Direct sample injection

Atomic absorption spectroscopy is an alternative to the colorimetric method. Arsine is stiU generated but is purged into a heated open-end tube furnace or an argon—hydrogen flame for atomi2ation of the arsenic and measurement. Arsenic can also be measured by direct sample injection into the graphite furnace. The detection limit with the air—acetylene flame is too high to be useful for most water analysis. 

Figure 13.7 Selectivity effected by employing different step gradients in the coupled-column RPLC analysis of a surface water containing 0.40 p-g 1 bentazone, by using direct sample injection (2.00 ml). Clean-up volumes, (a), (c) and (d) 4.65 ml of M-1, and (b) 3.75 ml of M-1 transfer volumes, (a), (c) and (d), 0.50 ml of M-1, and (b), 0.40 ml of M-1. The displayed cliromatograms start after clean-up on the first column. Reprinted from Journal of Chromatography, A 644, E. A. Hogendoom et al, Coupled-column reversed-phase liquid chromatography-UV analyser for the determination of polar pesticides in water , pp. 307-314, copyright 1993, with permission from Elsevier Science.

Direct sample injection and large-volume injection... 

S.J. Bogoslovski, K.A. Sakodynskii, and A.A. Serdan, in Diphil Sorbents for Direct Sample Injection of Drugs in Biological Matrices, 19th Int. Symp. Chromatogr., Aix-en-Provence, France (1992). 

Hollenbach et al. captured "Tc from standards or soil sample digestates on a TEVA-Resin column for on-line purification and preconcentration prior to ICP-MS determination.49 A wash solution of 0.5 M HN03 was used to remove interferences prior to elution with 8 M HN03 solution. A Re isotope, which behaves similarly to pertechnetate on TEVA-Resin, was used as an internal standard. Recoveries from the column varied from 97 to 99.5%, and columns could be reused over a hundred times. The use of the on-line column separation reduced detection limits by 10-fold and alleviated matrix and isobaric interferences compared to direct sample injection. This pioneering study adapted FIAS-200 and FIAS-400 FI systems to perform sample injection and extraction-chromatographic separations upstream from the ICP-MS. 

In addition to the examples discussed above, a number of other xenobiotics are measured by their phase I reaction products. These compounds and their metabolites are listed in Table 20.1. These methods are for metabolites in urine. Normally, the urine sample is acidified to release the phase I metabolites from phase II conjugates that they might have formed, and except where direct sample injection is employed, the analyte is collected as vapor or extracted into an organic solvent. In some cases, the analyte is reacted with a reagent that produces a volatile derivative that is readily separated and detected by gas chromatography. 

Grob, K., and Grob, G. (1972). Techniques of capillary gas chromatography. Possibilities of the full utilisation of high performance columns. Part I Direct sample injection. Chromatographic 5, 3-12. 

Thormann W, Minger A, Molteni S, Caslavska J, Gebauer P (1992) Determination of substituted purine in body fluids by micellar electrokinetic capillary chromatography with direct sample injection. J Chromatogr 593 275-288. 

A caveat for aU direct sample injection assays is an understanding of the analyte chemical stability in the biological fluid during the analysis period. Nonetheless, an increasingly growing body of literature is suggestive that direct injection of post-dose biological fluids for quantification purposes has become a routine and efficient procedure. 

Micellar electrokinetic capillary chromatography (MEKC) is used, often, for separating neutral and hydrophobic molecules. The surfactants in MEKC have the added advantage of solubilizing proteins. This can eliminate the need for extraction or deproteinization, allowing direct sample injection. The effect of sample matrix in MEKC is less dramatic than that in CZE. A... 

Helander A, Beck 0> Wennberg M, Wikstrom T, Jacobsson G. Determination of urinary 5-hydroxyindole-3-acetic acid by high-performance liquid chromatography with electrochemical detection and direct sample injection. Anal Biochem 1991 196 170-3. 

