A simple and reliable method using liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) for the determination of tetrodotoxin in the puffer-fish has been developed. The LC separation was performed on a Shodex RSpak NN-414 column (15 cm x 4.6 mm id) using 20 mM ammonium acetate-methanol (75 + 25) as the mobile phase at a flow rate of 0.5 ml min(-1). The positive ionization produced the typical [M + H]+ molecular ion of tetrodotoxin (m/z 320). The calibration graph for tetrodotoxin was rectilinear from 0.01 to 1 microg ml(-1) with selected ion monitoring (SIM). Tetrodotoxin was extracted with 0.1% acetic acid by heating in a boiling water-bath and the extracts were cleaned up on a Bond Elut C18 (500 mg) cartridge. The recoveries of the tetrodotoxin from the puffer-fish fortified at 1 microg g(-1) were 77.7-80.7% and the detection limit was 0.1 microg g(-1) (equivalent to ca. 0.5 mouse units per gram).
viscous fibers such as -glucan, is associated with lowering of blood cholesterol levels and normalizing blood Dietary fiber is an important quality parameter of barley (Hordeum glucose and insulin, making foods containing these fivulgare L.) but is extremely laborious to measure. Near-infrared (NIR) transmission and reflectance spectroscopy were investigated bers an important part of dietary strategies to minimize as rapid screening tools to evaluate the total dietary fiber content of cardiovascular disease and type-2 diabetes (American barley cultivars. The Foss Grainspec Rice Analyzer and NIR Systems Dietetic Association, 2002). 6500 spectrometer were used to obtain transmission and reflectance In contrast to its benefits in food, fiber is detrimental spectra, respectively, of polished grains and ground barley. Total diduring malting and brewing. In brewing, a high soluble etary fiber was determined for each cultivar by AOAC Method 991.43. fiber content, particularly of -glucan, causes blocking Modified PLS models developed for predicting total dietary fiber, of filters and reduced recovery of fermentable sugars using transmission spectra (850-1048 nm) of polished grains, had a (see review by Bamforth, 1985). Furthermore, high -glustandard error of cross validation (SECV) of 10.4 (range 58-197) g kg Ϫ1 can content can lead to colloidal instability and haze and R 2 of 0.82 indicating sufficient accuracy for selecting or rejecting formation in the final product. The major components high dietary fiber cultivars. NIR reflectance spectroscopy (1104-2494 nm) of ground barley samples resulted in a model with SECV of 5.2 of barley are protein, fiber, and starch; however, there (range 58-197) g kg Ϫ1 and R 2 0.96, indicating a high degree of precision appears to be a wide range in genetic variation of these in the prediction of total dietary fiber. The increased accuracy of the components (Oscarsson et al., 1996; Bhatty, 1999; Anreflectance model may be due in part to more information available dersson, 1999). Globally, covered or hulled barley is the in the wavelength region used. The precision, low cost per sample most widely produced and is the traditional barley used and speed of measurement of the technique allow making dietary for malting and brewing. Alternatively, naked or hullfiber selection decisions for large numbers of progeny in barley breedless barley is most often used for food since it does not ing programs.require processing to remove the hull, and thus nutrients and bioactive components are retained.The fiber content of plant material is measured as Published in Crop Sci. 45:2307-2311 (2005.
