検出限界

WordNet

restrict or confine, "I limit you to two visits to the pub a day" (同)circumscribe, confine
the mathematical value toward which a function goes as the independent variable approaches infinity (同)limit_point, point of accumulation
the greatest amount of something that is possible or allowed; "there are limits on the amount you can bet"; "it is growing rapidly with no limitation in sight" (同)limitation
the greatest possible degree of something; "what he did was beyond the bounds of acceptable behavior"; "to the limit of his ability" (同)bound, boundary
the boundary of a specific area (同)demarcation, demarcation line
as far as something can go
small in range or scope; "limited war"; "a limited success"; "a limited circle of friends"
mediocre (同)modified
having a specific function or scope; "a special (or specific) role in the mission" (同)special
including only a part
not excessive
not unlimited; "a limited list of choices"
the act of detecting something; catching sight of something (同)catching, espial, spying, spotting
a police investigation to determine the perpetrator; "detection is hard on the feet" (同)detecting, detective work, sleuthing
the perception that something has occurred or some state exists; "early detection can often lead to a cure" (同)sensing
strictly limiting the reference of a modified word or phrase; "the restrictive clause in `Each made a list of the books that had influenced him limits the books on the list to only those particular ones defined by the clause"

PrepTutorEJDIC

(空間・行為などの)『限界』,《+『of』+『名』》 / 《しばしば複数形で;単数扱い》『境界』,境界線範囲,区域 / (数量などの)許容量,制限 / 適度に / …‘を'『制限する』
限られた,狭い / 《米》(鉄道・バスなどが)特別の,特急の / 《英》(会社が)有限の(《米》incorporated) / 特急列車(バスなど)
発見,探知,発覚 / (電波の)検波
制限する,限定する

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/04/28 00:15:31」(JST)

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In analytical chemistry, the detection limit, lower limit of detection, or LOD (limit of detection), is the lowest quantity of a substance that can be distinguished from the absence of that substance (a blank value) within a stated confidence limit (generally 1%).^[1]^[2] The detection limit is estimated from the mean of the blank, the standard deviation of the blank and some confidence factor. Another consideration that affects the detection limit is the accuracy of the model used to predict concentration from the raw analytical signal.

There are a number of different "detection limits" that are commonly used. These include the instrument detection limit (IDL), the method detection limit (MDL), the practical quantification limit (PQL), and the limit of quantification (LOQ). Even when the same terminology is used, there can be differences in the LOD according to nuances of what definition is used and what type of noise contributes to the measurement and calibration.^[3]

The figure below illustrates the relationship between the blank, the limit of detection (LOD), and the limit of quantification (LOQ) by showing the probability density function for normally distributed measurements at the blank, at the LOD defined as 3 * standard deviation of the blank, and at the LOQ defined as 10 * standard deviation of the blank. For a signal at the LOD, the alpha error (probability of false positive) is small (1%). However, the beta error (probability of a false negative) is 50% for a sample that has a concentration at the LOD (red line). This means a sample could contain an impurity at the LOD, but there is a 50% chance that a measurement would give a result less than the LOD. At the LOQ (blue line), there is minimal chance of a false negative.

Illustration of the concept of detection limit and quantitation limit by showing the theoretical normal distributions associated with blank, detection limit, and quantification limit level samples..

Instrument detection limit

Most analytical instruments produce a signal even when a blank (matrix without analyte) is analyzed. This signal is referred to as the noise level. The IDL is the analyte concentration that is required to produce a signal greater than three times the standard deviation of the noise level. This may be practically measured by analyzing 8 or more standards at the estimated IDL then calculating the standard deviation from the measured concentrations of those standards. The detection limit (according to IUPAC) is the smallest concentration or absolute amount of analyte that has a signal significantly larger than the signal arising from a reagent blank. Mathematically, the analyte’s signal at the detection limit (Sdl) is given by: Sdl = Sreag + 3 * σreag

where Sreag is the signal for a reagent blank, σreag is the known standard deviation for the reagent blank’s signal.

Other approaches for defining the detection limit have also been developed. In atomic absorption spectrometry usually the detection limit is determined for a certain element by analyzing a diluted solution of this element and recording the corresponding absorbances. The experiment is repeated for 10 times. The 3σ of the recorded absorbance signal can be considered as the detection limit for the specific element under the experimental conditions used – wavelength, type of flame, instrument.

Method detection limit

Oftentimes there is more to the analytical method than just performing a reaction or submitting it to direct analysis. For example, it might be necessary to heat a sample that is to be analyzed for a particular metal with the addition of acid first (this is called digestion). The sample may also be diluted or concentrated prior to analysis on an instrument. Additional steps in an analysis add additional opportunities for error. Since detection limits are defined in terms of error, this will naturally increase the measured detection limit. This detection limit (with all steps of the analysis included) is called the MDL. The practical method for determining the MDL is to analyze 7 samples of concentration near the expected limit of detection. The standard deviation is then determined. The one-sided t-distribution is determined and multiplied versus the determined standard deviation. For seven samples (with six degrees of freedom) the t value for a 99% confidence interval is 3.14. Rather than performing the complete analysis of seven identical samples, if the Instrument Detection Limit is known, the MDL may be estimated by multiplying the Instrument Detection Limit or Lower Level of Detection by the dilution prior to analyzing the sample solution on the instrument. This estimation, however, ignores any uncertainty that arises from performing the sample preparation and will therefore probably underestimate the true MDL.

Limit of reporting

The LOQ is the limit at which we^[who?] can reasonably tell the difference between two different values. The LOQ may be drastically different between laboratories so another detection limit is commonly used that is referred to as the Practical Quantitation Limit (PQL).

References

^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "detection limit".
^ MacDougall, Daniel.; Crummett, Warren B.; et al. (1980), "Guidelines for Data Acquisition and Data Quality Evaluation in Environmental Chemistry", Anal. Chem. 52: 2242–49, doi:10.1021/ac50064a004 |first3= missing |last3= in Authors list (help)
^ Long, Gary L.; Winefordner, J. D. (1983), "Linearization of electron capture detector response to strongly responding compounds", Anal. Chem. 55 (7): 713A–724A, doi:10.1021/ac00255a030

External links

Interactive Java applet to illustrate some basic ideas of the limit of detection problem
Downloads of articles (a.o. harmonization of concepts by ISO and IUPAC) and an extensive list of references

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