Sample loading systems

The simplest of the portable modifications is a lightweight version of the original machine in which the hydrauhc loading system is replaced by a spring. This machine stiU requires a sample be cut from large pieces for testing. 

Fast chromatography involves the use of narrow-bore columns (typically 0.1-mm i.d.) that will require higher inlet pressures compared with the conventional wide-bore capillary columns. These columns require detectors and computing systems capable of fast data acquisition. The main disadvantage is a much-reduced sample loading capacity. Advances in GC column technology, along with many of the GC-related techniques discussed below, were recently reviewed by Eiceman et... 

Applications Van der Maeden et al. [646] first used GE-HPLC for the qualitative and quantitative analysis of oligomeric mixtures, such as low-MW resins (epoxy up to 16-mer, o-cresol novolak up to 16-mer, p-cresol novolak up to 13-mer), prepolymers (poly-(2,6-diphenyl-p-phenylene oxide) up to 20-mer), PET (up to 14-mer) and ethoxylated octaphenol surfactants (up to 19-mer). In many GE-HPLC separations of oligomeric mixtures, a compromise has to be found between sample loading, injection volume and compatibility of the sample solvent and the initial phase system. Therefore,... 

DP-MS suffers from system saturation sample loads of a few ig are to be used. DP-ToFMS equipped with El and FI sources is a thermal separation technique for solids which allows exact mass determination (Section 6.3.3). In order to detect and characterise polymer fragments of higher molecular weight, techniques such as DCI, in which the sample is thermally desorbed by the filament on which it is directly deposited, and laser desorption... 

For the analysis of nonvolatile compounds, on-line coupled microcolumn SEC-PyGC has been described [979]. Alternatively, on-line p,SEC coupled to a conventional-size LC system can be used for separation and quantitative determination of compounds, in which volatility may not allow analysis via capillary GC [976]. An automated SEC-gradient HPLC flow system for polymer analysis has been developed [980]. The high sample loading capacity available in SEC makes it an attractive technique for intermediate sample cleanup [981] prior to a more sensitive RPLC technique. Hence, this intermediate step is especially interesting for experimental purposes whenever polymer matrix interference cannot be separated from the peak of interest. Coupling of SEC to RPLC is expected to benefit from the miniaturised approach in the first dimension (no broadening). Development of the first separation step in SEC-HPLC is usually quite short, unless problems are encountered with sample/column compatibility. 

In ICP-AES and ICP-MS, sample mineralisation is the Achilles heel. Sample introduction systems for ICP-AES are numerous gas-phase introduction, pneumatic nebulisation (PN), direct-injection nebulisation (DIN), thermal spray, ultrasonic nebulisation (USN), electrothermal vaporisation (ETV) (furnace, cup, filament), hydride generation, electroerosion, laser ablation and direct sample insertion. Atomisation is an essential process in many fields where a dispersion of liquid particles in a gas is required. Pneumatic nebulisation is most commonly used in conjunction with a spray chamber that serves as a droplet separator, allowing droplets with average diameters of typically <10 xm to pass and enter the ICP. Spray chambers, which reduce solvent load and deal with coarse aerosols, should be as small as possible (micro-nebulisation [177]). Direct injection in the plasma torch is feasible [178]. Ultrasonic atomisers are designed to specifically operate from a vibrational energy source [179]. 

A second pyroreactor has been added to the system as back-up, to minimize the system down-time due to furnace heating element failure. The system has been expanded to also perform sulphur determination by oxidative combustion with UV fluorescence detection. The current sample load for the system is greater than 12 000 samples per year with a maximum capacity of the system, operating under optimum conditions, of greater than 40 000 samples per year. 

The solvent system, which is transparent at 254 nm, permits the use of a UV detector system. This is a distinct advantage for high performance GPC where low sample loadings are necessary and refractive index detectors may provide only marginal sensitivity. 

UHV surface preparation and analysis chamber, a variable pressure STM chamber, and a load lock and sample transfer system. Fig. 11 shows a schematic of the system. 

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