Showing papers in "Journal of AOAC International in 1998"

Routine analysis of proteins by Kjeldahl and Dumas methods: review and interlaboratory study using dairy products

Abstract: The Kjeldahl and Dumas (combustion) methods were compared in 11 laboratories analyzing samples of milk, skim milk powder, whole milk powder, whey protein concentrate, infant formula, casein, caseinate, 2 reference compounds (glycine and EDTA), and a secondary reference skim milk powder. The comparison was conducted by using international standards where applicable. Overall means were 8.818 g N/100 g by the Kjeldahl method and 8.810 g N/100 g by the Dumas method. No evidence was found for a consistent bias between methods that may be of concern in the trading of dairy produce. A review of more than 10 related trials revealed a lack of consensus in the bias between the 2 methods, suggesting that differences in methodology and sources of systematic error may be contributors. For samples containing > 2 g N/100 g, the Dumas relative repeatability and reproducibility standard deviations were consistently about 0.35 and 0.75%, respectively, whereas the corresponding Kjeldahl values declined generally with N content and were significantly larger. The Dumas precision characteristics may be due to the dominance of Leco analyzers in this trials, and in most other recent trials, rather than an inherent method attribute. Protein determination methods for dairy products need to be reviewed and updated. The Dumas method needs Codex Alimentarius status as a recognized test method.

Determination of 17 beta-estradiol and its metabolites in sewage effluent by solid-phase extraction and gas chromatography/mass spectrometry.

Abstract: The paper describes a simple and quantitative method for monitoring non-conjugated 17 beta-estradiol (E2) and its metabolites estrone (E1) and estriol (E3) as environmental contaminants in municipal sewage effluents. Estrogens were preconcentrated and cleaned up by solid-phase extraction using a reversed-phase C18 cartridge. They were derivatized with pentafluoropropionic acid anhydride, and the products were analyzed by gas chromatography/mass spectrometry. Recoveries from spiked distilled water and sewage were better than 87% at fortification levels of 100 and 20 ng/L. For a 1 L sewage sample and a concentration factor of 5000, detection limits were 5 ng/L for E1 and E2 and 10 ng/L for E3. In a brief survey of Canadian wastewater, these estrogens were detected in many raw sewage and effluent samples at concentrations ranging from 6 to 109 ng/L for E1, from < 5 to 15 ng/L for E2, and from < 10 to 250 ng/L for E3.

Indirect and direct determination of the casein content of milk by Kjeldahl nitrogen analysis: collaborative study

Abstract: The classic method for determination of milk casein is based on precipitation of casein at pH 4.6. Precipitated milk casein is removed by filtration and the nitrogen content of either the precipitate (direct casein method) or filtrate (noncasein nitrogen; NCN) is determined by Kjeldahl analysis. For the indirect casein method, milk total nitrogen (TN; Method 991.20) is also determined and casein is calculated as TN minus NCN. Ten laboratories tested 9 pairs of blind duplicate raw milk materials with a casein range of 2.42-3.05% by both the direct and indirect casein methods. Statistical performance expressed in protein equivalents (nitrogen x 6.38) with invalid and outlier data removed was as follows: NCN method (wt%), mean = 0.762, sr = 0.010, sR = 0.016, repeatability relative standard deviation (RSDr) = 1.287%, reproducibility relative standard deviation (RSDr) = 2.146%; indirect casein method (wt%), mean = 2.585, repeatability = 0.015, reproducibility = 0.022, RSDr = 0.560%, RSDR = 0.841; direct casein method (wt%), mean = 2.575, sr = 0.015, sR = 0.025, RSDr = 0.597%, RSDR = 0.988%. Method performance was acceptable and comparable to similar Kjeldahl methods for determining nitrogen content of milk (Methods 991.20, 991.21, 991.22, 991.23). The direct casein, indirect casein, and noncasein nitrogen methods have been adopted by AOAC INTERNATIONAL.

Stable carbon isotope ratio analysis of honey: validation of internal standard procedure for worldwide application

Abstract: Stable carbon isotope ratio analysis (SCIRA) of honey for undeclared presence of cane or corn sugars has been available for 20 years. Its use with domestic and imported honeys is reviewed. Six years of data from the internal standard isotope ratio analysis (ISCIRA) method support its worldwide validity for honey analysis. The ISCIRA database of pure honeys has been increased from 64 U.S. samples to 224 by addition of data from Germany, United Kingdom, Mexico, Italy, and Spain. ISCIRA analyses of 131 commercial honeys from the United States, Mexico, and Spain found that 17 are adulterated. Analyses of 303 Chinese honeys proves that they should have carbon isotope values similar to honeys from other areas, contrary to claims that the observed differences are intrinsic because of the variability of environmental conditions and of plants used in honey production in China. Addition of corn or cane (C4) sugars to honeys in amounts that do not produce a delta 13C value greater than -23.5 per thousand for the mixture cannot be detected by the original 1978 SCIRA procedure. Such adulteration however is detected by ISCIRA procedure from the delta 13C value of the protein contained in the honey, which shows the isotopic composition of the honey before addition of C4 sugars. Forty-three percent of 98 honeys received in the United States in 1994-1997 with delta 13C -23.5 per thousand were suspected and found to be adulterated

Analysis of fumonisin B1 and its hydrolysis product in tortillas.

