Direct sample introduction

Also, direct determination of additives by means of laser desorption in solid polymeric materials rather than in polymer extracts has been reported [266], Takayama et al. [267] have described the direct detection of additives on the surface of LLDPE/(Chimassorb 944 LD and Irgafos P-EPQ) after matrix (THAP)-coating. As shown in Scheme 7.13, direct inlet mass spectrometry is also applicable to transfer TLC-MS and TLC-MS/MS analyses without the need for prior analysis. For direct sample introduction a small amount of the selected... 

Jinno, K., Nakanishi, S. and Fujimoto, C. (1985) Direct sample introduction system for inductively coupled plasma emission spectrometric detection in microcolumn liquid chromatography. Anal. Chem., 57, 2229-2235. 

Extraction of acidified, hydrolyzed urine with dichloromethane, followed by gas chromatography Colorimetric determination of phosphates Extraction into benzene gas chromatographic analysis Gas chromatography with direct sample introduction Formation of volatile methyl ester gas chromatography... 

Falkovich AH, Rudich Y. 2001. Analysis of semivolatile organic compounds in atmospheric aerosols by direct sample introduction thermal desorption CC/MS. Environ SciTechnol 35 2326-2333. 

Fig. 13. Rapid capillary electrophoresis (CE) microchip measurements of TNT obtained by direct sample introduction into the separation channel 80 alternate injections of (a) 10 and (b) 5ppm TNT solutions. Reproduced with permission from Chen and Wang [34],...

The amount of sample required to obtain a spectrum is of the order of 0.01 mg (direct sample introduction system) to 1 mg (indirect sample introduction system). Purity of the sample is desirable, but in many cases not essential. Usually up to 10% of impurity (much more even of low molecular weight compounds) does not seriously interfere with the interpretation. In some instances, information about the structures of the different compounds may be obtained even from mixtures. 

Direct sample introduction without any derivatization is used as an alternative to derivatization and is most commonly applied to VFA. GC introduction techniques include direct aqueous and solvent injections, ° " ° headspace, and more recently solid-phase microextraction (SPME) Specially designed capillary GC columns with polar phases are typically followed... 

A number of important sample preparation techniques rely upon gas extraction or the analysis of samples in the gas phase. These samples usually contain low concentrations of volatile analytes and higher concentrations of water vapor in a low molecular weight gas or air. Direct sample introduction by syringe or valves is only suitable for small volumes of relatively concentrated samples (section 3.4.2). More common sample introduction methods involve analyte accumulation by sorbent or cryogenic trapping followed by vaporization in the presence of a flow of gas to transport the... 

An important characteristic of electrospray ionization is that it is readily adapted to direct sample introduction from high-performance liquid chromatography and capillary electrophoresis columns. These applications are described in Chapters 28 and, V), That there is little fragmentation of the analyte makes... 

A, a standard scries of 25-100 /zg I Pb B, 100 /ig I Pb in sea water matrix. C, recording obtained from standard series of 2.5-10 mg P Pb using conventional direct sample introduction. Reproduced by permission of Elsevier Science Publishers... 

A direct sample introduction system is suitable for pure liquids and solids. Here, the sample is placed on the point of a movable rod which can be introduced into the ion source through a special valve. The sample is then vaporized and broken down into ionized fragments. 

Since electron bombardment occurs in the gaseous phase, the volatility of the sample becomes a critical factor in mass spectrometry. This feature was mainly responsible for the slow development of mass spectrometry in organic chemistry, and more specifically in natural products chemistry. In 1955 the technique of direct sample introduction through a vacuum lock (13) into the ionizing chamber was applied (14-17). This modification allowed the study of samples of relatively low volatility and those which are thermally unstable. Polyfunctional compounds of low volatility can be rendered more volatile by a suitable selection of substituents or by chemical modification. 

DSI, direct sample introduction DMI, difficult matrix injection. 

Cramers, C.A. Vermeer, E.A. Direct sample introduction of high boiling compounds onto glass capillary columns. Comparison of manual and automatic sampling. Chromatographia 1975, 8 (9), 479-481. 

DIRECT SAMPLE INTRODUCTION MASS SPECTROMETRY (DSIMS) ANALYSIS OF SURROGATES IN CONTACT WITH PERMEABLE MATERIALS... 

FIGURE 22.10 Direct sample introduction mass spectra acquired from a polyethylene sample exposed to 1 pg of diethyl eth-ylphosphonate. (A) Spectrum acquired after 20 s in vacuum (Cac)- (B) Cac = 200 s. (C) Cac = 600 s. 

---