Sample introduction by laser ablation has many desirable features: reduction of the time involved in sample pre-analysis processing, avoiding the use of hazardous reagents and reducing the risk of contamination by reagent impurities. It is also possible to produce spatial analytical profiles across small sections of samples. Laser spots of < 10 μm diameter are possible With the latest commercial instrumentation. Additionally, for plasma spectrometry, the presence of molecular species derived from the plasma gases and the solvent vapour results in interferences, particularly for elements with an atomic mass of less than 80. Sampling with a laser removes the need for a solvent. The type of laser used for sampling is an important consideration. Ultraviolet lasers give better coupling between the laser and sample with ablation being mainly photochemical in nature. With infrared lasers, coupling with some samples is inefficient and is generally thermal m nature leading to poor crater definition. Calibration is one of the main difficulties associated with quantitative analysis by laser ablation. The majority of papers associated with the use of lasers for solid sampling give reference to the difficulty of reproducible calibration and in particular the lack of matrix matched standards The most commonly used calibration method to date involves the use of the National Institute of Standards and Technology (NIST) standard reference materials, particularly the 600 series glass standards. The disadvantages associated with these standards are: the analyst has no control over the elemental make up of the standard, they are relatively expensive and most importantly the matrix is fixed and cannot be matched to the sample. This thesis describes a calibration technique based on the ablation of aqueous standards. Water is transparent to the commonly used UV laser wavelengths, 193,248 and 266 nm resulting in poor energy coupling between the laser and the aqueous standard. The addition of a photo-stable chromophore results in modification of the standards absorption coefficient and enables them to mimic the behaviour of solid samples. the benefit of such standards is that they are easy to produce in any analytical laboratory. The elemental and matrix composition can be controlled by the analyst. The standards also offer the advantage of a constantly renewable surface. Initial work involved design and set-up of an optical system and laser to couple the laser with an ICP-MS. Poly( sodium 4-styrene-sulphonate) was identified as a suitable chromophore. The main criteria for the additive being that it absorbed at the excimer laser wavelengths and had an acceptable lifetime to allow adequate analytical data to be generated Investigation into the characteristics of the chromophore including effect of concentration, laser energy and laser frequency were investigated. Calibration and validation of the aqueous calibration technique was demonstrated by comparison with NIST standard reference materials. The absorption coefficient of the aqueous standard was matched with that of the NIST reference material. Both samples were then analysed by ICP-MS. The count rates observed were initially found to be similar for both samples, however the signal for the aqueous standard remained stable but the signal for the NIST glass decreased. This was thought to be due to the laser channelling into the solid sample causing loss of focus. The aqueous standard in effect provides a constantly renewable surface and no loss of focus. An internal standard was used to correct for the differing sensitivities obtained. The final part of the work involved application of the calibration method to two biological matrices: Bone samples from patients with osteoporosis and porcine liver samples. Elemental profiles across the samples are presented which are in general agreement with the expected and certified concentrations.

The performance of a quadrupole mass filter operated in the RF-only mode has been investigated. A discussion of both the formal and qualitative theories of quadrupole mass analyzers is given. Data is presented which demonstrates that the transmission properties of such devices deviate markedly from those which would be predicted from the Mathieu stability diagram. The transmission efficiency of ionic species, through an RF-only quadrupole, is shown to depend primarily on three factors. The first of these is the formal stability of the ion trajectory as summarized by the coordinates of the particle in a, q space. The second factor is the acceptance aperture of the quadruople in combination with the emittance of the ion source. The final factor is shown to be spacial focusing conditions which arise due to the nature of the frequency components that are contained within the trajectory of an ion as it traverses the quadrupole electrode structure. The theory of such spacial focusing conditions is reported. The measurement of naturally occurring isotope abundance ratios is used to demonstrate the magnitude of errors which may result due to the nonideal transmission properties of the RF-only quadrupole. Suggestions are provided to minimize such mass discrimination effects. Additional experiments dealing with the quadrupole notch filter are described. Performance of a unique voltage tuned quadrupole notch filter is demonstrated. The theory, design, and construction details of such a device are reported.

