MDL, minimum detection limit

LD less than detectable MDL - minimum detection limit MPN most probable number. 

With modern detectors and electronics most Enei -Dispersive X-Ray Spectroscopy (EDS) systems can detect X rays from all the elements in the periodic table above beryllium, Z= 4, if present in sufficient quantity. The minimum detection limit (MDL) for elements with atomic numbers greater than Z = 11 is as low as 0.02% wt., if the peaks are isolated and the spectrum has a total of at least 2.5 X 10 counts. In practice, however, with EDS on an electron microscope, the MDL is about 0.1% wt. because of a high background count and broad peaks. Under conditions in which the peaks are severely overlapped, the MDL may be only 1—2% wt. For elements with Z < 10, the MDL is usually around 1—2% wt. under the best conditions, especially in electron-beam instruments. 

The minimum detection limit, MDL, of an isolated peak on a uniform background is proportional to the square root of the FWHM. So a 20% reduction in spectrometer resolution will produce about a 10% improvement in MDL. If there is peak overlap, however, then it can be shown that a 20% improvement in resolution can reduce the interference between overlapping peaks by a factor of 3, which gives about a 50% improvement in MDL. 

It is apparent that PIXE exhibits its maximum sensitivity or minimum detection limit (MDL) in the two atomic number regions 20 < Z < 35 and 75 < Z < 85. These are attained at relatively low proton energies, which implies that small accelerators are most suitable for PIXE with the corresponding benefits in reliability and economics. Analysis times are typically a few minutes in duration. The MDL is very strongly influenced by the nature of the sample, especially if there are strong X-rays from the matrix visible in the spectrum or if the sample is strongly insulating. 

Systematic error is also known as bias. The bias is the constant value difference between a measured value (or set of values) and a consensus value (or true value if known). Specificity is the analytical property of a method or technique to be insensitive to interferences and to yield a signal relative to the analyte of interest only. Limit of reliable measurement predates the use of minimum detection limit (MDL). The MDL... 

Polished thin sections or iron oxides grains polished in epoxy mounts were analyzed using Universite Laval CAMECA SX-100 5-VVDS electron microprobe under a beam of 15 kV at 100 nA, using a range of natural and synthetic standards. After counting over the peak for 20 to 30 sec, background is measured on both sides for 10 sec. These settings yield minimum detection limits (mdl) as low as 20 ppm for elements such as K, Ca, Al, Si, Ti and Mg, 50 ppm for Mn, Cr and V, 200 ppm for Cu,... 

Natural water (pH 6.0) and sediment (organic content 36%) used in this study were fortified with both the insecticides and subsequently analyzed by the described methods. No response that interfered with the detection of active ingredients was found in any of the untreated controls during incubation. The recoveries for water were 93 4% at 400 ppb and 97 7% at 20 ppb for sediment they were 86 6% and 91 9%, respectively, at the same fortification levels. The minimum detection limit (MDL) for both insecticides was 0.1 ppb in water and 10 ppb in sediment (as sampled). 

DEHP was detected in samples (one from a commercial site and five from residential sites) of both dust and air obtained from all sites (Rudel et al 2001). In dust, the concentration of DEHP ranged from 69.4 to 524 g/g dust, with a mean concentration of 315 g/g dust. In air, 4/6 sites had DEHP at concentrations above the minimum detection limit (MDL), ranging from 0.02 to 0.114 g/m3, with a mean concentration of 0.061 g/m3. In another study, indoor measurements ofDEHP taken in six homes in the spring of 2000 ranged from 0.04 to 0.23 g/m3 (Otake et al. 2001). In one workplace (plastic melting facility), a value of 11.5 g/m3 was measured in air (Rudel et al. 2001). 

Minimum detectable limits (MDL) for these thiols using SDC are about 1-2 uM and were calculated according to the method of Turner et al( ). MDL values for thiols can be lowered an order of magnitude if DPP is used. Because our field samples are diluted in a buffer matrix to a maximum of 500 uL in 5 mL of buffer, the MDL for field samples is about 10 uM. The linear range for analysis of these thiols is from MDL to about 0.4 mM. 

Figure 5.18 Method detection limit (MDL), minimum detectable amount (MDA) and linear...

