Analytical methods GC,

However, measurements at small conversions are also limited by another factor, the analytic power. Regardless of the applied analytic methods (GC, MS, HPLC, etc.), there is a detection limit. For small conversions of reactants, the amount of products can be rather small, falling near the detection limit. 

In cases of consumption of low daily doses (< 5 mg) of methadone, the use of immunological methods can lead to uncertainty with regard to patient compliance, as, directly after consumption of these low doses, methadone is excreted almost exclusively in the form of the cyclic metabolites. The two instrumental analytical methods GC/MS and HPLC/DAD also determine these metabolites with high sensitivity. GC/MS detects the principal metabolite EDDP as well as methadone itself, as shown in Fig. 8-39. The sensitivity of this analytical procedure for the determination of methadone and EDDP from blood or urine without derivatization is better than 20 ng/ml, i.e. it even extends to the subtherapeutic range [62]. Table 8-26 shows the important masses found in the... 

Steranes are not found as such in living organisms but carry the biogenic information by the variability of structures and enantiomers. The MS, and especially the mass fragmentogram produced by a combination with other analytical methods (GC, HPLC, etc.), was proven to be a very powerful tool for both source and maturation determination of fossil fuels. The various analytical methods will be discussed when considering hydrocarbon mixtures, especially petroleum and sedimentary organic extracts. 

The EPA Contract Laboratory Program (CLP) has responsibility for managing the analysis programs required under the U.S. Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). The approved analytical methods are designed to analyze water, soil, and sediment from potentially hazardous waste sites to determine the presence or absence of certain environmentally harmful organic compounds. The methods described here all require the use of GC/MS. 

Before sample preparation, surrogate compounds must be added to the matrix. These are used to evaluate the efficiency of recovery of sample for any analytical method. Surrogate standards are often brominated, fluorinated, or isotopically labeled compounds that are not expected to be present in environmental media. If the surrogates are detected by GC/MS within the specified range, it is... 

Specifications and Analytical Methods. Butanediol is specified as 99.5% minimum pure, determined by gas chromatography (gc), sohdifying at 19.6°C minimum. Moisture is 0.04% maximum, determined by Kad-Fischer analysis (dkecdy or of a toluene a2eotrope). The color is APHA 5 maximum, and the Hardy color (polyester test) is APHA 200 maximum. The carbonyl number is 0.5 mg KOH/g maximum the acetal content can also be measured dkecdy by gc. 

Specifications and Analytical Methods. Purity is specified as 99.5% minimum, by gc area percentage, with a maximum of 0.1% moisture by Kad-Fischer titration. Color, as deUvered, is 40 APHA maximum samples may darken on long storage. 

Most common analytical methods for analysis of the major component or minor components of organic products are used for pyridines. These include gas chromatography, titration, free2ing point, nmr, in, hplc, and gc/ms. 

Mixtures can be identified with the help of computer software that subtracts the spectra of pure compounds from that of the sample. For complex mixtures, fractionation may be needed as part of the analysis. Commercial instmments are available that combine ftir, as a detector, with a separation technique such as gas chromatography (gc), high performance Hquid chromatography (hplc), or supercritical fluid chromatography (96,97). Instmments such as gc/ftir are often termed hyphenated instmments (98). Pyrolyzer (99) and thermogravimetric analysis (tga) instmmentation can also be combined with ftir for monitoring pyrolysis and oxidation processes (100) (see Analytical methods, hyphenated instruments). 

Modem analytical techniques have been developed for complete characteri2ation and evaluation of a wide variety of sulfonic acids and sulfonates. The analytical methods for free sulfonic acids and sulfonate salts have been compiled (28). Titration is the most straightforward method of evaluating sulfonic acids produced on either a laboratory or an iadustrial scale (29,30). Spectroscopic methods for sulfonic acid analysis iaclude ultraviolet spectroscopy, iafrared spectroscopy, and and nmr spectroscopy (31). Chromatographic separation techniques, such as gc and gc/ms, are not used for free... 

Capillary gc/ms, hplc, nmr, ir, and uv are all analytical methods used by the terpene chemist with a good Hbrary of reference spectra, capillary gc/ms is probably the most important method used in dealing with the more volatile terpenes used in the davor and fragrance industry (see Flavors and spices). The physical properties of density, refractive index, boiling point, melting point of derivatives, and specific rotation are used less frequendy but are important in defining product specifications. 

