Morphogenesis, ATP content and oxytetracycline production by Streptomyces rimosus in solid substrate cultivation

On agar plates, mycelia of Streptomyces rimosus TM-55 had a slender and smooth surface at 24 h, developed a shorter form and rough surface at 116 h, and lysed after 504 h incubation. Oxytetracycline potency reached a maximum at 94 h. During cultivation on solid substrate, mycelia rarely occurred on the surface at 24 h. The organism appeared as short rods at 166 h, and formed spores at 504 h. The ATP content was maximal at 166 h, while energy charge varied between 0.63 and 0.77 during cultivation. The oxytetracycline potency was maximal at 166 h and each gram of substrate produced 11 mg of antibiotic. ATP content and energy charge of mycelia showed a positive correlation with cell activity and oxytetracycline production.

Circulating soluble intercellular adhesion molecule-1 in type C viral hepatitis

BACKGROUND/AIMS

Intercellular adhesion molecule-1 (ICAM-1) is one of the members of the immunoglobulin supergene family; it expresses in response to inflammatory mediators and activation. Circulating soluble ICAM-1 (sICAM-1) levels in acute and chronic viral hepatitis C virus infection were studied.

MATERIALS AND METHODS

Thirty blood samples from 10 patients with acute hepatitis C, and 36 blood samples from 25 patients with chronic hepatitis C were compared with those from 10 healthy volunteers, using the enzyme immunoassay method.

RESULTS

The mean circulating sICAM-1 activities in healthy volunteers was 339 +/- 93 ng/ml. Maximum values of sICAM-1 activities in acute (1394 +/- 502 ng/ml, P = 0.004) and chronic (662 +/- 477 ng/ml, P = 0.047) hepatitis C were increased. Acute hepatitis had a higher maximum circulating sICAM-1 activity than chronic hepatitis (P = 0.009). Longitudinal circulating sICAM-1 activities roughly correlated with the serum aminotransferase (ALT) activities. In acute viral hepatitis C, three patients developed an increase in circulating sICAM-1 activities before the manifestation of abnormal ALT activity. Circulating sICAM-1 activities showed a positive correlation with serum ALT activities (P < 0.001) and serum total bilirubin levels (P = 0.001) and a negative correlation with serum albumin levels (P = 0.01).

CONCLUSIONS

The present study suggested that ICAM-1 plays a role in the hepatocellular injury during viral hepatitis C infection.

Recurrent eccrine acrospiroma of the hand

A rare case of a recurrent, benign, eccrine acrospiroma of the hand is described.

Effect of vapor phase corrosion inhibitor on microbial corrosion of aluminum alloys

Vapor phase corrosion inhibitors were used to investigate the antimicrobial activities and anticorrosion of aluminum alloy. Aspergillus flavus, A. niger, A. versicolor, Chaetomium globosum and Penicillium funiculosum had moderate to abundant growth on the aluminum alloy AA 1100 at Aw 0.901, while there was less growth at Aw 0.842. High humidity stimulated microbial growth and induced microbial corrosion. Dicyclohexylammonium carbonate had a high inhibitory effect on the growth of test fungi and the microbial corrosion of aluminum alloy, dicyclohexylammonium caprate and dicyclohexylammonium stearate were the next. Aluminum alloy coating with vapor phase corrosion inhibitor could prevent microbial growth and retard microbial corrosion.

SiCl 3 (+) and SiCl (+) affinities for pyridines determined by using the kinetic method with multiple stage mass spectrometry: Agostic effects in the gas phase