SUMMARY Internal quantum efficiency (IQE) is usually estimated from temperature dependence of photoluminescence (PL) intensity by assuming that the IQE at cryogenic temperature is unity. III-nitride samples, however, usually have large defect density, and the assumption is not necessarily valid. In 2016, we proposed a new method to estimate accurate IQE values by simultaneous PL and photo-acoustic (PA) measurements, and demonstratively evaluated the IQE values for various GaN samples. In this study, we have applied the method to InGaN quantum-well active layers and have estimated the IQE values and their excitation carrier-density dependence in the layers. key words: internal quantum efficiency, recombination, PAS, PL
The potential of liquid chromatography‐mass spectrometry (LC‐MS) using electrospray ionization (ESI) was investigated for the identification and quantification of organoarsenic species excreted in rats urine chronically exposed to dimethylarsinic acid (DMAA). Quantification was performed by both LC‐ESI‐MS and LC‐inductively coupled plasma mass spectrometry (ICP‐MS). The detection limits of organoarsenic species in LC‐ESI‐MS with cation‐exchange chromatography were 75–200 pg as arsenic. Although there are about ten times higher than that of LC‐ICP‐MS, LC‐ESI‐MS had a low enough detection limit to determine major metabolic arsenic species in the urine. LC‐ESI‐MS was applied to the identification of organoarsenic species in the urine. Major arsenic peaks in urine were identified as DMAA and trimethylarsine oxide using agreement of the spectra and retention times. Three unidentified arsenic peaks were found in the urine; one of these was determined to be tetramethylarsonium ion by agreement of both the spectrum and the retention time. LC‐ESI‐MS and LC‐ICP‐MS were also used to quantify organoarsenic in urine: good agreement between LC‐ESI MS and LC‐ICP‐MS was obtained. Copyright © 1999 John Wiley & Sons, Ltd.
It has been well known that inorganic arsenic compounds can be carcinogenic to humans.1 Most mammals convert inorganic arsenic compounds to low toxicity monomethylarsonic acid (MMAA), dimethylarsinic acid (DMAA) or trimethylarsine oxide (TMAO) by methylation. 2,3 As the toxicological properties of arsenic compounds depend on their chemical forms, it has been demonstrated that the analysis of every chemical form is very important. Although the LC-ICP/MS is sensitive and precise, the LC-ICP/MS does not give any information on speciation. [4][5][6] On the other hand, the LC/MS is a good tool for qualification and quantification. We have previously reported the appropriate mobile phase and the MS conditions for the arsenic compounds using LC/MS. 7 Since it is known that the addition of an organic solvent is useful to increase the sensitivity on electrospray ionization (ESI), we examined the postcolumn addition of methanol for improvement of the linearity, detection limit and repeatability of the method. ExperimentalOrganoarsenic species MMAA, DMAA, TMAO, tetramethylarsonium (TeMA) iodide, and arsenobetaine (AB), were purchased from Tri Chemical Laboratories Inc. (Yamanashi, Japan). Other reagents (each analytical grade) were purchased from Wako Pure Chemical Industries. Deionized water was obtained from a Milli-Q system (Nihon Millipore, Tokyo, Japan). The LC/MS equipment was Model HP1100 series HPLC with MS (Hewlett-Packard, DE, USA). Electrospray ionization (ESI) mode was selected as the ionization system. A Shodex RSpak NN-614 (Showa Denko, Tokyo, Japan) packed with a hydrophilic resin-based cation exchange resin (cation exchange capacity of 0.1 meq/g) was chosen as the separation column. The separation conditions were set by referring to those of the previous paper. 7Influence of postcolumn addition of methanol on sensitivity of arsenic compounds Figure 1 shows the relationships between the flow rate of methanol added by postcolumn addition and the peak areas of arsenic compounds. The graph demonstrates that the addition of methanol to the mobile phase was effective for increasing the sensitivity, and that around 0.2 ml/min was a suitable rate for the high sensitive detection. The reason for increasing of sensitivity is that the methanol allows the surface tension of droplet from nebulizer. To decrease is consequently easier to make smaller droplets and to vaporize the liquid of droplet than without the addition of methanol. Inc., Musashino, Japan Keywords HPLC/MS, arsenic compounds, electrospray ionization Fig. 1 The relationships between the flow rates of methanol and the peak areas of arsenic compounds. Conditions: carrier, 8 mM HNO3 / 5 mM NH4NO3, 0.4 ml/min; drying gas, N2 (13 l/min, 350 ˚C); nebulizer, N2 (60 psi); accelerating voltage, 80 V; polarity, positive scan mode; sample, 10 ng/µl each, 10 µl inject; postcolumn, methanol.
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