Persistent background

As well, HCH isomers, including lindane, occur infrequently in human fats. Levels of up to 2.6 mg kg-1 were reported in 1972 by Siyali (1972). More recently, Quinsey et al. (1995) detected low median levels ( 0.1mg kg-1) of HCH isomers, with a measure of 4.4mg kg-1, in human milk fats for Victorian women. The presence of HCH isomers in all of the milk fats suggests a persistent background level of contamination in body fats consistent with POPs profiles for total HCH. 

If persistent background is a problem, consider preincubating the anti-digoxy-genin antibody with embryonic acetone powder prior to use. Acetone powder is easy to make and the protocol can be found in Antibodies A Laboratory Manual (7). Additionally, background is usually reduced when BM purple AP substrate is used for the color development instead of NBT/BCIP in APB. 

Occasionally GC/O data may be misleading due to concentration effects. Odor characteristics of some flavor compounds can vary as a function of concentration. For example, skatole (3-methyl indole) has a characteristic fecal odor at high levels but becomes pleasant, sweet, and warm at very low levels. Fortunately, there are not many aroma compounds exhibiting such a large concentration-dependent odor character. Additional errors in the perceived intensity of a GC peak can be due to masking in mixtures (i.e., situations where components are not resolved on the GC column). Finally, in-line condensation of some compounds can result in persistent background odors. The GC column effluent splitter and the transfer lines to the sniffer should be well conditioned and adequately heated to render them odor free. Despite these... 

Flowever, it also necessitates a strictly constant ratio of field to frequency, over the duration of the experiment. Although the master frequency source can be held very constant by a thennostatted source, the field is always vulnerable to local movements of metal, and to any non-persistence of the magnet current. Therefore the field is locked to the frequency tlirough a feedback loop that uses continuous, background... 

Note The color of the zones persists for a long period, but changes to blue-violet [1]. Rosaniline [1, 2] can be employed instead of fuchsin. With sugar alcohols lead(IV) acetate alone yields white zones on a brown background (detection limit 1 — 2 pg per chromatogram zone) [3]. 

Detection and result The chromatogram was freed from mobile phase (heated to 110°C for 30 min) and then exposed to bromine vapor for 1 h in a chamber, after blowing off excess bromine from the layer it was immersed for 1 s in the reagent solution. On drying in air dibutyltin dilaurate hRf 25 — 30), dibutyltin dichloride (kR( 25 — 30), dioctyltin oxide (hR( 40), tributyltin oxide (hRf 80), tributyltin chloride (hRf 80) and tetrabutyltin (hRf 85-90) produced persistent blue zones on a yellow ochre background (Fig. 1). 

Monitoring of background concentrations of oxychlordane in wildlife, since this metabolite is more toxic and persistent than the parent chemical (Kawano et al. 1988)... 

Median concentrations for parameters that were significantly (p=0.95) different between the background and mineralized surface water samples are presented in Table 2 under the surface water heading. There are fewer significant differences between surface water compared to ground water parameters. Be, Co, and Pb are anomalous in ground but not in surface water. This may simply be due to dilution by runoff. Both the SQFP multielement suite associated with natural ARD and the high Mo concentrations associated with mineralization clearly persist into surface water. 

PCDD/PCDFs are today found in almost all compartments of the global ecosystem in at least trace amounts. They are ubiquitous in soil, sediments and air. Excluding occupational or accidental exposures, most human background exposure to dioxins and PCBs occurs through the diet, with food of animal origin being the major source, as they are persistent in the environment and accumulate in animal fat. 

Jaward, F.M. Meijer, S.N. Steinnes, E. Thomas, G.O. Jones, K.C. 2004, Further studies on the latitudinal and temporal trends of persistent organic pollutants in Norwegian and U.K. background... 

Late onset wheezing asthma, symptoms often persist throughout childhood and into adult life. An allergic/atopic background including eczema, upper airway inflammation in patients and/or family histories may be observed. 

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