Sample Dissolution Methods

Unfortunately, there is no single dissolution procedure that can be used for all types of solid samples. There are many different approaches to getting solid samples into solution. For some samples, this is fairly straightforward and fast, whereas for others it can be very complex and time consuming. However, all the successful sample dissolution procedures used in ICP-MS typically have a number of things in common  

Even though the contamination issues are exaggerated with ICP-MS, the most common approaches to getting samples into solution are very similar to the ones used for other trace element techniques. The most common dissolution techniques include the following  

Practical Guide to ICP-MS A Tutorial for Beginners, Second Edition 

Heating with fusion mixtures or fluxes such as lithium metaborate, sodium carbonate, or sodium peroxide in a metal crucible (e.g., platinum, silver, or nickel) and redissolving in a dilute mineral acid—typically used for ceramics, stubborn minerals, ores, rocks, and slags. ° 

Dry ashing using a flame, heat lamp, or a heated muffle furnace and redissolving the residue in a dilute mineral acid—typically used for organic or biological matrices.  

The reagents should not contaminate or interfere with the analysis. Equipment should show no chemical attack or corrosion. 

In speciation studies, the integrity of elemental form/valency state/species should be maintained. 

Other trace element techniques. The most common dissolution techniques include the following  

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A report that summarizes the state-of-the-art analytical methods for assay of SNF was published by the Expert Group on Assay Data of Spent Nuclear Fuel (EGADSNF 2011). Their stated objective was to view the techniques that serve for destructive post-irradiation examination (PIE) for analysis of the isotopic composition and concentrations in spent nuclear fuel sample. First, the sampling procedures and sample dissolution methods are considered, followed by techniqnes for separating the radionuclides and the measurement procedures. However, it should be emphasized that... 

Nyomora, A. M. S., Sah, R. N., Brown, P. H., and Miller, R. O. (1997). Boron determination in biological materials by inductively coupled plasma atomic emission and mass spectrometry Effects of sample dissolution methods. Fresenius J.Anal. Chem. 357(8), 1185. 

On the basis of IR and Raman spectroscopy (Table 5.2, Figure 5.12), which are relatively cheap, fast, and easy for technical operation and interpretation of data, and do not require sample dissolution methods, we presented the quantitative determination of the six binary mixtures with the studied cephalosporins in solid state, which was reported for the first time in the literature. The IR-LD analysis of oriented colloids as a liquid crystal suspension was applied for experimental IR band assignment and selection of appropriate bands for quantitative determination. This method gives additional supramolecular solid-state structural information at room temperature and atmospheric pressure. It also avoids the phase transition and guarantees the study of different forms without polymorph transitions. This approach has been applied recently for caffeine as a matrix compound and for studying the polymorphs of Paracetamol, Aspirin, Phenacetin , and Salophen. The spectroscopic data were... 

In addition to the spark emission methods, quantitative analysis directly on soHds can be accompHshed using x-ray fluorescence, or, after sample dissolution, accurate analyses can be made using plasma emission or atomic absorption spectroscopy (37). 

At present time the use of oxide single erystals sueh as bismuth germanate (Bi Ge O, ) and pai atellurite (TeO,) as deteetors in opto-eleetronies stimulate produetion of high purity Bi, Te, Ge and their oxides Bi O, GeO, TeO,. This requires development of analytieal teehniques for purity eontrol of these materials. For survey traee analysis atomie emission speetrometry (AES) and mass speetrometry (MS) with induetively eoupled plasma (ICP) is widely used. However, the deteetion limits of impurities aehievable by these methods for the analysis of high purity solids are limited by neeessity of sample dissolution in pure aeids and dilution up to 5 10 times for ICP-MS and 50-100 for ICP-AES. One of the most effeetive ways to improve the analytieal performanees of these methods is pre-eoneentration of miero-elements. 

