Atmospheric pressure digestions

Commercial grades of sodium aluminate are obtained by digestion of aluminum tnhydroxide in aqueous caustic at atmospheric pressure and near the boiling temperature (7). Digestion of the aluminum hydroxy oxide in aqueous sodium hycboxide [1310-73-2] requbes pressures of up to 1.38 MPa (13.6 atm) and temperatures of about 200°C. Dry sodium aluminate is obtained by evaporation of water. Several processes for the production of sodium aluminate are known that do not reqube the addition of water. In one process, bauxite reacts with molten sodium hycboxide at approximately 400°C (8) in... 

Purified CA (>99% assay) is produced by digesting the cmde product in 15—20% sulfuric acid. The digestion can be carried out at atmospheric pressure or above (103—105). The digested CA slurry is filtered and washed to remove residual sulfuric acid. A small portion of the filter cake (—10%) is dried conventionally at temperatures up to 200°C, granulated, and packaged for merchant sales. The remainder of the CA filter cake, which contains a small... 

Minimal pretreatment such as pelletizing, briquetting, grinding Acid digestion/dissolution in open vessels (atmospheric pressure)... 

If it is desired to start from potatoes (500 g.), they must be heated in a digester under 2-3 atmospheres pressure, since simple boiling till soft does not produce a breakdown sufficient for complete saccharification. 

The dilute-acid process consists of digesting sawdust, shavings or hogged wood with dilute mineral acid at steam pressures of 35 to 200 Ib./sq. in. (One atmosphere pressure equals about 14.7 pounds per square inch.) The carbohydrates are converted into a mixture of... 

Fig. 5. Arrhenius plots and optical yields of hydrogenations of MAA with MRNis. Catalyst RNi (digested at 20 2 "C and kept at 75-78 C for 45 min). Modifying conditions isoelectric point, O C. Reaction conditions MAA (neat), atmospheric pressure.

The introduction of inductively coupled plasma (ICP) in inorganic mass spectrometry means that there is an effective ion source operating at atmospheric pressure. Whereas solid mass spectrometric techniques allow direct analysis of solid samples in ICP-MS, the determination of trace impurities or isotope ratios in solid samples is often carried out after digestion and dissolution of the material. For the determination of trace impurities and isotope ratios in liquids, an additional nebulization... 

Similar to the CEM equipment, Milestone offers the modular MicroSYNTH platform, which is based on the ETHOS digestion instrument [40]. The diversity of different rotor and vessel systems enables reactions from 3 to 500 mL under open and sealed vessel conditions in batch/parallel manner up to 50 bar of pressure. The START package offers simple laboratory glassware for reactions at atmospheric pressure under reflux conditions (Fig. 6). A protective... 

Mermet, J.M. Focused-microwave-assisted reactions atmospheric-pressure acid digestion, on-line pretreatment and acid digestion, volatile species production, and extraction. In Kingston, H.M., Haswell, S.J. (eds.) Microwave-Enhanced Chemistry. Fundamentals, Sample Preparation, and Applications. ACS, Washington, DC (1997)... 

A recent modification of the atmospheric pressure ionization technique involving a special low dead volume interface was described by Thomson etal. [27]. They employed packed microbore columns (170 p, 320 p, and 500 p I. D. with lengths ranging from 5 to 15 cm) in conjunction with a low-volume, wall-coated capillary column as an interface. The total ion current chromatogram of the tryptic digest sample of about 1 picomole of human growth hormone is shown in figure 29. The column was packed with an octadecyl bonded phase... 

A 10% aliquot of the digestion mixture was analyzed on a Vydac C18 250 im ID fu silica cap aiy column connected on-line to ESI-MS (4). A linear gradient of 2% B to %% B in 45 minutes using solvent A (0.1% TFA) and solvent B (90% acetonitrile, 0.07% TFA) was used with a flow rate of 2 jul/min. Sample elution was monitored by UV detection at 200 nm. Mass spectra were recorded in the positive ion mode using a TSQ-700 triple quadrupole instrument (Fiimigan-MAT, San Jose, CA) with an electrospray ion source opo ating at atmospheric pressure. Scans were continuously acquired every three seconds between la/z 500 and 2(XX) in the centroid mode. 

This chapter describes the principal applications of microwaves to the pretreatment of solid samples, with special emphasis on digestion and extraction, which are their two main uses in analytical chemistry. The description is preceded by a discussion of the fundamentals of microwave energy and its interaction with matter, and also of the equipment used by analytical laboratories, which can be of the open or closed type depending on whether they operate at atmospheric pressure or a higher level and whether they use multi-mode or focused microwaves. Selected designs developed for specific purposes are also commented on. 

Dynamic systems for high-pressure microwave treatment were developed much later than open-vessel systems. Operating under a high pressure reduces the flexibility afforded by working at atmospheric pressure. However, some recently developed devices allow microwave-assisted high-pressure digestion and extraction in a dynamic manner [33,34]. 

As stated in Section 5.3, there are two main types of microwave units, namely closed-vessel systems, which use pressurized containers, and open-vessel systems, which use focused microwaves at atmospheric pressure. Both types of system have been used to digest solid samples and each has its own advantages and disadvantages, so it is impossible to recommend either as the more suitable overall. 

The 200-mg samples were digested with nitric acid in a microwave-irradiated closed system [11]. The instrumental determination was performed in a GBC atomic spectrometer with D2 lamp background correction. A Pd/Mg mixture [12] was used as chemical modifier. The dry-base correction factor was calculated by a parallel assay. The samples were dried in an oven at 60 °C under atmospheric pressure, and the CRM (certified reference material - NIST 1570a) was treated as specified by NIST [13]. 

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