Abstract: Fumonisins are toxic metabolites of Fusarium moniliforme, a fungus that occurs widely in corn. Fumonisins cause leukoencephalomalacia in horses and pulmonary edema in swine and have been suggested as a possible cause of an increased incidence of neural tube defects among people living along the Texas-Mexico border. As part of an effort to determine levels of fumonisins in human food, a liquid chromatographic (LC) method was devised for determining fumonisin B 1 (FB 1 ) and the total hydrolysis product of FB 1 (HB 1 ) in tortillas. The method uses acetonitrile-0.1 M phosphate buffer (pH 3; 1 + 1) extraction, solid-phase C 18 cleanup, o-phthalaldehyde and 2-mercaptoethanol derivatization, and reversed-phase LC. Average recoveries from tortillas spiked with FB 1 and HB 1 at 250, 500, and 1000 ng/g were 86.5% for FB 1 and 82.6% for HB 1 Tortillas (54) and masa (8) from the Texas-Mexico border were analyzed for FB 1 and HB 1 Average amounts of FB 1 and HB 1 in tortillas were 187 and 82 ng/g, respectively. Average amounts of FB 1 and HB 1 in masas were 262 and 64 ng/g, respectively. The results show that fumonisin B 1 and its hydrolysis product are present in tortillas consumed by a population experiencing an increased incidence of neural tube defects.

A simple membrane immunobead assay for detecting ciguatoxin and related polyethers from human ciguatera intoxication and natural reef fishes.

Abstract: A simple membrane immunobead assay (MIA) for detecting ciguatoxin (CTX) and related polyethers directly from fish tissue is presented A membrane laminated onto a solid plastic support is immersed with a piece of fish tissue in methanol The membrane is thoroughly dried and placed into an immunobead suspension containing polystyrene particles coated with monoclonal antibody to CTX (MAb-CTX) Two beads of different diameter and color are used The color intensity of the membrane is related to the concentration of the toxin bound to the membrane Twelve of 13 fish implicated in human ciguatera fish poisoning showed borderline or positive responses in the assay A Sphyraena barracuda sample that tested negative with the MIA and was highly toxic with the mouse toxicity bioassay showed only weak CTX-like toxin activity in the guinea pig atrial assay, indicating that the major toxin in the sample was not CTX-like Examination of 154 routinely caught reef fish from Hawaii, Kosrae, and Kwajalein by MIA found 132 (86%) negative and 8 (5%) positive for CTX, with 14 (9%) giving a borderline response Fish from Hawaii showed a higher frequency of borderline or positive responses than those from Kosrae and Kwajalein, probably because several species of fish from several islands of Hawaii were tested, whereas only one species from a single area was examined from each of the islands of Kosrae and Kwajalein

Gas chromatographic determination of azoxystrobin, fluazinam, kresoxim-methyl, mepanipyrim, and tetraconazole in grapes, must, and wine

Abstract: Azoxystrobin, fluazinam, kresoxim-methyl, mepanipyrim, and tetraconazole were determined in grapes, must, and wine by a gas chromatographic method with nitrogen-phosphorus (NP) and mass spectrometric (MS) detectors. Pesticides were isolated from the matrixes by online microextraction with acetone-hexane (50 + 50, v/v). Because of the high selectivity of NP and MS detectors, no interferent peaks were present and no cleanup was necessary. Recoveries from fortified grapes, must, and wine ranged from 80 to 111%, with coefficients of variation ranging from 1 to 14%. Limits of determination were 0.05 mg/kg for kresoxim-methyl and 0.10 mg/kg for the other compounds.

Evaluation of the European four-plate test as a tool for screening antibiotic residues in meat samples from retail outlets.