Ln(II) in LnFj Ln(II) were determined after samples dissolution in H PO in the presence of a titrated solution of NFI VO, which excess was titrated with the Fe(II) salt. It was found that dissolution of the materials based on CeF CeFj in H PO does not change the oxidation state of cerium, thus phosphate complexes of Ce(III, IV) can be used for quantitative spectrophotometric determination of cerium valence forms. The contents of Ln(II, III) in Ln S LnS may be counted from results of the determination of total sulfur (determined gravimetric ally in BaSO form) and sum of the reducers - S and Ln(II) (determined by iodometric method). 

The usual means of identifying and quantifying the level of these additives in polymer samples is performed by dissolution of the polymer in a solvent, followed by precipitation of the material. The additives in turn remain in the Supernatant liquid. The different solubilites of the additives, high reactivity, low stability, low concentrations and possible co-precipitation with the polymer may pose problems and lead to inconclusive results. Another sample pretreatment method is the use of Soxhlet extraction and reconcentration before analysis, although this method is very time consuming, and is still limited by solubility dependence. Other approaches include the use of supercritical fluids to extract the additives from the polymer and Subsequent analysis of the extracts by microcolumn LC (2). 

In trace organic analysis there is usually an extraction or clean-up process, rather than a sample dissolution. Here not only must the matrix effect be considered, but also the recovery yield of the extraction. Frequently an external spike standard is added, but there is often no way of knowing if the recovery of the spike standard matches the analyte in question. There is considerable evidence that the U S E P A method for VOA analysis (Minnich 1993) is subject to such error, as reported by Schumacher and Ward (7997). The analyst must always consider the possibility of such an error, especially when using CRMs to control methods that are applied in routine mode. 

Luo S, Ku T-L (1991) U-series isochron dating A generalized method employing total-sample dissolution. Geochim Cosmochim Acta 55 555-564... 

For the purpose of the identification and quantification of additives (broadly defined) in polymeric materials extraction and dissolution methods are favoured (Sections 3.3-3.7). However, additives are also made accessible analytically by digestion of the sample matrix (cf. Section 8.2). Such wet chemical techniques, that remove the sample matrix first, are often limited to mg amounts because of pressure build-up in destruction vessels. Another reactive extraction approach to facilitate additive analysis is depolymerisation by acid hydrolysis or saponification, sometimes under pressure. This is then frequently followed by chemical methods such as titrimetry or photometry for final identification and quantification. 

Principles and Characteristics Extraction or dissolution methods are usually followed by a separation technique prior to subsequent analysis or detection. While coupling of a sample preparation and a chromatographic separation technique is well established (Section 7.1), hyphenation to spectroscopic analysis is more novel and limited. By elimination of the chromatographic column from the sequence precol-umn-column-postcolumn, essentially a chemical sensor remains which ensures short total analysis times (1-2 min). Examples are headspace analysis via a sampling valve or direct injection of vapours into a mass spectrometer (TD-MS see also Section 6.4). In... 

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). 

Application to solid polymer/additive formulations is restricted, for obvious reasons. SS-ETV-ICP-MS (cup-in-tube) has been used for the simultaneous determination of four elements (Co, Mn, P and Ti) with very different furnace characteristics in mg-size PET samples [413]. The results were compared to ICP-AES (after sample dissolution) and XRF. Table 8.66 shows the very good agreement between the various analytical approaches. The advantage of directly introducing the solid sample in an ETV device is also clearly shown by the fact that the detection limit is even better than that reported for ICP-HRMS. The technique also enables speciation of Sb in PET, and the determination of various sulfur species in aramide fibres. ETV offers some advantages over the well-established specific sulfur analysers very low sample consumption the possibility of using an aqueous standard for calibration and the flexibility to carry out the determination of other analytes. The method cannot be considered as very economic. 

What is meant by fusion as a method for sample dissolution ... 

One popular method of separating an analyte species from a complicated liquid sample is the technique known as liquid-liquid extraction or solvent extraction, first mentioned in Chapter 2. In this method, the sample containing the analyte is a liquid solution, typically a water solution, that also contains other solutes. The need for the separation usually arises from the fact that the other solutes, or perhaps the original solvent, interfere in some way with the analysis technique chosen. An example is a water sample that is being analyzed for a pesticide residue. The water may not be a desirable solvent and there may be other solutes that may interfere. It is a selective dissolution method—a method in which the analyte is removed from the original solvent and subsequently dissolved in a different solvent (extracted) while most of the remainder of the sample remains unextracted, i.e., remains behind in the original solution. 

