Sampling sensitivity

Mass Spectrometry. The mass spectra were obtained on a CEC 21-llOB mass spectrometer with the batch inlet system maintained at 250°C to assure complete vaporization of the samples. Sensitivity factors for quantitative analysis were obtained from standards of di-, tetra-, hexa-, and octa-chlorodibenzo-p-dioxin. The factors for the intermediate chlorinated species were estimated by interpolation. The analyses were based... 

Headspace analysis involves examination of the vapours derived from a sample by warming in a pressurized partially filled and sealed container. After equilibration under controlled conditions, the proportions of volatile sample components in the vapours of the headspace are representative of those in the bulk sample. The system, which is usually automated to ensure satisfactory reproducibility, consists of a thermostatically heated compartment in which batches of samples can be equilibrated, and a means of introducing small volumes of the headspace vapours under positive pressure into the carrier-gas stream for injection into the chromatograph (Figure 4.25). The technique is particularly useful for samples that are mixtures of volatile and non-volatile components such as residual monomers in polymers, flavours and perfumes, and solvents or alcohol in blood samples. Sensitivity can be improved by combining headspace analysis with thermal desorption whereby the sample vapours are first passed through an adsorption tube to pre-concentrate them prior to analysis. 

Currently a balance seems to have been reached in the use of the various techniques for the determination of metals at trace levels. In its modern form AAS remains important and competitive where small ranges of elements need to be determined in samples. Sensitivities obtainable by flame AAS are often similar to those for ICP-AES and where graphite furnace volatilization is used they are not infrequently superior (Table 8.4). 

In order for mass spectrometry to be used as an effective tool in LC, the analyte must be ionized in the interface region (source) since MS can only detect charged species. Consequently, the role of the ionization source is twofold (1) it is responsible for interfacing the chromatographic instrument with the detector and (2) it provides an effective and efficient means for sample ionization. It should be pointed out that source ionization efficiency plays a significant role in sample sensitivity for LC-MS analysis. The application of LC is ideally... 

The Bruceton test affords a fairly good estimate of the 10, 50 and 90% firing points for minimum trials, but depends heavily on the assumption that the sample sensitivity follows a normal distribution about the median firing height... 

Impact Sensitivity. PicArsn app, 2-kg wt 9n with 24mg sample 10" with 12mg sample Sensitivity to Initiation. 0.30g Pb Azide min detonating charge... 

Iman, R.L. and Conover, W.J. (1980). Small sample sensitivity analysis techniques for computer models, with an application to risk assessment. Communications in Statistics A—Theory and Methods, 9, 1749-1842. 

When spectroscopy with polarized light or other optical polarization measurements are performed the studied sample becomes one element of the optical train which transmits the beam from the radiation source to the detector. Four optical phenomena might take place in a sample sensitive to polarized radiation. We list them below together with their physical definition ... 

There are several important characteristics of a good detector sensitivity, dynamic range, stability, and for specific ones selectivity. Sensitivity should be in fact characterized by two parameters the ratio of the detector response to the amount of sample (sensitivity slope) and the minimum detectable level of a given compound (commonly measured for a signal to noise ratio of 3). The dynamic range is the range... 

Concentration detection limits in CE-MS with the ESI interface are similar to those with UV detection. Sample sensitivity can be improved by using ion-trapping or time-of-flight (TOE) mass spectrometers. MS analysis can also be performed off-line, after appropriate sample collection, using plasma desorption-mass spectrometry (PD-MS) or matrix-assisted laser desorption-mass spectrometry (MALDI-MS). 

LC/MS of the isolated impurity indicated the presence of two peaks, corresponding to a dimer-like degradant and the parent drug. A full set of NMR experiments was performed to elucidate the structure. Despite having an adequate amount of sample, sensitivity was limited by low solubility. Deuterium oxide as the solvent eliminated the ability to detect exchangeable protons, although this was not deemed to be a significant limitation for this structural elucidation. The NMR analysis confirmed that there were two primary components present in a ratio of approximately 2.5 to 1,... 

Bayne et al. developed a gas chromatographic-mass spectrometric method for the determination of scopolamine in plasma and urine samples - sensitive to 50 pg/ml for a 4 ml sample. 

Lucker et al. (2004) evaluated the ability of GC-MS using several brain-specific fatty acids to identify and quantify CNS tissue in meat products. The researchers determined specific fatty acid content of brains from cattle, calves, sheep, pigs, turkeys, as well as muscle and adipose tissue. They determined that species and age characterizations could be made based on the concentration of specific fatty acids present in a sample. Sensitivity of GC-MS CNS tissue detection was reported to be 0.01% raw weight, but the practical sensitivity was 0.1-0.5% raw weight CNS due to the fatty acid baseline content in muscle and adipose tissue. 

Unlike fully quantitative methods that utilize the reference standard curve to estimate the analyte levels in the study samples, sensitivity of ADA assays perse is not a critical validation characteristic. This is because, for the reasons described in Section 8.2, the screening, confirmation, and characterization of ADA-positive samples are based on the assay response unit rather than the ADA concentration levels. In addition,... 

Advantages Most forms of chemical analysis require vaporization, dissolution, or alteration of the analyzed sample in some way. Neutron activation analysis is a nondestructive process that can be used to study liquid, solid, or gaseous samples. Sensitive items, such as forensic evidence, meteorites, or artifacts, can be analyzed without harm. 

The behaviour of the power transmission, reflection and sample sensitivity as a function of the cavity coupling k is plotted in Figure 2.10. 

The peak absorption coefficient of OCS, 10 m", occurs at 462 GHz. This is by no means, however, the optimum working frequency due to the non-ideal behaviour of most MMW detectors. Commercial Schottky barrier mixer diode detectors show a quadratic roll-off in sensitivity at frequencies >100 GHz. If this is factored into Equation 6.1, the peak sample sensitivity occurs around 300 GHz, and the response is so flat that even at 100 GHz it has only fallen off by a factor of two. What is common to both curves is the dramatic fall-off in sample sensitivity at frequencies <100 GHz, reinforcing the point that the band 26-40 GHz is ill suited to high-sensitivity analytical spectroscopy. 

Figure 6.1 Peak absorption coefficient A and sample sensitivity B for OCS Plotted vs. frequency. B = 0.202 cmT at 300 K kT 200 cmT ...

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