Solid samples digestion

It is further important to note that if only solid samples are taken, the calibration curve passes through the origin as is obvious in Figure 4.4. An intercept usually caused by blank values from reagents and digestion vessels in wet analysis can be excluded except in the case of matrix modification. 

Pd removal was determined as follows. An aliquot of a representative liquid or solid sample was accurately weighed and subsequently digested by refluxing in nitric and/or hydrochloric acid using a closed vessel microwave procedure (CEM MARS5 Xpress or Milestone Ethos EZ). Cooled, digested samples were diluted, matrix matched to standards, and referenced to a linear calibration curve for quantitation an internal standard was employed to improve quantitation. All samples were analyzed by an Inductively Coupled Plasma Mass Spectrometer or ICP/MS (Perkin Elmer SCIEX Elan DRCII) operated in the standard mode. 

Destructive solid sample preparation methods, such as digestion and mineralisation, are well known as they have been around for some time they are relatively cheap and well documented [13-15]. Decomposition of a substance or a mixture of substances does not refer so much to the dissolution, but rather to the conversion of slightly soluble substances into acid- or water-soluble (ionogenic) compounds (chemical dissolution). 

In the Wickbold method, solid samples are vaporised in an oxygen stream and fed into an oxyhydrogen flame, which bums in a cooled quartz tube. The combustion products are condensed here, or are captured in an absorption solution as gaseous materials. Although combustion in a Wickbold apparatus is a quick and effective method for destroying organic material of all types, incomplete destruction may occur [19]. In special digestion vessels, known as cold-plasma ashers (CPA),... 

Wbter, extracts or digests of waste Filtration or digestion as appropriate (depends on matrix, dissolved or total, acid leachable, etc.) ICP/MS (EPA Method 6020) No data 71-137% (11-23% RSD) for aqueous solutions 90-104% (6-28% RSD) for solid samples EPA 1994e... 

Wet digestion/ashing Sample heated with strong acid(s) Metals in organic/inorganic solid samples (e.g. metals in soil samples)... 

The digestion of solid samples to produce a solution is discussed in Section 13.2. For solution-based ICP MS analysis, the liquid is taken up through a thin tube via a peristaltic pump. This feeds directly into the instrument nebulizer, where argon gas is introduced into the liquid and a fine mist of droplets is expelled from the tip of the nebulizer. This sample aerosol is sprayed into the condenser to reduce the size of the droplets, ensuring an even sample loading and preventing cooling of the plasma. About 1% of the sample solution uptake is transported to the plasma torch, and any unused solution is drained away and may be recycled. 

Digestion of solid samples preparatory to chemical analysis... 

Elemental analysis of sample digests Non-destructive analysis of solid samples... 

Feldman [37] digested solid samples with potassium dichromate, nitric acid, perchloric and sulphuric acid. Bishop et al. [38] used aqua regia and potassium permanganate for digestion. 

The ultimate Q.C. protocol should anticipate the potential error sources in the whole analytical procedure. Destructive analyses that require extensive treatment for sample decomposition can lead to large analytical errors. Solid sample fusions and digestions should... 

Sample Dissolution — Sample introduction into most ICP systems, is by liquid nebuli-zation. This constraint partially limits the quality of the emission analysis to be dependent on the digestion, in the case of solid samples. The fact that several elements are easily monitored simultaneously places a greater demand on the care and choice of sample preparation. Also there are both advantages and disadvantages to the use of dissolved samples in analysis. Some disadvantages are ... 

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. 

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... 

An advantage of ICP-MS compared to all other atomic mass spectrometric techniques including TIMS is that usually only simple sample preparation (e.g., by microwave induced digestion of solid samples) is necessary. Sample preparation steps for ICP-MS analyses are similar to those of ICP-OES. Concentrated solutions are analyzed after dilution with high purity water only. In order to correct mass drifts of the instrument, an internal standard element like In or Ir with known concentration (e.g., I Op.g 1) is added. The solution is then acidified with HN03 to stabilize the metal ions in aqueous solution. 

Solid samples are digested with suprapure sub-boiled HN03 to avoid contamination in an acid mixture using HF, HC1 or 4 (e.g., in an open vessel directly or in a closed vessel by microwave induced digestion). The sample digestion of difficult-to-dissolve sample material in closed vessels,... 

For liquid matrices such as milk, a pretreatment step for fat removal that is accomplished by centrifugation (1 -3) or hexane extraction (4) may be required. Solid samples such as muscle, kidney, and liver necessitate usually more intensive sample pretreatment through use of a mincing and/or a homogenizing apparatus. In some cases, as in the analysis of apramycin in swine kidney tissue, protein digestion with concentrated ammonium hydroxide may be needed to achieve better recovery of the analyte from the matrix (5). 

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