Ion-exchange chromatographic determination of hypoglycin A in canned ackee fruit

An ion-exchange chromatographic method was developed to determine hypoglycin A (HG-A) levels in canned ackee fruit by using an amino acid analyzer. HG-A was extracted by homogenizing the sample in 80% alcohol. An isocratic buffer system, consisting of 30% sodium citrate buffer (pH 3.15) and 70% sodium chloride-sodium acetate buffer (pH 7.40) was used to obtain baseline separation between HG-A and the other amino acids. The system can detect HG-A levels as low as 4.8 micrograms/mL. HG-A levels in the edible portion of fruit in 6 cans ranged from 11.0 to 66.5 mg HG-A/can. Recoveries by standard addition averaged 102.5%.     

Liquid chromatographic determination of miconazole nitrate in creams and suppositories

A rapid method has been developed for the determination of miconazole nitrate in creams and suppositories. The sample is dissolved in ethanol, diluted in acetonitrile-water (1 + 1), and injected onto a C18 column. The mobile phase consists of 55% acetonitrile, a triethylammonium phosphate buffer, and an ion-pairing agent. The total run time is less than 4 min, and the active ingredient is determined using absorbance detection at 214 nm. The mean recovery of miconazole from spiked placebo samples was 99.7 +/- 0.7% for the cream samples at the 2% level and 98.8 +/- 0.3% for the suppository samples at the 4% level.     

Gas-liquid chromatographic determination of nitrate and nitrite in cheese, ham, fish sausage, cod roes, and salmon roes

The 2,4-xylenol method was modified and a gas-liquid chromatographic (GLC) method was developed for nitrate and nitrite determinations in several foods. Either a flame ionization (FID) or an electron capture detector (ECD) can be used. Proteins and fats are removed from warm alkaline water with zinc sulfate and filtered. The filtrate is evaporated to dryness, redissolved in water, and reacted with 2,4-xylenol in the presence of sulfuric acid to form 6-nitro-2,4-xylenol. Interfering chlorides are precipitated with silver sulfate and the nitrosylenol is extracted with hexane, concentrated, and injected. Nitrite in the filtrate is distilled at pH 5, collected in alkaline solution, and dried. The residue is oxidized to nitrate with permanganate in the presence of sulfuric acid, and then chromatographed in the same manner as nitrate. Recoveries from several foods were 83--100% for nitrate and 80--100% for nitrite. The limit of sensitivity was 0.1 ppm for both residues.     

Collaborative study of the colorimetric determination of nitrate and nitrite in cheese.

A quantitative colorimetric method for the determination of nitrate and nitrite in cheese has been subjected to collaborative study. The method includes clarification of an aqueous extract of cheese with zinc hydroxide, reduction of nitrate to nitrite via a spongy cadmium collumn (the nitrite originally present is unaltered), diazotization of sulfanilic acid with the nitrite, and coupling with 1-naphthylamine hydrochloride to form a pink azo dye whose absorbance is measured at 522 nm. The spectrophotometric responses are compared to a standard curve. In samples containing both nitrate and nitrite, nitrate is determined by difference. A standard deviation of 5.5 was obtained (5 of 6 collaborators) when a cheese sample spiked with 276 ppm sodium nitrate was analyzed by the method. The method has been adopted as official first action.     

Normal-phase liquid chromatographic determination of menadione in animal feeds

A simple method is presented for determination of menadione in vitamin premixes and feedstuffs by normal-phase liquid chromatography (LC). Vitamin K3 is extracted and converted to free menadione, which can be determined directly by LC analysis. Peak area or height is measured at 251 nm, and menadione is quantitated by comparison with the working standard. Menadione can be estimated with a detection limit of 2.5 ppm. Recoveries for premixes ranged from 97.3 to 98.3% and for feedstuffs from 93.7 to 96.8%. The method allows the assay of all commercial K3 compounds in pure or stabilized form and is applicable to a wide variety of feeds and premixes.     