No description available.

A presente dissertação tem por objetivo o estudo da existência de ponte de hidrogênio intramolecular na o-mercapto-N,N-dimetilbenzamida (I), composto ainda não descrito na literatura (ver arquivo). É apresentado um apanhado bibliográfico dos trabalhos mais significativos sobre a habilidade do mercapto grupo, em benzenotióis, para formar pontes de hidrogênio inter e intramoleculares. Nesta revisão pudemos notar que dentre os tióis aromáticos orto substituídos estudados, somente existem evidências espectroscópicas de pontes de hidrogênio intramoleculares relativamente fortes, no ácido tiosalicílico e nos respectivos ésteres. São descritas as sínteses dos seguintes compostos: N, N-dimetilbenzamida, o-mercapto-N, N-dimetilbenzamida, p-mercapto-N, N-dimetilbenzamida, o-metiltio-N, N-dimetilbenzamida, p-metiltio-N, N-dimetilbenzamida, o-mercapto-N, N-dimetilbenzamida S-deuterada e p-mercapto-N, N-dimetilbenzamida S-deuterada. A p-mercapto-N, N-dimetilbenzamida não descrita na literatura foi caracterizada e analizada. É apresentado um estudo espectroscópico comparativo da o-mercapto-N, N-dimetilbenzamida e compostos correlacionados, sendo fornecidos os dados de frequência de estiramento no IV e de deslocamento químico na RMN de SH, em vários solventes e os das frequências de estiramento do grupo carbonílico. São também apresentados os valores das constantes de associação dos complexos SH .... DMSO. A existência da ponte de hidrogênio intramolecular em o-mercapto-N, N-dimetilbenzamida é sugerida dos seguintes dados: 1. A banda de absorção correspondente à vibração de estiramento S-H da o-mercapto-N, N-dimetilbenzamida, em tetracloreto de carbono, é deslocada para frequências menores e intensificada quando comparada com a p-mercapto-N, N-dimetilbenzamida. 2. Enquanto que os espectros no IV, em clorofórmio, do benzenotiol e da p-mercapto-N, N-dimetilbenzamida apresentam uma banda de SH ligeiramente deslocada para frequências menores, o da o-mercapto-N, N-dimetilbenzamida apresenta uma banda de SH anormalmente deslocada para frequências maiores e há o aparecimento de uma outra banda na região de frequência normal de SH, que pode ser atribuída ao grupo SH não associado. Para explicar estes dados foi sugerida a existência, em clorofórmio, do seguinte equilíbrio: (ver arquivo) 3. Nas medidas efetuadas no IV com DMSO em tetracloreto de carbono, observa-se, nos três benzenotióis, a existência de duas bandas de SH. Enquanto que o deslocamento de frequência (&#916;vSH) no caso da p-mercapto-N, N-dimetilbenzamida é maior do que no do benzenotiol, no da o-mercapto-N, N-dimetilbenzamida é ainda menor do que no de benzenotiol, resultado este contrário a ordem de acidez esperada. 4. Enquanto nos espectros de RMN, em tetracloreto de carbono, os sinais de SH para o benzenotiol e p-mercapto-N, N-dimetilbenzamida não diferem significativamente em posição, o da o-mercapto-N, N-dimetilbenzamida aparece em campo mais baixo. 5. A comparação dos dados da RMN em clorofórmio deuterado com os de tetracloreto de carbono mostram que, enquanto os sinais do próton de SH no benzenotiol e na p-mercapto-N, N-dimetilbenzamida se deslocam para campos mais baixos, o de SH na o-mercapto-N, N-dimetilbenzamida se desloca para campo mais alto. Este fato é concordante com a contribuição da forma não associada do grupo S-H em clorofórmio deuterado e apoia a existência do equilíbrio sugerido pelos dados do IV. 6. A comparação dos dados de RMN em tetracloreto de carbono, contendo DMSO, com os em tetracloreto de carbono confirmam os obtidos pelo IV, isto é o valor &#916;v(SH) para o o-mercapto-N, N-dimetilbenzamida é menor do que o do para derivado. 7. Os valores das constantes de associação (Kass) de SH----DMSO indicam que a constante de associação da p-mercapto-N, N-dimetilbenzamida é consideravelmente maior do que a do orto derivado. 