Abstract: A modified 4-plate test was used to screen 4795 meat samples from retail outlets in the European Community (EC). This microbial inhibition test uses 3 media seeded with Bacillus subtilis at different pH values (6, 7.2, or 8) and a fourth medium seeded with Micrococcus luteus. Positive samples were confirmed by a receptor test for macrolides, a thin-layer chromatographic method for sulfonamides, or an enzyme-linked immunosorbent assay test for tetracyclines. Inhibition on M. luteus plates, often by beef and veal samples, could not be confirmed. Circumstantial evidence indicated these test results had to be considered presumptively false positives. Of the samples, 95 inhibited at least one plate seeded with B. subtilis. Usually, samples were positive on more than one plate: 70 samples were positive on all 3 plates, and only 6 samples did not inhibit the plate at pH 6. The majority of positive results on plates seeded with B. subtilis, 77 of 89 samples tested, contained tetracycline antibiotics. One sample also contained sulfadimidine. Two other samples contained high levels of enrofloxacine and ciprofloxacine. The 4-plate test is not sensitive enough to detect sulfonamides and quinolones at the EC maximum residue limits, but higher levels may cause inhibition. The 4-plate test can be used to detect meat samples containing tetracycline residues, but the method is too complicated when used only for that purpose.

Liquid chromatographic determination of methylxanthines and catechins in herbal preparations containing guaraná.

Abstract: Herbal preparations derived from the dried seeds of guarana (Paullinia cupana) have become a popular nutritional supplement used for stimulatory purposes. Once considered a drug substance in the United States, guarana currently is classified as a food additive and dietary supplement. The pharmacological activity of guarana-containing products is primarily due to methylxanthine alkaloids. For guarana preparations, methylxanthine levels and, more significantly, the presence of several polyphenol compounds (i.e., catechins) provide phytochemical markers of authenticity. Methylxanthines and polyphenols are extracted from sample matrix with a heated phosphate buffer-methanol solution, the cooled extract is filtered, and the extract is injected into the liquid chromatographic (LC) system. A Nova-Pak C18 column eluted with phosphate buffer-methanol mobile phase (pH = 3.50) and monitored at 272 nm gave satisfactory resolution for the methylxanthines theobromine, theophylline, caffeine and the polyphenols (+)-catechin and (-)-epicatechin. Twenty-four products including dried seeds, dried paste, seed powders, tablets, and capsule formulations were assayed and conclusions were drawn about their authenticity. The LC system responded linearly to methylxanthines over the 100-fold range in concentration from 0.043 to 4.30 micrograms/mL for theobromine and caffeine and from 0.041 to 4.10 micrograms/mL for theophylline. Precision data for the 3 methylxanthines obtained from 10 different products (n = 5) gave relative standard deviation (RSD) values of 1.18-15.52% within a concentration range of 0.01-52.28 mg/g. Recoveries of methylxanthines from fortified products varied from 87.5 to 120.0%. The response for catechins was linear over a 200-fold range in concentration of 0.05-10.0 micrograms/mL. Precision data from 5 products (n = 5) gave RSD values of 1.08-5.54% within a concentration range of 0.34-32.65 mg/g. Recoveries from these products ranged from 87.7 to 109.7%. Results and chromatographic profiles for 14 commercial products in solid dosage form indicate that a number of these products may not contain authentic guarana as an active ingredient or contain less than the declared quantity of guarana. The proposed procedure also was applied to 2 carbonated soft drinks and a sample of mate.

Optical immunobiosensor assay for determining enrofloxacin and ciprofloxacin in bovine milk.

Abstract: A rapid, sensitive optical immunobiosensor assay was developed and used to determine enrofloxacin and its main metabolite, ciprofloxacin, in milk from healthy cows and cows with clinical signs of mastitis after intramuscular administration of enrofloxacin. Liquid chromatography (LC) was used to confirm results of the biosensor assay. Despite incomplete cross-reactivity between polyclonal enrofloxacin antibodies and ciprofloxacin, the biosensor assay could be used for semiquantitative analysis of the sum of the 2 substances. LC analysis showed that ciprofloxacin persisted at levels exceeding the expected future maximum residue limit in milk for several days after the end of the withdrawal period.

Bacterial inhibition tests used to screen for antimicrobial veterinary drug residues in slaughtered animals

Abstract: Bacterial inhibition tests used to screen milk, tissues, blood, and urine for antimicrobial veterinary drug residues must be high volume, quick, rugged, inexpensive, and sensitive. Bacterial inhibition tests--such as the Swab Test on Premises (STOP), the Calf Antibiotic and Sulfa Test (CAST), the Fast Antibiotic Screen Test (FAST), the Charm Farm Test (CFT), the Antimicrobial Inhibition Monitor 96 (AIM-96) assay, the German Three Plate Test, the European Union Four Plate Test and the New Dutch Kidney Test--have been used to screen tissues for antimicrobial activity. The CFT and the Brilliant Black Reduction Test (BBRT) also have been used to screen plasma. The Live Animal Swab Test (LAST) was developed to screen urine. This review examines the use and limitations of these screening tests for regulatory control and avoidance of veterinary drug residues in meat. The ideal bacterial inhibition test for screening antimicrobial residues in slaughtered animals does not exist. Each of the current and potential tests has limitations.

