Instrument detection limit

Out of these efforts have come a multitude of terras such as Limit of Detection, Method Detection Limit, Instrument Detection Limit, Limit of Quantitation, Criterion of Detection and a multitude of symbols such as the less than sign, RD, TR (for trace), U, M, J, T and w, and K. EPA is now proposing LTL (less than lower limit of detection) and LTC (less than criteria of detection) in computer standards. Some of the conventions come with rigid definitions for prescribed use and others come with vague definitions and allow for "analytical judgment" and flexibility. 

Precision When the analyte s concentration is well above the detection limit, the relative standard deviation for fluorescence is usually 0.5-2%. The limiting instrumental factor affecting precision is the stability of the excitation source. The precision for phosphorescence is often limited by reproducibility in preparing samples for analysis, with relative standard deviations of 5-10% being common. 

Detection limit. The detection limit of an instrument should be differentiated from its sensitivity. The detection limit reflects the smallest flow of sample or the lowest partial pressure that gives a signal that can be distinguished from the background noise. One must specify the experimental conditions used and give the value of signal-to-noise ratio corresponding to the detection limit. 

Historically, EELS is one of the oldest spectroscopic techniques based ancillary to the transmission electron microscope. In the early 1940s the principle of atomic level excitation for light element detection capability was demonstrated by using EELS to measure C, N, and O. Unfortunately, at that time the instruments were limited by detection capabilities (film) and extremely poor vacuum levels, which caused severe contamination of the specimens. Twenty-five years later the experimental technique was revived with the advent of modern instrumentation. The basis for quantification and its development as an analytical tool followed in the mid 1970s. Recent reviews can be found in the works by Joy, Maher and Silcox " Colliex and the excellent books by Raether and Egerton. ... 

With the increasingly lower limits of detection being achieved in various types of instrumental analysis, there is an ever growing demand for reagents of... 

Sensitivity, Linearity, and Stability of Instruments. Quinine sulfate has been suggested as a standard for determining the limit of detection and linearity of Instruments (44). Some organic materials dissolved In plastics have been suggested as standards because of their stability (22), and many Inorganic Ions dissolved In glasses are quite stable. 

A series of calibration standards (CS) is made up that covers the concentration range from just above the limit of detection to beyond the highest concentration that must be expected (extrapolation is not accepted). The standards are made up to resemble the real samples as closely as possible (solvent, key components that modify viscosity, osmolality, etc.). A series of blinded standards is made up (usually low, medium, high the analyst and whoever evaluates the raw data should not know the concentration). Aliquots are frozen in sufficient numbers so that whenever the method is again used (later in time, on a different instrument or by another operator, in another laboratory, etc.), there is a measure of control over whether the method works as intended or not. These so-called QC-standards (QCS) must contain appropriate concentrations of all components that are to be quantified (main component, e.g., drug, and any impurities or metabolites). 

For detection, MS is rapidly becoming the method of choice for multiclass, multiresidue analysis owing to its many advantages, recent improvements in technology, and availability of cost-effective commercial instrumentation. Detection systems in general are continually being improved, and in combination with the improvements in chromatographic instruments and techniques, an exceptionally low limit of detection (LOD) is possible for pesticide residues. 

The limit of detection for this instrument is about 10 pg/ ml for polystyrene in 2-butanone,163 which is close to two orders of magnitude higher than that of the deflection-type DRI. Moreover, the response of the ELSD is linear over only two decades in concentration.163 The ELSD is a useful backup detector when the DRI or UV detectors are not appropriate, e.g., when the UV absorbance or RI change is a function of copolymer composition as well as concentration or in gradient elution systems where changes in solvent composition cause drift in baselines of the UV and DRI detectors. Compounds about as volatile as the solvent are poorly detected by ELSD. 

Temperature programming packed-capillary and open capillary HTLC-ICP-MS (up to 200 °C) has been reported [738]. //.HTLC-ICP-MS instrumental coupling has been applied to organotin (tetraethyltin, tributyltin chloride and triphenyltin chloride) and organolead (tetramethyllead and tetraethyllead) compounds [756]. HTLC-ICP-MS can be used for the determination of organometallic compounds at low concentrations. The observed limit of detection (LOD) was 5pg for Pb in... 

The enormous dynamic range of proteins in the sample represents an additional difficulty in proteome analysis. The best example is semm with a protein abundance ranging over eleven orders of magnitude (Anderson and Anderson, 2002). To detect the low abundant species, one has to load a sufficient amount of digest on a column to meet the limit of detection (LOD) of the MS instrument. Some reports published used up to 2.5 L of plasma with an extensive fractionation of intact proteins prior to LC-MS analysis on the peptide level (Rose et al., 2004). 

For many purposes, only an approximate value of the limit of detection is required and this is calculated by using either equation (4.2a) or (4.2b). If the instrument signal-to-noise ratio is obtained in terms of the response it will need to be converted to concentration units ... 

How do you distinguish between the instrument detection limit (IDL) and the method detection limit (MDL) ... 

A number of experimental considerations must be addressed in order to use XRF as a quantitative tool, and these have been discussed at length [75,76]. The effects on the usual analytical performance parameters (accuracy, precision, linearity, limits of detection and quantitation, and ruggedness) associated with instrument are usually minimal. 

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