Filters sampling with

On the basis of the results of Table IV, it was decided to extract the filter samples with buffer because l) this extraction medium yields greater stability of MMA at room temperature, and with refrigeration recoveries might be even more improved and 2) this extraction medium is the eluent used for separation and analysis of MMA, p-APA, and As(V). 

Treat 20 g of filtered sample with acetone at 30° until a total volume of 100 ml is obtained. Shake and leave at 30° zb 2° for eighteen hours centrifuge or siphon off the supernatant liquid. Add another 20 ml of acetone at 30° and remove as before. Repeat with 20 ml of acetone but transfer the mixture to a filter paper. Wash the crystals with five small portions of acetone at 30° dry thoroughly at a temperature below the melting-point of the glycerides. Determine the m.p. in a sealed capillary tube. 

The main panel of Figure B1.5.6 portrays a typical setup for SHG. A laser source of frequency to is directed to the sample, with several optical stages typically being introduced for additional control and filtering. The combination of a... 

Total airborne particulates are determined using a high-volume air sampler equipped with either cellulose fiber or glass fiber filters. Samples taken from urban environments require approximately 1 h of sampling time, but samples from rural environments require substantially longer times. 

The liquid was applied and dried on cellulose filter (diameter 25 mm). In the present work as an analytical signal we took the relative intensity of analytical lines. This approach reduces non-homogeneity and inequality of a probe. Influence of filter type and sample mass on features of the procedure was studied. The dependence of analytical lines intensity from probe mass was linear for most of above listed elements except Ca presented in most types of filter paper. The relative intensities (reduced to one of the analysis element) was constant or dependent from mass was weak in determined limits. This fact allows to exclude mass control in sample pretreatment. For Ca this dependence was non-linear, therefore, it is necessary to correct analytical signal. Analysis of thin layer is characterized by minimal influence of elements hence, the relative intensity explicitly determines the relative concentration. As reference sample we used solid synthetic samples with unlimited lifetime. 

Aldehydes, general procedure (3). A solution of nilnie 1 (1 mol) in EtOAc saturated with HO gas al 0°C is added to a solution ol SnCl2 (1.1 mol) in EtOAc previously saturated wlh HCI at 0°C. After several hours at 0°C the aldimine complex (R.CHNH2 3 SnCle separated as pale yellow prisms. The complex was filtered, washed with EtjO and dried over KOH under vacuum to afford a pure sample of 2. Steam distillation of 2 gave aldehyde 3 in the distlRate if the aldehyde was volatile. Alternatively, the aldehyde was extracted from the residue of the steam distillate... 

Because a filter sample includes particles both larger and smaller than those retained in the human respiratory system (see Chapter 7, Section III), other types of samplers are used which allow measurement of the size ranges of particles retained in the respiratory system. Some of these are called dichotomous samplers because they allow separate measurement of the respirable and nonrespirable fractions of the total. Size-selective samplers rely on impactors, miniature cyclones, and other means. The United States has selected the size fraction below an aerodynamic diameter of 10 /xm (PMiq) for compliance with the air quality standard for airborne particulate matter. 

Open face Sampling with the top portion of a filter holder or cassette removed to ensure the full filter surface is exposed. 

A solution of 85.8 g (0.2 moles) of 3/ -acetoxy-27-norchoIest-5-en-25-one in 500 ml of anhydrous thiophen-free benzene is added to a Grignard solution prepared from 24.3 g (1 g-atom) of magnesium and 149 g (1.05 moles) of freshly distilled methyl iodide in 575 ml of anhydrous ether. The mixture is refluxed for 3 hr and allowed to stand overnight. After cooling to 5° the complex is decomposed by the slow addition of 200 ml of ice water and 400 ml of 50% acetic acid solution, and steam distilled until no more oil passes over. The residual product is filtered, washed with water and dried at 80°. Crystallization from methanol gives 70 g (87%) of cholest-5-ene-3)5,25-diol mp 179.5-181°. The analytical sample melts at 181.5-182.5° [a]o —39° (CHCI3). 