Determination of deoxynivalenol in white flour, whole wheat flour, and bran by solid-phase extraction/liquid chromatography: interlaboratory study.

Abstract: A liquid chromatographic (LC) method for determining deoxynivalenol (DON) in white flour, whole wheat flour, and bran at or above the U.S. Food and Drug Administration advisory level of 1 microgram/g was evaluated by an interlaboratory study. Test samples of processed wheat (flour and bran) were extracted by blending with acetonitrile-water (84 + 16). Extracts were filtered and passed through a solid-phase extraction (SPE) column. The eluate was then chromatographed on a reversed-phase LC column with a water-methanol gradient. DON was measured at 220 nm. Naturally contaminated white flour, whole wheat flour, and bran samples and spiking solutions of DON to be added to the 3 commodities at 0.5, 1.0, and 2.0 micrograms/g were sent to 4 collaborators in Kansas, Louisiana, Missouri, and Washington states. Three collaborators completed the study. Average recoveries of DON from the 3 commodities spiked at 0.5, 1.0, and 2.0 micrograms/g were 94, 87, and 97%, respectively. Within-laboratory relative standard deviations for repeatability (RSDr) ranged from 3.1 to 21.7% and between-laboratory relative standard deviations for reproducibility (RSDR) ranged from 10.8 to 38.7%. On the basis of the results of this study, the SPE/LC method for DON in white flour, whole wheat flour, and bran was adopted as a peer-verified method by AOAC INTERNATIONAL.

Variability associated with testing shelled corn for fumonisin.

Abstract: Variances associated with sampling, sample preparation, and analytical steps of a test procedure that measures fumonisin in shelled corn were estimated. The variance associated with each step of the test procedure increases with fumonisin concentration. Functional relationships between variance and fumonisin concentration were estimated by regression analysis. For each variance component, functional relationships were independent of fumonisin type (total, B1, B2, and B3 fumonisins). At 2 ppm, coefficients of variation associated with sampling (1.1 kg sample), sample preparation (Romer mill and 25 g subsample), and analysis are 16.6, 9.1, and 9.7%, respectively. The coefficient of variation associated with the total fumonisin test procedure was 45% and is about the same order of magnitude as that for measuring aflatoxin in shelled corn with a similar test procedure.

Determination of Magnesium and Calcium in Foods by Atomic Absorption Spectrometry after Microwave Digestion: NMKL Collaborative Study

Abstract: On the basis of results of the performed collaborative study, the 49th Annual General Meeting of the Nordic Committee on Food Analysis (NMKL) in The Faroe Islands, August 1995, approved this method to be printed and included in NMKL's collection of methods of analysis of foods. Eleven laboratories participated in an interlaboratory methods-performance (collaborative) study of a method for determining magnesium and calcium in foodstuffs by atomic absorption spectrometry (AAS) after wet microwave digestion. The study was preceded by a practice round of familiarization samples. The method was tested on 7 materials: 5 foods (apple, milk powder, minced fish, wheat bran, and chocolate cake) and 2 composite diets ranging in Mg content from 240 to 3900 mg/kg and in Ca content from 290 to 9300 mg/kg. The materials were presented to study participants as blind duplicates, and participants were asked to perform single determinations on each sample. Repeatability relative standard deviations (RSDr) ranged from 1.9 to 4.9% for Mg and from 2.2 to 8.1% for Ca. Reproducibility relative standard deviations (RSD R ) ranged from 4.0 to 13% for Mg and from 5.9 to 23% for Ca. For Ca, lowest RSD R values were found for samples with high concentrations of Ca (>3800 mg/kg sample) and with nitrate ion residues of <1.3% (w/v).

Determination of total fat in foods and feeds by the caviezel method, based on a gas chromatographic technique.

Abstract: This peer-verified method specifies a fast, easy, and reliable quantitative method to determine total fat in foods and feeds in compliance with the new definition of fat from the U.S. Food and Drug Administration. The method takes into consideration all fatty acids, from C4 to C24, and when fat is present at 0.3-100%. The validation study included 9 matrixes, with fat levels ranging from 1 to 79%. Sample and internal standard (IS; tridecanoic acid) are added to solvent (n-butyl alcohol). Fat is extracted and simultaneously saponified by potassium hydroxide. The fatty acid potassium salts are converted to fatty acids by adding an acidic aqueous salt solution, which produces a 2-phase system. The upper phase, containing the fatty acids and IS, is injected into the fat determination system. After gas chromatographic separation, the fat content is calculated from IS and fatty acid peak areas. The fat content is automatically converted to triglyceride content with a pre-determined factor. Ten replicates of 9 different food samples, which cover the whole range of different contents in fat, proteins, and carbohydrates, were analyzed by the submitting and the peer laboratories. Repeatability relative standard deviation (RSDr) values ranged from 0.47 to 4.62%. Reproducibility relative standard deviation (RSDR) values ranged from 0.85 to 9.52%. These estimates include between-run variability. The method shows good accuracy. Values for standard reference materials (SRMs) are in agreement with certified values. Regression analysis of the correlation between observed fat and certified value over all matrixes and fat levels indicated good precision and absence of method bias (5 SRMs; 1-30% fat; correlation coefficient, R2 = 99.98%).