Rapid liquid chromatographic determination of patulin in apple juice

A rapid method is described for the quantitative determination of patulin in apple juice. The mycotoxin is extracted from the sample with ethyl acetate and the extract is cleaned up by extraction with a sodium carbonate solution. Patulin is determined by reverse phase liquid chromatography using a muBondapak C18 column and a 254 nm ultraviolet detector. The lower detection limit in patulin standard solution is 0.32 ng and recovery is greater than 75%.     

Ion-pairing liquid chromatographic determination of benzimidazole fungicides in foods

A method is described for determining residues in foods of thiabendazole, thiophanate methyl, the di-oxygen analogue metabolite [dimethyl 4,4'-O-phenylene bis (allophanate)] that is the metabolite name of the latter, and methyl-2-benzimidazole carbamate, which is the major metabolite and fungitoxic principle common to both thiophanate methyl and benomyl. The residues are extracted from the product using methanol and are partitioned into dichloromethane after initial acidification and again after subsequent alkalinization of the extract. Residues are separated and quantified by reverse-phase liquid chromatography using an ion-pairing mobile phase with UV and fluorescence detectors in tandem. Recoveries from 7 different food crops fortified at 0.2-35 ppm levels ranged from 64 to 105%.     

Simultaneous liquid chromatographic determination of some tetracyclines in serum

A sensitive liquid chromatographic method has been developed for the simultaneous determination of oxytetracycline, minocycline, tetracycline, and doxycycline in serum. A serum sample is vortex-mixed with a solution of mobile phase for tetracyclines and 2% (v/v) phosphoric acid. The mixture is filtered using a 30,000 molecular weight cutoff microseparation tube which separates high-molecular-weight solutes following low-speed centrifugation. Tetracyclines are separated from other serum components by reverse phase liquid chromatography (LC) with buffered methanol mobile phase. Ultraviolet absorbance of the column effluent is monitored at 267 nm. Concentrations as low as 0.2 micrograms/mL of tetracyclines in serum are quantitatable, with recoveries from 76.2 to 102.6% and coefficients of variation from 2.69 to 5.36%. The method has been tested in bovine, porcine, equine, caprine, ovine, canine, feline, and avian (turkey) serum.     

Ion chromatographic determination of nitrate in 2 M KC1 soil extracts

A method for the analysis of NO₃-N in a 2 m KCL soil extract, using ion chromatography, is discussed. It involves the treatment of the KCl extract with Ag⁺-activated cation exchange resin to remove excess Cl^–, followed by analysis using a Dionex ion chromatograph. The results of NO₃-N in soil extracts agreed closely with those obtained by steam distillation. The method was linear up to 20 mg N dm^–3 with a detection limit of 0.1 mg Ndm^–3. Quantitative recovery of NO_3-N added to soil extracts over the linear range were observed.
Standard deviations of samples containing 2.57 and 15.11 mgN dm^–3 were found to be 0.06 and 0.11 respectively.     

Improved liquid chromatographic determination of riboflavin in milk and dairy products

Reported here is a simple liquid chromatographic (LC) method for the determination of riboflavin in milk (liquid, evaporated, and dry), yogurt, and cheese. The method involves passing liquid samples or filtrates of semisolid and solid samples through a C18 cartridge. Retained riboflavin is then eluted with an aliquot of 50% methanol in 0.02M acetate buffer of pH 4. A volume of the eluate is injected into the LC system consisting of a C18 column, a solvent of water-methanol-acetic acid (65 + 35 + 0.1, v/v) with a flow rate of 1 mL/min, and a UV detector set at 270 nm. The method is precise and accurate and compares favorably with the present AOAC method. Moreover, it involves fewer sample preparation steps and has a total analysis time of less than 1 h.     

