Spectrophotometric Determination of Roxarsone in Animal Feeds

Roxarsone is administered in the feed as a growth stimulant for chickens, turkeys, and swine. The drug is extracted with 2% dibasic potassium phosphate solution, the extract is centrifuged, the centrifugate is adjusted to the isoelectric point of proteins with hydrochloric acid, and the precipitated proteins are removed by centrifugation. Interferences are removed by treating the solution with activated charcoal at pH 12, which leaves a solution of roxarsone of intense color that can be measured spectrophotometrically at 410 nm. This method was subjected to a collaborative study. The average recovery from 13 collaborators was 99.25% with an average coefficient of variation of 6.91%. It is concluded that satisfactory results were reported and is therefore recommended that this method be adopted as official first action.

Academy of medicine, Singapore-Ministry of Health clinical practice guidelines: management of food allergy

The Academy of Medicine, Singapore (AMS) and the Ministry of Health (MOH) publish clinical practice guidelines to provide doctors and patients in Singapore with evidence-based guidance on managing important medical conditions. This article reproduces the introduction and executive summary (with recommendations from the guidelines) from the AMS-MOH clinical practice guidelines on the Management of Food Allergy, for the information of readers of the Singapore Medical Journal. Chapters and page numbers mentioned in the reproduced extract refer to the full text of the guidelines, which are available from the Academy of Medicine website: http://www.ams.edu.sg/guidelines.asp#foodallergy. The recommendations should be used with reference to the full text of the guidelines. Following this article are multiple choice questions based on the full text of the guidelines.

Graphite furnace atomic absorption spectrophotometric determination of 4-hydroxy-3-nitrobenzenearsonic acid, other organic arsenicals, and inorganic arsenic in finished animal feed

4-Hydroxy-3-nitrobenzenearsonic acid (roxarsone) is administered in animal feed as a growth stimulant over a concentration range of 25-50 ppm. The drug is extracted from 5 g feed with 200 mL aqueous 1.0% ammonium carbonate solution and 5 min of mechanical shaking. Undissolved feed particles are allowed to settle and 1.0 mL aliquot of extract is diluted with 9.0 mL 15% methanol solution. This solution is subjected to sample atomization by a graphite furnace and arsenic detection by atomic absorption spectrophotometry (AAS). Roxarsone recovery from nonmedicated commercial feed fortified at 25 ppm was 103.6% with a relative standard deviation (RSD) of 4.0%. Recovery for 50 ppm fortification was 104.5% (RSD 4.3%). Roxarsone assay results by furnace AAS were compared with results by the current AOAC spectrophotometric method and the AOAC total arsenic method. Results by the 3 methods compare well. The procedure was also used to determine other organic arsenicals and inorganic arsenic in laboratory-fortified feed samples; these recoveries were essentially theoretical.

High pressure liquid chromatographic determination of nifursol in finished feeds

Nifursol is extracted from feed with acetonitrile, and then washed with carbon disulfide to remove feed interferences. An aliquot is concentrated, diluted with 5% NaCl solution, filtered, and then subjected to high pressure liquid chromatography on a strong anion exchange column, using 365 nm photometric detection. The average recovery of nifursol from fortified feed samples was 100.6% with an average coefficient of variation of 3.5%. The nifursol determination is not subject to interference from the other commonly used nitrofurans.

High Pressure Liquid Chromatographic Determination of Sulfamethazine or Sulfathiazole and Colorimetric Determination of Sulfathiazole in Feeds: Collaborative Studies

A high pressure liquid chromatographic method for sulfamethazine or sulfathiazole in feeds was studied collaboratively. The sample is extracted in 50% methanol and filtered, and an aliquot is injected into a liquid chromatograph. The column is μBondapak C18, the eluting solvent is acetonitrile–water (20+80), and the detection wavelength is 280 nm. Nine collaborators analyzed 3 different synthetic samples and 2 commercial samples labeled to contain 0.011% sulfamethazine, plus procaine penicillin and chlortetracycline. Average recoveries for the synthetic samples were 102.2% at the 0.005% level, 100.2% at the 0.01% level, and 103.6% at the 0.02% level; per cent standard deviations were 12.7, 10.4, and 8.67, respectively. Average sulfamethazine content of the 2 commercial samples was 77.8 and 82.9% of label with per cent standard deviations of 8.56 and 9.16. The same 2 samples, analyzed according to the official colorimetric procedure by 6 analysts, had an average sulfamethazine content of 81.7 and 89.4% of label with per cent standard deviations of 3.69 and 6.66. Eight collaborators analyzed 3 different synthetic samples and 2 commercial samples labeled to contain 0.011% sulfathiazole, plus procaine penicillin and chlortetracycline. Average recoveries of the synthetic samples were 101.6% at the 0.005% level, 103.0% at the 0.01% level, and 100.4% at the 0.02% level; per cent standard deviations were 9.52, 7.00, and 6.54. Average sulfathiazole content found by 9 collaborators was 0.0103% or 93.4% of label for Sample 1 and 0.0100% or 91.1% of label for Sample 2, with per cent standard deviations of 14.1 and 12.2. Colorimetric assays for sulfathiazole were made according to method 42.172–42.174 for sulfamethazine. Two synthetic samples were analyzed by 7 collaborators. Average recovery was 97.6% at the 0.01% level and 99.8% at the 0.02% level with per cent standard deviations of 5.05 and 8.16. The same 2 commercial samples used for the HPLC study were analyzed by 9 collaborators. Average sulfathiazole found was 86.4 and 87.9% of label with per cent standard deviations of 7.41 and 6.15.