The aniline and sulphuric acid are cautiously mixed in a round flask (250 c.c.) and heated to 180—190° in an oil or metal bath for four to five hours until a sample dissolved in water remains clear on the addition of caustic soda in excess and no aniline separates. The product is poured into cold water, which precipitates the sulphanilic acid as a grey ciystalline mass.It is filtered, washed with a little cold water, recrystallised from hot water with the addition of a little animal charcoal, and dried in the air. Yield, 25 — 30 grams. 

A solution of 14 g of 21 -hydroxypregnane-3,20-dione and of 14 g of recrystallized succinic anhydride in 140 ml of dry pyridine was allowed to stand at room temperature for 18 hours, then cooled in an ice bath and poured in a fine stream into 1.5 liters of ice water. Excess pyridine was neutralized with 3N hydrochloric acid and the solution further diluted with 2 liters of ice water. The precipitated product was filtered, washed with water and dried in vacuo at 50°C affording 18 g of solid MP 192°C to 195 t. Recrystallization of a small sample afforded analytically pure material, MP 200°C. 

After allowing the mixture to evaporate to dryness, water was added and the sulfonamide filtered, washed with water, and dried in vacuo. The crude product (32.5 grams, 96%) obtained melts at 163.5° to 165°C. One crystallization from ethanol chloroform yielded an analytical sample, MP 164.5 to 166.5°C. 

Photoelectric-Colorimetric Method. Although the recording spectrophotometer is, for food work at least, a research tool, another instrument, the Hunter multipurpose reflectometer (4), is available and may prove to be applicable to industrial quality control. (The newer Hunter color and color difference meter which eliminates considerable calculation will probably be even more directly applicable. Another make of reflection meter has recently been made available commercially that uses filters similar to those developed by Hunter and can be used to obtain a similar type of data.) This instrument is not a spectrophotometer, for it does not primarily measure the variation of any property of samples with respect to wave length, but certain colorimetric indexes are calculated from separate readings with amber, blue, and green filters, designated A, B, and G, respectively. The most useful indexes in food color work obtainable with this type of instrument have been G, which gives a... 

About 5 ml of sample is withdrawn for every 4-6 hours. The absorbance reading of the sample at 580 nm was measured using a Hitachi U-2000 spectrophotometer. The sample is filtered in a vacuum through Whatman filter paper with a pore size of 2.5 pin and diameter of 47 mm. The dry weight of cells is measured to monitoring microbial cell population and cell density. A plot of optical density reading from the spectrophotometer against cell dry... 

Iodine was determined by an iodometric titration adapted from White and Secor.(3) Instead of the normal Carius combustion, iodide was separated from the samples either by slurrying in 6M NaOH, or by stirring the sample with liquid sodium-potassium (NaK) alloy, followed by dissolving excess NaK in ethanol. Precipitated plutonium hydroxides were filtered. Iodine was determined in the filtrate by bromine oxidation to iodate in an acetate buffer solution, destruction of the excess bromine with formic acid, acidifying with SO, addition of excess KI solution, and titrating the liberated iodine with standard sodium thiosulfate. The precision of the iodine determination is estimated to be about 5% of the measured value, principally due to incomplete extraction of iodine from the sample. 

The addition of celite or HyfloSupercel to increase the contact surface with the extraction solvent and help filtration is often utilized during extraction. In case of interaction of such filter aids with the food, treated sand can be employed instead. Weak bases such as NaHCOj, MgC03, or CaC03 (1 g/10 g sample) to neutralize acids liberated from tissues and antioxidants (0.1% BHT, 5% pyro-gallol, ascorbic acid, and sodium ascorbate) to avoid oxidation can be added during extraction. ... 

Samples with higher protein levels (yogurts), are initially treated with hydrochloric acid and after protein precipitation the supernatant is filtered and injected into the HPLC column. The separations performed with a LiChroCART RP18 column used a mixture of acetonitrile and formic acid as the mobile phase. A baseline quantification of the carminic acid was possible in the presence of other coloring agents, with excellent recuperation, selectivity, accuracy, and precision. ... 

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