Analysis of nitrosamines by GC2 with a photoionization detector

The use of a photoionization detector (PID) coupled to a glass capillary gas chromatography (GC²) separation system for the detection of carcinogenic nitrosamines was investigated. The components analyzed gave a linear response with a lower detection limit of 50 to 100 pg with the 10.2 eV ionization source. No detector response was obtained with an ionization energy of 9.5 eV. Chromatography of meat extracts indicated their complex molecular composition. Simple liquid chromatographic cleaning procedures significantly decreased the complexity of these samples, but not sufficiently for the accurate quantition of nitrosamine components.     

Application of a swept-potential electrochemical detector in the liquid-chroamtographic determination of nitrosamines

A swept-potential detector, operating in the square-wave voltammetric mode, is used in the liquid-chromatographic determination of a mixture of eight nitrosamines. Only three compounds were completely separated by the C-18 column. Three more were resolved by educing constant-potential chromatograms from the computer buffer. Mathematical deconvolution via fast-Fourier transform was applied to the remaining components.     

Direct separation and detection of biogenic amines by ion-pair liquid chromatography with chemiluminescent nitrogen detector

Analysis of biogenic amines is critical to pharmaceutical and food industry due to their biological importance. For many years, the determination of biogenic amines has relied on high performance liquid chromatography (HPLC) coupling with pre-, on-, or post-column derivatization procedures to enable UV or fluorescent detections. In this study, 14 biogenic amines were separated on a Phenomenex Luna Phenyl-Hexyl column by an ion-pair liquid chromatography method using perfluorocarboxylic acids as ion-pair reagents and detected by a chemiluminescent nitrogen detector (CLND). This direct separation and detection HPLC method eliminated the time consuming and cumbersome derivatization procedures. Compared with HPLC-UV (post-column derivatization with ninhydrin) and HPLC-charged aerosol detector (CAD) methods, this HPLC-CLND technique provided narrower peaks, better baselines, and improved separations and detections. Excellent linearity was acquired by CLND for each of the 14 biogenic amines ranging from less than 1 ng to about 1000 ng (on-column weights). The relative response factors determined by this LC-CLND method were proportional to the numbers of nitrogen atoms in each compound, which has been the characteristic of the equimolar determinations by CLND. In addition, a number of samples including beer, dairy beverage, herb tea, and vinegar were analyzed by the LC-CLND method with satisfactory precision and accuracy.     

Carbon response characteristics of a micro-flame ionization detector

The carbon response characteristics of a recently noted micro-flame ionization detector (μFID) mode are examined in detail. The μFID supports an extremely small (30 nL) “upside-down” flame that is generated from a low counter-current flow of oxygen immersed in hydrogen. Ionization measurements made in the μFID are directly compared to those obtained from a conventional FID. In terms of reproducibility of response and relative sensitivity towards different types of hydrocarbons, the μFID and a conventional FID produce no major differences with respect to either of these characteristics for a variety of compounds examined. Of note, for replicate measurements made in each detector, the average %R.S.D. of response typically differs by less than 2% between the two devices, while the average normalized sensitivity differs by less than 4%. In contrast to this, regarding absolute sensitivity, the analyte signal from the conventional air-rich FID is found to be three times larger than that of the hydrogen-rich μFID mode explored here. This discrepancy is ascribed directly to the difference in flame stoichiometry between the two detectors.     

Directional response of a scintillation detector to gamma-rays

The directional response of a scintillation detector to γ-rays has been studied for the full energy peak. The directivity measured has a lower value than that one corresponding to the total spectrum. This behaviour was attributed to the degradation of the peak-to-total ratio with the angle of γ-ray incidence.     

Characteristics of sulfur response in a micro-flame photometric detector

A recently reported micro-flame photometric detector (microFPD) has been examined in greater detail for its sulfur response characteristics. While supporting an "upside down" flame on a stainless steel capillary burner (delivering oxygen) in a counter flowing stream of premixed hydrogen and oxygen, the extremely small flame of the muFPD (30 nL) was observed to produce linear sulfur emission as HSO(*). In this mode, linear sulfur response was obtained over four orders of magnitude with a minimum detectable flow of 2 x 10(-10) g S/s. Additionally, a broad series of sulfur compounds ranging in chemical structure were examined in the microFPD in order to determine the extent of equimolarity and reproducibility of response toward this element. Results of exploring both the linear (HSO(*)) and quadratic (S(2)(*)) modes indicate that the %RSD and equimolarity of sulfur response are comparable between that of the microFPD and a conventional flame photometric detector (FPD).     