Atomic absorption spectrophotometric determination of dibutyltin dilaurate in finished feeds: collaborative study

Dibutyltin dilaurate is administered in the feed as an active drug for the removal of large roundworms, cecal worms, and several species of tapeworms from chickens and turkeys. The drug is extracted from finished feed with warm CHCl3, the CHCl3 extract is filtered, and a 25 ml aliquot is concentrated in the presence of methanol until all traces of CHCl3 are removed. The methanol solution is diluted and filtered to remove feed interferences, and then aspirated into an atomic absorption spectrophotometer with a triple-slot burner head, using an air/acetylene flame. The instrument response to tin at 286.3 nm is recorded. Recoveries of 100.5-101.9% tin were obtained for laboratory-prepared feeds. This method was collaboratively studied. The average recovery for dibutyltin dilaurate from 3 feed samples for 8 collaborators was 98.3% with an average coefficient of variation of 5.83%. The method has been adopted as official first action.

Gas-liquid chromatographic determination of nifursol in frozen turkey tissues to ten parts per billion

Nifursol (3,5-dinitrosalicylic acid (5-nitrofurfurylidene) hydrazide) is extracted into ethyl acetate from 10 g tissue in the presence of sodium sulfate. Tissue interferences are removed from the tissue extract by washing with petroleum ether after the extract has been transferred into an aqueous solution by evaporation of ethyl acetate. The drug is hydrolyzed under acid conditions to form 5-nitro-2-furaldehyde (5NF). After partition of 5NF from the aqueous phase into benzene the extract is further cleaned up on a Florisil column. The 5NF is eluted from the Florisil column with benzeneethyl acetate. Electron capture gas-liquid chromatography of a 10 mul injection of the concentrated column eluate is the determinative step. Quantitation is accomplished by comparison of the peak height of the sample to the peak height of the standard which is carried through the method simultaneously. Studies of method performance on turkey muscle, liver, kidney, and skin tissues fortified to contain 10 ppb nifursol show a recovery range of 87.4-95.0% and a coefficent of variation range of 5.7-11.2%.

Analysis of Feeds Containing a Combination of Sulfanitran, Aklomide, and Arsanilie Acid

Aklomide and sulfanitran can be determined, in the presence of arsanilie acid by removal of arsanilie acid from the methanol extract of t he feed by alumina chromatography. The column effluent is then assayed by the official AOAC colorimetric methods for aklomide and sulfanitran. Arsanilie acid is determined directly on a separate feed sample, using citric acid as the extractant. Recoveries were 94–98% for arsanilie acid, 97% for aklomide, and 95–100% for sulfanitran, with an average coefficient of variation between 3 and 4% for each drug assay.

Improved Colorimetric Method for the Determination of Nitarsone in Feeds

An improved procedure for the determination of nitarsone in poultry feeds has been developed. The drug is extracted from feed with 50% dimethylsulfoxide; interferences are removed by column chromatography of the extract on alumina. The drug is eluted from the column with 4% NaOH and assayed colorimetrically with the Bratton-Marshall reaction after reduction of the nitro group with aqueous 4% titanous chloride. The average recovery of nitarsone from laboratory-medicated feed was 97.0% of theoretical with an average coefficient of variation of 3.4%. The method was applicable to both fresh feeds and feeds stored for periods up to 6 months. This method was subjected to a collaborative study for the determination of nitarsone in medicated feeds. The average recovery from 6 collaborators was 103.5% with an average coefficient of variation of 12.7%. Most of the collaborators reported satisfactory results and therefore this method is recommended for adoption as official first action.