. These samplers have been placed at fixed monitoring sites on a roof or in a trailer (4). The use of active sampling, however, has not been without problems. For instance, the use of substrates such as filters and sorbents can affect the measured concentration by artifact formation, breakthrough, and blow-off associated with individual compounds or classes (22). 

Activated charcoal High retention of nonpolar volatiles Water absorption. Artifact formation. Some difficulties with desorption Less used for aroma compounds... 

Artifact formation during the extraction is demonstrated. The effect ofNi flushing and of antioxidant addition is shown. 

As was illustrated in the first survey, all known halogenated terrestrial diterpenes are chlorohydrins (1), and that continues to be mainly the case. Obviously, one must be alert to the possibility of artifact formation from ring opening of the corresponding epoxide during isolation. Many nonhalogenated terrestrial diterpenoids also continue to be isolated (622). 

Figure 1.4 Simple selection scheme for a suitable sorbent under different conditions Boiling point range, humidity of the air sample, desorption type. Please see text for other considerations (artifact formation, surface activity).

Figure 1.6 presents an example for the formation of a reaction product on the surface of a sorbent. The result of a solvent extraction of activated charcoal with CS2 and CS2/methanol, respectively, shows quite different artifact formation after a 48-hour storage period. Four new compounds could be found in the sample containing methanol as a desorption agent. All of them could be identified as substances formed by the reaction of CS2 and methanol in the presence of activated charcoal. 

Zielinska, B., Arey, J., Ramdahl, T., Atkinson, R. and Winer, A.M. (1986) Potential for artifact formation during Tenax sampling of polycyclic aromatic hydrocarbon. Journal of Chromatography, 363, 382-6. 

Artifact Formation Caused by Reactive Cases in Indoor Air... 

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