Sensitivity and Detection Limits

Sensitivity in mass spectrometry is defined as the ratio of the ionic current change to the sample change in the source. The recommended unit is Cpg-1. It is important that the relevant experimental conditions corresponding to sensitivity measurement should always be stated. 

Another factor influencing the sensitivity corresponds to the length of time of signal integration. Of course, the longer that time is, the more intense is the signal. The data 

Detection limit obtained in mass spectrometry in the case of dihydrocholesterol. 

As a reminder, the scan consists of measuring complete spectra between two limit masses several times. The detection of selected ions consists of tuning the analyser so as to focus on to the detector only those ions with a specific m/z ratio. If several ions with 

Detection of the heptafluorobutyryl derivative of methtrypto-line using GC. Top SIM of the 362Th negative ion. Bottom SRM of the 362- 179Th fragmentation. Reprinted (modified) from Yost R.A., Adv Mass Spectrom, 10B, 1479, 1985, with permission. 

The sensitivity and LOD of mass spectrometers depend on several factors. The first and most important factor is the ionization efficiency of analytes. Ionization efficiency is analyte-dependent because it is normally higher for analytes of higher polarity, higher 

(2004) Mass Spectrometry A Textbook, 1st Edition. Springer, Berlin. 

Marshall, A.G., Hendrickson, C.L., Shi, S.D.H. (2002) Scaling MS Plateaus with High-resolution FT-ICRMS. Anal. Chem. 74 253a-259a. 

Nikolaev, E.N., Boldin, I.A., Jertz, R., Baykut, G. (2011) Initial Experimental Characterization of a New Ultra-high Resolution FTICR Cell with Dynamic Harmonization. J. Am. Soc. Mass Spectrom. 22 1125-1133. 

Hunter, R.L., Mclver, R.T. (1996) Ultrahigh-resolution Fourier Transform Mass Spectrometry of Biomolecules Above m/z 5000. Int. J. Mass Spectrom. Ion Proc. 157 175-188. 

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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... 

Reasonable estimates of ultimate sensitivity and depth resolution in ERDA can hardly be given because of the large range of projectiles and energies (from He ions of several MeV up to 200-MeV Au ions), and the use of different detection systems. In addition, stability of the sample under irradiation (which, of course, depends on the target material) is also important in the discussion of sensitivity and detection limits. The sensitivity is mainly determined by the recoil cross-section, the solid an-... 

With the multitude of transducer possibilities in terms of electrode material, electrode number, and cell design, it becomes important to be able to evaluate the performance of an LCEC system in some consistent and meaningful maimer. Two frequently confused and misused terms for evaluation of LCEC systems are sensitivity and detection limit . Sensitivity refers to the ratio of output signal to input analyte amount generally expressed for LCEC as peak current per injected equivalents (nA/neq or nA/nmol). It can also be useful to define the sensitivity in terms of peak area per injected equivalents (coulombs/neq) so that the detector conversion efficiency is obvious. Sensitivity thus refers to the slope of the calibration curve. 

Sensitivity by itself is not sufficient to completely evaluate an LCEC system for analytical purposes. The minimum detectable quantity (detection limit) is of more practical importance. The detection limit takes into consideration the amount of baseline noise as well as the response to the analyte. The detection limit is then defined as the quantity of analyte which gives a signal-to-noise ratio of three (a S/N of 3 is the generally accepted criterion although other values have been used). For a complete description of an LCEC application, both the sensitivity and detection limit, along with the S/N criteria used, should be provided. 

Combined with the attractive performance of a Prussian blue-based hydrogen peroxide transducer, the proposed immobilization protocol provides elaboration of the most advantageous first-generation glucose biosensor concerning its sensitivity and detection limit. 

Flame AAS can be used to measure about 70 elements, with detection limits (in solution) ranging from several ppm down to a few ppb (and these can be enhanced for some elements by using a flameless source). Both sensitivity and detection limits (as defined fully in Section 13.4) are a function of flame temperature and alignment, etc. The precision of measurements (precision meaning reproducibility between repeat measurements) is of the order of 1-2% for flame AA, although it can be reduced to <0.5% with care. The accuracy is a complicated function of flame condition, calibration procedure, matching of standards to sample, etc. 

We have spoken frequently in this chapter about sensitivity and detection limit in reference to advantages and disadvantages of the various techniques. Sensitivity and detection limit have specific definitions in atomic absorption. Sensitivity is defined as the concentration of an element that will produce an absorption of 1% (absorptivity percent transmittance of 99%). It is the smallest concentration that can be determined with a reasonable degree of precision. Detection limit is the concentration that gives a readout level that is double the electrical noise level inherent in the baseline. It is a qualitative parameter in the sense that it is the minimum concentration that can be detected, but not precisely determined, like a blip that is barely seen compared to the electrical noise on the baseline. It would tell the analyst that the element is present, but not necessarily at a precisely determinable concentration level. A comparison of detection limits for several elements for the more popular techniques is given in Table 9.2. 

Because the sensitivity of NMR is the highest for protons compared to other nuclei, all examples of quantitation work described in this chapter are based on proton NMR data. The signals from other NMR active nuclei such as 19F or 13C may also be used for quantitation. The quantification of TFA using 19F NMR is a good example. However, except for 19F, the sensitivities and detection limits are usually compromised in these measurements because nuclei other than H and 19F typically have a lower natural abundance and a lower magnetogyric ratio. 

