Cysteine acetate

Newsome [6] determined methyl mercury compounds in wheat flour and ground oats by extraction with benzene-formic acid followed by purification and gas-liquid chromatography. Interfering substances were removed from the extracts by column chromatography on silicic acid and partitioning with cysteine acetate solution. The method is sensitive in the 0.01-0.9 ppm range with a recovery of generally better than 95%. 

Many other household products can be analysed in similar ways to those described above for chemicals. Household bleach is essentially an inorganic chemical. There has been concern expressed about mercury levels in hypochlorite bleach because of the way it is manufactured. The cold vapour reduction/aeration method referred to above is a good way of determining low mercury levels with minimal matrix problems [82]. In the past organo-mercurial compounds have been used (e.g. as bactericides) in some household products these may be selectively determined by extraction with an organic solvent (e.g. carbon tetrachloride or benzene), and then application of the cold-vapour method following the addition of cysteine acetate, or by coupled gas chromatography/atomic absorption [83],... 

The between bottle homogeneity was verified by the determination of total and methyl mercury on sample intakes of 0.2 g. For the determination of total mercury, the samples were mineralised by digestion using nitric acid. The final determination was performed by CVAAS. Methyl mercury was determined by CGC/ECD after extraction of 0.2 g fish powder in toluene, back extraction with a cysteine acetate solution and further extraction with toluene. Calibrations were performed by standard additions. The study showed that the two materials are homogeneous at an analytical portion of 0.2 g and above for total and methyl mercury [7]. 

Total Hg determined by CVAAS after pressurized digestion with H2SO4/HNO, reduction with SnCU and gold preconcentration. For MeHg. 2000 mg pre-treated by addition of HCI and toluene, back-cxtraction with cysteine acetate, and re-extraction into toluene, separation by capillary gas chromatography, followed by electron capture detection (Lab.03)... 

Munaf et al. (1990) utilized microcolumn technique for preconcentration and LC separation of mercury compounds in waste water samples, using cystein-acetic acid as the mobile phase. After separation, the mercury compounds were digested on-line" with peroxodisulphate at room temperature, using Cu(ll) as a catalyst. The mercury was then reduced by alkaline Sn(ll) and determined by CV-AAS. The detection limit was calculated at 5 ng/L. 

Cleaned extract. Sub-samples of the raw extract were extracted twice with 150 mL of cysteine acetate. After acidification with HCl, the mixtures were back-extracted twice with toluene. This cleaned extract was dried by addition of anhydrous Na2S04 and samples were distributed in 100 mL bottles. 

Cysteine acetate solution 1%. Dissolve l.Og of cysteine hydrochloride monohydrate, 0.775g of sodium acetate trihydrate, and 12.5g of anhydrous sodium sulphate in water and make up to 100ml. 

The cysteine acetate modification (fish, egg, meat). containing more than O.lmg of total mercury/kg. 

Liver gives lower yields than egg-yolk (which gives 80 - 90% yield) in this procedure, and hence, liver cannot be accurately analysed with a single extraction using 1% cysteine acetate solution. 

Excess mercuric ions were added to an aqueous liver suspension containing known amounts of a methylmercury salt. The analysis was performed according to the cysteine acetate modification, ... 

Method B described earlier). More than 100% of the methylmercury was recovered. When the acidified liver suspension containing mercuric ions was kept at room temperature overnight, the recovery increased. This indicated a synthesis of methylmercury ions from mercuric ions by the liver under the conditions used. Thus, this combined mercuric ion-cysteine acetate procedure for analysis of methylmercury could not be applied to liver. Some results obtained without addition of methylmercury compounds are seen in Table 15. 

For egg-yolk with low content of methylmercury the cysteine acetate procedure gave less than 90% recovery, (Method B described earlier). with the combined method using cysteine and mercuric ions the recovery of methylmercury salt decreased almost to zero. But for sediments in aquaria and sludge, which similarly could not be analysed by the original cysteine acetate modification, the combined method gave good results (Table 16). The combined cysteine/mercuric ion method was also applied to fish muscles with good recoveries. ... 

A second attempt to improve the recovery in the cysteine acetate method (Method B) involved a precipitation of the proteins in liver by molybdic acid. This increased the recovery of added... 

In futher modification of Method B, when applied to egg-yolk with low methylmercury content, repeated extractions with 1% cysteine acetate solution were used with success (100% recovery), but one single extraction with 10% cysteine acetate was more rapid and also gave good results (about 90% recovery),... 

In both the original and the modified cysteine acetate methods a smaller aliquot of the cysteine extract was used then earlier (Method B, described earlier), to save time at the centrifugation. For the same reason sodium chloride was added at the first extraction. 

Combined cysteine acetate mercuric chloride method... 

Follow cysteine acetate procedure only adding 2ml (10ml for 50g sample) of purified aqueous 5% mercuric chloride solution before the first extraction with benzene, (see Method A described earlier in this section). 

Rapid determination of methylmercury salt in liver. Follow cysteine acetate procedure only adding Ig of molybdic acid/lOg of sample to the liver suspension and shake for 30 seconds. Then add the sodium chloride, hydrochloric acid and benzene at once. Shake and centrifuge immediately. When preparing the calibration curve according to this procedure, add the methylmercury salt immediately beofre the first extraction with benzene. 

Follow cysteine acetate procedure using 50g of sample up to and including the transfer of 250ml of the first benzene extract to a separating funnel. Shake this extract with 4ml then two 3ml... 

The 15 - 55ml fraction of the percolate is extracted with cysteine acetate solution (6ml) and treated as before. The benzene extracts are submitted to gas chromatography on a glass column (40cm x 4mm) packed with 2% of butanediol succinate on Chromosorb W (AW-DMCS)... 

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