Methodologies for the practical determination and use of method detection limits

Underwater NaI(T1) and HPGe detectors are used in the environmental measurements programs at the Savannah River Site (SRS). A 22.9 cm × 10.2 cm NaI(T1) detector on the Savannah River continuously monitors effluent releases from both SRS (DOE) and Plant Vogtle (Georgia Power). Correlations with known releases indicate a sensitivity of 4 mBq/l for⁵⁸Co with 1500 min spectra; such levels are well below those of hazardous or legal concern. A 30%-efficient HPGe detector has appraised radionuclides in SRS cooling pond sediments; the dominant gamma-emitting radionuclide detected was¹³⁷Cs, at levels ranging up to 2.0 MBq/m². The pond activities were adequately quantified by 1 min counts with the HPGe detector; resulting contour maps of sediment¹³⁷Cs provided guidance for partially draining the ponds for dam repairs.     

The limits of decision,detection, and determination in anti-Compton gamma-ray spectrometry

The improvement in the limits of decision, detection, and determination effected by anti-Compton gamma-ray spectrometry are considered. A simple procedure for the experimental determination is presented.     

Detectors and detection limits in INAA

Expressions have been derived which link detection limits in INAA with the Ge-detector specifications, provided by the vendors: relative efficiency, peak-to-Compton ratio and resolution. Situations have been distinguished in which a peak has to be detected on a Compton background, or on a natural background. The expressions allow for a direct indication of the improvement in detection limits, or the shortening of tumaround-time to attain equal detection limits, when a given detector is replaced by a detector with better specifications.     

Detectors and detection limits in INAA

The kinetic behavior of deuteriation of 2-chloro-, 3-chloro- and 4-chlorobenzoic acids in the presence of homogeneous platinum salt catalyst in a medium containing solution of deuteriated acetic acid in heavy water has been studied at 130°C. The quasiunimolecular H/D exchange rate constants for particular position of aromatic ring hydrogens were determined by¹H NMR integration signal.     

Basic calculations about the limit of detection and its optimal determination

The limit of detection (LOD) is based strictly on an accepted probability for a false positive decision (type 1 error). For the needed standard deviation of the blank, a basic value for the calculation, three experimental different methods are described, which should be applicable in every case. Table values for simple but exact calculation, not only for single, but also for mean values, and with probabilities for the type 1 error of 1% and 5% are presented. Demands for an acceptable uncertainty of the LOD and for the validation of the result are specified.     

Once again the question of cyclization of pyrazolones-5 unsubstituted at the nitrogen into tripyrazolynenes

The experimental data were refined and the yields were improved significantly in cyclization of pyrazolones-5 into tripyrazolylenes-1,5 with phosphorus oxychloride.K. A. Timiryazev Moscow Agricultural Academy, Moscow 127550, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 704–705, May, 1998.     

Pushing the limits of NAA: Accuracy,uncertainty and detection limits

This paper describes some highlights from the author’s efforts to improve neutron activation analysis (NAA) detection limits through development and optimization of radiochemical separations, as well as to improve the overall accuracy of NAA measurements by identifying, quantifying and reducing measurement biases and uncertainties. Efforts to demonstrate the metrological basis of NAA, and to establish it as a “Primary Method of Measurement” will be discussed.     

Automated determination of detection limits and selectivity coefficients of ion-selective electrodes by using a microcomputer-controlled potentiometric system

The detection limit and the potentiometric selectivity coefficients of ion-selective electrodes are determined automatically with a microcomputer-controlled potentiometric system. Measurements of these parameters for three commercially available electrodes of the liquid membrane type (chloride, nitrate and calcium electrodes) gave results in good agreement with those reported in the literature. The non-linear least-squares fit evaluation of data (potential activities) and the selection of the appropriate transfer functions are described. The reproducibility of the results is discussed.     

A novel approach for the determination of detection limits for metal analysis of environmental water samples

Despite the widespread use of the USEPA method (U.S. Environmental Protection Agency, 40 CFR 136 Appendix B) for the determination of method detection limit (MDL), criticisms have been raised that the method does not account for measurement bias and outliers that subsequently lead to a common misunderstanding of the requirement for the determination of MDL. This paper demonstrates that it is difficult to follow the USEPA method for verifying the MDL for analysis involving multiple metals and proposes a precision and bias criterion for determining the MDL. A multiple-point fitted profile, based on the correlation between relative standard deviation (RSD) and concentration, is used to derive a robust MDL value. Representative examples of As, Ca, Cr, and Cu are used to illustrate this procedure. A procedure for identifying outliers is also discussed.     