Rapid liquid chromatographic determination of dimetridazole and ipronidazole in swine feed

A simple and rapid method is described for the determination of dimetridazole (DMZ) and ipronidazole (IPR) in swine feeds at various levels (0.11-110 ppm). The drugs are released from feed by prewetting with a buffer, followed by extraction with either methanol or methylene chloride, depending on the drug level; if necessary, an acid-base cleanup is used before the liquid chromatographic analysis. The analytes are separated on a C18 column and monitored at 320 nm for detection and quantitation. Recoveries of DMZ from several feed formulations averaged 108% at the 92.8 ppm level with a standard deviation (SD) of 4.00% and a coefficient of variation (CV) of 3.70%, 101% at the 11.2 ppm level with an SD of 11.9% and a CV of 11.8%, and 100% at the 0.112 ppm level with an SD of 9.27% and a CV of 9.25%. Recoveries of IPR averaged 77.1% at the 12.9 ppm level with an SD of 1.75% and a CV of 2.27%; IPR recoveries averaged 35.2% at the 0.129 ppm level with an SD of 3.39% and a CV of 9.63%.     

Reverse-phase liquid chromatographic determination of benzoic and sorbic acids in foods

An isocratic liquid chromatographic (LC) technique is described for the determination of benzoic acid and sorbic acid in foods such as beverages, fruits, seafood, vegetables, sauces, and dairy, bakery, and confectionery products. A C18 column is used with methanol-phosphate buffer (5 + 95) as mobile phase and 4-hydroxyacetanilide or 3,5-dinitrobenzoic acid as internal standard. Sample preparation is simple, rapid, and produces a sample extract that has a minimum effect on the column performance and life. Specificity of the method was checked against common food additives such as L-ascorbic acid, caffeine, artificial sweeteners (saccharin, cyclamate, aspartame), antioxidants (BHT, BHA) and artificial colors. Also described are 2 procedures for confirmation of the preservatives, using either redox reaction of sorbic acid with potassium permanganate or gas chromatography/mass spectrometry. Mean recoveries of 90-105% were obtained with a precision of 1-6% and a detection limit of 20 mg/kg for the 2 preservatives.     

Reverse-phase liquid chromatographic determination of paraquat and diquat in agricultural products

A simple, rapid, highly sensitive liquid chromatographic method is described for the quantitative determination of paraquat and diquat residues in agricultural products. Paraquat and diquat are extracted with hot dilute hydrochloric acid and are cleaned up on an Amberlite CG-50 column, followed by reverse-phase liquid chromatography on an NH2 column, with ultraviolet detection at 257 nm (paraquat) and 310 nm (diquat). The minimum detectable concentration of both paraquat and diquat was 0.5 ng per injection, which corresponds to a lower detection limit of approximately 0.02 microgram/g in the original samples. Recoveries of paraquat and diquat added to various samples were greater than 79%, and averaged 91 and 90%, respectively, at the 0.1 and 1.0 microgram/g spiking levels.     

High performance liquid chromatographic determination of clocapramine in feed and plasma

A high performance liquid chromatographic method is described for the determination of clocapramine in animal feed and plasma. Samples are made alkaline and then extracted with chloroform containing opipramol as internal standard. For plasma samples, the organic phase is evaporated to dryness under a stream of nitrogen, and the residue is dissolved in dichloromethane-methanol. Extracts are chromatographed on silica gel with dichloromethane-methanol-ammonia (100 + 10 + 0.25) as eluant, and quantitated using an internal standard. Within-day precision for plasma extracts (n = 15) was 3.39, 5.7, and 4.13% at 5, 10, and 15 mg clocapramine/L plasma, respectively, and day-to-day precision was 4.6, 6.8, and 4.4% at the same levels. The detection limit was 0,5 mg/L. Recovery from feed over the concentration range 2-6 g/kg was greater than 96%.     

High pressure liquid chromatographic determination of aflatoxins in corn.

