Below detection, limit assessment

Nitrite photochemistry in surface waters has often been underestimated because ion chromatography, the standard technique adopted for anion (and therefore nitrate) quantification in such matrices is poorly sensitive for nitrite, which would often be below detection limit although its photochemistry could still be very significant. Accordingly, the assessment of nitrite photochemistry in surface water samples requires more sensitive, dedicated analytical techniques [104, 106, 107]. 

To assess compliance with the no deterioration objective (concentrations of substances are below detection limits, declining or stable and there is no obvious risk of increase) of tire Water Framework Directive. 

Optimal assessment of the minimum detection limit would require a design x well below the current standard concentrations and including the blank. 

Treatment duration - The recommended duration of treatment for patients previously untreated with interferon is 24 to 48 weeks. Assess virologic response after 24 weeks of treatment. Consider treatment discontinuation in any patient who has not achieved an HCV-RNA below the limit of detection by... 

It is eoncluded that the determination of dioxin-like activity in cleaned sediment extracts using the DR-Luc bioassay has a consistent reproducibility, and can be used as a reliable and robust tool in the hazard assessment of dredged materials in a licensing system. Its advantage over ehemical analysis is that it also detects the effects of combined exposure as well as the effect of unidentified congeners or chemicals present in concentrations below the limit of detection of chemical analysis with a similar mode of action. In addition the use of cleaned sediment extracts circumvents the problem of disturbing sediment matrix effects. 

Recommended dosage and monitoring requirements PEG-Intron is administered once weekly for 1 year. The dose should be administered on the same day of each week. Initial dosing should be based on body weight. Serum hepatitis C virus (HCV) should be assessed after 24 weeks of treatment. Discontinuation of treatment should be considered in patients who have not achieved HCV RNA below the limit of detection after 24 weeks of therapy. Patients should be monitored for neuropsychiatric events, bone marrow toxicity, endocrine disorders, cardiovascular events, colitis, pancreatitis, autoimmune disorders, pulmonary disorders, and hypersensitivity. 

Analysis of urinary trans, trans-muconic acid (t,t-MA) seems to be a better indicator than phenol for assessing exposure to low levels of benzene (Ducos et al. 1990). However, muconic acid is a minor metabolic route and background levels of muconic acid in urine are much lower than levels of phenolic metabolites and are frequently below the limit of detection of the method used to determine them (Inoue et al. 1989). The detection of low levels of t,t-muconic acid in urine was difficult by earlier methods because of low recovery of t,t-muconic acid (37% with ether) by the commonly used solvent extraction method (Gad-El Karim et al. 1985). An improved method for the determination of urinary t,t-muconic acid utilizes solid phase extraction with SAX sorbent in combination with the HPLC/UV for quantitation. The detection limit is 0.06-0.1 mg/L, and recovery is very good (90%) (Boogaard and van Sittert 1995 Ducos et al. 1990). The relative standard deviation of the method was 5% in the concentration range 1-20 ng/L. t,t-muconic acid has been determined directly by HPLC/UV with similar sensitivity (detection limit =... 

Eight samples of un-irradiated reactor pressure vessel (RPV) steel, two each from Trawsfynydd (TRA), Dungeness A (DNA), Sizewell A (SXA) and Bradwell (BWA) reactors were analysed. ICP-MS analysis was carried out using a high resolution magnetic sector instrument. Despite the sensitivity of this method, i.e. lower limit of detection (LLD) of around 8 pg g for procedural blanks, it failed to detect Li and achieved a detection limit of 80 ng g, which was well above the level of interest. However, the results were consistent and did show that the Li concentration was well below that found from the earlier analytical attempts (ICP-OES) and below the levels conservatively assumed in the waste inventory assessments. 

Data to assess the compatibility of results provided by independent sampling are more restricted, being limited to just two samples per annum from three sites (Cardiff, Dungeness and Heysham). In addition, interpretation of the available results is complicated by the fact that activity concentrations in these samples were veiy low in comparison to the other sampling sites. More specifically, concentrations of Co and Am were below detection, in all but the Fucus Vesiculosus (seaweed) samples obtained... 

Pedersen et al. (1994) conducted a monitoring study to assess the levels of trace metals, including mercury, in table wine, fortified wine, beer, soft drinks, and various juices. These authors reported that in all samples tested, mercury concentrations were at or below the detection limit (6 g/L [6 ppb]). 

Methanol Methanol was the main contributor to COD in the enrichment reactors. Methanol comprised 51-72% of the COD in the foul condensate wastes. This wide range was caused by the varying nature of the foul condensates, and ultimately, to the composition of the wood feedstocks entering the mill. The enriched consortia in all of the reactors consumed methanol to levels below the 100 mg l methanol (HPLC) detection limit by HRT 8 (Fig. 5a-c). This indicates fimctional stability in the system by HRT 8 with respect to methanol consumption. To ensure community stability in the reactors, as well as to assess the long-term functional stability of the consortia, the reactors were further run to... 

Three independent laboratories, each using a different method, were selected to analyze crude oil samples. One objective of the project was to identify methods and procedures that could be used by industrial or academic laboratories to analyze crude oil for mercury in a practical fashion. The practicality of a method is a function of sample processing steps, reagent availability, instrumental analysis time, instrument expense, detection limit, and accuracy of result. Crude oils exhibiting total mercury concentrations (THg) below 1-2 pg/kg are not problematic to refining, but some specifications for refined products (naphtha) are set close to 1 pg/kg thus a method detection limit (MDL) of 0.1-0.3 pg/kg was deemed acceptable for routine quality assurance (QA) purposes. Differentiating mercury concentrations below 1 pg/kg may have academic utility, but an MDL of 10 ng/kg (parts per trillion) is not necessary for oil quality determinations or for assessment of atmospheric emissions attributable to petroleum. 

Health Canada and Environment Canada (1998) National ambient air quality objectives for particulate matter. Executive summary. Part 1 science assessment document. A report by the CEPA/FT AC Working Group on Air Quality Objectives and Guidelines. Public Works and Government Services Ottawa, ON, Canada, p 25 Helsel DR (1990) Less than obvious statistical treatment of data below the detection limit. Environ Sci Technol 24 1766-1774... 

Hecht, H. Honikel, K.O. (1995) Assessment of data sets containing considerable values below the detection limits. Z Lebensm. Unters. Forsch. 201, 592-597. 

As the LSMS chemical analysis technique is no longer available to us, current chemical analysis is by secondary ion mass spectrometry (SIMS) which has been used to assess the impurity levels in this recent ACRT material. The distributions of known donors and acceptors in CMT were measured. The Cr, Al, K, Br, I, H, C and Si were at, or below, the detection limits of the technique, while Na, Ga, In and Cl were at or above the detection limits. The Na and Ga were only present at the mid-10 atoms cm level, while the Cl was present in the low-10 atoms cm region. The silica used for the growth ampoules was a chlorine-free synthetic type that perhaps still has a small residue present. This chemical analysis attests to the high purity and reproducibility of this ACRT material. 

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