Limits to Sensitivity

The general application of LEI spectrometry to the determination of trace metals has been somewhat limited but progress in this area should continue. Alloy analyses are particularly amenable to LEI spectrometry because of the absence of an ionizable sample matrix. Indium (303.9 nm) has been determined in a nickel-based high temperature alloy31. Atomic absorption spectrometry of this sample requires time-consuming extraction procedures to remove concomitant metals which contribute to spectral interferences. After dissolution of the alloy sample with acids, the concentration of indium was determined to be 35 pg/g by LEI spectrometry. 

This agreed within experimental error with a value of 37 pg/g obtained with a graphite furnace. Manganese was also determined in a National Bureau of Standards (NBS) Standard Reference Material (SRM) No. 1261 steel sample to within 0.66% of the certified value 31). 

Rubidium has been determined in pine needles (SRM 1575) to demonstrate the resistance to interferences of the immersed electrode with CW laser excitation38). The concentration of matrix components such as calcium and potassium were on the order of 40 pg/ml. The measured rubidium concentration of 11.1 pg/g agreed well with the certified value. 

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Polymethine and Related Dyes. Cyanine dyes (qv) (46) aie the best known polymethine dyes. Nowadays, thek commeicial use is limited to sensitizing dyes for sdvei halide photogiaphy. However, derivatives of cyanine dyes provide important dyes for polyacrylonitrile. 

It is important to note in this regard that there are practical limits to sensitivity. For example, an electron-beam resist with a sensitivity greater than 10-8 C/cm2 might well undergo thermal reactions at room temperature and would consequently be unsatisfactory because of an unacceptably short shelf-life of both the resist solution and spun films. The lower limit of sensitivity is governed by throughput considerations. Figure 4 illustrates the sensitivity... 

A strong inhibitor is one that causes a >fivefold increase in the plasma AUC values or more than 80% decrease in clearance of CYP substrates (not limited to sensitive CYP substrate) in clinical evaluations... 

Sensitivity is the measure of the smallest amount that can be reliably measured. An instrument that can measure microgram (0.000001 g) quantities is much more sensitive than one that can only measure milligrams (0.001 g). Precision is thus an important limit to sensitivity. If the uncertainty, or imprecision, of a measurement is 0.0005 g, then the instrument is incapable of reliable microgram (0.000001 g) measurements, but can easily measure milligram (0.001 g) quantities. 

Homonuclear correlation of signals using scalar homonuclear 3j and/or coupling. The experiment is limited to sensitive nuclei with high natural abundance. The ID analogous experiment of the 2D COSY experiment. 

The extension of their previously developed low temperature method to an 18.8 T system has been described by Lipton et al. A new probe was used with a cross coil and variable capacitors that are operational at cryogenic temperatures. The limitations to sensitivity are discussed, including a new diode network, the utilisation of a cryogenic band pass filter, and the consequences of the RF profiles of the coil. Further, details of the spectroscopy of quadrupolar nuclei in a protein are discussed, such as the observation of the outer transitions and how to distinguish them from the desired 1/2 transition. 

The effects of pressure are especially sensitive at high temperatures. The analytical expression [4.71] given by the API is limited to reduced temperatures less than 0.8. Its average error is about 5%. 

The first of them to determine the LMA quantitatively and the second - the LF qualitatively Of course, limit of sensitivity of the LF channel depends on the rope type and on its state very close because the LF are detected by signal pulses exceeding over a noise level. The level is less for new ropes (especially for the locked coil ropes) than for multi-strand ropes used (especially for the ropes corroded). Even if a skilled and experienced operator interprets a record, this cannot exclude possible errors completely because of the evaluation subjectivity. Moreover it takes a lot of time for the interpretation. Some of flaw detector producers understand the problem and are intended to develop new instruments using data processing by a computer [6]. 

The INTROS Flaw Detector is able to inspect ropes moving through the magnetic head at speed 0...2 m/s. Limit of sensitivity to wire brake is 1% of the rope meatallic cross-section area, the LMA measure accuracy is not less than 2%. 

Scale of Operation The scale of operation for precipitation gravimetry is governed by the sensitivity of the balance and the availability of sample. To achieve an accuracy of 0.1% using an analytical balance with a sensitivity of 0.1 mg, the precipitate must weigh at least 100 mg. As a consequence, precipitation gravimetry is usually limited to major or minor analytes, and macro or meso samples (see Figure 3.6 in Chapter 3). The analysis of trace level analytes or micro samples usually requires a microanalytical balance. 

It might be thought that the small number of molecules in a typical supersonic jet or beam would seriously limit the sensitivity of observation of the spectra. Flowever, the severe rotational cooling which may be produced results in a collapsing of the overall intensity of a band into many fewer rotational transitions. Vibrational cooling, which greatly increases the population of the zero-point level, concentrates the intensity in few vibrational transitions, and these two effects tend to compensate for the small number of molecules. 

Thiosulfate titration of iodine is limited to an iodine concentration of 7.5 fig/mL (69). The use of organic solvents such as benzene, toluene, chloroform, and carbon tetrachloride as indicators in the titration of iodine have been proposed (70—72). These procedures increase the sensitivity of the titration so that 6.0 fig/mL of iodine can be detected, although a sensitivity of 2 fig/mL has been claimed (73). 

A more economical route to MQ resin uses low cost sodium sihcate and trimethylchlorosilane as inputs (eq. 35) (395). The sodium sihcate process is initiated by acidifying an aqueous sodium sihcate solution to a pH of 2. The resulting hydrosol quickly builds molecular weight. The rate of this increase is moderated by the addition of an alcohol such as 2-propanol. The hydrosol is subsequentiy silylated by the addition of trimethylchlorosilane. This process, which is kinetically sensitive and limited to synthesizing M/Q ratios of 1 or less, is preferred when MQ resins having high (>1%) OH content are required (395). 

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