Infrared Spectroscopy (ir). Infrared curves are used to identify the chemical functionality of waxes. Petroleum waxes with only hydrocarbon functionality show slight differences based on crystallinity, while vegetable and insect waxes contain hydrocarbons, carboxyflc acids, alcohols, and esters. The ir curves are typically used in combination with other analytical methods such as dsc or gc/gpc to characterize waxes. 

Identification of stmctures of toxic chemicals in environmental samples requires to use modern analytical methods, such as gas chromatography (GC) with element selective detectors (NPD, FPD, AED), capillary electrophoresis (CE) for screening purposes, gas chromatography/mass-spectrometry (GC/MS), gas chromatography / Fourier transform infra red spectrometry (GC/FTIR), nucleai magnetic resonance (NMR), etc. 

Although GC/MS is the most widely used analytical method that combines a chromatographic separation with the identification power of mass spectrometry, it is not the only one. Chemists have coupled mass spectrometers to most of the instruments that are used to separate mixtures. Perhaps the ultimate is mass spectrometry/mass spectrometry (MS/MS), in which one mass spectrometer generates and separates the molecular ions of the components of a mixture and a second mass spectrometer examines their fragmentation patterns ... 

LC is not only a powerful analytical method as such, but it also allows effective sample preparation for GC. The fractions of interest (heart-cuts) are collected and introduced into the GC. The GC column can then be used to separate the fractions of different polarity on the basis of volatility differences. The separation efficiency and selectivity of LC is needed to isolate the compounds of interest from a complex matrix. 

The predominant method of analyzing environmental samples for methyl parathion is by GC. The detection methods most used are FID, FPD, ECD, and mass spectroscopy (MS). HPLC coupled with ultraviolet spectroscopy (UV) or MS has also been used successfiilly. Sample extraction and cleanup varies widely depending on the sample matrix and method of detection. Several analytical methods used to analyze environmental samples for methyl parathion are summarized in Table 7-2. 

Many biologically interesting molecules, for instance hormones, can be determined using any of a number of analytical methods, such as GC, GC-MS, and RIA. In blood serum and similarly complex matrices, the more traditional methods (colorimetry, titration, TLC) suffer from interference and/or lack of sensitivity. 

GC/MS has been employed by Demeter et al. (1978) to quantitatively detect low-ppb levels of a- and P-endosulfan in human serum, urine, and liver. This technique could not separate a- and P-isomers, and limited sensitivity confined its use to toxicological analysis following exposures to high levels of endosulfan. More recently, Le Bel and Williams (1986) and Williams et al. (1988) employed GC/MS to confirm qualitatively the presence of a-endosulfan in adipose tissue previously analyzed quantitatively by GC/ECD. These studies indicate that GC/MS is not as sensitive as GC/ECD. Mariani et al. (1995) have used GC in conjunction with negative ion chemical ionization mass spectrometry to determine alpha- and beta-endosulfan in plasma and brain samples with limits of detection reported to be 5 ppb in each matrix. Details of commonly used analytical methods for several types of biological media are presented in Table 6-1. 

However, compared with the traditional analytical methods, the adoption of chromatographic methods represented a signihcant improvement in pharmaceutical analysis. This was because chromatographic methods had the advantages of method specihcity, the ability to separate and detect low-level impurities. Specihcity is especially important for methods intended for early-phase drug development when the chemical and physical properties of the active pharmaceutical ingredient (API) are not fully understood and the synthetic processes are not fully developed. Therefore the assurance of safety in clinical trials of an API relies heavily on the ability of analytical methods to detect and quantitate unknown impurities that may pose safety concerns. This task was not easily performed or simply could not be carried out by classic wet chemistry methods. Therefore, slowly, HPLC and GC established their places as the mainstream analytical methods in pharmaceutical analysis. 

The PSP toxins represent a real challenge to the analytical chemist interested in developing a method for their detection. There are a great variety of closely related toxin structures (Figure 1) and the need exists to determine the level of each individually. They are totally non-volatile and lack any useful UV absorption. These characteristics coupled with the very low levels found in most samples (sub-ppm) eliminates most traditional chromatographic techniques such as GC and HPLC with UVA S detection. However, by the conversion of the toxins to fluorescent derivatives (J), the problem of detection of the toxins is solved. It has been found that the fluorescent technique is highly sensitive and specific for PSP toxins and many of the current analytical methods for the toxins utilize fluorescent detection. With the toxin detection problem solved, the development of a useful HPLC method was possible and somewhat straightforward. 

