Sensitivity, loss

It seems that the broadband HMBC is more effective for small molecules, as emphasized by Equations (24)-(26). For cyclosporine, indeed, as shown by Figures 15 and 16, there is no advantage in recording broadband and wZfra-broadband HMBC as compared to standard optimized HMBC schemes. On the contrary, the ultra-broadband HMBC spectrum shown in Figure 16 does not exhibit more cross-peaks than the standard HMBC (Figure 15A), and there is besides a severe sensitivity loss. 

The following additional, even more important, requirements are put on background correction, namely there should be no analytical sensitivity loss... 

Thus, the magnetization is transferred from the amide proton to the attached nitrogen and then simultaneously to the intra- and interresidual 13C spins and sequential 13C spin. The 13C chemical shift is labelled during /, and 13C frequency during t2. The desired coherence is transferred back to the amide proton in the identical but reverse coherence transfer pathway. The 15N chemical shift is frequency labelled during t3, and implemented into the 13C 15N back-INEPT step. The sensitivity of the HNCOmCA-TROSY experiment is excellent and nearly similar to HNCA-TROSY except for the inherent sensitivity loss by a factor of /2, arising from additional quadrature detection needed for 13C frequency discrimination in the fourth dimension. The excellent sensitivity is due to a very efficient coherence transfer pathway,... 

As in the case of the HN(CO)CA-TROSY scheme, the HN(CO)CANH-TROSY experiment can be readily expanded to a four-dimensional HN(CO)CANH-TROSY experiment without increasing the overall length of the pulse sequence. This can be accomplished by labelling the 13C (f) chemical shift during additional incremented time delay, implemented into the 13C — 13C INEPT delay. As a result, a well-dispersed 13C (i- 1), 13C (i- 1), 15N(i), Hn(0 correlation map is obtained with minimal resonance overlap albeit with the inherent sensitivity loss by a factor of y/2. 

The order in which various NMR data are acquired is largely one of user preference. Acquisition of the proton reference spectrum will invariably be undertaken first. Whether a user next seeks to establish homo- or heteronuclear shift correlations is where individual preferences come into play. Many spectro-scopists proceed from the proton reference spectrum to either a COSY or a TOCS Y spectrum next, while others may prefer to establish direct proton-carbon chemical shift correlations. This author s preference is for the latter approach. From a multiplicity-edited HSQC spectrum you obtain not only the carbon chemical shifts, which give an indication of the location of heteroatoms, the degree of unsaturation and the like, but also the number of directly attached protons, which eliminates the need for the acquisition of a DEPT spectrum [51, 52]. The statement in the prior sentence presupposes, of course, that there the sensitivity losses associated with the acquisition of multiplicity-edited HSQC data are tolerable. 

Tune the probe to one sample and then use an adapted 90° pulse for other solvents where the tuning is not optimal. This, of course, also leads to sensitivity losses. 

The literature is rather vague concerning the question of what happens to the sensitivity of a sensor when it is implanted in a biological fluid. In our hands, subcutaneous sensors immediately and rapidly lose sensitivity, a process that takes place in minutes. Despite losses in sensitivity of 10-30%, these sensors will function satisfactorily over periods in excess of 4 days. Indeed, the performance of the sensor frequently improves with time. The origin of this sensitivity loss has been studied in detail and some results are shown in Figure 1.5.55 If the sensor is removed from the tissue and quickly calibrated in buffer solution (10 min), essentially the same in vitro sensitivity is obtained as for the in vivo value. Further incubation in buffer causes the sensitivity to rise until eventually the original in vitro value is obtained. The important... 

Reaction cells appear to be a much better way to reduce signals due to Ar-containing molecular ions and Ar+ itself than the use of cold plasma conditions. Because normal plasma conditions are used, elements with high ionization energies, such as Se and As, do not suffer from sensitivity losses, unlike cold plasma conditions. The severe chemical matrix effects that are typical of cold plasma conditions are prevented. The first commercial ICP-MS instrument to use this concept was introduced by Micromass UK Ltd. However, as noted, reaction product ions must be controlled or removed to prevent other (new) spectral overlaps. 

Acetylcholineesterase The aqueous fermentation solution containing cholineesterase (90-100 mg/mL) was added to nitro-cellulose in butyl acetate (30 mg/mL). From 1 to 5pL of the mixture was spotted onto a small area of FET and dried in the air. The FET was treated with 5% of glutaraldehyde for 5-10 min, washed with lOmM borate buffer (pH 9.18) for 15 min, dried and stored at 4°C. Acetylcholine iodide was studied in 15 mM NaCl and 13 mM borate buffer of pH 9-10. Detection limit for acetylcholine was 40 pM. Sensitivity losses was < 40% over 20 days. [107]... 

When one deals with complex mixtures, it is often advantageous to simplify their spectra to parent peaks either by the use of low-voltage technology (2,9,10) or field ionization (11). This simplification results in additional difficulties because of the inherent loss of sensitivity. In some cases sensitivity loss can be compensated for by charging large amounts of sample, up to 10-20 mg. 

The direct determination of some major elements (Ca, K, Mg, Na, and P) and Zn by ICP-AES was performed in powdered milk [14]. Samples were diluted with a 5 or 10 percent (v/v) water-soluble, mixed tertiary amine reagent at pH 8. This reagent mixture dissociated casein micelles and stabilized liquid phase cations. No decrease in analyte emission intensities was observed. Reference solutions were prepared in 10 percent (v/v) mixed amine solution, and no internal reference element was needed for ICP-AES. The direct technique is as fast as slurry approaches, without particle size effects or sensitivity losses. 

USEBLASTING - Not suitable due to the volatility of the fuel sensitizer. Could be used if the volatile nature were taken into account and steps taken to counter act this fuel sensitizer loss due to evaporation. A powerful higher velocity explosive as opposed to AN-fuel oil explosives. Also cost effective due to the ready access and low cost of the sensitizer. 

In aqueous matrices, most compounds have quite small values (< 0.25), so the headspace has a low analyte trapping capacity. As a result, the sensitivity of headspace SPME is almost the same as that of direct SPME. The sensitivity loss is only significant when the target analytes partition well into the headspace (i.e. when they possess large... 

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