Communication detection limits

Groundwater has also been surveyed for methyl parathion. In a study of well water in selected California communities, methyl parathion was not detected (detection limit of 5 ppb) in the 54 wells sampled (Maddy et al. 1982), even though the insecticide had been used in the areas studied for over 15 years. An analysis of 358 wells in Wisconsin produced the same negative results (Krill and Sonzogni 1986). In a sampling of California well water for pesticide residues, no methyl parathion was detected in any of the well water samples (California EPA 1995). In a study to determine the residue levels of pesticides in shallow groundwater of the United States, water samples from 1,012 wells and 22 springs were analyzed. Methyl parathion was not detected in any of the water samples (Kolpin et al. 1998). In a study of water from near-surface aquifers in the Midwest, methyl parathion was not detected in any of the water samples from 94 wells that were analyzed for pesticide levels (Kolpin et al. 1995). 

In 1966 and 1967, when the use of endrin was not restricted, endrin was detected in 5 of 67 raw water samples from the Mississippi and Missouri Rivers (Schafer et al. 1969). At a later time when endrin use was substantially restricted, an Iowa study of 33 community water supplies using surface water found no detectable concentrations of endrin in the distribution systems (Wnuk et al. 1987). In an extensive water quality monitoring program conducted by the California Department of Health Services, endrin was detected (detection limit not specified) in only 2 of 5,109 public drinking water sources sampled from 1984 to 1992, at mean and maximum concentrations of 0.06 and 0.10 ppb, respectively (Storm 1994). Concentrations did not exceed the Maximum Concentration Level (MCL) of 0.2 ppb. In another recent study, endrin was not detected (detection limit not specified) in 32 samples each of raw water and highly treated reclaimed waste water undergoing evaluation as a possible supplement to raw water sources in San Diego, California (De Peyster et al. 1993). 

The bias observed between experimental measurements and Kieffer s model predictions is due to the relative paucity of experimental data concerning cutoff frequencies of acoustic branches, and also to the assumption that the frequencies of the lower optical branches are constant with K and equivalent to those detected by Raman and IR spectra (corresponding only to vibrational modes at K = 0). Indeed, several of these vibrational modes, and often the most important ones, are inactive under Raman and IR radiation (Gramaccioli, personal communication). The limits of the Kieffer model and other hybrid models with respect to nonempirical computational procedures based on the equation of motion of the Born-Von Karman approach have been discussed by Ghose et al. (1992). 

Table 11.2 gives reported detection limits for some gases that have also been measured in the atmosphere by FTIR. As expected, the sensitivity of TDLS is significantly better than that of FTIR. For most species of atmospheric interest, detection limits are 0.1 ppb for measurement times of 1 min in a 200-m White cell (G. Mackay, personal communication, 1998). 

Hansel, A., Jordan, A., Warneke, C. et al. (1998) Improved detection limit of the proton transfer reaction mass spectrometer on-line monitoring of volatile organic compounds at mixing ratios of a few PPTV. Rapid Communications in Mass Spectrometry, 12 (13), 871-5. 

However, the communication challenge of results below the limit of detection is not quite so easily resolved. Each environmental-monitoring technique, including those of biomonitoring, has a limit in the amount of a chemical that it can reliably and validly measure in a given matrix. Below that limit, it is impossible to tell how much of the substance, if any, is in the sample. Experience with or modification of the technique or invention of a new one can lower the detection limit eventually, but in the short run it is fixed. That is one reason, when multiple biomonitoring methods are available, that the method chosen can have an appreciable effect on the results and their interpretation (Helsel 1990, cited by Bates et al. 2005). 

High Pressure Liquid Chromatography. In serum canrenone, sensitivity 5 ng/ml, UV detection—F. Besenfelder and R. Endele, J. High Resolut. Chromat., Chromat. Commun., 1981, 4, 419-421. In serum or urine canrenone, detection limit 5 ng/ml in serum, UV detection—G. B. Neurath and D. Ambrosius, J. Chromat., 1979,163, Biomed. Appl., 5, 230-235. 

Thin-layer Chromatography. In serum detection limit 20 pg—G. Andermann and C. Andermann, J. High Resolut. Chromat. Chromat. Commun., 1980, 3, 36-37. 

California Dept, of Food and Agriculture s HPLC detection limit for abamectin residues is 1 ppb, and contaminated strawberries are likely to have on the order of 2 to 5 ppb of residue. (Dr. Mark Lee, Calif. Dept, of Food Agriculture, personal communication to Dr. Karu). The first two spikes in Table III are thus comparable to residues that could be left on field samples. Given the efficiency of recovery of the spikes and the errors, it is reasonable to expect that the E1A method could detect 2 to 5 ppb above the column blank. ... 

Wei, H. Nolkrantz, K. Powell, D.H. Woods, J.H. Ko, M.-C. Kennedy, R.T. Electrospray Sample Deposition for Matrix-Assisted Laser Desorption/lonization (MALDI) and Atmospheric Pressure MALDI Mass Spectrometry With Attomole Detection Limits, Rapid Commun. Mass Spectrom. 18, 1193-1200 (2004). 

In the medical community it is well known that humans exhale volatile metabolites which potentially carry important information about their health status. Thus, successful and fast detection of potential products of different metabohc processes becomes attractive, especially if the detection limits of the spectrometric methods used are low enough and the instruments become available at moderate price levels to be used as standard methods in hospitals or point-ofcare centers. The vision of the authors is to contribute to the use of human breath as a carrier of information of the health status of the body in addition to human blood and urine. 

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