Skrinska V, Hahn S. High-performance Hquid chromatography of 5-hydroxyindole-3-acetic acid in urine with direct sample injection. J Chromatogr 1984 311 380-4. 

The chromatogram of a cooling water is displayed in Fig. 8-20. The sample was diluted 1 10 with de-ionized water to avoid overloading the separator column. A direct sample injection is not feasible due to its high electrolyte content, since the conductance is not proportional to the solute concentration in this concentration range. 

Bentrop, D. Warren, F.V., Jr. Schmitz, S. Bidlingmeyer, B.A. Analysis of carbamazepine in serum by Uquid chromatography with direct sample injection and surfactant-containing eluents. J.Chromatogr., 1990, 535, 293-304... 

Schmitz, S. Warren, F.V. Bidlingmeyer, BA. Analysis of carbamazepine and its 10,11-epoxide in serum by direct sample injection using surfactant containing eluents and column switching. 

Shibukawa, A. Terakita, A. He, J.Y. Nakagawa, T. High-performance frontal analysis-high-performance liquid chromatographic stem for stereoselective determination of unbound ketoprofen enantiomers in plasma after direct sample injection. J.Pharm.Sci., 1992,81, 710—715 [plasma column-switching column temp 15 chiral LOD 1 nM human rat]... 

Most AEC methods use direct sample injections vial a sample loop, thus achieving adequate detection limits." " Aqueous sample matrices usually do not require any sample pretreatment other than possibly filtration prior to injection. For matrices such as airborne particles, soil, or filters from air collection devices, organic acids are commonly transferred into an aqueous solution which can then be injected directly into the ion chromatograph. ° ° ... 

Nishi H, Fukuyama T, Matsuo M (1990). Separation and determination of aspoxicillin in human plasma by micellar electrokinetic chromatography with direct sample injection./. Chromatogr. 515 245-255. 

Yang, Y. H., Wu, W. Y, Yeh, H. H., and Chen, S. H. Simultaneous determination of cefepime and vancomycin in plasma and cerebrospinal fluid by MEKC with direct sample injection and application for bacterial meningitis. Electrophoresis, 28, 1788, 2007. 

A. Shibukawa et al.. Stereoselective determination of free warfarin concentration in protein binding equilibrium using direct sample injection and an on-line liquid chromatographic system. Analytical Chemistry, 62, no.7(1990)712. 

M. Lin, N. Wu and J.H. Aiken, Micellar HPLC Separation of Serum Bilirubin Species with Direct Sample Injection, J. Liq. Chromatogr., 18 1219 (1995). 

I. Perez Martinez, S. Sagrado and M.J. Medina Hernandez, A Rapid Procedure for the Determination of Caffeine, Theophylline and Theobromine in Urine by MLC and Direct Sample Injection, Anal Chim. Acta, 304 195 (1995). 

Procedures based on separation techniques such as HPLC and IC have been developed for single element analysis for the following two reasons. The first reason is to remove interferents in complicated sample matrices that can give rise to incorrect results, in particular for trace analysis in samples with a high organic content, such as the determination of total iodine in egg products. The second reason is to differentiate the total and free forms of a specific element, such as the determination of the free iodide ion and bounded iodine in food additives. The free iodide ion is determined by direct sample injection into the IC column, whereas the total iodine content is determined after oxygen flask combustion. Thus, both the free and bounded forms of iodine in food samples can be determined. 

Brunetto, M.R. Morales, A.R. Gallignani, M. Burguera, J.L. Burguera, M. Determination of paraquat in human blood plasma using reverse-phase ion-pair high-performance liquid chromatography with direct sample injection. Talanta 2003, 59, 913-921. 

Riboflavin, flavin mononucleotide, and flavin-adenine dinucleotide, precursors to skuny odors in some beverages, were determined from a direct sample injection. These compounds were separated on a C,g column (A = 265 nm, ex 525 nm, em) in 9min using a complex 8-min 95/5 5/95 water (50 mM NaH2P04 to pH 3.0 with... 

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