Hollow needle

The SPME process, adapted for solid or viscous matrix, is shown in Figure 10.1. A fused silica fibre, coated with a polymer, is installed inside a stainless steel hollow needle. In the first step, the needle is introduced in the sample vial through the septum. The fibre is then exposed to the headspace above the sample and the organic analytes adsorb to the coating of the fibre. After a variable sampling time, the fibre is drawn into the needle and the needle is withdrawn from the sample vial. Finally, in the same way, the fibre is introduced into the chromatograph injector where the analytes are thermally desorbed. 

A manufacturing method predominately used by the thermoplastic industry for the manufacture of hollow components, also used for thermosetting rubber. The polymer is forced against the inside of the mould surface by gas pressure applied either by a hollow needle or by the decomposition of a blowing agent. 

In this technique (http //en.wikipedia.org/wiki/Tissue microarray), a hollow needle is used to remove tissue cores of various diameter (from as small as 0.6 4 mm) from regions of interest in paraffin-embedded tissues (clinical biopsies or tumor samples) (Figs. 13.10, 13.11). 

Fia 6 Effect of A on shock sensitivity of various explosives. NQ-f is low-bulk-density nitroguanidine with hollow-needle crystals of about 5 n diam X 60-65 it long. NQ-h is the high-bulk-density material made up of solid particles of about GO-65 n diam. DATB, TNT, and Tetryl are, respectively, dia-minotrinitrobenzene, trinitrotoluene and trinitro-phenylmethylnitramine. RDX is cyclotrimethyl-enetrinitramine which contains 2.5% lubricant. Measurements were carried out with a standardized test (Ref 16) in which a 3.65-cm-diam test explosive confined in 0.55-cm-thick steel is the acceptor and polymethyl methacrylate is the gap material MGl = NCro filt ro uasiM i ... 

Figure 4.9. Scanning electron microscope photographs showing the roughening transition of 111) faces of a TiOj crystal and the formation of hollowed needle crystals as impurities are added [19]. Growth occurs by liquid phase epitaxy on a (001) substrate. Fe203 is added as an impurity in the following amounts (a) 0%. (b) 1.3 mol%,...

Solid-phase microextraction uses a 1-cm length of focused silica fiber, coated on the outer surface with a stationary phase and bonded to a stainless steel plunger holder that looks like a modified microliter syringe. The fused-silica fiber can be drawn into a hollow needle by using the plunger. In the first process, the coated fiber is exposed to the sample and the target analytes are extracted from the sample matrix into the coating. The fiber is then transferred to an instrument for desorption. The technique has been promoted by Pawliszyn (69). 

Several modifications of the ESI technique have been introduced, principally micro-electrospray14 and nano-electrospray15 that have the advantage of using much lower flow rates, reducing the amount of analyte needed for a mass-spectrometric analysis this is performed using adapted probed tips. When performing nanospray, the sample is loaded into a fine hollow needle with a... 

An excellent material for checking the validity of the corrected Kelvin equation is chrysotile, Mg3(0H)4.Si20s, which consists of hollow needles, the pore volume distribution of which can be measured both by means of calibrated electron microscopy and nitrogen capillary condensation [18]. It appears that capillary... 

The type of molding machine available has an important influence upon the blow opening system used. Some machines, for instance, use needle blowing exclusively. Hollow needle insertion at the mold parting line is considered when a very small opening is required that may even need closing or if the hollow object must be blown up on the side, e.g., on carousels with a series of molds. 

The carrier gas can be any non-reacting gas (e.g. nitrogen, argon or helium) with no more than, say, 100 ppm humidity. To achieve good reproducibility, only metal or viton tubes must be used between the gas bottle and the sample container. The latter can be in the shape of a U-tube, with the sample in the bottom, or in the shape of a standard adsorption bulb into which a long, hollow, needle is introduced and used as the gas inlet. 

Scientists use microscopes to observe objects less than 0.004 in (0.1 mm) in diameter. Scientists can also make thin slices of microscopic substances, including living material, with a microtome. Micropipettes are miniature pipettes (hollow needles) used to inject substances into something else, such as a cell. Microelectrodes can measure an electrical charge across a cellular membrane microelectrodes are also used to detect in-... 

Problems with recovery are avoided when sampling the extracellular brain tissue by means of a push-pull cannula. A push-pull cannula consists of two coaxial assembled hollow needles (cannulae) which are implanted into the brain. Artihdal cerebrospinal fluid is infused through the inner cannula and withdrawn through the outer cannula [5-8],... 

Lee and co-workers demonstarted that a micromachined parylene nozzle could serve as an electrospray emitter on a silicon chip. This hollow-needle structure extended more than a millimeter beyond the edge of the silicon substrate. MS/MS analysis of the mixture of peptides obtained from the trypsin digest of cytochrome c was demonstrated with this micromachined emitter, and... 

Furthermore, microneedle systems have recently been the subject of investigation. Needles with a diameter of between 2 and 10 pm can be used to overcome the stratum corneum, leaving only very small holes that are comparable to those caused by the techniques mentioned above. The needles can be solid and sharp (solid needle), hollow and sharp (hollow needle), or hollow and blunt (hollow tubes). They have a length of about 50-100 pm, which is not long enough to reach the pain adaptors in the deeper skin. When assembled in an 3 X 3 mm array of about 400 needles, the total diameter of the microneedles is similar to a 30-G needle, and this provides a suitable application tool. Initial trials with the application of insulin have shown promising results [159]. Examples of microneedles are shown in Fig. 1.7 (from Refs. [160, 161]). 

A microscale SPE technique was developed in 1992 by Janusz Pawliszyn at the University of Waterloo, Ontario Canada. According to J. Berg of Varian Assoc., Walnut Creek, CA, the device shown in Figure 12-11, p. 135, "consists of a holder and a replaceable fiber assembly. The assembled unit looks much like a syringe, but in place of the hollow needle is a fiber inside a protective sheath. The fiber is attached to the holder plunger, so that it may be exposed by moving it out of the sheath. The fiber itself consists of a piece of fused silica rod coated with an adsorbent. 

Alternatively, the centrifuge tube may be punctured at its base using a fine hollow needle. As the drops of gradient pass from the tube through the needle they may be collected using a fraction collector and further analyzed. Analysis of the contents of the displaced gradient can be achieved by ultraviolet spectrophotometry, refractive index measurements, scintillation counting or chemical analysis. 

The second type of inlet, called a splitter (Fig. 22.7), again uses a syringe to inject the sample. The sample is vaporized and effectively mixed with carrier gas in the mixing tube, after which the vapor passes over a tapered hollow needle. Because of the difference between the inside diameter of the mixing tube outlet and that of the tapered needle, a fraction of the total sample is introduced into the column as a narrow zone. The splitting ratio is a function of the pressure in the inlet, and can be varied. Such a sample splitter is used with capillary columns and high-resolution columns because of their relatively low capacity. 

The pin array can be fabricated out of metal or constructed with needles in a plastic/modeling clay holder. Hollow needles are preferred so that a vacuum does not form when the pins are removed from the frozen OCT. Syringe needles of 23-G work well. The layout of the needles in the mold can be user defined, but should be asymmetric to include at least one locating pin. Needles can be... 

Hollow needles are used for injection or aspiration of liquid samples. The external shaft may be insulated by, for example, lacquer layer insulation the internal tube is usually... 

Figure 7.35 Hollow needle electrode magnified. Courtesy Hdvard Kalvoy.

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