8. A banda de absorção da carbonila em o-mercapto-N, N-dimetilbenzamida é simétrica e deslocada ligeiramente para frequências menores, em comparação com o para derivado. Este fato sugere que o grupo SH é ligado ao oxigênio carbonílico e não ao nitrogênio amídico. / This thesis investigates the existence of intramolecular hydrogen bonding in the o-mercapto-N, N-dimethylbenzamide (I), compound not previously reported (see file). The literature report on the hability of mercapto group in benzenethiols to form inter and intramolecular hydrogen bonds, is presented. It shows that the thiosalicylic acid and its esters are the only o-substituted aromatic thiols, in which the significative intramolecular hydrogen bonding was reported to occur. The syntheses of the following compounds are presented: N, N-dimethylbenzamide, o-mercapto-N, N-dimethylbenzamide, p-mercapto-N, N-dimethylbenzamide, o-methylthio-N, N-dimethylbenzamide, p-methylthio-N, N-dimethylbenzamide, S-deuterated-o-mercapto-N, N-dimethylbenzemide and S-deuterated p-mercapto-N, N-dimethylbenzamide. A comparative spectroscopic study of the o-mercapto-N, N-dimethylbenzamide and related compounds is presented, being measured SH stretching frequencies and chemical shifts in carbon tetrachloride, chloroform and carbon tetrachloride, containing DMSO, as well the carbonyl stretching frequencies. The association constants for SH----DMSO complex formation are also determined. The existence of intramolecular hydrogen bonding in the o-mercapto-N, N-dimethylbenzamide is suggested from the followings data: 1. The absorption band due to SH stretching of the o-mercapto-N, N-dimethylbenzamide, in carbon tetrachloride, is shifted to lower frequencies and intensified. 2. Although, in the i. r. spectra of benzenethiol and p-mercapto-N, N-dimethylbenzamide, in chloroform, a slight shift of the SH band to lower frequencies is observed, in comparison with the spectra in carbon tetrachloride, in the o-mercapto-N, N-dimethylbenzamide a band at higher frequency appears, together with a band at the normal SH frequency. These data suggest that in chloroform the fol1owing equilibrium takes place: (see file). 3. In the IR spectra of the three benzenethiols, in carbon tetrachloride, containing DMSO, the existence of two bands in the SH region is observed. The frequency shift (&#916;vSH) in the case of p-mercapto-N, N-dimethylbenzamide in larger than in that of benzenethiol. However, the shift for the o-mercapto-N, N-dimethylbenzamide is smaller than that for benzenethiol. The latter result is in disaccord with the acidity order. 4. In the NMR spectra, in carbon tetrachloride, while the position of the SH signals for benzenethiol and p-mercapto-N, N-dimethylbenzamide do not differ, that for the o-mercapto-N, N-dimethylbenzamide appears at lower field. 5. The comparison of the NMR data in deuterated chloroform with those in carbon tetrachloride indicates a shift of SH signals in benzenethiol and p-mercapto-N, N-dimethylbenzamide to lower f1elds and of that in the corresponding p-derivative to higher field. This fact gives a support to the contribution of the SH non-associated in deuterated chloroform and to the existence of equilibrium suggested from the IR data. 6. The comparison of the NMR data, in carbon tetrachloride, containing deuterated DMSO, with those in carbon tetrachloride alone, confirms the IR, as the &#916;v(SH) data for the o-mercapto-N, N-dimethylbenzamide is smaller than that for the para derivative. 7. The Kass value of SH----DMSO complex formation for the p-mercapto-N, N-dimethylbenzamide is larger than that for the orto-derivative. 8. The carbonyl stretching absorption for the o-mercapto-N, N-dimethylbenzamide is symmetric and slightly shifted to lower frequency, in comparison with the para-derivative. This fact suggests that the SH group is bonded to the carbonyl-oxygen and not to the nitrogen.