According to the dissolution method, precision is determined by testing at least six aliquots of a homogenous sample for each dosage strength. The precision should be assessed at each specification interval for the dosage form. The precision can be determined by calculating the relative standard deviation (RSD) of the multiple aliquots from each solution. 

Therefore, the development and validation of a scientifically sound dissolution method requires the selection of key method parameters that provide accurate, reproducible data that are appropriate for the intended application of the methodology. It is important to note that while more extensive dissolution methodologies may be required for bioequivalency evaluations or biowaivers (i.e., multiple media, more complex dissolution media additives, and multiple sampling time points), it is also essential for the simplified, routine quality control dissolution method to discriminate batch-to-batch differences that might affect the product s in vivo performance. 

QA requires the efficient analysis of many samples to support routine production release and stability programs. Methods are typically established in the analytical development group. Efficiency and convenience issues, including the speed of media preparation and the relative convenience of data handling and documentation, are important here. While compliance is important in all aspects of the pharmaceutical industry, QA functions must approach compliance perfection. Depending upon the facility, the automated apparatus may be tailored to specific methods with fixed configurations. Dissolution methods may be routine enough that a custom system, optimized for productivity, may be justified. Compliance of USP and use of industry standard apparatus is important to maintain compatibility with other company laboratories or in the case contract laboratory services are required. 

In this example, of transfer of a drug product dissolution method, the samples are independent (as test is destructive in nature) and additional variability due to different baths/standard sets are assumed to be negligible (dissolution baths were independently calibrated as per USP criteria). Based on the receiving site s familiarity with the methodology to be transferred, only one analyst/dissolution bath per site was used. The analyses were performed at USP level 2, i.e. 12 individual samples were tested. The standard deviation on 12 replicate analyses from an earlier study was 3.02 (Borman et al., 2009). The authors indicated that as this estimate is based on a limited number of replicates, it was good practice to use a pre-defined multiplier, which allows for uncertainty (Hahn and Meeker, 1991), in this case 1.255 (multiplier for... 

The earliest applications for quantitative analysis of liquid samples and solid preparations entailed sample dissolution in an appropriate solvent. A number of moisture determinations in APIs and pharmaceutical preparations based on both reflectance and transmission measurements have been reported. Their results are comparable to those of the KF method. The high sensitivity provided by the NIR technique has fostered its use in the determination of moisture in freeze-dried pharmaceuticals. ° The noninvasive nature of NIR has been exploited in determination of moisture in sealed glass vials. " " ... 

The dissolution method for the immediate-release/sustained-release tablet requires the following parameters USP paddle method, 900 ml of water, SO rpm paddle speed, 37°C, and samphng points at 20 minutes, 40 minutes, 1, 2, 4, 6, 8 and 10 hours. Robotically, ahquots (8 ml) were removed, filtered through a 10 jm polyethylene filter and transferred to the storage rack. The volume (8 ml) was replaced with heated media. The samples were assayed hy HPLC using the external standard method. 

The validation requirements are discussed as they apply to both the sample preparation and sample analysis aspects of a dissolution method. The focus of the discussion in this chapter is on the validation considerations that are unique to a dissolution method. Validation is the assessment of the performance of a defined test method. The result of any successful validation exercise is a comprehensive set of data that will support the suitability of the test method for its intended use. To this end, execution of a validation exercise without a clearly defined plan can lead to many difficulties, including an incomplete or flawed set of validation data. Planning for the validation exercise must include the following determination of what performance characteristics to assess (i.e., strategy), how to assess each characteristic (i.e., experimental), and what minimum standard of performance is expected (i.e., criteria). The preparation of a validation protocol is highly recommended to clearly define the experiments and associated criteria. Validation of a test method must include experiments to assess both the sample preparation (i.e., sample dissolution) and the sample analysis. ICH Q2A [1] provides guidance for the validation characteristics of the dissolution test and is summarized in Table 4.1. 

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