Sensitivity measurement procedure

The measuring procedure used must be appropriate to the chemical agent to be measured, its limit value, and the wotkplace atmosphere so that the results show the concentration of the agent in the same terms as the limit value. Also, the limits of detection, sensitivity, and precision of the measuring procedure must be appropriate to the limit value. 

Shipping analysis is an extremely sensitive electrochemical technique for measuring trace metals (19,20). Its remarkable sensitivity is attributed to the combination of an effective preconcentration step with advanced measurement procedures that generate an extremely favorable signal-to-background ratio. Since the metals are preconcentrated into the electrode by factors of 100 to 1000, detection limits are lowered by 2 to 3 orders of magnitude compared to solution-phase voltammetric measurements. Hence, four to six metals can be measured simultaneously in various matrices at concentration levels down to 10 10 i. utilizing relatively inexpensive... 

Sensitive analytic procedures enable detection and measurement of very low tracer levels. In tracer studies, an identifiable tracer material is injected through one or more injection wells into the reservoir being studied. Water or other fluid is then injected to push the tracer to one or more recovery wells in the reservoir. The output of the recovery wells is monitored to determine tracer breakthrough and flow through the recovery wells. Analysis of the breakthrough times and the flows yields important information regarding how to perform the secondary or enhanced recovery processes. 

The detection limits, accuracy, and precision of any analytical methodology, as well as the composition of the sample medium, are important parameters in determining the appropriateness of a method to quantify a specific analyte at the desired level of sensitivity within a particular matrix. The lower limit of detection (LLD) has been adopted to refer to the intrinsic detection capability of a measurement procedure (sampling... 

With the maturation of tandem mass spectrometry (MS/MS) instruments and methodologies, many commercial laboratories are switching to this technique, and high-sensitivity measurements on high volumes of samples are becoming routinely achieved. Since the future of steroid hormone analysis is MS/MS, only MS techniques will be described in this chapter. Immunoassay procedures have been well described and reviewed over the years and will cease to be mainstream methodologies within the next decade. 

The fact that twelve molybdate ions are bound to each phosphate unit in molybdophosphate has been exploited as an amplifying factor. The molybdophosphoric acid is extracted from the original solution into a mixture of diethyl ether or chloroform with butanol, in order to eliminate the excess of molybdate reagent it is then re-extracted into an aqueous phase and broken down with alkali. The molybdate ions are reacted with ammonium rhodanide90 or aminochlorobenzenethiol76 to give coloured products with absorption maxima at 470 and 710 nm, respectively. One phosphate ion thus yields twelve molybdate units, the optical absorbance is amplified with respect to that of the heteropoly phosphate complex and its measurement provides a sensitive determination procedure. 

The most straightforward way to measure the effect of low temperatures on recovery is by means of a compression set or tension set test. Tests in compression are favoured and a method has been standardised internationally. The procedure is essentially the same as set measurements at normal or elevated temperatures and has been discussed in Chapter 10, Section 3.1. As the recovery of the rubber becomes more sluggish with reduction of temperature the dynamic loss tangent becomes larger and the resilience lower (see Chapter 9), and these parameters are sensitive measures of the effects of low temperatures. Procedures have not been standardized, but rebound resilience tests are inherently simple and quite commonly carried out as a function of temperature. It is found that resilience becomes a minimum when the rubber is in its most leathery state and rises again as the rubber becomes hard and brittle. 

A typical CC-measurement procedure (for a pH-sensitive LAPS structure) is depicted in Fig. 6.3. From the raw data material of the CC-mode measurement of all measurement spots under the pH-sensitive layer, a calibration plot can be derived. For example, for the above example, an average pH sensitivity of 54.2 mV/pH with a standard deviation of 0.5 mV/pH between the different measurement spots can be calculated. This initial calibration measurement allows furthermore the determination of different measurement parameters, e.g., the hysterisis, overall drift, stability, selectivity and the influence of external disturbances such as light and temperature. These parameters are important to evaluate the performance of the complete LAPS-based measurement system. 