A major advantage of infrared absorption spectroscopy derives from the characteristic fingerprints associated with infrared-active molecules. On the other hand, interferences from common atmospheric components such as C02 and HzO are significant, so that the sensitivity and detection limits that can be obtained are useful primarily for polluted urban air situations. For atmospheric work, long optical path lengths are needed. 

The development of surface analytical techniques such as LA-ICP-MS, GDMS and SIMS focuses on improvements to sensitivity and detection limits in order to obtain precise and accurate analytical data. With respect to surface analytical investigations, an improvement of spatial and depth resolution is required, e.g., by the establishment of a near field effect or the apphcation of fs lasers in LA-ICP-MS. There is a need for the improvement of analytical techniques in the (j,m and nm range, in depth profiling analysis and especially in imaging mass spectrometry techniques to perform surface analyses faster and provide more accurate data on different materials to produce quantitative 3D elemental, isotopic and molecular distribution patterns of increased areas of interest with high spatial and depth resolution over an acceptable analysis time. 

A large part of the success of the combination of FI and atomic spectrometry is due to its ability to overcome interference effects. The implementation of some pretreatment chemistry in the FI format makes it possible to separate the species of the analyte from the unwanted matrix species e.g. by converting each sample into a mixture of analyte(s) and a standard background matrix, designed not to interfere in the atom formation process and/or subsequent interaction with radiation in the atom cell). Often such separation procedures result also in an increased analyte mass flux into the atom source with subsequent improvements in sensitivity and detection limits. 

The use of dual-electrode amperometric detectors provides advantages in sensitivity and detection limits. Series configuration and parallel configuration are both possible. Ion-selective electrodes allow the selective quantification of selected analytes even in complex matrices. 

Li, M., Alnouti, Y., Leverence, R., Bi, H., and Gusev, A. I. (2005a). Increase of the LC-MS/ MS sensitivity and detection limits using on-line sample preparation with large volume plasma injection. J. Chromatogr. B Anal. Technol. Biomed. Life Set 825 152-160. 

Atomic absorption flame is replaced by an electrically heated graphite tube into which sample is directly introduced. All of the analyte is atomized. This significantly enhances the sensitivity and detection limit. The general principle of this technique, otherwise, is same as flame-AA. 

Single element determination capability limited to fewer elements analysis time longer than flame the sensitivity and detection limits, however, are much greater than flame technique, and significantly better than ICP techniques. 

Multielement determination sensitivity and detection limits exceptionally good (over 100 times greater than furnace techniques for some metals) isotopes also may be measured also has the capability to determine nonmetals (at a much lower sensitivity) broad linear-working range high cost. 

The sensitivity and detection limits of an analytical technique are determined by the SNR of the measurement, an important metric for assessing both the instrumental performance and analytic limits of the spectral measurement. Following typical analytical practices, 3 and 10 times the noise have been suggested as limits of detection and of quantification for IR spectroscopy, respectively. The performance of interferometers in the continuous-scan mode, which is simpler compared with that of the step-scan mode, has been analyzed well. The SNR of a spectrum measured using a Michelson interferometer is given by12... 

The PAHBAH calibration curve is not linear over a wide range, but for small ranges appears linear (with slope changes). The range reported here was used for determination of sensitivity and detection limit. 

The concentration of analytes that can be measured in various materials has been decreasing over the years as sensitivity and detection limits of analytical techniques have improved. The method detection limit (MDL) is the order of magnitude of the smallest quantity or concentration of substance which can be detected in principle the limit of detection (LOD), on the contrary, is a precisely calculable statistical value for a particular, defined analytical procedure. The instrument detection limit (IDL) is the smallest signal above background noise that an instrument can detect reliably. It is expressed either as an absolute limit (in units of mass, eg, ng), or as a relative limit (in terms of concentration, eg, g mL 1). 

The multielement detection limits with the echelle/image dissector are comparable to, or better than, single element detection limits reported for a silicon vidicon and conventional optics. Detection limits for Cr, Cu, and Mn with the echelle/ image dissector compare favorably with single element data reported for a conventional atomic absorption instrument with a photomultiplier detector, but detection limits obtained here for Ni and Co are higher by factors of 10 or more than for the conventional instrument. The echelle/image dissector system should be adaptable to a so-called flameless atomizer and be subject to the same improvements in sensitivities and detection limits as conventional detector systems. 

Calcium. Calcium like barium is best determined by AAS, since flame emission suffers from background effects where other alkali metal are present. P CAM 173 does not recommend the use of nitrous oxide/acetylene instead of air/acetylene, although the former offers greater sensitivity and detection limit when 1000 ppm potassium is added to the standards and samples. The nitrous oxide/acetylene flame needs the potassium to minimize the ionization of Ca. 

To get the desired sensitivity and detection limit a long absorption path can be obtained by using a multi-pass White cell. The absorption line can be scanned in a fraction of a second and the response time of the measurement is normally limited by the residence time of the sampled gas in the White cell which is typically a few seconds. 

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