A presente dissertação tem por objetivo o estudo da existência de ponte de hidrogênio intramolecular na o-mercapto-N,N-dimetilbenzamida (I), composto ainda não descrito na literatura (ver arquivo). É apresentado um apanhado bibliográfico dos trabalhos mais significativos sobre a habilidade do mercapto grupo, em benzenotióis, para formar pontes de hidrogênio inter e intramoleculares. Nesta revisão pudemos notar que dentre os tióis aromáticos orto substituídos estudados, somente existem evidências espectroscópicas de pontes de hidrogênio intramoleculares relativamente fortes, no ácido tiosalicílico e nos respectivos ésteres. São descritas as sínteses dos seguintes compostos: N, N-dimetilbenzamida, o-mercapto-N, N-dimetilbenzamida, p-mercapto-N, N-dimetilbenzamida, o-metiltio-N, N-dimetilbenzamida, p-metiltio-N, N-dimetilbenzamida, o-mercapto-N, N-dimetilbenzamida S-deuterada e p-mercapto-N, N-dimetilbenzamida S-deuterada. A p-mercapto-N, N-dimetilbenzamida não descrita na literatura foi caracterizada e analizada. É apresentado um estudo espectroscópico comparativo da o-mercapto-N, N-dimetilbenzamida e compostos correlacionados, sendo fornecidos os dados de frequência de estiramento no IV e de deslocamento químico na RMN de SH, em vários solventes e os das frequências de estiramento do grupo carbonílico. São também apresentados os valores das constantes de associação dos complexos SH .... DMSO. A existência da ponte de hidrogênio intramolecular em o-mercapto-N, N-dimetilbenzamida é sugerida dos seguintes dados: 1. A banda de absorção correspondente à vibração de estiramento S-H da o-mercapto-N, N-dimetilbenzamida, em tetracloreto de carbono, é deslocada para frequências menores e intensificada quando comparada com a p-mercapto-N, N-dimetilbenzamida. 2. Enquanto que os espectros no IV, em clorofórmio, do benzenotiol e da p-mercapto-N, N-dimetilbenzamida apresentam uma banda de SH ligeiramente deslocada para frequências menores, o da o-mercapto-N, N-dimetilbenzamida apresenta uma banda de SH anormalmente deslocada para frequências maiores e há o aparecimento de uma outra banda na região de frequência normal de SH, que pode ser atribuída ao grupo SH não associado. Para explicar estes dados foi sugerida a existência, em clorofórmio, do seguinte equilíbrio: (ver arquivo) 3. Nas medidas efetuadas no IV com DMSO em tetracloreto de carbono, observa-se, nos três benzenotióis, a existência de duas bandas de SH. Enquanto que o deslocamento de frequência (&#916;vSH) no caso da p-mercapto-N, N-dimetilbenzamida é maior do que no do benzenotiol, no da o-mercapto-N, N-dimetilbenzamida é ainda menor do que no de benzenotiol, resultado este contrário a ordem de acidez esperada. 4. Enquanto nos espectros de RMN, em tetracloreto de carbono, os sinais de SH para o benzenotiol e p-mercapto-N, N-dimetilbenzamida não diferem significativamente em posição, o da o-mercapto-N, N-dimetilbenzamida aparece em campo mais baixo. 5. A comparação dos dados da RMN em clorofórmio deuterado com os de tetracloreto de carbono mostram que, enquanto os sinais do próton de SH no benzenotiol e na p-mercapto-N, N-dimetilbenzamida se deslocam para campos mais baixos, o de SH na o-mercapto-N, N-dimetilbenzamida se desloca para campo mais alto. Este fato é concordante com a contribuição da forma não associada do grupo S-H em clorofórmio deuterado e apoia a existência do equilíbrio sugerido pelos dados do IV. 6. A comparação dos dados de RMN em tetracloreto de carbono, contendo DMSO, com os em tetracloreto de carbono confirmam os obtidos pelo IV, isto é o valor &#916;v(SH) para o o-mercapto-N, N-dimetilbenzamida é menor do que o do para derivado. 7. Os valores das constantes de associação (Kass) de SH----DMSO indicam que a constante de associação da p-mercapto-N, N-dimetilbenzamida é consideravelmente maior do que a do orto derivado. 