Sample preparation methods ashing

Oxidative decomposition by wet ashing is the most widely used sample preparation method for milk samples. Acid digestion involves the use of mineral acids and oxidizing agents to dissolve the sample. Some of the acids commonly used in these procedures are HC1, HNO3, H2S04, and HCIO4. Wet decomposition can be performed with either open or closed systems. Open systems entail... 

The second consideration for quantitative analysis is that if the elements are present in trace quantities the problems of multiple sample preparation by ashing increase. A vicious circle is endured when the quantity and percentage recovery of the element cannot be determined until the quantity of the element present is known for dilution limits and range of standard calibration curve required. If the quantity is known, the percentage recovery may be determined by calibration curve or by standard addition. The percentage recovery results should be 100% 2% to allowing for errors and loss. Drawbacks to this method are ... 

Avoid ashing of sample as sample preparation method especially where volatile elements need to be determined. 

The determination of ionic substances, or substances that can be converted into ionic form from solid samples, is an important field of application of ion chromatography. This includes the analysis of sods, sediments, dusts, geological materials, various industrial products, as well as biological samples and all types of foodstuffs. The sample preparation methods for solid substances can be classified according to whether treatment with a liquid, fusion, ashing, or combustion of the dry sample is necessary. 

Potential problems associated with the S SVG method include decomposition of the adsorbate as a result of intimate contact with adsorbent reactive sites. This effect has been observed for adsorbed HD and VX recently, and seems to be exacerbated by the presence of water vapor. Efforts to minimize this effect include use of low-ash adsorbents, operating at as low a temperature as possible, and avoiding the presence of water. The latter includes sample preparation methods to reduce water contamination and use of ultra-dry carrier streams since water vapor in the carrier... 

Sulfated Ash Sample Preparation Method— ASTM Method D-874. 

Sulfated Ash Sample Preparation Method—ASTM Method D-874. http //www.aslm. org/Standards/D874.htm. 

As microwave sample preparation has evolved, standard microwave procedures have been developed and approved by numerous standard methods organisations (ASTM, AOAC International, EPA, etc.), see ref. [64]. Examples are standard test methods for carbon black/ash content (ASTM Method D 1506-97), lead analysis in direct paint samples (ASTM Method E 1645-94), etc. Table 8.15 shows some microwave ashing references (detection weight). A French AFNOR method utilises the atmospheric pressure single-mode microwave method as an alternative sample preparation procedure for Kjeldahl nitrogen determination [84], The performance of a microwave-assisted decomposition for rapid determination of glass fibre content in plastics for QC has been described [85]. 

HS-I diet and fecal samples were dry ashed and HS-II and -III samples were prepared by a combination dry-wet ashing procedure (Hill et al. unpublished). The approved method of American Association of Cereal Chemists (7) was used for determining neutral detergent fiber. 

Food-control laboratories seeking to be accredited for the purposes of the Directive should include, as a minimum, the following techniques in generic protocols HPLC, GC, atomic absorption and/or ICP (and microscopy). A further protocol on sample preparation procedures (including digestion and solvent dissolution procedures) should also be developed. Other protocols for generic methods which are acceptable to UKAS may also be developed. Proximate analyses should be addressed as a series of specific methods including moisture, fat, protein and ash determinations. 

Usually, samples are presented for analysis as liquids. Thus, solid samples must be dissolved. Analytical or ultra-high-purity grade reagents must be used for dissolution to prevent contamination at trace levels. Certain volatile metals (e.g. cadmium, lead and zinc) may be lost when dry ashing, and volatile chlorides (e.g. arsenic and chromium) lost upon wet digestion. It is particularly easy to lose mercury during sample preparation. Appropriate steps must be taken in the choice of method of dissolution, acids and conditions (e.g. whether to use reflux conditions) to prevent such losses. 

Some problems developed in sample preparation and irradiation because of the variety of sample matrices submitted for INAA. Some samples were particulates (coal, fly ash, bottom ash, ore), some were volatile hydrocarbons (gasoline, jet fuel, etc.), some were aqueous, and some were solids. Our methods of sample preparation were refined to provide all samples in sealed quartz and polyethylene vials for irradiation (see Figure 1). Depending on the contents of the quartz vials, the length of irradiation was varied from 3-12 hrs to minimize vial breakage from... 

Although in many laboratories the methods described above remain the methods of choice for determining the proximate analysis of coal, there is also a test method for the proximate analysis of coal by instrumental procedures, assuming that calibration is an integral part of the procedure (ASTM D-5142). This method covers the determination of moisture, volatile matter, and ash and the calculation of fixed carbon in the analysis of coal and coke samples prepared in accordance with standard protocols (ASTM D-2013). The results may require a correction for bias or be corrected for instrument calibration using samples of known proximate... 

A common result of the sample preparation is the dissolution of the entire sample, producing a clear solution. The digestion method must be selected to suit the type of sample, the metals being determined, and finally, the analytical method. Of the methods listed above, most require a liquid sample, except for x-ray fluorescence, which often is used on solid samples. Wet digestion in acid solution, dry ashing, and extraction of the analytes from... 

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