Amalgamation trap

Solvent extraction, coprecipitation and ion-exchange techniques are the main concentration methods used for seawater analysis. Other interesting concentration techniques, such as electrodeposition, amalgam trap (for mercury), a cold trap-vaporization system for hydride generation, and recrystallization, are often used by marine and analytical chemists. The first three methods are briefly reviewed here. 

Fig. 13-2. Scheme for measuring Hg content of soil using thermo-emission method 1 = temperature control, 2 = thermo-electric sensor, 3 = sample, 4 = furnace, 5 = Na2C03 filter, 6 = Au wire amalgamation trap, 7 = vacuum pump, 8 = Hg detector. 

Since mercury is present already in the atomic state in the cold vapor technique, there is no need for an atomiser as such. The sample vapor is swept directly from the reduction cell or the amalgamation trap in the carrier gas stream to a 10 cm length T-shaped quartz tube that is moderately heated (to ca. 200 °C to prevent condensation of mercury). This quartz cell is located in the light path of a conventional AA spectrometer where the attenuation of a characteristic Hg line source is measured. Dedicated AA spectrometers (which, in this case, often have a continuum light source) may also be used with longer absorption cells (300 mm pathlength) to increase the sensitivity. 

As the cold-vapor mercury sample is already in the atomic state, there is no need of an atomizer, per se. The vapor, transferred directly from the cell or desorbed as a plug from a heated amalgamation trap, is commonly swept into a moderately heated (resistance wound heating to 200°C) 10 cm quartz T-tube located within the optical beam of a conventional AA spectrometer. Attenuation of an intense electrodeless discharge lamp line source at 253.7nm is used as a measure of the absorption. Alternatively, dedicated continuum source AA-based spectrometers fitted with long path absorption cells (30 cm) are frequently used to increase sensitivity and detection limit. 

Partial or complete poisoning of the amalgamation trap is more likely to occur when NaBH4 is used as a reductant and the precautions outlined earlier are not... 

Other halogen carriers may be used, e.g., 1-2 g. of iron filings, or 1 g. of aluminium amalgam. The bromine must then be added slowly from a dropping funnel to the benzene warmed on a water bath the apparatu.s shown in Fig. II, 13, 9 is suitable and a trap for the hydrogen bromide must, however, be inserted into the top of the condenser. After all the bromine has been introduced, the mixture is heated on a water bath until no red vapours are visible above the liquid. The Subsequent procedure is as above. 

Pyridyne (26) has been shown to exist by trapping it with furan. It must be considered to be an intermediate in the reaction of 3-bromo-2-chloropyridine (49) with lithium amalgam because in the presence of furan a small amount (2%) of quinoline (50) is formed. ... 

The high mobility and tendency to dispersion exhibited by mercury, and the ease with which it forms alloys (amalgams) with many laboratory and electrical contact metals, can cause severe corrosion problems in laboratories. A filter-cyclone trap is described to contain completely mercury ejected accidentally by overpressuring of mercury manometers and similar items. 

In 1937 Hunter and Hlynka were able to reduce a methanolic solution of 4(5)-nitroimidazole (27 R = H) with sodium amalgam and trap the 4(5)-aminoimidazole (25 R = H) with cyanic acid giving the urea derivative (31) (37BJ488). Other reducing agents gave inferior results. Subsequently, 4(5)-aminoimidazole (25 R = H) was obtained as either its dihydrochloride (30%) or dipicrate salt but the isolation procedures were lengthy and difficult (41 Mil). 

In many applications, such as the analysis of mercury in open ocean seawater, where the mercury concentrations can be as small as 10 ng/1 [468,472-476], a preconcentration stage is generally necessary. A preliminary concentration step may separate mercury from interfering substances, and the lowered detection limits attained are most desirable when sample quantity is limited. Concentration of mercury prior to measurement has been commonly achieved either by amalgamation on a noble-metal metal [460,467, 469,472], or by dithizone extraction [462,472,475] or extraction with sodium diethyldithiocarbamate [475]. Preconcentration and separation of mercury has also been accomplished using a cold trap at the temperature of liquid nitrogen. 