Several methods are available for the analysis of trichloroethylene in biological media. The method of choice depends on the nature of the sample matrix cost of analysis required precision, accuracy, and detection limit and turnaround time of the method. The main analytical method used to analyze for the presence of trichloroethylene and its metabolites, trichloroethanol and TCA, in biological samples is separation by gas chromatography (GC) combined with detection by mass spectrometry (MS) or electron capture detection (ECD). Trichloroethylene and/or its metabolites have been detected in exhaled air, blood, urine, breast milk, and tissues. Details on sample preparation, analytical method, and sensitivity and accuracy of selected methods are provided in Table 6-1. 

Reliable analytical methods are available for determination of many volatile nitrosamines at concentrations of 0.1 to 10 ppb in a variety of environmental and biological samples. Most methods employ distillation, extraction, an optional cleanup step, concentration, and final separation by gas chromatography (GC). Use of the highly specific Thermal Energy Analyzer (TEA) as a GC detector affords simplification of sample handling and cleanup without sacrifice of selectivity or sensitivity. Mass spectrometry (MS) is usually employed to confirm the identity of nitrosamines. Utilization of the mass spectrometer s capability to provide quantitative data affords additional confirmatory evidence and quantitative confirmation should be a required criterion of environmental sample analysis. Artifactual formation of nitrosamines continues to be a problem, especially at low levels (0.1 to 1 ppb), and precautions must be taken, such as addition of sulfamic acid or other nitrosation inhibitors. The efficacy of measures for prevention of artifactual nitrosamine formation should be evaluated in each type of sample examined. 

Low resolution MS yields specificity comparable to that of high resolution MS, if a relatively pure sample is delivered to the ion source. Either high resolution GC or additional sample purification is required. To obtain sufficient specificity, it is necessary to demonstrate that the intensities of the major peaks in the mass spectrum are in the correct proportions. Usually 10 to 50 ng of sample is required to establish identity unambiguously. Use of preparative GC for purification of nitrosamines detected by the TEA ( ) is readily adaptable to any nitrosamine present in a complex mixture and requires a minimum of analytical method development when new types of samples are examined. 

PLC is used for separations of 2 to 5 mg of sample on thin-layer chromatography (TLC) plates (0.25-nun layer thickness) or high-performance TLC (HPTLC) plates (0.1-mm thickness). In these instances, the method is termed micropreparative TLC. The isolation of one to five compounds in amounts ranging from 5 to 1000 mg is carried out on thicker layers. PLC is performed for isolation of compounds to be used in other tasks, i.e., further identification by various analytical methods, such as ultraviolet (UV) solution spectrometry [1] or gas chromatography/mass spectrometry (GC/MS) [2], obtaining analytical standards, or investigations of chemical or biological properties [3]. 

The most significant differences (i.e. independence) in the analytical methods are provided in the final chromatographic separation and detection step using GC/ MS and LC-FL. GC and reversed-phase LG provide significantly different separation mechanisms for PAHs and thus provide the independence required in the separation. The use of mass spectrometry (MS) for the GC detection and fluorescence spectroscopy for the LG detection provide further independence in the methods, e.g. MS can not differentiate among PAH isomers whereas fluorescence spectroscopy often can. For the GC/MS analyses the 5% phenyl methylpolysiloxane phase has been a commonly used phase for the separation of PAHs however, several important PAH isomers are not completely resolved on this phase, i.e. chrysene and triphenylene, benzo[b]fluoranthene and benzofjjfluoranthene, and diben-z[o,h]anthracene and dibenz[a,c]anthracene. To achieve separation of these isomers, GC/MS analyses were also performed using two other phases with different selectivity, a 50% phenyl methylpolysiloxane phase and a smectic liquid crystalline phase. 

Owing to the complexity of multi-residue methods for products of animal origin, it is not possible to outline a simple scheme however, readers should refer to methods described in two references for detailed guidance (Analytical Methods for Pesticides in Foodstuffs, Dutch method collection and European Norm EN 1528. ) There is no multi-method specifically designed for body fluids and tissues. The latter matrix can be partly covered by methods for products of animal origin. However, an approach published by Frenzel et al may be helpful (method principle whole blood is hemolyzed and then deproteinized. After extraction of the supernatant, the a.i. is determined by GC/MS. The LOQ is in the range 30-200 ag depending on the a.i.). 

Confirmatory techniques must be submitted if the analytical method is not highly specific. A confirmatory method will not be required if the original method uses GC/MS, provided that at least three fragment ions with an m z ratio of >100 are used for identification/quantitation. The rationale for the selection of the ions monitored should also be provided. When a confirmatory method/technique is required to demonstrate specificity, the properties of the analyte should be considered when deciding on an appropriate method/technique. In SANCO/825/00 acceptable confirmatory techniques are specified as follows ... 

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