Improved detector response characterization method in ISOCS and LabSOCS

The In-Situ Object Calibration Software (ISOCS) and the Laboratory Sourceless Calibration Software (LabSOCS) developed and patented by Canberra Industries have found widespread use in the gamma-spectrometry community. Using the ISOCS methodology, one can determine the full energy peak efficiencies of a germanium detector in the 45 keV-7 MeV energy range, for practically any source matrix and geometry. The underlying mathematical techniques used in ISOCS (and LabSOCS) have undergone significant improvements and enhancements since their first release in 1996. One of these improvements is  a spatial response characterization technique that is capable of handling the large variations in efficiency that occurs within a small region. The technique has been in use in ISOCS and LabSOCS releases since 1999, and has significantly improved the overall quality of the close-in and off-axis response characterization for HPGe detectors, especially for Canberra’s Broad Energy Germanium (BEGe) detectors. In this method, the detector response is characterized by creating a set of fine spatial efficiency grids at 15 energies in the 45 keV-7 MeV range. The spatial grids are created in (r,⊝) space about the detector, with the radius r varying from 0 to 500 meters, and the angle ⊝ varying from 0 to π. The reference efficiencies for creating the spatial grids are determined from MCNP calculations using a validated detector model. Once the efficiency grids are created, the detector response can be determined at any arbitrary point within a sphere of 500-meter radius, and at any arbitrary energy within the specified range. Results are presented highlighting the improved performance achieved using the gridding methodology.     

Universal response model for a corona charged aerosol detector

The universality of the response of the Corona Charged Aerosol Detector (CoronaCAD) has been investigated under flow-injection and gradient HPLC elution conditions. A three-dimensional model was developed which relates the CoronaCAD response to analyte concentration and the mobile phase composition used. The model was developed using the response of four probe analytes which displayed non-volatile behavior in the CoronaCAD and were soluble over a broad range of mobile phase compositions. The analyte concentrations ranged from 1μg/mL to 1mg/mL, and injection volumes corresponded to on-column amounts of 25ng to 25μg. Mobile phases used in the model were composed of 0-80% acetonitrile, mixed with complementary proportions of aqueous formic acid (0.1%, pH 2.6). An analyte set of 23 compounds possessing a wide range of physicochemical properties was selected for the purpose of evaluating the model. The predicted response was compared to the actual analyte response displayed by the detector and the efficacy of the model under flow-injection and gradient HPLC elution conditions was determined. The average error of the four analytes used to develop the model was 9.2% (n=176), while the errors under flow-injection and gradient HPLC elution conditions for the evaluation set of analytes were found to be 12.5% and 12.8%, respectively. Some analytes were excluded from the evaluation set due to considerations of volatility (boiling point <400°C), charge and excessive retention on the column leading to elution outside the eluent range covered by the model. The two-part response model can be used to describe the relationship between response and analyte concentration and also to offer a correction for the non-linear detector response obtained with gradient HPLC for analytes which conform to the model, to provide insight into the factors affecting the CoronaCAD response for different analytes, and also as a means for accurately determining the concentration of unknown compounds when individual standards are not available for calibration.     

Formation of n-alkyl-n(1-hydroperoxyalkyl)nitrosamines from n-alkyl-n-(1-acetoxyalkyl)nitrosamines

N-alkyl-N-(1-hydroperoxyalkyl)nitrosamines were prepared by treatment of the corresponding 1-acetoxyalkyl nitrosamines with hydrogen peroxide in acetic acid through an acid-catalyzed nucleophilic substitution.     

Chemical ionization mass spectrometry of nitrosamines

The mass spectra of eight nitrosamines have been recorded, with excitation by chemical ionization (CI) and electron impact (EI). Comparison of the intensities of the base peaks under CI and El conditions gives intensity ratios in the range 1.4-1.9 for low resolution measurements and up to 10 for high resolution measurements, confirming the enhanced sensitivity available in the CI mode.     

Isolation and characterization of N-alkyl-N- (hydroxymethyl)nitrosamines from N-alkyl-N- (hydroperoxymethyl)nitrosamines by deoxygenation

N-Alkyl-N- (hydroxymethyl)nitrosamines, postulated intermediates in the metabolic activation of carcinogenic nitrosamines, were prepared by deoxygenation of the corresponding hydroperoxymethyl nitrosamines and characterized.     

Nuclear track detector response to energetic heavy ions: study case

Journal of Radioanalytical and Nuclear Chemistry - Nuclear track methodology (NTM), is employed to analyze PADC detectors response to different energetic ion beams. Due to the passive device...