Sampling artifacts

Does not separate sizes sampling artifacts for nitrate, sulfate not automated... 

Sampling artifacts. The use of in situ pumps to collect water samples for " Th analysis permits simultaneous collection (and separation) of different particle fractions as well as dissolved Th. As pumping systems have been modified to permit determination of POC on the pump filters, it became possible to compare POC determined from the pump samples with conventional POC determinations made on small volume samples (0.5 - 2 L) taken from hydrocasts. The JGOFS data from multiple studies show large discrepancies between these two sample collection methods, with pump POC values 3 to 100 times lower than bottle POC values. Possible artifacts with each approach have been identified. For example Moran et al. (1999) have suggested that DOC is adsorbed onto... 

While many sets of data appear to follow Eq. (VV) relatively well, with slopes of mr 1 as predicted, deviations in the values of mT and br are often observed. There are a number of reasons for such deviations (e.g., see Pankow and Bidleman, 1992). For example, changes in temperature, concentrations of SOC, and relative humidity during sampling, nonattainment of equilibrium, and sampling artifacts can all lead to deviations from the predicted, equilibrium relationship. In addition, if (A7/d AHvap) in Eq. (UU) is not constant along the series, relationship (VV) will not hold because the value of ft. is changing. 

Turpin, B. J., J. J. Huntzicker, and S. V. Hering, Investigation of Organic Aerosol Sampling Artifacts in the Los Angeles Basin, Atmos. Environ., 28, 3061-3071 (1994). 

Fibrous mat type filters include the frequently used paper (cellulose) fiber filter, for example, the Whatman paper filter, and glass fiber filters. A common fibrous mat filter used for sample collection and air cleaning is known as the HEPA filter (/zigh efficiency particulate air filter) and is made of a combination of cellulose and mineral fibers. A widely used type of fibrous mat filter is the high-volume filter, commonly referred to as Hi-Vol, shown in Fig. 11.56. A modification of the Hi-Vol filter to increase the total air flow allows the collection of sufficient particulate matter in relatively short time periods (e.g., 2 h) to cany out chemical analysis this is important for studies of the diurnal variation of various chemical components of the aerosol as well as for minimizing sampling artifacts (Fitz el ai, 1983). 

Eatough, D. J., L. J. Kewis, M. Eatough, and E. A. Lewis, Sampling Artifacts in the Determination of Particulate Sulfate and S02(g) in the Desert Southwest Using Filter Pack Samplers, Environ. Sci. Technol., 29, 787-791 (1995). 

The apparent particle-phase and vapor-phase PAH concentrations and the sampling artifacts were determined from the system of simultaneous equations ... 

Al fundamental question about the interpretation of acidic aerosol data is whether researchers can characterize past and current atmospheric concentrations and distributions (spatial and temporal) with sufficient accuracy for studies of their effects on ecosystems and human health. Part of the answer to this question can be provided by a review of the methods that have been used to measure the strong acid content of aerosol particles collected from the atmosphere. This chapter serves as such a review, and, in evaluating analytical procedures, it specifically assesses the ability of each procedure to overcome sampling artifacts, to distinguish between strong and weak acids, to properly partition strong acidity between gas-phase and aero-sol-phase species, and to quantitate strong acidity at the levels at which it is found in the ambient atmosphere. 

With these nonspectroscopic approaches there is no guarantee of specificity, and even for the spectroscopic techniques, problems may exist. An essential component of technique development is the evaluation of potential sampling artifacts and interferences. This evaluation well may require more time and effort than the instrument development itself. 

Wet deposition may be an important source of PCBs to the Great Lakes. Unfortunately, like dry particle deposition, it is difficult to measure directly because of the low PCB concentrations, the problem of sampling artifacts, and the distribution of rain and PCB concentrations over space and time. Some trends are evident, however [ 189]. Snow has been shown to be much more effective than rain in scavenging PCBs from both vapor and particulate phases at a site in Minnesota [190,191]. This leads to a seasonal effect, in that precipitation concentrations of PCBs are highest in the winter in Chicago (Hites, personal communication), as with the concentrations of many other persistent organic pollutants [192], Possible reasons include sorption to an aqueous or... 

Schauer, C., Niessner, R. and Poshl, U. (2003) Polycyclic aromatic hydrocarbons in urban air particulate matter decadal and seasonal trends, chemical degradation, and sampling artifacts. Environmental Science and Technology, 37, 2861-8. 

Slopes (mr) of these plots derived from ambient air sampling data are often different from the expected value of -1 (Equation 8) possibly because of kinetic limitations and/or sampling artifacts or thermodynamic factors (Pankow and Bidleman, 1992). Goss and Schwartzenbach (1998) and Simcik et al. (1998) argued that slopes differing from -1 do not necessarily mean that the aerosols are out of equilibrium with the gas phase. In these situations, the intercept (br) partly depends on the slope and cannot be used to estimate 0 (Pankow and Bidleman, 1992). Table 10.2 lists reported values of these parameters. 

McDow, S.R. 1999. Sampling artifact errors in gas/particle partitioning measurements. In Lane, D.A., Ed., Gas and Particle Measurements of Atmospheric Organic Compounds. Gordon and Breach Science Publishers, Amsterdam, pp. 105-126. 

Puls, R. W., Clark, D. A., and Bledsoe, B. (1992). Metals in ground water Sampling artifacts and reproducibility. Hazard. Waste Hazard. Mater. 9(2), 149—162. 

When applying acid hydrolysis, one must be aware of the possible isomerization and destmction of some of the less stable sterol species caused by the treatment with acid. The acid treatment is known to cause, for example, the isomerization of A -avenasterol to stigmastadienol (Kamal-Eldin et al., 1998), which will alter the sterol composition of the sample (artifacts). Furthermore, when acid hydrolysis is performed on an extract of sterols (not direct hydrolysis, where solid material is also present), the treatment must be sensitive enough not to destroy the labile sterols (weaker acid concentration, less heating, shorter reaction time). 

Si(OH)4 Must be sampled Artifacts, except in 2-60 cm Artifacts, except Fanning and Pilson (1971),... 

Immunohistochemically, the fusiform and pleomorphic cells of STCs express vimentin. Labeling for keratin and EMA is also seen, but it may be quite focal (Fig. 11.34). This finding opens the door to the possibility that a small biopsy specimen could fail to demonstrate any epithelial markers because of sampling artifact. 

Kavouras, I. G., Lawrence, J., KoutraMs, P., Stephanou, E. G., and Oyola, P., Measurement of particulate ahphatic and polynuclear aromatic hydrocarhons in Santiago do Chile source reconcihation and evaluation of sampling artifacts, Atmos. Environ., 33, 4977-4986, 1999. 

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