Figure 6.4a shows typical CC-mode data of the measurement procedure. For a constant pH value at pH 3, only a small deviation is observable, due to slightly different pH adjustments, when using different Cd2+-ion concentrations. The calibration plots in Fig. 6.4b clarify, therefore, a good sensitivity towards Cd2+ in the cadmium-sensitive part of the LAPS with a slope, in this example, of about 27 mV/decade, whereas the pH-sensitive area of the LAPS is not influenced by the different Cd2+-ion concentrations. For more details concerning the pH-and cadmium-sensitive behaviour of the LAPS sensor, see elsewhere [10-12],... 

According to ISO/IEC 17025, validation is confirmation by the examination and provision of objective evidence that the particular requirements for a specific intended use are fulfilled. Performance parameters can be divided into two groups. The first group refers to the properties of the measurement procedure detection limit and determination limit, working range, linearity, and sensitivity. The second group covers the properties of the results obtained with this particular measurement procedure, that is, traceability and uncertainty (including recovery, robustness, precision, and accuracy).9... 

A number of companies supply reagent or spectroquality solvents that have been purified to remove UV-absorbing impurities. Some of them, particularly dimethyl sulfoxide, may be suitable for general electrochemical use as purchased. However, small quantities of electroactive impurities (particularly water) often are present in spectroquality solvents. Therefore, a particular batch of solvent always should be tested by measurement of the residual current with an appropriate supporting electrolyte and a platinum, gold, or carbon electrode (to test the anodic limits) and a platinum electrode (to test the cathodic limits). The voltage window or domain of electroactivity is a sensitive measure of the adequacy of the purification procedures. 

Several vapor pressure osmometers are now commercially available. Although they are mainly used for determining number-average molecular weights in aqueous and organic solvents, they can also be employed to evaluate the total osmolality of biological solutions or dissociation and activity coefficients. Each model has its own technical characteristics. However, all are comparable in terms of general measurement procedure and sensitivity. 

The standard measurement procedure for odor determination (VDI, 1994) is called olfactometry. It uses the human olfactory sense (Gostelow et al, 2001) for the determination of odor qualities. The human nose is an extremely sensitive odor detector and is used in subjective and objective sensory measurements. The latter expresses the strength of odor in terms of the number of dilutions of odor-free air required to reduce the sample odor to threshold concentration (Gostelow et al, 2001). The threshold concentration is reached when the human nose can just smell the odorous substance. Because every nose has different sensitivity, the standard test procedure involves four people at the same time. Prior to olfactory... 

Measurement procedures using solutions in standard cuvettes are well developed. Some condensed phase samples such as large crystals and polymer films are relatively robust and easily mounted. Two areas of interest which have led to innovation are in the mounting of small, enviromnentally sensitive, single crystals and in the sample cells used for frozen glasses, particularly those having a substantial aqueous phase, such as proteins. 

With proper safety procedures, radiation can be very useful in many scientific experiments. Neutron activation analysis is used to detect trace amounts of elements present in a sample. Computer chip manufacturers use this technique to analyze the composition of highly purified silicon wafers. In the process, the sample is bombarded with a beam of neutrons from a radioactive source, causing some of the atoms in the sample to become radioactive. The type of radiation emitted by the sample is used to determine the types and quantities of elements present. Neutron activation analysis is a very sensitive measurement technique capable of detecting quantities of less than 1 X 10 9 g. 

These systems had already proved suitable for routine use. However, their disadvantage was, that the measuring procedure was relatively slow and that all spots on the track surpassing the peak sensitivity value were registered. The easily accessible and very clearly designed software worked out by Ebel, Hocke and Kaal, however, allowed the user to make improvements 34,35). 

Validation of measurement methods has been used for a very long time in chemistry. It is mostly based on the examination of a measurement procedure for its characteristics such as precision, accuracy, selectivity, sensitivity, repeatability, reproducibility, detection limit, quantification limit and more. 

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