Cluster ions, Py1SiCl 3 (+) Py2 and Py1SiCl(+)Py2, where Py1 and Py2 represent substituted pyridines, formed upon reactive collisions of mass-selected SiCl 3 (+) or SiCl(+) cations with a mixture of pyridines, are shown to have loosely bound structures by multiple stage mass spectrometry experiments in a pentaquadrupole mass spectrometer. The fragment ion abundance ratio, ln([Py1SiCl n (+) ]/[Py2SiCl n (+) ]) (n=1 or 3) is used to estimate the relative SiCl 3 (+) or SiCl(+) affinities of the constituent pyridines by the kinetic method. In the case of clusters comprised of meta- and/or para-substituted pyridines (unhindered pyridines), the SiCl 3 (+) and SiCl(+) affinities are shown to display excellent linear correlations with the proton affinities (PAs). On the assumption that the effective temperatures of the SiCl 3 (+) - and SiCl(+)-bound dimers are 555 K (i. e., the same as those of the corresponding Cl(+)-bound dimers), SiCl 3 (+) and SiCl(+) affinities of the substituted pyridines, relative to pyridine, are estimated to be 3-MePy (2.1 kcal/mol), 4-MePy (3.2 kcal/mol), 3-EtPy (3.7 kcal/mol), 4-EtPy (4.2 kcal/mol), 3,5-diMePy (4.8 kcal/mol), and 3,4-diMePy (5.4 kcal/mol). The SiCl 3 (+) and SiCl(+) cation affinities are related to the proton affinities by the expressions: relative (SiCl 3 (+) ) affinity = 0.95 ΔPA and relative (SiCl(+)) affinity = 0.60 ΔPA. The smaller constant in the relationship between the relative SiCl affinity and the relative proton affinity is the result of weaker bonding.Steric effects between the ortho-substituted alkyl group and the central SiCl 3 (+) cation reduce the SiCl 3 (+) affinities of dimers that contain ortho-substituted pyridines. The magnitude of the steric acceleration of fragmentation is used to measure a set of gas-phase steric parameters (S (k)). The steric effects in the SiCl 3 (+) dimers are similar in magnitude to those in the corresponding Cl(+)-bound dimers but weaker than those produced by the bulky [OCNCO](+) group. An inverted steric effect is observed in those SiCl(+)-bound dimers that incorporate ortho-substituted pyridines and is ascribed to auxiliary Si-H-C bonding, which stabilizes the ortho-substituted pyridine-SiCl(+) bond. This auxiliary bonding appears to correspond to agostic bonding, which is well characterized in solution and occurs in competition with steric effects that weaken the pyridine-SiCl(+) interaction.Ion-molecule reactions of pyridines with halosilicon radical cations SiCl 2 (+) and SiCl 4 (+) as well as alkylated halosilicon cations Si(CH3)2Cl(+) and Si(CH3)Cl 2 (+) also are investigated. In these cases, charge exchange and associated reactions are the main reaction channels, and clustering is not observed.

Electrohydraulic lithotripsy of upper ureteral calculi with semirigid ureteroscope

Forty-three patients with single ureteral calculi located above the pelvic brim were treated by electrohydraulic lithotripsy (EHL) using a semirigid mini-ureteroscope. Of the 43 calculi, 36 (84%) were fragmented in one procedure. Six calculi (14%) were pushed back to the renal pelvis and treated successfully by complementary extracorporeal shockwave lithotripsy (SWL). The total success rate of ureteroscopic manipulation thus was 98%. The operation time (mean 26.4 minutes) and postoperative hospital stay (mean 2.53 days) were relatively short. Complications were limited to four (9%) minor perforations of the ureter managed by internal stenting. Among these patients with complications, there were no significant ureteral strictures noted on excretory urography or ureteroscopic examination 1 to 3 months after ureterolithotripsy. The costs of ureteroscopy with EHL are lower than that of SWL or ureteroscopic lasertripsy. The total fees for ureteroscopy with EHL are about two thirds those for SWL in Taiwan. Despite the longer learning curve required for ureteroscopy, ureteroscopy associated with EHL is a cost-effective alternative for the treatment of upper ureteral calculi, especially when SWL is not readily available.

DNA flow cytometric analysis of chest-wall chondroma and chondrosarcoma

DNA flow cytometric analysis was performed for prediction of malignancy potential, and hence of outcome, in 17 patients aged 29-76 (mean 52) years with cartilaginous tumour of the chest wall. Histologically there were nine chondromas and eight chondrosarcomas. The chondrosarcomas (3 grade I, 4 grade II, 1 grade III) were significantly larger than the chondromas (13.6 +/- 7.8 vs 4.2 +/- 2.0 cm, p < 0.001). DNA flow cytometry was performed on paraffin-embedded blocks of resected tumour. In eight of the 17 tumours (6 chondromas, 1 grade I and 1 grade II chondrosarcoma) measurement of DNA content failed because of low cellularity and severe calcification. Aneuploid DNA content was detected only in three chondrosarcomas (2 grade II, 1 grade III). The synthetic phase fraction was less than 15% in all the studied chondromas, but exceeded 25% in four of six chondrosarcomas. This case series though small, may indicate a trend towards association between higher histologic grading and greater incidence of aneuploidy with higher synthetic phase fraction. Tumour size, histologic grade, DNA ploidy and adequacy of surgical resection are the main influences on prognosis.