Simultaneous determination of chloramphenicol, florfenicol, and thiamphenicol residues in milk by gas chromatography with electron capture detection

Abstract: A gas chromatographic (GC) method is described for determining residues of chloramphenicol (CAP), florfenicol (FF), and thiamphenicol (TAP) in raw milk, with meta-nitrochloramphenicol (mCAP) as internal standard. Milk is extracted with acetonitrile, centrifuged, evaporated, reconstituted in water, and passed through a C18 solid-phase extraction (SPE) column. The SPE column is eluted with 60% methanol, and then the eluate is evaporated and derivatized with Sylon BFT ?N,O-bis(trimethylsilyl)trifluoroacetamide [BSTFA]-trimethylchlorosilane [TMCS], 99 + 1?. After derivatization, toluene is added directly to the sample, followed by water, to quench the derivatization process. After centrifugation, the organic layer is carefully removed. Analytes are determined by GC with electron capture detection (ECD). Milk was fortified with fenicols (the collective name for CAP, FF, and TAP) at 5, 10, 20, 40 and 80 ng/mL (target level = 10 ng/mL). Overall recoveries were 92, 100, and 104% for CAP, FF, and TAP, respectively. Overall interassay (between-day) variabilities were 6.1, 6.7, and 6.0% for CAP, FF, and TAP, respectively. Raw milk samples containing incurred residues of FF were also analyzed.

Determination of the Fusarium mycotoxins nivalenol, deoxynivalenol, 3-acetyldeoxynivalenol, and 15-O-acetyl-4-deoxynivalenol in contaminated whole wheat flour by liquid chromatography with diode array detection and gas chromatography with electron capture detection

Abstract: A rapid and sensitive method was developed for simultaneous detection of nivalenol (NIV), deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-A-DON), and 15-O-acetyl-4-deoxynivalenol (15-A-DON) in wheat flour. Samples were extracted with acetonitrile-water (84 + 16), and the extract was filtered and purified by a column containing a combination of charcoal, celite, and other adsorbents. For screening analysis, the column eluate was only extracted with ethyl acetate. After evaporation of the solvent, the dried residue was redissolved in acetonitrile-water (2 + 8) and then analyzed by reversed-phase liquid chromatography (LC) with diode array detection. Recoveries of NIV, DON, 3-A-DON, and 15-A-DON from whole wheat flour spiked at 2 levels were 49-55, 92-97, 98-100, and 100-105%, respectively. To quantitate mycotoxin amounts lower than 1 ppm, purified column extracts were evaporated to dryness, derivatized with heptafluorobutyric anhydride, and analyzed by gas chromatography with electron capture detection (GC-ECD). Average recoveries of NIV, DON, 3-A-DON, and 15-A-DON from whole wheat flour spiked at 2 levels, were 45-52, 91-103, 81-85, and 84-92%, respectively. GC-ECD detection limits for all mycotoxins tested at a signal-to-noise ratio of 4:1 were < 30 ng/g. Results of GC-ECD analysis for whole wheat flour samples spiked with mycotoxins at 3 and 10 ppm compared well with results (2.8 and 9.9 ppm) for the same samples analyzed by LC.

Specificity of the BAX polymerase chain reaction system for detection of the foodborne pathogen Listeria monocytogenes.

Abstract: The polymerase chain reaction (PCR) can be used for rapid and specific detection of foodborne pathogens. One commercial kit, the Qualicon BAX system uses PCR to detect Listeria monocytogenes in enrichment cultures derived from food and environmental samples. The specificity and sensitivity of the BAX system for detecting L. monocytogenes were characterized by using both pure and mixed cell cultures, and optimal conditions for production of cell lysates were determined. The BAX system was highly specific for L. monocytogenes, and no interference was seen in the presence of either other Listeria species or microbes from other genera. The assay detected L. monocytogenes at 10 5 -10 6 colony-forming units/mL. This sensitivity is adequate for detecting viable cells after enrichment but prevents false-positive signals from nonviable cells.

