Marsh Apparatus

Although extraction of lipids from membranes can be induced in atomic force apparatus (Leckband et al., 1994) and biomembrane force probe (Evans et al., 1991) experiments, spontaneous dissociation of a lipid from a membrane occurs very rarely because it involves an energy barrier of about 20 kcal/mol (Cevc and Marsh, 1987). However, lipids are known to be extracted from membranes by various enzymes. One such enzyme is phospholipase A2 (PLA2), which complexes with membrane surfaces, destabilizes a phospholipid, extracts it from the membrane, and catalyzes the hydrolysis reaction of the srir2-acyl chain of the lipid, producing lysophospholipids and fatty acids (Slotboom et al., 1982 Dennis, 1983 Jain et al., 1995). SMD simulations were employed to investigate the extraction of a lipid molecule from a DLPE monolayer by human synovial PLA2 (see Eig. 6b), and to compare this process to the extraction of a lipid from a lipid monolayer into the aqueous phase (Stepaniants et al., 1997). 

Marsh et al. [47] have described an apparatus based on an autoanalyser system for the automatic preparation of soil extracts for mineral nitrogen determination. It consists of a reagent adder, which adds the correct volume of extractant for an approximately weighed amount of soil, and a sample preparation unit, which mixes, filters, dilutes and loads samples on to an autoanalyser sampler. A labour saving of 60% is achieved in this method compared to manual method. Examples are given of the determination of nitrate plus nitrate nitrogen and ammonium nitrogen. 

For routine work at around 0°C on any form of data collection device, a simple low-temperature attachment may be constructed from a copper coil, a refrigerated ethanol bath, a headess air drier, a compressor, and a flexible hose (Marsh and Petsko, 1973). Such an apparatus costs less than 2000 to build and has essentially no operating costs. It fulfllls the most important criterion for a successful low-temperature device that it be so easy to operate as to encourage its use. Its disadvantage is that very low temperatures are not attainable without more sophisticated—and expensive—hardware. 

Arsenic. —Add 0.1 gm. of potassium chlorate to 200 gm. of hydrochloric acid, and evaporate on the water-bath. A Marsh apparatus is started, using 20 gm. of arsenic-free, granulated zinc and dilute (1 5) sulphuric acid then the... 

Arsenic. -- A Marsh apparatus is sol in opcniliun. using 20 gm. of arsenic-free. granulated zinc,, uiul arsenic free, dilute, sulphuric, acid (I fi). As soon us Ihe air has lieeii expelled from the apparatus, beat Ihe miiit-lion lube l<> redness, and then introduce a cooled mixture of ID cc. of the acid (sp. gr. 1. SI) to be lesled and al) cc. of water. No deposit or arsenic should be visible in the reduction lulte within halt an hour. 

Arsenic. —Introduce 10 gm. of arsenic-free, granulated zinc into the generating flask of a Marsh apparatus, and start the stream of hydrogen by adding dilute (1 5) sulphuric acid. After the apparatus and reagents have been tested in the usual manner, dissolve 2 gm. of calcium biphosphate in 5 cc. of hydrochloric acid and 15 cc. of water. Introduce this solution into the Marsh apparatus, and maintain the flow of gas for about one hour. No deposit of arsenic should be visible in the reduction tube within this time. 

Arsenic. — Pour 100 cc. of hydrochloric, acid over 20 gm. of potassium chlorate in a capacious porcelain dish. As soon as the evolution of chlorine lias slackened) evaporate the solution on the water-bath to dryness. A Marsh apparatus is set in operation, containing 20 gm. of arsenie-free, granulated zinc and dilute (1 5) sulphuric, acid. The residue from the above evaporation, dissolved in 00 cc. of water, is then introdued into the generating flask of Uie apparatus in small portions at a time. No deposit of arsenic, should be visible in the reduction tube within two hours. 

The Marsh Apparatus should be set up with a 200 cc. generating flask. 

The Gutzeit Test.3—This test is as accurate as the Marsh test and the apparatus necessary is comparatively simple. It consists in allowing the arsine to react with strips or discs of dry filter paper impregnated with silver nitrate or, in the more recent modifications of the method, mercuric chloride or bromide. 

To determine arsenic in a volatile liquid, this may be poured into a Marsh apparatus and burned at the jet, partly as vapour and partly as reduction products, the products of combustion being aspirated through... 

Arsenic.—50 grams of the minced sample are weighed into a round-bottomed flask and heated over a naked flame with 10 c.c. of concentrated sulphuric acid when the mass becomes dense, 30 c.c. of the same acid are added, the heating being continued and further small quantities of acid added until the liquid is completely decolorised. When cold, the solution is poured carefully into 150 c.c. of cold water, the resulting liquid being filtered and the filtrate tested for arsenic in the Marsh apparatus see later, 5, b) and also for any other metals (zinc, nickel, etc.). 

Detection of Arsenic.—This may be effected in Marsh s apparatus (see Flesh Foods). To determine the arsenic, an acidified solution of the... 

Ml. Marsh, W. H., Fingerhut, B., and Kirsch, E., Determination of urea nitrogen with the diacetyl method and an automatic dialyzing apparatus. Am.. Clin. Pathol. 28, 681-688 (1957). 

Arsenic. — A Marsh apparatus is set in operation, using 20 gm. of arsenic-free, granulated zinc, and arsenic-free. 

Ket a Marsh apparatus in operation, using. 50 gm. of ai senic-free, granulated xiiie. and dilute (1 5) siil )liiiric acid, then introduce the cop )cr sulphate solution in small ipiantities at 11 lime, ami niaiiiljuii the How of gas for ahoiit two liour.s. No depo.sil. (if arsi iiic should Ix. vi.sihlc in the reduction tubo wnthin this time. 

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