Rupture of the flexor pollicis longus tendon after 30 years due to migration of a retained foreign body

Delayed rupture of a flexor tendon in the hand due to the presence of a retained foreign body is rare. We present the case of a late flexor pollicis longus rupture 30 years after traumatic implantation of a glass fragment. The foreign body had migrated distally a distance of 4.5 cm from the site of the original injury and eroded into the flexor tendon sheath. Thumb function was restored with a flexor digitorum superficialis tendon transfer from the ring finger with excellent results.

Characteristics of a group of nonnucleoside reverse transcriptase inhibitors with structural diversity and potent anti-human immunodeficiency virus activity

Current thrust in controlling the Acquired Immune Deficiency Syndrome (AIDS) focuses on antiviral drug development targeting the infection and replication of the human immunodeficiency virus (HIV), the causative agent of AIDS. To date, treatment of AIDS has relied on nucleoside reverse transcriptase inhibitors such as AZT, ddI, and ddC, which eventually become ineffective upon the emergence of resistant mutants bearing specific nucleotide substitutions. The Anti-AIDS Drug Screening Program of the NCI conducts and coordinates a high-capacity semi-robotic in vitro screening of synthetic or natural compounds submitted by academic, research and pharmaceutical institutions world-wide. About 10,000 synthetic compounds are screened annually for anti-HIV activity. Confirmed active agents are subjected to in-depth studies on range and mechanism of action. Emerging from this intense screening activity were a number of potentially promising categories of nonnucleoside reverse transcriptase inhibitors (NNRTI) with structural diversity but strong and reproducible anti-HIV activity. Over 2500 active compounds were evaluated for their inhibitory activity against a panel of both laboratory and clinical virus isolates in the appropriate established cell line or fresh human peripheral blood leukocyte and macrophage preparations. Out of these, 40 agents could be placed structurally in nine categories with an additional 16 unique compounds that share the characteristics of NNRTI. These NNRTIs were shown to inhibit reverse transcriptase enzymatically using homopolymeric or ribosomal RNA as templates. NNRTIs demonstrated similarity in their inhibitory pattern against the HIV-1 laboratory strains IIIB and RF, and an AZT-resistant strain; all were inactive against HIV-2. These compounds were further tested against NNRTI-resistant HIV-1 isolates. NNRTI-resistant HIV-1 isolates were selected and characterized with respect to the change(s) in the viral reverse transcriptase nucleotide sequence. Also, differential cross-resistance or sensitivity patterns to NNRTIs were studied in detail among NNRTI-resistant mutants. When tested in combination with AZT, all of the NNRTI's uniformly exhibited synergistic inhibition of HIV-1, suggesting that combination antiviral therapy of NNRTIs with AZT may be therapeutically promising for AIDS treatment.

The NCI's AIDS antiviral drug screening program

The Developmental Therapeutics Program (DTP) in the National Cancer Institute has an unique mission by serving as a resource for all academic and private research institutions, the National Institutes of Health in the USA, and the global scientific community in the quest for effective therapeutic agents for treating patients with Acquired Immune Deficiency Syndrome (AIDS) as well as for cancer patients. This communication will concentrate on the developmental therapeutic program on anti-AIDS drug discovery.

Elimination of threshold-induced distortion in the power spectrum of narrow-band laser speckle

The distortion in the power spectrum of narrow-band laser speckle that results from irradiance thresholding is quantified. A method for compensation of this distortion is presented. An optimal threshold level is presented that simplifies the compensation method.

Differential interactions of human Sos1 and Sos2 with Grb2

The guanine nucleotide exchange factor Son of sevenless (Sos) performs a crucial step in the coupling of receptor tyrosine kinases to Ras activation. Mammalian cells contain two related but distinct Sos proteins, Sos1 and Sos2. Although they share a high degree of overall similarity, it is not known to what extent their biological and biochemical properties overlap. In the present study, we have compared the interactions of the two human homologues of Sos, hSos1 and hSos2, with the adaptor protein Grb2. We show that hSos2 interacts with Grb2 via its proline-rich COOH-terminal domain and that this interaction is dependent on the SH3 domains of Grb2. In general, these characteristics are similar to the ones reported previously for the interaction of hSos1 with Grb2. However, the apparent binding affinity of hSos2 for Grb2 is significantly higher relative to that of hSos1 both in vitro and in vivo. The region conferring this higher binding affinity has been mapped to residues 1126-1242 of the hSos2 COOH-terminal domain. These results suggest that Sos1 and Sos2 may differentially contribute to receptor-mediated Ras activation.