One-step solid-phase extraction cleanup and fluorometric analysis of deoxynivalenol in grains

Abstract: A rapid, quantitative, inexpensive, efficient method was developed to determine deoxynivalenol (DON) in wheat, barley, corn, wheat middlings, wheat flour, bran, malted barley, and oats. Samples are ground and extracted with acetonitrile-water (86 + 14). A portion of the extract is cleaned up by passage through a MycoSep No. 225 column, evaporated to dryness, and derivatized with zirconyl nitrate and ethylenediamine in methanol. The resulting fluorescent derivative of DON is identified and quantitated with a calibrated fluorometer containing a broad wavelength pulsed xenon light source. This method quantitated DON concentrations from 0.5 to 50 ppm without dilution and was linear when applied to samples of noncontaminated wheat spiked at 0.5, 5, 10, 25, and 50 micrograms DON/g. Correlation coefficients of the method with LC for multiple analyses (n > or = 14 for each commodity) applied to wheat, corn, barley, wheat flour, and wheat middlings were 0.99, 0.99, 0.99, 0.93, and 0.98, respectively. Individual analyses were conducted in < 30 min, and 24 samples were analyzed in 2 h.

Compound-Specific Gas Chromatographic/Mass Spectrometric Analysis of Alkylated and Parent Poly cyclic Aromatic Hydrocarbons in Waters, Sediments, and Aquatic Organisms

Abstract: Polycyclic aromatic hydrocarbons (PAHs) and their alkylated and heterocyclic analogs are ubiquitous contaminants in aquatic environments, including estuaries and marine systems. Methodology for compound-specific analysis of 63 parent, alkylated, and heterocyclic PAHs using gas chromatography/mass spectrometry (GC/MS) in both scanning and selected-ion monitoring modes has been developed and applied to sediment, natural waters and effluents, and marine organisms including oysters, mussels, and fish. Relative response factors and relative retention times for the 63 alkylated, heterocyclic, and parent PAHs compared with 6 deuterated PAHs are given. Analyses of natural sea water samples, enriched at concentrations ranging from 5 to 100 ng/L, show good accuracy (8% mean difference at the 5 ng/L level) and precision (mean RSD of 9%), and method detection limits are in the parts-per-trillion range. Results for sediments and tissues of aquatic organisms exposed to petroleum contamination demonstrate that analysis of parent PAHs alone vastly underestimates levels in sediments and tissues and the potential toxic effects of such residues in food webs. Multiple analyses of a reference tissue material show good precision (mean RSD of 15%) and accuracy (mean difference of 17%) for both alkylated and parent PAHs.

Confirmation of fluoroquinolones in catfish muscle by electrospray liquid chromatography/mass spectrometry.

Abstract: A multiresidue liquid chromatography/mass spectrometry (LC/MS) confirmation method for fluoroquinolones in catfish muscle was developed by using an electrospray interface. Residues of ciprofloxacin, enrofloxacin, sarafloxacin, and difloxacin were positively identified in catfish muscle fortified at 10-80 ppb as well as in incurred tissue. The extraction procedure is based on an LC method with fluorescence detection for determination of these compounds in catfish. Residues were extracted from catfish muscle with an acidic ethanol solution, and the extracts were cleaned up on a propyl sulfonic acid solid-phase extraction column. Chromatographic conditions were optimized to be compatible with the electrospray interface. Internal electrospray voltages were optimized so that 3 fragment ions, in addition to the protonated molecular ion, could be monitored for each residue. To obtain maximum sensitivity, separate MS acquisition programs were developed for ciprofloxacin/enrofloxacin and sarafloxacin/difloxacin pairs.

Solid-phase extraction cleanup and liquid chromatography with ultraviolet detection of ephedrine alkaloids in herbal products

Abstract: A solid-phase extraction (SPE) cleanup and a liquid chromatographic (LC) method with UV detection is presented for analysis of up to 7 ephedrine alkaloids in herbal products. Alkaloids from herbal products are extracted with acidified buffer, isolated on a propylsulfonic acid SPE column, eluted with a high-ionic-strength buffer, and separated by LC with detection at 255 nm. LC separation is performed by isocratic elution on a YMC phenyl column with 0.1 M sodium acetate-acetic acid (pH = 4.8) containing triethyl-amine and 2% acetonitrile. Ephedrine alkaloids are completely separated in 15 min. Average recovery of 5 common alkaloids from 3 spiked matrixes is 90%, with an average relative standard deviation (RSD) of 4.4% for alkaloid spikes between 0.5 and 16 mg/g. Average quantitation of ephedrine and pseudoephedrine from 6 herbal products is 97% of declared label claims, and average quantitation of synephrine from an herbal dietary product is 85% of label claim (RSD, 3.2%). Recoveries of synephrine, norephedrine, ephedrine, pseudoephedrine, N-methylephedrine, and N-methylpseudoephedrine spiked in 4 herbal products averaged 95%. Results of ruggedness testing and of a second laboratory validation of the procedure are also presented.

