Gold traps

Organomercury compounds Extraction with dithizone solution Gold trap cold vapour AAS - [537]... 

In addition to analysing samples directly on-hne, the instrument can be used for routine tests of samples from other samphng points. These samples are brought to the instrument after collection in suitable gold traps. Care must be exercised in this type of measurement, as with aU others for mercury—the levels of measurement are very low and background levels can distort the result. 

Basically, these involve the addition of three electronically activated Teflon valves to direct the flow of gas from the gas-hquid separator and over the Galahad instrument. One valve is controlled directly from the vapour generator and this only diverts the argon containing mercury stream over the gold trap for a preset time. The additional two valves are controlled by the Galahad cycle so that the revaporized mercury can be directed to the Merlin detector for measurement. In this manner the flows for preconcentration and the flows for measurement can be optimized individually. The operation of these valves is shown schematically in Fig. 7. IS. 

Fig. 7.17 Atomic fluorescence detector response from samples preconcentrated on gold traps prior to revaporization.

The most common procedure for analyzing mercury in precipitation is oxidation with BrCl, prereduction with NH2OH HC1, followed by reduction of the aqueous Hg to Hg° using SnCl2. Hg is purged onto gold traps, thermally desorbed, and analyzed using CV-AFS.61516... 

The formation of ionic gold trapped in an oxide lattice is thought to be responsible for the stability of some Toyota catalysts there was no reduction in T5o% conversion for propene after treatment at 1073 K for 5h (Table 14.1). A standard AU/AI2O3 catalyst under the same conditions suffered significant degradation.32... 

Bergdahl IA, Schutz A, Hansson G-A. 1995. Automated determination of inorganic mercury in blood after sulfuric acid treatment using cold vapour atomic absorption spectrometry and an inductively heated gold trap. Analyst 120 1205-1209. 

Enrichment of Mercury. Due often to very low mercury contents of the samples to be analysed, enrichment procedures are required. Mercury can be extracted with PDDC into MIBK or with dithiazone into chloroform. It can also be electrolysed on the copper or silver cathode. The mercury vapour can be collected in several traps such as various solution traps, gold trap, and active carbon. Adsorption solutions may be nitric acid, bromine water—nitric acid, or potassium permanganate solutions. 

Implementation of various speciation strategies in flowing systems Enrichment via gold-trap collection Speciation between inorganic mercury and organomercurials... 

Only a few analytical techniques have been developed so far for the reliable determination of organo-mercury species in water samples. In many studies, mercury compounds in aquatic environments are speciated according to their ability to be reduced to the elemental state. Dimethylmercury and Hg° (the most volatile mercury compounds) can be isolated by aeration and adsorption on a suitable adsorbent (dimethylmercury on Carbotrap or Tenax and Hg° on gold trap) or by cryotrapping, or coupled with noble metal amalgamation (for Hg°), immediately after sampling. Alternatively, they can be directly analyzed by separation on GC columns and detected by one or more suitable mercury detectors. Samples should not be acidified prior to such separations since dimethylmercury and Hg° are transformed into... 

At each sample point identified in the sample selection process a series of FSTM (chemieally impregnated earbon) traps and gold traps were collected. The initial sampling proeess eonsisted of the eolleetion of a series of short and medium term samples and then a set of longer duration (1-4 days) to provide an integrated average concentration over the extended period. 

Argon is the preferred inert gas, because it can be used for both sweeping the Hg° from solution via gold traps to the detector, and for purging the optical path. Nitrogen causes interferences in the detection step, and the oxygen in air is partly converted into ozone under UV irradiation which results in losses in sensitivity. 

Some years ago, a microprocessor-controlled flow-stream system was introduced for the determination of ultratrace levels of easily reducible mercury in water samples (Stockwell et. al., 1989). The system is based on an autosampler, reduction unit, gas-liquid separator, gold trap and APS monitor and allows processing of 8 samples per hour. For sample volumes of 4S mL, a detection limit (3 s of the blank values) of 0.1 ng/L was found with an analytical precision of 5 % (Cossa et al., 1995). 

M.V. Balarama Krishna, D. Karimasagar, S.V. Rao, and J. Arunachalam. Preconcentration and speciation of inorganic and methyl mercury in waters using polyaruline and gold trap-CVAAS. Talanta 68 329-335, 2005. 

The most sensitive technique for solution analysis is cold vapor AAS or AFS using collection of the mercury vapor on a gold trap or directly in the graphite tube, treated with a permanent modifier. 

Amalgamation in a gold trap is also employed in environmental analysis of organic mercury compounds such as methyl mercury. The mercury is commonly determined by cold vapor atomic absorption spectroscopy. 

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