Early interferon therapy and abortion of posttransfusion hepatitis C viral infection

We studied the role of an "early" 4-month course of interferon therapy on posttransfusion viral hepatitis C (PTH-C). Paired serum samples of 51 consecutive recipients, taken before and 7-20 days after blood transfusion, were prospectively tested for hepatitis C virus ribonucleic acid (HCV RNA) using the polymerase chain reaction assay. Seven recipients experienced seroconversion of HCV RNA after transfusion. Two of the seven patients underwent an early 4-month course of interferon alpha therapy at a dose of 3 mU per day for 5 days during the first week, then three times a week for the subsequent 15 weeks. The first patient was treated at a very early stage of acute PTH-C and responded well to interferon therapy. Acute PTH-C in the second patient was prevented by interferon therapy. Both patients had normal serum alanine aminotransferase levels and tested negative for anti-HCV and HCV RNA 12 months after the end of treatment. Four of the five patients not on interferon therapy developed abnormal serum alanine aminotransferase activities more than five times the normal upper limit (383 +/- 143 IU/L) at 2-18 weeks after transfusion. All four patients experienced seroconversion of anti-HCV, and three patients developed chronic hepatitis. This study suggests that early long-term interferon therapy has the potential to prevent PTH-C.

Arthroscopic surgery of the knee in the geriatric patient

There remains some controversy and confusion regarding arthroscopic surgery of the knee in the elderly population, particularly for patients with osteoarthritis. A retrospective review was undertaken of 105 knees in patients 60 years or older who had arthroscopy during a 4-year period. The surgical outcomes were evaluated using a postoperative knee scoring system at a mean followup period of 11.7 months. Good and excellent results were obtained in 65% of knees. The most significant predictors of good outcome were preoperative mechanical symptoms, such as those resulting from loose bodies or flap tears of the meniscus, and only mild articular degeneration seen at arthroscopy. A review of the literature reflects similar success rates. Although the results are equivocal by orthopaedic standards, in selected patients arthroscopic surgery can offer significant relief of acute symptoms and defer more extensive surgical procedures with minimal risk.

[Amylase production of Streptomyces rimosus TM-55 and their 2-deoxyglucose resistant mutants]

Streptomyces rimosus TM-55 was treated with 3% ethyl melthylsulfonate for 60 minutes to generate mutants producing high amount of amylase, and 1,283 mutants were isolated from yeast extract starch (YS) medium containing 0.1% 2-deoxyglucose. Amylase activity was primarily screened by clear zone formation on YS medium after spraying with iodine solution. Two mutants designed as D-35 and D-62 had higher amylase activity than that of the parent strain. Amylase activity of the mutants in the YS broth was 2.97- and 3.45-fold of the parent strain, respectively. With the addition of 0.1% lactose, and 2-deoxyglucose, amylase activity of the mutants D-35 and D-62 was 27-73% and 4-7% higher than that of the parent strain. With the addition of 0.1% sucrose, amylase activity of the mutant D-35 was 18.37% lower than that of the parent strain. Moreover, with the supplement of 0.1% glucose, amylase activity of both the mutants D-35 and D-62 was 3.67 and 3.40 fold of the parent strain.

Histopathology of fetal diastrophic dysplasia

We report on three cases of diastrophic dysplasia in second trimester fetuses and discuss the differential diagnosis and clinical, radiologic, and histopathologic findings. Manifestations of typical diastrophic dysplasia in infants and older patients include abnormal pinnae, scoliosis, and joint contractures; these were absent in the fetuses, in keeping with the tendency for the clinical and radiologic aspects of this disease to become more severe with age. The histopathologic characteristics of the cartilage appear to be similar in the fetus and older patient, and therefore may be useful in differentiating diastrophic dysplasia from other osteochondrodysplasias in the second trimester.

Morphogenesis, biomass and oxytetracycline production of Streptomyces rimosus in submerged cultivation

The minimal concentration of adenosine triphosphate (ATP) which could be detected with spectrophotometry, HPLC and luciferin-luciferase methods was 1.0 microM, 3.3 microM and 100 nM, respectively. In submerged cultivation, most Streptomyces rimosus TM-55 was in hyphae fragment form at 65 h, became short-rod mycelia at 166 h, and lysed at 504 h incubation. The ATP content had maximal value at 24 h, then gradually decreased during cultivation. The oxytetracycline potency increased as incubation occurred, had maximal potency 178.9 micrograms/ml at 166 h, and then gradually decreased. Morphogenesis was very important in oxytetracycline production in submerged cultivation of Streptomyces; short-rod mycelia had high oxytetracycline production.

