Mass detection

Electrothermal vaporization can be used for 5-100 )iL sample solution volumes or for small amounts of some solids. A graphite furnace similar to those used for graphite-furnace atomic absorption spectrometry can be used to vaporize the sample. Other devices including boats, ribbons, rods, and filaments, also can be used. The chosen device is heated in a series of steps to temperatures as high as 3000 K to produce a dry vapor and an aerosol, which are transported into the center of the plasma. A transient signal is produced due to matrix and element-dependent volatilization, so the detection system must be capable of time resolution better than 0.25 s. Concentration detection limits are typically 1-2 orders of magnitude better than those obtained via nebulization. Mass detection limits are typically in the range of tens of pg to ng, with a precision of 10% to 15%. 

Fig. 3.20. Schematic d rawi ng of a Mattauch-Herzog magnetic-sector instrument with simultaneous mass detection.

FIGURE 16.23 Inulln isolated from small (—). medium ( ) and large (A) tubers separated on P-6 (140 X 1.5 cm) flow rate 0.33 ml/min eluenf. H20(dest) + 0.002% NaNa mass detection Waters 403 R differential refractive index detector, sensitivity 8X applied sample solution volume I ml of a 20-mg/ml aqueous inulin solution. 

TOP (Section 12.4) Time-of flight mass spectrometry a sensitive method of mass detection accurate to about 3 ppm. 

High mass detectability (zeptomole range) ultramicroanalysis... 

Waters Corp., Polyolefin Additives Determination with UV and Mass Detection, (Integrity System Publications), Waters Corp., Milford, MA (n.d.)... 

Method3 Mass detection limit (moles) Concentration detection limit (molar)b Characteristics... 

Fluorescence detection can be up to four orders of magnitude more sensitive than UV absorbance, especially where laser induced excitation is used, mass detection limits being as low as 10-20—10 21 mole. Pre- and post-column derivatization methods are being developed to extend the applicability of fluorescence detection to non-fluorescent substances. Several types of electrochemical and mass spectrometric detector have also been designed. Detector characteristics are summarized in Table 4.21. 

Mass detection limit Concentration detection Advantages/disadvantages... 

Gupta, A. Akin, D. Bashir, R., Single vims particle mass detection using microresonators with nanoscale thickness, Appl. Pkys. Lett. 2004, 84, 1976 1978... 

The circles in Fig. 16.6a show the calculated sensitivity, AX/Am for these different cases. As can be seen, the innermost holes are the most sensitive to any refractive index changes in the local environment as opposed to the holes that are further away from the cavity. These results can be explained by noting that the evanescent field is largest inside the innermost holes and decreases inside holes that are situated further away from the cavity. This is important to note because targeting only the inner most holes for functionalization allows for the lowest possible limit of mass detection for this device. In the case where only the inner two holes are functionalized we find that the resonance shifts by 3.5 nm when 1 fg of DNA binds to the resonator. Therefore, a mass change of 10 ag would result in a mass surface density of 0.84 ng cm 2 and an approximate shift of 0.01 nm, which can be experimentally detected. We therefore take this as the potential LOD of the device. 

The recovery of M2D-C3-0-(E0)n-CH3 after exposure to various solid media has been investigated by API-MS, high performance liquid chromatography light scattering mass detection (HPLC-LSD) and HPLC-APCI-MS methods [10]. Recoveries with extraction immediately following application were determined (surfactant concentration 0.1%, surfactant/solid lOmgg-1) with complete recoveries obtained on all media other than the clays illite and montmorillonite (Table 5.5.2) [10]. 

In a further application of MI-SPE, theophylline could be separated from the structurally related caffeine by combining the specific extraction with pulsed elution, resulting in sharp baseline-separated peaks, which on the other hand was not possible when a theophylline imprinted polymer was used as stationary phase for HPLC. A detection limit of 120 ng mb1 was obtained, corresponding to a mass detection limit of only 2.4 ng [45]. This combination of techniques was also used for the determination of nicotine in tobacco. Nicotine is the main alkaloid in tobacco and is the focus of intensive HPLC or GC analyses due to its health risk to active and passive consumers. However, HPLC- and GC-techniques are time-consuming as well as expensive, due to the necessary pre-purification steps required because the sample matrices typically contain many other organic compounds besides nicotine. However, a simple pre-concentration step based on MI-SPE did allow faster determination of nicotine in tobacco samples. Mullett et al. obtained a detection limit of 1.8 jig ml 1 and a mass detection limit of 8.45 ng [95]. All these examples demonstrate the high potential of MI-SPE to become a broadly applicable sample pre-purification tool. 

Utilization of capillary columns in conjunction with micro ESI devices is becoming a new trend in the field of LC/MS. Capillary HPLC has become a particularly important technique in situations where the supply of analyte is limited, such as in proteomic analysis. According to studies conducted by Smith et al., only one in a hundred thousand of analyte molecules present in solution eventually reach mass detection in a conventional ESI interface. Smith et al. attributed this poor electrospray... 

FIGURE 13 An HPLC report using mass detection and chemical structure libraries. 

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