Rapid gas chromatographic method for simultaneous determination of cholesterol and alpha-tocopherol in eggs.

Abstract: A new method was developed for simultaneous determination of cholesterol and alpha-tocopherol in eggs. It involves rapid and simple sample preparation accomplished in one tube and chromatographic separation that does not require derivatization of analytes. Total analysis time per sample is 40 min. Labor, cost, and use of hazardous chemicals are minimized. To ensure selectivity, accuracy, and precision, critical analytical parameters were investigated. Overall recoveries were 98.8 and 99.2% for cholesterol and alpha-tocopherol, respectively. Linearity was acceptable for both analytes (r = 0.9964 for cholesterol and 0.9996 for alpha-tocopherol) in the fortification range examined. Precision data based on within-day and between-days variation gave overall relative standard deviations of 2.0% for cholesterol and 7.0% for alpha-tocopherol. The method was applied successfully for quantitation of cholesterol and alpha-tocopherol in eggs.

Liquid chromatographic determination of five benzoylurea insecticides in fruit and vegetables.

Abstract: A liquid chromatographic (LC) method was developed to determine 5 benzoylureas--diflubenzuron, hexaflumuron, teflubenzuron, flufenozuron, and lufenuron--in peppers, tomatoes, eggplants, cucumbers, and oranges. Preparation of samples involve extraction with acetone and partitioning into dichloromethane-petroleum ether. A portion of this extract is cleaned up with a solid-phase extraction aminopropyl disposable column. With LC analysis using an RP-8-DB microbore column, acetonitrile-water (70 + 30, v/v) as mobile phase, and photodiode array detection at 254 nm, recovery and repeatability data were collected for the 5 benzoylureas on 4 vegetables and citrus in the range 0.04-2.0 mg/kg. Validated limits of detection and quantitation were 0.01 and 0.04 mg/kg, respectively. The method is reliable for routine analysis of vegetables and fruits.

Stability of organochlorine and organophosphorus pesticides when extracted from solid matrixes with microwave energy

Abstract: A stability study of 44 organochlorine pesticides (OCPs) and 47 organophosphorus pesticides (OPPs) was conducted. Compounds were spiked into solvent only (hexane-acetone, 1 + 1; methylene chloride-acetone, 1 + 1; methyl tert-butyl ether [MTBE]; and toluene-methanol, 10 + 1), solvent/dry soil suspensions, and solvent/wet soil suspensions (20% water, w/w). Spiked matrixes were heated in closed vessels with microwave energy at 2 temperatures (50° and 145°C) for 5 or 20 min. For comparison and for determination of nitrogen blowdown losses, spiked matrixes that had not been exposed to microwave energy were concentrated by using the blowdown technique and analyzed for each of the spiked compounds. For OCPs, temperature had the most significant effect on compound recovery, followed by matrix. All 3 pairwise comparisons of the 3 matrix types were statistically significant. The solvent factor was also significant, with average recoveries of 97.8% with methylene chloride-acetone, 96.3% with toluene-methanol, 92.8% with hexane-acetone, and 92.3% with MTBE. Of the 6 pairwise comparisons among the 4 solvents, all but 2 - methylene chloride-acetone versus toluene-methanol and hexane-acetone versus MTBE - were statistically significant. For OPPs, temperature also had the most significant effect on recovery, followed by matrix. All 3 pairwise comparisons of the 3 matrix types were statistically significant in the same order as for OCPs. The solvent factor was also significant, but average recoveries - 89.5% with hexane-acetone, 89.4% with methylene chloride-acetone, and 81.5% with either MTBE or toluene-methanol - are in a slightly different order from that for OCPs. Of the 6 pairwise comparisons among the 4 solvents, all but 2 - hexane-acetone versus methylene chloride-acetone and MTBE versus toluene-methanol - were statistically significant. Compounds that appear to degrade under microwave-assisted extraction conditions include TEPP, phosphamidon, trichlorfon, naled, monocrotophos, demeton-O, and demeton-S.

High-performance liquid chromatographic method for the determination of moniliformin in corn

Abstract: A high-performance liquid chromatographic method using UV absorption was developed for determining moniliformin in corn. The toxin was extracted with water containing 1% tetrabutylammonium hydrogen sulfate (w/v). Paired moniliformin was partitioned into dichloromethane, which was evaporated to dryness at 50 degrees C. The residue was dissolved in water and applied to a disposable strong-anion exchange solid-phase extraction tube. Adsorbed moniliformin was eluted from the tube with 0.05M sodium dihydrogen phosphate monohydrate (pH 5). It was determined by ion-pair reversed-phase chromatography and UV measurement at 229 nm. The minimum detectable amount of pure moniliformin was 0.25 ng/injection (signal-to-noise ratio = 3:1). The detector response was linear from 0.25 to at least 20 ng. The limit of determination was 0.025 microgram/g corn. Recoveries of moniliformin from corn spiked at 0.025, 0.05, 0.25, and 1.0 microgram/g averaged 96.5, 96.2, 97.2, and 97.8% respectively.