Portal blood flow in acute hepatitis with and without ascites: a non-invasive measurement using an ultrasonic Doppler

To evaluate the role of portal blood flow in severe acute hepatitis leading to the formation of ascites, we studied the portal blood flow of 30 patients with severe acute hepatitis (20 without ascites and 10 with ascites), 20 patients with mild acute hepatitis and 20 healthy normal volunteers using duplex sonography. The portal blood flow of patients with severe acute hepatitis and ascites (421 +/- 94 mL/min) was lower than that of the volunteers (725 +/- 131 mL/min), the mild acute hepatitis (658 +/- 148 mL/min), and the severe acute hepatitis (633 +/- 108mL/min) without ascites (P < 0.001). The congestion index of severe acute hepatitis and ascites (0.16 +/- 0.04 cm.s) was higher than that of the volunteers (0.09 +/- 0.03 cm.s, P < 0.001), the mild acute hepatitis (0.09 +/- 0.02 cm.s, P < 0.001), and the severe acute hepatitis (0.12 +/- 0.04 cm.s, P < 0.02) without ascites. Portal blood flow was negatively correlated with prolonged prothrombin time (P < 0.001) and serum total bilirubin level (P = 0.002) and congestion index was positively correlated with heart rate (P = 0.006), prolonged prothrombin time (P < 0.001) and serum total bilirubin level (P = 0.001). Our study shows that in severe acute hepatitis, portal blood flow was reduced in patients with ascites. The non-invasive ultrasonic Doppler is a safe and helpful method in the clinical evaluation of portal hypertension in severe acute hepatitis.

Polar [4+2(+)] diels-alder cycloaddition to nitrilium and immonium ions in the gas phase: Applications of multiple stage mass spectrometry in a pentaquadrupole instrument

Multiple stage MS(2) and MS(3) mass spectrometric experiments, performed using a pentaquadrupole instrument, are employed to explore the gas-phase ion-molecule chemistry of several nitrilium [R-C≡N(+)-H (1), R-C≡N(+)-CH3 (2), and H-C≡N(+)-C2H5 (3)] as well as immonium ions RR(1)C=N(+)R(2)R(3) (4) with the neutral diene isoprene. Polar [4+2(+)] Diels-Alder cycloaddition is observed for nitrilium ions when the energy gap between the lowest unoccupied molecular orbital (LUMO) of the ion and the highest occupied molecular orbital (HOMO) of the isoprene is small and the competing proton transfer reaction is endothermic. Thus, C-protonated methyl isonitrile H-C≡N(+)-CH3 (2a) and its higher homolog H-C≡N(+)-C2H5 (3a) form abundant [4+2(+)] cycloadducts with isoprene, but several protonated nitriles 1 do not; instead they show exothermic proton transfer as the main ion-molecule reaction. Replacement of the methyne hydrogen in 2a by a methyl, ethyl, or phenyl group (2b-d) raises the LUMO-HOMO gap, which greatly decreases the total yield of ion-molecule products and precludes cycloaddition. On the other hand, the electron-withdrawing acetyl and bromine substituents in 2e and 2f substantially lower the LUMO energy of the ions and cycloaddition reaction occurs readily. The simplest member of the immonium ion series, CH2=NH 2 (+) (4a), reacts readily by cycloaddition, whereas alkyl substitution on either the carbon or nitrogen (4b-f) dramatically lowers the overall reactivity, which substantially decreases or even precludes cycloaddition. In strong contrast, the N-phenyl (4g) and N-acetyl (4h) ions and the N-vinyl-substituted immonium ion, N-protonated 2-aza-butadiene (4i), react extensively with isoprene, mainly by [4+2(+)] cycloaddition. However, the isomeric C-vinyl-substituted ion (4j) displays only modest reactivity in both the proton-transfer and the cycloaddition channels.Collision-induced dissociation (CID) of the cycloadducts performed by on-line MS(3) experiments demonstrates that they are covalently bound and supports their assignments as cycloaddition products. Retro Diels-Alder fragmentation is a major process for cycloadducts of both the immonium and the nitrilium ions, but other fragmentation processes also are observed. The cycloadduct of 4a with butadiene displays CID fragmentation identical to that of the authentic ion produced by protonation of 1,2,3,6-tetrahydropyridine, which thus strengthens the [4+2(+)] cycloaddition proposal. AM1 calculations also support the formation of the [4+2(+)] cycloadducts, which are shown in several cases to be much more stable than the products of simple addition, that is, the ring-open isomers.

