Additives, determination chromatography , with

The effects of pH on electrokinetic velocities in micellar electrokinetic chromatography was studied by using sodium dodecyl sulfate solutions [179]. Micellar electrokinetic capillary chromatography with a sodium dodecyl sulfate pseudostationary phase has been used to determine the partition constants for nitrophenols, thiazolylazo dyes, and metal chelate compounds [180]. A similar technique was used to separate hydroquinone and some of its ether derivatives. This analysis is suitable for the determination of hydroquinone in skin-toning creams [181]. The ingredients of antipyretic analgesic preparations have also been determined by this technique [182], The addition of sodium dodecyl sulfate improves the peak shapes and resolution in chiral separations by micellar electrokinetic chromatography [183]. 

The introduction of g.l.c. for oligosaccharide analysis constituted a major breakthrough in the field. In addition to strategies for accurate and sensitive quantitation of monosaccharide type (19,20), chiral procedures may be adopted for enantiomeric (d and l) determination (21). The sensitivity of h.p.a.e. chromatography with pulsed amperometric detection now provides an alternative to g.l.c. for oligosaccharide compositional analysis (22). 

Karasek et al. [1] determined hydrocarbons in benzene water extracts (pH7) of soil and in incinerator or fly ash by a variety of techniques including gas chromatography with flame ionization, electron capture and mass spectrometric detectors. Benzene water extractants were adjusted to pH4, 7 and 10 before the extraction in order to selectively extract various types of acidic and basic organic compounds in addition to hydrocarbons. 

Structure elucidation of semiochemicals by modern NMR-techniques (including HPLC/NMR) is often hampered by the very small amounts of available material and problems in the isolation of pure compounds from the complex mixtures they are embedded in. Thus, the combination of gas chromatography and mass spectrometry, GC/MS, is frequently the method of choice. Determination of the molecular mass of the target compound (by chemical ionisation) and its atomic composition (by high resolution mass spectrometry) as well as a careful use of MS-Ubraries (mass spectra of beetle pheromones and their fragmentation pattern have been described [27]) and gas chromatographic retention indices will certainly facihtate the identification procedure. In addition, the combination of gas chromatography with Fourier-transform infrared spec-... 

Unlike the previous techniques, sensitivity is not an issue for AAA. There are few interfering substances because the method involves hydrolysis, derivatization, and chromatography with detection at a unique wavelength. Most excipients will not affect the hydrolysis step, but one has to be careful to ensure that the amino acids used to quantitate the protein are not destroyed. In addition, it must be determined if the excipients interfere with the derivatization chemistry or the chromatography. A BSA standard in the same buffer formulation is routinely run in parallel to the target protein to ensure the accuracy of the method. 

Although the focus of many tests is analysis of the hydrocarbon constituents of naphtha and other petroleum fractions, heteroatoms compounds that contain sulfur and nitrogen atoms cannot be ignored, and methods for their determination are available. The combination of gas chromatography with element-selective detection gives information about the distribution of the element. In addition, many individual heteroatomic compounds can be determined. 

Determination of Inorganic Oxyhalide Disinfection By-products in Drinking Water using Ion Chromatography with the Addition of a Postcolumn Reagent for Trace Bromate Analysis... 

V Seidel, E Poglits, K Schiller, W Lindner. Simultaneous determination of ochratoxin A and zearalenone in maize by reversed-phase high-performance liquid chromatography with fluorescence detection and/8-cyclodextrin as mobile phase additive. J Chrom 635 227-235,1993. 

Figure 11.14 Analysis of amphetamines by GC-NPD following HS-SPME extraction from human hair (a) Normal hair (b) normal hair after addition of amphetamine (1.5 ng) and methamphetamine (16.1 ng) (c) hair of an amphetamine abuser. Peak identification is as follows 1, a-phenethylamine (internal standard) 2, amphetamine 3, methamphetamine 4, N-propyl-/)-phenethyamine (internal standard). Reprinted from Journal of Chronatography, B 707,1. Koide et al., Determination of amphetamine and methamphetamine in human hair by headspace solid-phase microextraction and gas chromatography with nitrogen-phosphorus detection, pp. 99-104, copyright 1998, with permission from Elsevier Science.

A technique for the determination of methylmercury in aqueous samples (natural and seawater) involved the conversion of methylmercury to gaseous methyl-ethylmercury by reaction with sodium tetraethylborate (Bloom, 1989 Bloom and Watras, 1989). The volatile derivative was purged from the solution and concentrated on a graphitic column at room temperature. The derivative was thermally desorbed from the column, and then analysed by cryogenic gas chromatography with cold vapour atomic fluorescence detection. In addition to methylmercury, labile Hg11 species could be determined (as diethylmercury) as well as dimethylmercury (which is not ethylated). The detection limit for... 

Takeda et al. [4] studied the migration behaviour of phthalate esters in micellar electrokinetic chromatography with and without the addition of butyl alcohol. This procedure was applied to the determination of phthalate esters in environmental waters. 

For the determination of nitrate, use a 1 dram vial with a polyethylene stopper (Kimble No. 60975-L) as a reaction vessel. Introduce a 0.20ml aliquot of aqueous sample into the vial, followed by 1.0ml of thiophen free benzene. Catalyse the reaction by addition of 1.0ml of concentrated sulphuric acid. Shake the vial for lOmin. Remove the benzene layer immediately from the reaction vial with a Pasteur pipette, place it in a separate vial and analyse by gas chromatography with electron capture detection for the nitrobenzene concentration generated. Treat standard solutions of potassium nitrate in the same manner to generate a standard calibration plot relating nitrobenzene concentration to peak height. If higher precision is desired (approximately 4% relative standard deviation), add 2,5-dimethylnitrobenzene to the benzene prior to reaction. 

SPECIES-SPECIFIC DETERMINATION OF METAL(LOID)-CONTAINING FOOD ADDITIVES AND CONTAMINANTS BY CHROMATOGRAPHY WITH ICP-MS DETECTION... 

Gas chromatography has been used to determine arsine in hydrogen-rich mixtures. The arsine was detected on a column containing dioctyl phthalate on polyoxyethylene-glycol as adsorbent with hydrogen as the carrier gas. The limit of detection as arsenious oxide was 0.001 mg. In addition, determinations of down to 4.2 x 10 gl of arsine in silane on various columns have been developed , using dry nitrogen as carrier gas and a... 

FDA Use of ETU as a food additive is prohibited. EPA (1995) Health Advisory for long-term exposure is 0.4 mg/L. Can be monitored in water by EPA Method 509 - Determination of Ethylene Thiourea (ETU) in Water Using Gas Chromatography with a Nitrogen-Phosphorus Detector. FAO/WHO (1993) ADI 0.004 mg/kg BW. 

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