8. A banda de absorção da carbonila em o-mercapto-N, N-dimetilbenzamida é simétrica e deslocada ligeiramente para frequências menores, em comparação com o para derivado. Este fato sugere que o grupo SH é ligado ao oxigênio carbonílico e não ao nitrogênio amídico. / This thesis investigates the existence of intramolecular hydrogen bonding in the o-mercapto-N, N-dimethylbenzamide (I), compound not previously reported (see file). The literature report on the hability of mercapto group in benzenethiols to form inter and intramolecular hydrogen bonds, is presented. It shows that the thiosalicylic acid and its esters are the only o-substituted aromatic thiols, in which the significative intramolecular hydrogen bonding was reported to occur. The syntheses of the following compounds are presented: N, N-dimethylbenzamide, o-mercapto-N, N-dimethylbenzamide, p-mercapto-N, N-dimethylbenzamide, o-methylthio-N, N-dimethylbenzamide, p-methylthio-N, N-dimethylbenzamide, S-deuterated-o-mercapto-N, N-dimethylbenzemide and S-deuterated p-mercapto-N, N-dimethylbenzamide. A comparative spectroscopic study of the o-mercapto-N, N-dimethylbenzamide and related compounds is presented, being measured SH stretching frequencies and chemical shifts in carbon tetrachloride, chloroform and carbon tetrachloride, containing DMSO, as well the carbonyl stretching frequencies. The association constants for SH----DMSO complex formation are also determined. The existence of intramolecular hydrogen bonding in the o-mercapto-N, N-dimethylbenzamide is suggested from the followings data: 1. The absorption band due to SH stretching of the o-mercapto-N, N-dimethylbenzamide, in carbon tetrachloride, is shifted to lower frequencies and intensified. 2. Although, in the i. r. spectra of benzenethiol and p-mercapto-N, N-dimethylbenzamide, in chloroform, a slight shift of the SH band to lower frequencies is observed, in comparison with the spectra in carbon tetrachloride, in the o-mercapto-N, N-dimethylbenzamide a band at higher frequency appears, together with a band at the normal SH frequency. These data suggest that in chloroform the fol1owing equilibrium takes place: (see file). 3. In the IR spectra of the three benzenethiols, in carbon tetrachloride, containing DMSO, the existence of two bands in the SH region is observed. The frequency shift (&#916;vSH) in the case of p-mercapto-N, N-dimethylbenzamide in larger than in that of benzenethiol. However, the shift for the o-mercapto-N, N-dimethylbenzamide is smaller than that for benzenethiol. The latter result is in disaccord with the acidity order. 4. In the NMR spectra, in carbon tetrachloride, while the position of the SH signals for benzenethiol and p-mercapto-N, N-dimethylbenzamide do not differ, that for the o-mercapto-N, N-dimethylbenzamide appears at lower field. 5. The comparison of the NMR data in deuterated chloroform with those in carbon tetrachloride indicates a shift of SH signals in benzenethiol and p-mercapto-N, N-dimethylbenzamide to lower f1elds and of that in the corresponding p-derivative to higher field. This fact gives a support to the contribution of the SH non-associated in deuterated chloroform and to the existence of equilibrium suggested from the IR data. 6. The comparison of the NMR data, in carbon tetrachloride, containing deuterated DMSO, with those in carbon tetrachloride alone, confirms the IR, as the &#916;v(SH) data for the o-mercapto-N, N-dimethylbenzamide is smaller than that for the para derivative. 7. The Kass value of SH----DMSO complex formation for the p-mercapto-N, N-dimethylbenzamide is larger than that for the orto-derivative. 8. The carbonyl stretching absorption for the o-mercapto-N, N-dimethylbenzamide is symmetric and slightly shifted to lower frequency, in comparison with the para-derivative. This fact suggests that the SH group is bonded to the carbonyl-oxygen and not to the nitrogen.

