Sample consumption

Sample consumption is chiefly determined by the concentration of the analyte solution and the liquid flow. Por example, during a 2.5-min measurement conventional ESI consumes 10 pmol when a lO M solution at a flow rate of 4 pi min is employed. For nanoESI this reduces to 100 fmol for the same solution at 40 nl min  

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Screening of process conditions was one driver for performing polyethylene synthesis [1]. Thus, test-throughput frequency, the number of possible samples per day, is a target value. Also, flexibility with regard to temperature and pressure at low sample consumption is a major issue. In addition to fastness and flexibility, the quality of the information and the insight obtained is seen as a motivation for micro-channel studies. 

These estimates, though approximate, established that — excluding sample consumption for testing — the yield could not have been less than 20% and perhaps as much as 50%. Since another 10 pg of hementin were known to have been lost into the filtrate of the initial ultrafiltration and another 5 to 10 pg into IEC peaks II and III, no less than 40% and up to 80% of the material was accounted for. 

Application to solid polymer/additive formulations is restricted, for obvious reasons. SS-ETV-ICP-MS (cup-in-tube) has been used for the simultaneous determination of four elements (Co, Mn, P and Ti) with very different furnace characteristics in mg-size PET samples [413]. The results were compared to ICP-AES (after sample dissolution) and XRF. Table 8.66 shows the very good agreement between the various analytical approaches. The advantage of directly introducing the solid sample in an ETV device is also clearly shown by the fact that the detection limit is even better than that reported for ICP-HRMS. The technique also enables speciation of Sb in PET, and the determination of various sulfur species in aramide fibres. ETV offers some advantages over the well-established specific sulfur analysers very low sample consumption the possibility of using an aqueous standard for calibration and the flexibility to carry out the determination of other analytes. The method cannot be considered as very economic. 

Capillary electrophoresis has also been combined with other analytical methods like mass spectrometry, NMR, Raman, and infrared spectroscopy in order to combine the separation speed, high resolving power and minimum sample consumption of capillary electrophoresis with the selectivity and structural information provided by the other techniques [6]. 

Flow injection analysis can be used to speed up the preconcentration process and reduce sample consumption. 

In recent years, rapid advancements in photonic technologies have significantly enhanced the photonic bio/chemical sensor performance, especially in the areas of (1) interaction between the light and analyte, (2) device miniaturization and multiplexing, and (3) fluidic design and integration. This has led to drastic improvements in sensor sensitivity, enhanced detection limit, advanced fluidic handling capability, lower sample consumption, faster detection time, and lower overall detection cost per measurement. 

When a pharmaceutical is in the early stages of drug development (e.g., preclinical phases), the amount of material is limited and little is known about the characteristics of the molecule. Thus, CE is an attractive technique for developmental work due to its low sample consumption. Multiple injections can be made from a few microliters of sample, thus allowing optimization and early qualification of methods. 

Note In MALDI-MS, the combination of the actual analyte and the procedure of sample preparation represent the true limiting factors for sample consumption and detection limit. 

Example The reduced sample consumption of nanoESI allows for the sequencing of the peptides (Chap. 9.4.7) obtained by tryptic digestion of only 800 fmol of the protein bovine semm albumin (BSA, Fig. 11.6). [66] The experiment depicted below requires each of the BSA-derived peptide ions in the full scan spectrum to be subjected to fragment ion analysis by means of CID-MS/MS on a triple quadrupole instmment (Chaps. 2.12 and 4.4.5). 

Note Besides its low sample consumption, nanoESI is free of memory effects because each sample is supplied in a fresh capillary by means of disposable micropipettes. Furthermore, the narrow exits of nanoESI capillaries prevent air-sensitive samples from rapid decomposition. 

Several advantages offered by CE, such as a high efficiency, rapid method development, simple instrumentation, and low sample consumption, are the main reasons for its success in a variety of fields. UV-VIS spectrophotometry is probably the most widely used detection technique with CE because of the simplicity of the on-line configuration. However, its sensitivity, directly related to the optical path length afforded by the I.D. of capillaries, which is in the micrometer range, is low, and it remains the major bottleneck of this technique (see... 

Either the information obtained during the data-dependent acquisition is sufficient or a fraction of interest can be re-analyzed by chip-based infusion at a flow rate ca. 200 nl min. Due to the miniaturization sample consumption is very low (typically 1-3 pi) and acquisition time is no longer critical. Therefore various MS experiments can be performed on various instruments, including MS and accurate mass measurements. An additional advantage is that the eluent can be removed and the infusion solvent can be optimized for positive or negative ion detection or for deuterium exchange measurements. 

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