A high pressure liquid chromatographic (HPLC) method is proposed for determining aflatoxins in corn. The sample is extracted with methanol-10% NaCl (4 + 1), pigments are precipitated with zinc acetate, and the extract is cleaned up on a small (2 g) silica gel column. Aflatoxins in the purified extract are resolved by normal phase HPLC on a microparticulate (10 micrometer) silica gel column with water-saturated chloroform-cyclohexane, acetonitrile solvent, and detected by fluorescence on a silica gel-packed flowcell. The method was compared with chloroform-water extraction of the official CB method on 15 samples of contaminated corn. In 5 of the 6 samples containing aflatoxins B1, B2, G1, and G2, methanol-10% NaCl extracted more aflatoxin than did cloroform-water, as measured both by HPLC and by thin layer chromatography. In samples containing only B1 and B2, the 2 extraction solvents were virtually equivalent. Agreement was good between HPLC and TLC for each extraction solvent. Average recovery of aflatoxins B1, B2, G1, and G2 added to yellow cornmeal at 3 levels was greater than 90%.     

Reverse phase liquid chromatographic determination of bisacodyl in dosage forms

A method is described for the determination of bisacodyl in enteric-coated tablets and suppositories by liquid chromatography (LC). The method will also determine the hydrolysis degradation products monoacetylbisacodyl and desacetylbisacodyl. The sample is dissolved in 2-propanol, and the extract is diluted with the mobile phase and injected into a liquid chromatograph fitted with a mu Bondapak C18 column and an ultraviolet detector set at 254 nm. The column is eluted with methanol-acetonitrile-0.01M citric acid (25 + 25 + 50). The pooled mean recovery value for bisacodyl from commercial enteric-coated tablets and suppositories was 99.7% with a pooled coefficient of variation (CV) of 0.72%. For content uniformity assays, the CVs were 0.7 and 1.0% for groups of 10 individual commercial suppositories and tablets, respectively. Differences between assay values by the LC and USP XX methods were 0.2% of declared for enteric-coated tablets (n = 5) and 1.0% of declared for suppositories (n = 2). The LC method can determine as little as 0.015 microgram of the monoacetyl or desacetyl degradation product.     

High pressure liquid chromatographic determination of zearalenone in chicken tissues

A method is reported for the extraction and analysis of zearalenone in chicken fat, heart muscle, and kidney tissue by using high pressure liquid chromatography (HPLC). Zearalenone is extracted with acetonitrile, cleaned up with hexane, and extracted further with ethyl acetate. Zearalenone is determined by HPLC using a reverse phase radial compression separation system, an ultraviolet absorbance detector, and a mobile phase of acetonitrile-water (60 + 40) (v/v). Recoveries of zearalenone added at levels from 50 to 200 ng/g are in the range 82.6-95.1%.     

High pressure liquid chromatographic determination of arprinocid in feed.

Arprinocid [9 - (2 - chloro - 6 - fluorophenylmethyl)-9H-purin-6-amine] is determined in feed by high pressure liquid chromatography with a silica column and ultraviolet detection. The drug is extracted from the feed into chloroform in the presence of pH 7 phosphate buffer, transferred to 0.1N HCl, and separated from interfering substances by partitioning with hexane. The acidic solution is neutralized, and the analyte is extracted into chloroform for injection into the chromatograph. This procedure has been applied to feeds containing 0.0030--0.0090% arprinocid with a precision of less than 5% relative standard deviation at the 0.0060% formulated concentration level. The results of this chromatographic procedure also correlate with those from a colorimetric analysis.     

High pressure liquid chromatographic determination of nitrofurazone in milk.

A rapid high pressure liquid chromatographic (HPLC) screening method for the quantitative determination of nitrofurazone in milk has been developed. The drug is extracted with ethyl acetate from a 2.0 ml milk serum sample, the organic layer is evaporated to dryness, and the residue is dissolved in the mobile phase and injected into the liquid chromatogarph. A reverse phase muBondapak C18 column is used with monitoring at 365 nm. The detection limit is 5 ppb and recoveries are 57--67%. Mass spectroscopic confirmation of the HPLC nitrofuran peak is described.