Uncertainty--a chemist's view.

Abstract: Complete characterization of the performance of analytical methods requires an evaluation of the halo of uncertainty bracketing the reported result. Achieving a satisfactory estimate of this uncertainty is more important than how this estimate is produced. Enumeration of all conceivable error components--the so-called error budget approach--is one way to estimate the uncertainty, but it is not the only way. In fact, when applied to analytical chemistry this approach is likely to (1) overlook important variables and double count others, (2) avoid considering unknown and unknowable interactions and interferences, and (3) adjust for missing variables with an uncontrollable "Type B" component. The problem is one of experimental design. Alternative and more efficient ways of estimating uncertainty in analytical chemistry include the Youden ruggedness procedure, accompanied by a bonus of optimization, and the all-encompassing interlaboratory method-performance trial.

Simultaneous Liquid Chromatographic Analysis of the β-Lactam Antibiotics Cefazolin, Cefadroxil, Cephalexin, Ampicillin, and Cephradine in Solution

Abstract: A liquid chromatographic method was developed for the determination of nanogram quantities of 5 broad-spectrum structurally related beta-lactam antibiotics (cefazolin, cefadroxil, cephalexin, cephradine, and ampicillin) in solution. The method uses a C18 reversed-phase column, UV absorption (240 nm) detection, and an aqueous mobile phase containing isopropyl alcohol and acetic acid. Relative resolution between the antibiotic peaks ranged from 1.7 to 5.9 for all peaks. Chromatographic retention times were 2.97, 3.92, 4.57, 5.37, and 6.56 min for cefazolin, cefadroxil, cephalexin, ampicillin, and cephradine, respectively. Accuracy, precision, linearity, and long term analytical reproducibility were determined by statistical analysis. Use of the proposed method to evaluate the degradation of cephradine solutions stored at room temperature illustrated its potential as a stability-indicating assay.

In vitro study of nicotine release from smokeless tobacco.

Abstract: Four brands (Copenhagen Snuff, Skoal Bandit Classic, Skoal Wintergreen Long Cut, and Skoal Wintergreen Fine Cut) of smokeless tobacco products were tested for their rate of nicotine release into artificial saliva via direct contact or through a dialysis bag. Nicotine was determined by reversed-phase liquid chromatography. When samples were in direct contact with artificial saliva, most of the nicotine was released from the tobacco in the first minute. Nicotine release from Skoal Bandit Classic, marketed as smokeless tobacco in a sachet, was slower with the sachet intact than without the sachet. When smokeless tobacco and artificial saliva were placed inside a dialysis bag, nicotine release was much slower and primarily depended upon the permeability of the dialysis membrane. Although total nicotine was lowest for Skoal Bandit Classic, little difference was seen in nicotine release rates among the brands tested. When smokeless tobacco was placed in dialysis bags with artificial saliva outside, a significant difference was seen in rates of nicotine migration through the membrane. In this model, nicotine release from Copenhagen Snuff was much faster than from Skoal Bandit Classic with or without the sachet. This difference may be related to the pH of the smokeless tobacco products.

Liquid chromatographic determination of oxytetracycline in edible fish fillets from six species of fish

Abstract: The approved use of oxytetracycline (OTC) in U.S. aquaculture is limited to specific diseases in salmonids and channel catfish. OTC may also be effective in controlling diseases in other fish species important to public aquaculture, but before approved use of OTC can be augmented, an analytical method for determining OTC in fillet tissue from multiple species of fish will be required to support residue depletion studies. The objective of this study was to develop and validate a liquid chromatographic (LC) method that is accurate, precise, and sensitive for OTC in edible fillets from multiple species of fish. Homogenized fillet tissues from walleye, Atlantic salmon, striped bass, white sturgeon, rainbow trout, and channel catfish were fortified with OTC at nominal concentrations of 10, 20, 100, 1000, and 5000 ng/g. In tissues fortified with OTC at 100, 1000, and 5000 ng/g, mean recoveries ranged from 83 to 90%, and relative standard deviations (RSDs) ranged from 0.9 to 5.8%. In all other tissues, mean recoveries ranged from 59 to 98%, and RSDs ranged from 3.3 to 20%. Method quantitation limits ranged from 6 to 22 ng/g for the 6 species. The LC parameters produced easily integratable OTC peaks without coelution of endogenous compounds. The method is accurate, precise, and sensitive for OTC in fillet tissue from 6 species of fish from 5 phylogenetically diverse groups.