Flame with added

Fluorescence profiles for SO in a rich flame with added H2S are presented in Figure 15. The corresponding profiles for S02 are shown in Figure 16. Similarity of the SO and S02 profiles suggest that they are chemically coupled. 

Figure 12. SH A2X — X2U fluorescence profiles above the burner surface for Hg-Ot-Nt (4 1 6) flames with added HtS (a),l. 0% (b), 0.5% (c), 0.25%. Laser excitation at 323.76 nm with detection at 328.0 nm.

Indicates grade with flame retardant added. 

The PBDEs (decaBDE, octaBDE, and pentaBDE) and are used as flame retardants in plastics, electronic equipment, printed circuit boards, vehicles, furniture, textiles, carpets, and building materials. Global demand has increased rapidly since the 1970s with 70,000 tonnes produced in 2001. Their flame retardant activity relies on decomposition at high temperatures, leading to the release of bromine atoms. This slows the chemical reactions that drive 02-dependent fires. HBCDs are a flame retardant added to extruded and expanded polystyrene that is used as thermal insulation in buildings. 

Fire Retardent Paints. Fire retardant paints are based on chlorinated rubber and chlorinated plasticizers with added SbO. These reduce the rate of spread of flames. Addn of NH4H2PO4, PE, or dicyandiamide produces an intumescent or swelling paint that forms a thick insulating layer over the surface to which it is applied when exposed to flames Fire retardant paints do not control fires and are no substitute for an automatic sprinkler system. They are best used where the only hazard is exposed, combustible, interior finish materials or in isolated buildings where sprinklers will not be installed. The paint must be applied at the rate specified on the container if spread thinner the proper... 

Another type of interference that can arise in the atomiser is called ionisation interferences . Particularly when using hot atomisers, the loss of an electron from the neutral atom in metals with low ionisation energy may occur, thus reducing the free atom population (hence the sensitivity of the analyte determination, for which an atomic line is used, is reduced). These interferences can be suppressed in flames by adding a so-called ionisation suppressor to the sample solution. This consists in adding another element which provides a great excess of electrons in the flame (he. another easily ionisable element). In this way, the ionisation equilibrium is forced to the recombination of the ion with the electron to form the metal atom. Well-known examples of such buffering compounds are salts of Cs and La widely used in the determination of Na, K and Ca by FAAS or flame OES. 

Finally, the use of extremely hot flames with certain elements can cause ionisation of the latter, which decreases the concentration of free atoms in the flame. This effect can be corrected by adding an ionisation suppresser in the form of a cation whose ionisation potential is less than that of the analyte. A potassium salt at the level of 2 g, 1 is often chosen as an ionisation suppresser. 

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.). 

SYNTHESIS A solution of 76.6 g 2,5-dimethoxyaniline in 210 mL H20 containing 205 mL fluoroboric acid was cooled to 0 °C. with an external ice bath. There was then added, slowly, a solution of 35 g sodium nitrite in 70 mL H20. After an additional 0.5 h stirring, the precipitated solids were removed by filtration, washed first w ith cold H20, then with MeOH and finally Et20. Air drying yielded about 100 g of the fluoroborate salt of the aniline as dark purple-brown solids. This salt was pyrolyzed with the cautious application of a flame, with the needed attention paid to both an explosion risk, and the evolution of the very corrosive boron trifluoride. The liquid that accumulated in the receiver was distilled at about 120 °C at 20 mm/ Hg, and was subsequently washed with dilute NaOH to remove dissolved boron trifluoride. The product, 2,5-dimethoxyfluorobenzene, was a fluid, straw-colored oil that weighed 7.0 g. 

To the above filtrate is added 3 g. of charcoal, and the mixture is then evaporated in a beaker over a free flame with continuous stirring to a volume of 650 to 700 ml. and filtered by suction while hot. More product is isolated from the solution as described above. The total yield is 55 g. (53%). The product may be recrystallized from a volume of water, faintly acidified with acetic acid, equal to thirty times the weight of the dry material. This gives an analytically pure sample, but the crude nonelectrolyte as obtained above is quite satisfactory for further synthetic use. 

Figure 9. SH A2S — X2n laser-excitation spectra in flames with 1 % HsS added to the unburnt gas (a), H2-02-N2 (4 1 6) (b), Di substituted for H2 in the burner core. Fluorescence detected at 328.0 nm.

Figure 11. Comparison of SH A2X — X2 fluorescence and synthetic emission spectra for a CtHf-Or-Nt (2 2.5 10) flame with 0.5% H,S added to the unburnt gas. Fluorescence excited at 323.76 nm.

Figure 14. SO B3T — X3X fluorescence spectrum for H2-02-N, (4 1 6) flame with 1 % HjS added to the unburnt gas. Laser excitation at 266.5 nm.

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