No description available.

Electrospray (ES)-based ambient ionization techniques have been rapidly developed and became indispensable tools for direct sample analysis using mass spectrometry. In this study, it was found that with the use of porous substrate, analytes present in complex samples could be detected by directly introducing untreated sample on porous tips. Moreover, the specific feature, micro-channels of the porous tips, allows efficient sample loading and facilitates electrospray ionization (ESI), which is beneficial for the direct sample analysis. Systematic study on the influences of the physical and chemical factors of various porous materials (polyester, polyethylene and wood) on the detection sensitivity and ionization efficiency was firstly investigated. It was found that the chemical interaction between the porous materials and analytes could significantly affect the detection sensitivity for analytes. Hydrophobic spraying tips showed better detection sensitivity for polar analytes while better detection for non-polar analytes was obtained when hydrophilic spraying tip was used. Moreover, the electrostatic properties of spraying tips could also affect the detection sensitivity for analytes. Hydrophobic materials (i.e., polyethylene and polyester) which tend to form negative charge on the surface could facilitate the ionization of analytes in negative ion mode. With a clear understanding of the effect of porous spraying materials on detection sensitivity, tip spray ionization mass spectrometric method was developed and successfully applied to direct analysis of pharmaceutical, forensic, clinical and food samples. Rotary sample stages compatible to the ion source of two commercial mass spectrometers were designed and constructed for the automation of tip spray ionization mass spectrometry, which allowed the analysis of 12 samples in less than 15 minutes. In addition, instead of using porous substrates for the sample deposition, the developed technique was further applied to the direct chemical analysis of American ginseng tissue, demonstrating the feasibility of performing direct analysis on raw herbs in solid state. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Chromium can act either as an essential micronutrient or a chemical carcinogen, depending on its oxidation state. Of the two most stable chromium oxidation states, Cr(VI) is a known carcinogen, while Cr(III) is an essential element. Determination of total Cr cannot therefore be used to evaluate food safety of dairy products, as speciation is required for accurate assessment of potential toxicity. In this study, total Cr was determined by DRC-ICP-MS after mineralisation of freeze-dried milk samples. Chromabond NH2 ion-exchange columns were used to separate Cr(VI) from Cr(III). During the separation process, Cr(VI) was selectively adsorbed onto the Chromabond NH2 column. The retained Cr(VI) was subsequently eluted with two column volumes of 2 M HNO3 and diluted to a final volume of 10 mL. After separation, the Cr(VI) was quantified by DRC-ICP-MS, using O2 as the reactive gas, to alleviate polyatomic ion interference. An O2 gas flow rate of 0.85 ml/min and a high-pass rejection parameter q (Rpq) ¼ 0.5, provided the best compromise signal-to-noise ratio. The method was validated through determining the recovery in milk samples spiked with Cr(VI). The recoveries were quantitative and ranged from 96.4 to 99.2%. A whole milk powder reference material (NIST SRM 8435) was used to evaluate the accuracy of the total Cr quantification method. The observed value showed concordance with the certified value. The limits of detection (LOD) were 0.091 and 0.085 mg/L for total Cr and Cr(VI), respectively. These findings are important for the determination of maximum residue levels (MRLs) of Cr(VI) in dairy products.

No description available.

No description available.