To extend the levels of detection for mercury stiU lower, several workers, especially in this area of atomic absorption techniques, have chosen to collect the mercury on gold or other noble metal trapping systems prior to revaporizing the mercury into the measurement technique. Figure 7.14 shows the configuration of a specific system to concentrate mercury onto an amalgam preconcentrator prior to analysis. 

Gold flakes trapped in the ground ore may be recovered by amalgamation. Mercury and water are added to the ore and the mixture is passed over mercury-coated copper plates. Gold forms an amalgam with mercury and the amalgam adheres to the copper plates. Amalgam is scrapped off the copper plates. Mercury is removed by distillation. 

Sb. Figure 9.4.21 shows a photograph of Sb ultrafine particles produced by a gas flow-solution trap method. The diameter of primary particles is in the range of 10-20 nm. The color of the suspension was dark grey. The chainlike structure found in the picture may be due to the amalgamation of the primary particles owing to the low melting point of Sb. 

Pyridynes are also formed from ort/m-dihalides and alkali metals. Thus, reaction of 3-bromo-4-chloropyridine (889) with lithium amalgam and furan gives product (891) by trapping of the 3,4-pyridyne (890). Although 2,3-pyridyne is not formed from 3-halopyridines, because of the weaker acidity of the 2- as compared to the 4-hydrogen atom (see Section 3.2.1.8.2), it can be trapped by furan in small yield from the reaction of 3-bromo-2-chloropyridine with lithium amalgam. 

Arsenic in the form of an amalgam is used to a small extent in medicine. It also finds application as a poison in fly-traps.3... 

Fig. 7.4. Mercury pickup devices, (a) Vacuum pickup device. Collected mercury is trapped in the flask for recycling or disposal. (b) Amalgamated copper wire pickup device. The wire is first cleaned in nilric acid, then dipped into a solution of mercuric nitrate to give a thin coating of mercury. Droplets of mercury readily cling to the spiral and may be shaken off into a mercury waste container.

The vapor can be atomized in inert gas-hydrogen diffusion flames, in narrow-bore quartz tubes electrically heated or heated over an air-acetylene flame, and in plasmas. Additionally, the atomizer can act as a vapor preconcentration medium just before atomizing. This is what happens in graphite furnace atomizers (in situ trapping) or on silver or gold wires for direct amalgamation of mercury. 

The traps should be dried at about 40°C in a mercury-free N2 flow for 5 min prior to analysis, after which they should be connected to the AFS detector on-line with the helium gas flow. The mercury is then thermally desorbed either directly into the detector or onto an analytical trap. If an analytical trap is used, a second heating step should be performed before the detection. The advantages of dual amalgamation are that the influence of any interfering substances adsorbed on the first trap may be reduced and that the mercury adsorbed on the second analytical trap will be more easily desorbed, thus yielding a sharper peak. 

Twenty-seven grams (1 mole) of aluminum wire or foil which has just been cleaned with emery paper and wiped with a clean cloth (if turnings are employed, it may be necessary to dean, amalgamate, and dry them according to the procedure of Wislicenus)64 66 is placed in a 1-1. round-bottomed flask containing 300 cc. of anhydrous isopropyl alcohol (distilled from calcjum oxide) and 0.5 g. of mercuric chloride. The flask is attached to an efficient reflux condenser, which is protected from moisture by a mercury trap or a calcium chloride drying tube, and the mixture is heated on the steam bath or a hot plate. When the liquid is boiling, 2 cc. of carbon tetrachloride, which is an effective catalyst for the... 

The first step in this multistage reaction is the nucleophilic addition of sulfone anion 28 to aldehyde 8 (Scheme 14.6). This produces a p-alkoxysulfone intermediate 29 which is trapped with acetic anhydride. The resulting P acetoxysulfone mixture 22 is then subjected to a reductive elimination with Na/Hg amalgam to obtain alkene 23. The tendency of Julia-Lythgoe-Kocienski olefinations to provide ( )-1,2-disubstituted alkenes can be rationalised if one assumes that an a-acyloxy anion is formed in the reduction step, and that this anion is sufficiently long-lived to allow the lowest energy conformation to be adopted. Clearly, this will... 

Fig. 95. Production diagram of tetraethyllead by electrolysis of complex salts 1 -4 - synthesis apparatuses 5 - electrolyser 6 - trap 7 - apparatus for decomposing sodium amalgam...

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