Legislative limits below detection capability1

 A study of contaminant emission data collected for paper and pulp mills in the United Kingdom over a 1-year period is presented. For most sites and analytes, the data could not demonstrate positive compliance with absolute emission limits to water in the 1 g range in large (million tonne) effluent streams, even though some sites were apparently removing contaminants from their water supply. The implications are discussed, with particular reference to the implications of results quoted at 'detection limits' or 'reporting limits'. Received: 6 February 2000 / Accepted: 27 March 2000     

Validation of chromatographic methods: evaluation of detection and quantification limits in the determination of impurities in omeprazole

To guarantee that an analytical procedure gives reliable, exact and interpretable information about a sample, it must be validated. Two ambiguous parameters are detection limit and quantification limit. The determination of these limits is still of great concern and there are still a variety of procedures described in the current literature. The fundamental objective of the present work is to apply the different recommendations suggested by official guidelines for the quantitative determination of omeprazole and its impurities (omeprazole sulphone and 5-hydroxy-omeprazole) in capsules and tablets using high performance liquid chromatography with UV detection. The importance of calibration linearity in the context of the quantification limit is considered, since one of the approaches, the estimated concentrations of this limit, are deduced from the regression line. The values of the detection limit and the quantification limit obtained show that, in chromatographic analyses, the best method is that based on the use of the parameters obtained from the analytical curve, which are statistically reliable. It was shown that smaller values of the detection limit and the quantification limit were obtained by the visual approach and by the method using the signal-to-noise ratio. However, these values may reflect a subjective evaluation, prone to error and large variations. This was confirmed by showing that these methods result in values that fall outside the linear range of the method.     

Assessment of limits of detection and quantitation using calculation of uncertainty in a new method for water determination

 An approach to the assessment of the limit of detection and the limit of quantitation using uncertainty calculation is discussed. The approach is based on the known evaluation of the limits of detection and quantitation as concentrations of the analyte equal to three and ten standard deviations of the blank response, respectively. It is shown that these values can be calculated as the analyte concentrations, for which relative expanded uncertainty achieves 66% and 20% of possible results of the analyte determination, correspondingly. For example, the calculation is performed for the validation of a new method for water determination in the presence of ene-diols or thiols, developed for analysis of chemical products, drugs or other materials which are unsuitable for direct Karl Fischer titration. A good conformity between calculated values and experimental validation data is observed. Received: 27 July 1998 · Accepted: 29 November 1998     

Spectral interferences in inductively coupled plasma atomic emission spectrometry-I: A theoretical and experimental study of the effect of spectral bandwidth on selectivity,limits of determination,limits of detection and detection power

This article links up with recent work on high resolution spectroscopy in this laboratory [1] and primarily deals with the effect of the spectral resolution on the “selectivity” in the case of samples that emit line-rich spectra. The concept of selectivity, as developed by KAISER [8] on the basis of the set of calibration equations for a multicomponent system, is considered as a useful starting-point but is rejected as a meaningful analytical figure of merit. Instead the concept of “line selectivity” is introduced as a criterion and related to the analytical error. This approach leads to a definition of the limit of determination such that its dependence on the spectral resolution can be clearly and unambiguously revealed in any concrete situation, that is, once the sample type has been specified. Such a specification is necessary since the numerical values of quantities related to selectivity are inherently linked with sample composition.Thus the theory is illustrated with practical examples including the results of a multiplicity of simulated line overlap situations using representative experimental line profiles measured at two extreme levels of resolution, referred to as “medium” and “high” resolution.It is shown that in the case of line overlap the limit of determination may exceed the limit of detection by one or even two orders of magnitude, unless line selection is based on a selectivity criterion so that the limit of detection is inherently coupled to the limit of determination. It is also shown that the prime benefit of high resolution spectroscopy is the reduction of the limit of determination, not that of the limit of detection. This benefit is found only if the spectral resolution can improve the selectivity, thus if there exist situations of line overlap.     

Evaluation of detection limits in emission spectroscopy

Summary The didactical method for defining the practical noise level considered in Part I is supplemented by a treatment that avoids the disruption of the statistical combination of the error due to the graininess of the emulsion and the error originating from intensity fluctuations in the source. The relationships between the basic standard deviations occurring in the alternative treatments are discussed and the inherent detection limits are compared. The procedure finally adopted is demonstrated with examples.

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Zusammenfassung Anlehnend an die didaktische Methode zur Erfassung der praktischen Nachweisgrenze [I. Teil, diese Z. 220, 241 (1966)] bringt die vorliegende Arbeit eine ergänzende Theorie, welche das Unterbrechen des statistischen Zusammenwirkens von Körnigkeitsstreuung und Intensitätsschwankungen in der Lichtquelle umgeht. Die Beziehungen zwischen den Standardabweichungen, welche den beiden Betrachtungsweisen zugrunde liegen, werden diskutiert, und die zugehörigen Nachweisgrenzen werden mit einander verglichen. Das endlich gewählte Verfahren wird an Hand von Beispielen demonstriert.

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Part I: see this journal220, 241 (1966).

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Dedicated to Prof. Dr. H.Kaiser on his 60th birthday.     

