Sensitivity, 47-2. Detection limit, 47-3. Precision

Precise and accurate isotope analyses by mass spectrometry have attained growing importance in the last few years due to instrumental improvements with respect to sensitivity, detection limits, precision and accuracy.1 As mentioned before, because the isotope abundances of several elements are not constant and vary as a result of nuclear, biological, chemical, geochemical and physical processes, isotope ratio measurements are required for different research and application fields. Isotope ratio measurements are therefore necessary for elements with two or more isotopes for inves-... 

Menis, O., Rains, T. C., Sensitivity, Detection Limit, Precision and Accu-... 

Capabilities of an analytical technique are sensitivity, detection limit, precision and accuracy, spatial, energy or mass resolution, amount and quality of information and also productivity (throughput). There are several valid reasons for developing new methods of analysis [6], such as ... 

Specifications How good do the numbers have to be Write specifications Pick methods to meet specifications Consider sampling, precision, accuracy, selectivity, sensitivity, detection limit, robustness, rate of false results Employ blanks, fortification, calibration checks, quality control samples, and control charts to monitor performance Write and follow standard operating procedures... 

The criteria used for evaluating analytical methods are called figures of merit. Based on these characteristics, one can predict whether a method meets the needs of a certain application. The figures of merit are listed in Table 1.2. Accuracy and precision have already been discussed other important characteristics are sensitivity, detection limits, and the range of quantitation. 

Methods are not presented in detail, space considerations alone would not permit this. Instead, the chemist is presented with details of methods available for a variety of types of water samples. Methods are described in broad outline, giving enough information for the chemist to decide whether he or she wishes to refer to the original paper. To this end information is provided on applicability of methods, advantages and disadvantages of one method compared to another, interferences, sensitivity, detection limits and data relevant to accuracy and precision. 

Analytical method attributes measures of the quality, reliability, and uncertainty of the determinations obtained with an analytical method. Typical analytical method attributes are selectivity, sensitivity, detection limits, signal/noise, recovery, accuracy, bias, precision, and validation. Analytical method attributes are sometimes called figures of merit. 

Analytical methods are validated by investigating the specificity, sensitivity, detection limits, quantification limits, accuracy (of the individual result), precision (variation between different tests), applicability and practicability under laboratory conditions and the robustness (susceptibility to interference) of the method. This enables the organization itself to employ these tests much more consciously and with better results, but it also serves the purpose of enabling the registration authorities to use these tests for the regular batch control tests. Official guidelines by the regulatory authorities for the validation of analytical methods and processes are available for consultation. 

In addition to the usual evaluation parameters for analytical methods (Chapter 16), the sensitivity, detection limit, dynamic range, and precision profile, biosensors are also characterized with respect to the rapidity of their response and recovery. This... 

Analytical procedures are characterized by a number of figures of merit such as accuracy, precision, sensitivity, detection limit, and dynamic range. We discussed in Chapter 5 the general concepts of accuracy and precision. Here, we describe those additional figures of merit that are commonly used and discuss the validation and reporting of analytical results. 

Consider sampling, precision, accuracy, selectivity, sensitivity, detection limit, robustness, and rate of false results. 

If a trace element is trapped as a very thin deposit (preferably in the monolayer range), XPS and AES can provide quantitative determination with high sensitivity (detection limits < ppb), as well as good accuracy and precision. The number of publications dealing with XPS/AES applications in trace element analysis is quite small. Some examples are given in Table 4.5. 

In an attempt to broaden the applicability of the RSF method to snbstrates for which reference materials were not available, the matrix-tranrferable RSF approach was snggested. This is covered in Section A.9.1. Shortly thereafter, another approach that also did not reqnire matrix-matched reference materials was suggested. This method, termed the Infinite Velocity method, is discnssed in Section A.9.2. These, however, suffered in that they could not provide the precision levels required for high sensitivity/detection limits commonly expected of SIMS. 

Gas chromatography-mass spectrometry of nine nltroaromatic compounds was carried out in order to evaluate its potential as an analytical method for the determination of TNT and possible related impurities in environmental samples such as water and soil [8]. Nitrobenzene, the three mononitrotoluenes (MNTs), 1,3-DNB, 2,4-DNT, 2,6-DNT, and TNB were analyzed in addition to TNT. The MS ionization techniques included El, positive-ion chemical ionization (Cl) and negative-ion Cl (NCI), all recorded in both full-scan and selective ion monitoring (SIM) modes. They were compared with GC analysis with electron capture detection (ECD). The comparison included sensitivity (detection limits), linear response range, and precision. The GC ECD was recommended for those analyses where there was no uncertainty in the identity of the analytes. 

The primary figures of merit that are used to characterize ICP-MS instruments and methods include selectivity, stability, robustness (susceptibility to interferences), sensitivity, detection limits, accuracy, and precision. Selectivity, stability, and robustness have all been discussed in some detail in previous chapters. The focus in this chapter will be on sensitivity, detection limits, accuracy, and precision. 

Designing an experimental procedure involves selecting an appropriate method of analysis based on established criteria, such as accuracy, precision, sensitivity, and detection limit the urgency with which results are needed the cost of a single analysis the number of samples to be analyzed and the amount of sample available for... 

Most of the transition elements that are of primary interest in the semiconductor industry such as Fe, Cr, Mn, Co, and Ni, can be analyzed with very low detection limits. Second to its sensitivity, the most important advantage of NAA is the minimal sample preparation that is required, eliminating the likelihood of contamination due to handling. Quantitative values can be obtained and a precision of 1-5% relative is regularly achieved. Since the technique measures many elements simultaneously, NAA is used to scan for impurities conveniently. 

Overall, the RDE provides an efficient and reproducible mass transport and hence the analytical measurement can be made with high sensitivity and precision. Such well-defined behavior greatly simplifies the interpretation of the measurement. The convective nature of the electrode results also in very short response tunes. The detection limits can be lowered via periodic changes in the rotation speed and isolation of small mass transport-dependent currents from simultaneously flowing surface-controlled background currents. Sinusoidal or square-wave modulations of the rotation speed are particularly attractive for this task. The rotation-speed dependence of the limiting current (equation 4-5) can also be used for calculating the diffusion coefficient or the surface area. Further details on the RDE can be found in Adam s book (17). 

Consideration must be given to equipment calibration and method suitability in terms of sensitivity, limits of detection, accuracy, precision, repeatability. 

Several methods are available for the analysis of trichloroethylene in biological media. The method of choice depends on the nature of the sample matrix cost of analysis required precision, accuracy, and detection limit and turnaround time of the method. The main analytical method used to analyze for the presence of trichloroethylene and its metabolites, trichloroethanol and TCA, in biological samples is separation by gas chromatography (GC) combined with detection by mass spectrometry (MS) or electron capture detection (ECD). Trichloroethylene and/or its metabolites have been detected in exhaled air, blood, urine, breast milk, and tissues. Details on sample preparation, analytical method, and sensitivity and accuracy of selected methods are provided in Table 6-1. 

Use of 10 pm LiChrosorb RP18 column and binary eluent of methanol and aqueous 0.1 M phosphate buffer (pH 4.0) according to suitable gradient elution program in less than 20-min run time with satisfactory precision sensitivity of spectrophotometric detection optimized, achieving for all additives considered detection limits ranging from 0.1 to 3.0 mg/1, below maximum permitted levels Simultaneous separation (20 min) of 14 synthetic colors using uncoated fused silica capillary column operated at 25 kV and elution with 18% acetonitrile and 82% 0.05 M sodium deoxycholate in borate-phosphate buffer (pH 7.8), recovery of all colors better than 82%... 

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