Analytical detection limits

There are no measurements of the actual concentrations of diisopropyl methylphosphonate in groundwater at the RMA during the years of active production of the nerve gas Sarin (i.e., 1953-1957) (EPA 1989). The first actual measurements of the concentration of diisopropyl methylphosphonate in the groundwater on the arsenal and surrounding property to the north and west were made in 1974 (Robson 1981). The concentrations of diisopropyl methylphosphonate in the groundwater ranged from 0.5 g/L (analytical detection limit) to as much as 44,000 g/L near the abandoned waste disposal ponds. Diisopropyl methylphosphonate was discharged into a lined reservoir at the RMA in 1956 and was still present 20 years later in concentrations of about 400,000 g/L (Robson 1977). 

Cation Solid adsorbent Analytical Detection limit Reference... 

Based upon the available data, derivation of AEGL-1 values was considered inappropriate. The continuum of arsine-induced toxicity does not appear to include effects consistent with the AEGL-1 definition. The available human and animal data affirm that there is a very narrow margin between exposures that result in little or no signs or symptoms of toxicity and those that result in lethality. The mechanism of arsine toxicity (hemolysis that results in renal failure and death), and the fact that toxicity in humans and animals has been reported at concentrations at or below odor detection levels (-0.5 parts per million (ppm)) also support such a conclusion. The use of analytical detection limits (0.01 to 0.05 ppm) was considered as a basis for AEGL-1 values but was considered to be inconsistent with the AEGL-1 definition. 

No published data were available on effects and fate of famphur in aquatic ecosystems. This seems to be a high-priority research need in view of the increasing and illegal use of famphur to kill migratory waterfowl (White et al. 1989). In the absence of these data, it is recommended that concentrations of famphur and famoxon in water and in tissues of aquatic organisms not exceed current analytical detection limits of 0.005 mg/L in water or 0.01 mg/kg FW tissue. 

Toxaphene elimination rates vary between species. In rats, the half-time persistence of toxaphene (time to 50% excretion = Tb 1/2) was 1 to 3 days (USEPA 1980a). If the trend persisted, virtually all toxaphene would be eliminated in five half-lives. Elevated blood toxaphene levels in a human subject who had eaten catfish fillets containing 52 mg of toxaphene/kg dropped 67% in 11 days. By 14 days after the initial measurement, toxaphene blood levels were below analytical detection limits (USEPA 1980a). Persistence seems to be longer in some fishes. Lake trout (Salvelinus namaycush) given a single intraperitoneal injection of 7 mg toxaphene/kg BW had a Tb 1/2 of 322 days for white suckers (Catostomus commersoni), this value was 524 days (Delorme et al. 1993). 

Most elements of interest in the Talbot 250 pm and <2pm separates are well above analytical detection limits, except PGEs. Clay separates have, on average, 50% higher concentrations of most elements than silt + clay fraction of the soils. 

A note concerning terminology Lp (Ref. 2) and Sp have been used interchangeably to denote the detection limit for the net signal (y-B) xp is used here to denote the analyte detection limit (concentration or amount). Lq (or Sc or xq) denotes the decision level it is also called the critical point or level, test level, or threshold by various authors. The directly observed gross signal (y) is here referred to as the response.]... 

Case II - Analyte Detection (A - assumed). Here, the analyte- rather than signal-detection limit is calculated, but the systematic error in A, applied in the estimation of x from Equation 2c imposes systematic error bounds which must be applied to the analyte detection limit. The limit is no longer purely probabilistic in nature ( ). 

The beauty of this completely random approach to the analyte detection limit is the direct applicability of the statistical hypothesis testing formalism. Also, long-term trends in calibration slope or backgrounds have little influence. One important assumption is made that the form of the calibration curve [Equation 2c] is fixed. Also, a subtle change has occurred, the operation is no longer linear, with A in the denominator. Thus, the distribution of x is only asymptotically normal, as the relative standard deviation of becomes smaller. 

Exposure Levels in Environmental Media. There were no quantitative data on current atmospheric levels of 3,3 -dichlorobenzidine emissions or on the chemical s potential to act as a surface eontaminant of soil environments. It is difficult to determine 3,3 -dichlorobenzidine levels in the aquatic environment because the concentrations tend to be at or below analytical detection limits. In general, it may only be possible to ascertain fully the environmental fate of 3,3 -dichlorobenzidine as analytical advances permit the routine determination of very low concentrations. Moreover, determination of the nature and environmental fate of breakdown products of 3,3 -dichlorobenzidine would be useful. 

General Electric Company, under an EPA permit, incinerated nearly 6,000 L (1,500 gal.) of 20% liquid DDT formulations in a liquid injection incinerator near Pittsfield, Massachusetts, in September 1974 (4). The facility utilized a vortex combustor of the type normally used for disposal of oils and solvents. Operating temperatures ranged from 870 to 980°C with retention times of 3 to 4 s and 120 to 160% excess air. Overall destruction efficiency exceeded 99.99%. Concentrations of DDT, DDE, and DDD in the stack gas and scrubber water were below analytical detection limits. 

Samples/ matrix Equipment/sample preparation Analyte Detection limits References... 

In the EU Directive on Drinking Water Quality [35], 23 individual chemical parameters have specific limits together with two group limits for polycyclic aromatic hydrocarbons and pesticides. In the case of pesticides, no individual pesticide is permitted to exceed 0.1 pgL , and pesticides in total should not exceed 0.5 xgL" . These limits were a compromise, the original demand having been for a zero limit for pesticides in drinking water, and these standards were set, in 1998, as the effective analytical detection limit. The revision of this directive and its application to pharmaceuticals is currently under discussion, although it seems unlikely that specific limits will be set for individual pharmaceuticals [36]. 

Permeate solute levels were often below analytical detection limits. When this situation occurred, the rejection values shown in Tables IV and V were calculated by using detection limits, and the values were stated as minimums (i.e., rejection >90 ). At very low concentrations, interferences and matrix effects became critical. Proper attention to analytical detail should be a primary concern of studies at the low parts-per-billion levels. 

Alternative 2 Set RMCLs at the Analytical Detection LIMIT. Because of limitations in analytical techniques, it will always be impossible to say with certainty that the substance is not present. In theory, RMCLs at zero will always be unachievable (or at least not... 

The verifiable detection limits (i.e., the RMCLs) would probably fall in the vicinity of 5 /zg/L, depending upon the specific chemical. The USEPA suggested that approach was justifiable in that zero is analytically undefinable and the detection limit may be the functional equivalent of zero. Analytical detection limits are moving targets as the state of the art of analytical chemistry progresses, but at least they do provide a measurable target. 

Great activity has also been evidenced in microlithographically fabricated arrays of microelectrodes, which are typically formed in one plane on an insulating substrate [7,8,13,34-45] for experiments involving either an array of electrodes held at a common potential [37,40,42,43], or an array of noninteracting electrodes held at two or more different applied potentials [42,44], or an array of interdigitated electrodes held at two different potentials [13,34,36,38,39,45-47]. Arrays have significantly better analytical detection limits than continuous electrodes of the same overall dimensions, due to enhanced mass transport fluxes that arise from an increase in the spatial dimensionality of mass transport due to the alternation of electrode zones with pas-... 

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