Evaluation of detection limits in emission spectroscopy

Summary The paper considers the evaluation of detection limits in photographic emission spectroscopy in case of the analytical line being superimposed on a blank line, caused by either a molecular band or a residual impurity in the electrodes, the admixture, or the atmosphere. The theory developed is a generalization of Kaiser's treatment of detection limits for a smooth background. The theory permits to compare the ideal detection limit, attainable in the absence of a blank with the practical detection limit, reached when a given blank interferes, all other conditions being equal. The relation between the evaluation of the practical detection limit and the determination of the blank concentration (addition method) is discussed.

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Zusammenfassung Die Auswertung von Nachweisgrenzen in der photographischen Emissionsspektroskopie wird für den Fall betrachtet, daß die Analysenlinie einer Blindlinie überlagert ist, die durch eine Molekülbande oder eine Verunreinigung in den Elektroden, im Zusatz oder in der Atmosphäre verursacht wird. Die aufgestellte Theorie ist eine Verallgemeinerung der Kaiserschen Berechnung von Nachweisgrenzen für glatten Untergrund. Sie ermöglicht es, die praktische Nachweisgrenze, erreicht mit einer gegebenen Blindwertstörung, und die ideale Nachweisgrenze, erzielbar ohne Blindwert, aber unter sonst gleichen Bedingungen, miteinander zu vergleichen. Die Beziehung zwischen der Auswertung der praktischen Nachweisgrenze und der Bestimmung der Blindkonzentration (Restgehaltsbestimmung nach dem Zugabeverfahren) wird diskutiert.

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Nomenclature G nominal concentration (or absolute amount) of an analysis element in a sample or standard - G detection limit - ¯G _B average concentration (or absolute amount) of the analysis element in the blank - I photographic intensity (= exposure) - I _L intensity of an analytical line corrected for the background and without a contribution from the blank - I _L antilogarithm of Y _L - I _U intensity of the background at the wavelength of an analytical line - ¯I _U antilogarithm of ¯Y _U - I _LU sum of intensities of analytical line and background - I _B deintensity emitted by a blank at the wavelength of an analytical line - ¯I _B antilogarithm of ¯Y _B - I _B antilogarithm of Y _B - I _BU sum of intensities contributed by blank and background at the wavelength of an analytical line - I _LB intensity at the wavelength of an analytical line resulting from the contributions from the sample and the blank, but corrected for the background - I _LBU sum of intensities I _LB and I _U - Y logarithmic intensity - Y _L logarithm of I _L - Y _L smallest significant value evaluated for log I _L in a sample - Y _U logarithm of I _U - ¯Y _U mean value of log I _U for a series of spectra taken under standard conditions characteristic for the analysis method - Y _LU logarithm of I _LU - Y _LU smallest significant reading of log I _LU in case there is a smooth background - Y _B logarithm of I _B - ¯Y _B mean value of log I _B calculated from measurements in at least twenty blank spectra taken under standards conditions - ¯Y _B minimum value of Y _B defined by equation (20) - Y _BU logarithm of I _BU - Y _LB logarithm of I _LB - Y _LBU logarithm of I _LBU - Y _LBU smallest significant reading of log I _LBU - Y _U Y _L-¯Y_U, noise level in case there is a smooth background, to be connected with a calibration curve normalized to the background [equation (11)] - (Y _U ) _B Y _L-¯Y_U, noise level in case there is a blank, to be connected with a calibration curve normalized to the background [equation (11)] - Y _B Y _L-¯Y_B, noise level in case there is a blank, to be connected with a calibration curve normalized to the blank [equation (36)] - Y _L,U Y _L-¯Y_U, logarithm of intensity of analytical line normalized to the background, i.e. logarithm of intensity ratio I _L/¯I_U - ¯Y _B-¯Y_U, logarithm of ratio ¯I _B/¯I_U - Y_L,B Y_L-¯Y_B logarithm of intensity of analytical line normalized to the blank, i.e. logarithm of intensity ratio I _L/¯I_B - _U standard deviation in logarithmic intensity due to the graininess - _B standard deviation of Y _B - slope of working curve log G vs Y _L [equations (9) and (31)] - K constant in the working curve log G vs Y _L [equations (9) and (31)] - n number of independent readings - P 32 _U - q 3 _B - r ¯I _b/¯I_U The authors acknowledge Prof. Dr. H. Kaiser and his co-workers for their readiness to discuss the subject and for their critical remarks.     

Attogram detection limits using laser induced fluorescence

Laser induced fluorescence has produced outstanding detection limits in liquid phase analysis. This paper presents a general method for optimizing detection limits as a function of sample volume.     

Comparison of the detection limits of microcalorimeters

Different calorimetric methods are compared with regard to the minimum detectable total heat effect that can be measured. This heat effect is shown to be dependent on: (a) the peak-to-peak uncertainty in the primary measurement which should be expressed in either degrees Kelvin or watts depending on whether the primary measurement is of temperature or power, (b) the time constant of the calorimeter system, and (c) the total energy equivalent of the reaction vessel and contents if the primary measurement is temperature.