Doppler echocardiography in normal functioning valve prostheses

Even though there has been some criticism regarding the Doppler evaluation in prosthetic valves because of inter-observer and intra-observer variability, among other factors, and Doppler study has a tendency to have falsely high gradients compared to invasive studies, especially mechanical aortic prostheses, Doppler evaluation can provide reliable hemodynamic information about valve function. This test may be particularly useful if used serially, when baseline values are known. Doppler measurement of gradient and valve area has an expected normal range that is specific for the prosthetic type, size, anatomical position, and chronological age. Clearly, a database involving these aspects is needed to provide a more accurate normal range. This study is intended to provide guidance for echocardiographers.

Prenatal screening for cardiac anomalies: the value of routine addition of the aortic root to the four-chamber view

OBJECTIVE

To determine whether the addition of the aortic-root view would detect more congenital cardiac anomalies than a standard four-chamber view alone.

METHODS

The study included fetuses of 14 weeks' gestation or more who were scanned in our unit during a 28-month period. Outcome information was obtained from postnatal echocardiograms and autopsies. Abnormal hearts were classified as to whether the four-chamber or aortic-root view was abnormal.

RESULTS

There were 5967 fetuses in whom a four-chamber view could be obtained. In 5111 of these, an aortic-root view could also be obtained. The four-chamber view detected 24 (47%) of the 51 fetuses with abnormal hearts. Adding the aortic-root view increased the sensitivity to 78%.

CONCLUSIONS

Visualization of the aortic root is a quick and easy means of evaluating the aortic outflow tract during routine scanning. Adding the aortic-root view to the standard four-chamber view will result in the detection of most cardiac anomalies prenatally.

Impact of screening blood donors for hepatitis C antibody on posttransfusion hepatitis: a prospective study with a second-generation anti-hepatitis C virus assay

BACKGROUND

Hepatitis C is the major cause of posttransfusion hepatitis. Blood components that are positive for antibody to hepatitis C virus (anti-HCV) can transmit posttransfusion hepatitis.

STUDY DESIGN AND METHODS

To investigate the effect on posttransfusion hepatitis of screening blood donors with a second-generation test for anti-HCV, 249 transfusion recipients who underwent cardiovascular surgery were prospectively followed. Six recipients who were positive for anti-HCV before transfusion and 51 subjects with incomplete follow-up were excluded from this study.

RESULTS

Eleven (13.8%) of 80 subjects who received unscreened blood had two successive serum alanine aminotransferase levels > 90 U per L. Seven (8.8% of total) developed anti-HCV and HCV RNA and two (2.5% of total) developed IgM antibody to cytomegalovirus (IgM anti-CMV). By contrast, 3 (2.7%) of the 112 subjects who received anti-HCV-screened blood had two successive serum alanine aminotransferase levels > 90 U per L. None of these three developed anti-HCV and HCV RNA, but two (1.8% of total) showed the development of IgM anti-CMV. The study shows that screening for anti-HCV in blood donors with a second-generation test almost abrogated posttransfusion viral hepatitis C.

CONCLUSION

After anti-HCV screening, other body fluid-transmitted viruses such as CMV may become important in posttransfusion hepatitis.

Determination of aldicarb, aldicarb sulfoxide and aldicarb sulfone in tobacco using high-performance liquid chromatography with dual post-column reaction and fluorescence detection

A screening method for the determination of aldicarb (AS) and its sulfoxide (ASX) and sulfone (ASN) metabolites in tobacco at low ppm levels is described. Tobacco samples are extracted using methanol with the aid of sonication at ambient conditions. The extract is filtered and then injected into a high-performance liquid chromatograph equipped with a dual post-column reaction system and a fluorescence detector. Chromatographic separation is performed on a C18 column with a mixture of methanol-acetonitrile-water containing 0.1% of triethanolamine as the mobile phase. Triethanolamine is added to improve peak shape of AS residues and to reduce the undesired interaction between residual silanols and interferences, mainly amino acids and other amines. The average recoveries for AS residues spiked in tobacco are higher than 95% for AS, 91% for ASN and 85% for ASX at levels of 0.5-10 ppm (w/w). The detection limit is 0.5 ppm for each of the target compounds.