The precision results for selected samples shown in Table 5 were obtained by making 100 repeat analyses of each sample using a count time of 100 s per analysis. A detection limit was obtained using the empirical method. The Minimum Detection Limit (MDL) here is defined as the 3ff observed standard deviation of 100 analyses of a blank sample containing no sulfur. Using heavy mineral oil as the blank sample, the MDL for sulfur was observed to be 0.02 %. 

An accepted measure of sensitivity is the minimum detectable limit (MDL). This is equal to the value of p at zero concentration, which is seen to be 0.068 mg/kg S. 

The differences in sample size, sample preparation procedures, counting time, accuracy, isotope composition, and minimum detectable limits (MDL) should be noted. Some of these methods will be briefly surveyed here. The methods for determining uranium in urine are nsually also suitable for measuring the concentration of uranium in water, and those that are described in detail in Section 4.4.1 will not be discussed here to avoid duplication. 

As an example. Figure 8.43 shows the chromatogram of a 1 pg/L bromate standard that was obtained by injecting 500 pL standard solution onto an lonPac AS9-HC separator. As can be seen from this chromatogram, a minimum detection limit (MDL) of 0.5pg/L bromate can be achieved without any problem when injecting such large volumes. 

MDL minimum detection hmit, method detection limit... 

Linearity of calibration plots and minimum detection limits (MDLs) were determined by injecting progressively lower concentrations of each species until the detection limit was reached. This was defined as a signal-to-noise ratio of about 2 1, using the absolute back-ground/baseline noise level as reference. In HPLC-Uy both selenite and selenate showed linear responses at concentrations up to about 50 ppm (50 /tl injections). Detection limits were on the order of about 0.1 ppm (100 ppb) for selenate and 10 ppb for selenite. Calibration plots were... 

The MDL and practical quantitation limit (PQL) should be appropriate for the objectives of the analysis. MDL refers to the minimum concentration of the compound of interest that can be measured and reported with a specified confidence (99% probability) that the concentration is above zero. The registrants must provide or develop an analytical method for water for the parent pesticide and its degradates that has an MDL of 0.01% of the label application rate (calculated as the average concentration in the top six inches of soil), or 0.05 pgL , whichever is lower. PQL refers to the lowest concentration at which the laboratory can confidently quantify the concentration of the compound of interest. The study authors must report all samples with concentrations above the MDL as detections, including those below the PQL in which the concentration cannot be quantified. In addition, the study authors must provide sample equations to demonstrate how the PQL was calculated. 

Quantification of the limits of detection (LOD), or minimum detectable levels (MDL statistically defined in Section 13.4), is an important part of any analysis. They are used to describe the smallest concentration of each element which can be determined, and will vary from element to element, from matrix to matrix, and from day to day. Any element in a sample which has a value below, or similar to, the limits of detection should be excluded from subsequent interpretation. A generally accepted definition of detection limit is the concentration equal to a signal of twice (95% confidence level) or three times (99% confidence) the standard deviation of the signal produced by the background noise at the position of the peak. In practice, detection limits in ICP-MS are usually based on ten runs of a matrix matched blank and a standard. In this case ... 

Sensitivity is the capability of a method or instrument to discriminate between measurement responses for different concentration levels (EPA, 1998a). It is determined as a standard deviation at the concentration level of interest and, therefore, it is concentration-dependent. It represents the minimum difference between two sample concentrations with a high degree of confidence. Laboratories establish a method s sensitivity by determining the method detection limit (MDL). The MDL is the minimum concentration of a substance that can be measured and reported with 99 percent confidence that the analyte concentration is greater than zero (EPA, 1984a). 

Detector sensitivity is best explained in terms of signal to noise ratio, which is the minimum detectable quantity with a signal to noise ratio of two (Willard, 1988). Detector sensitivity is linked to the method detection limit, a concept that we routinely use in environmental project work. (The definitions of detection limits in environmental pollutant analysis are discussed in Chapter 4.5.1.) The MDLs, however, while being related to detector sensitivity, greatly depend on the analytical method, sample matrix, and the analyte itself. In this chapter, we will address detector sensitivity in relative terms by comparing sensitivities of various chromatography detectors. 

Method detection limit MDL, the minimum amount of an analyte that can be analysed by a given method with satisfactory precision, also referred to as limit of quantitation. 

Method Detection Limit CMDLl. "The method detection limit (MDL) is defined as the minimum concentration of a substance that can be measured and reported with 99% confidence that the analyte concentration is greater than zero and is determined from analysis of a sample in a given matrix containing the analyte"... 

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