Semiautomated method for riboflavin in food products: collaborative study

A collaborative study was conducted comparing a semiautomated riboflavin method with a manual riboflavin method for 10 food products. Six laboratories provided results from the semiautomated method and 16 laboratories used the manual technique. The semiautomated method was more repeatable within a laboratory than was the manual method. The semiautomated method results compared favorably with the manual method for all 10 products.     

Collaborative study of a semiautomated fluorometric method for the determination of reserpine in tablets.

A semiautomated fluorometric method for the determination of resperpine in tablets was collaboratively studied by 7 laboratories. The method is a modification of the semiautomated method of Urbányi and Stober, which involves formation of a fluorogen with vanadium pentoxide. Collaborators were supplied with 3 composites, each from a different dosage level of commercial tablets. The results obtained agreed well with the AOAC manual fluorometric method; coefficients of variation ranged from 0.45 to 2.70%. The method has been adopted as official first action.     

Collaborative study of a semiautomated colorimetric analysis of digoxin tablets.

A semiautomated thiobarbituric acid colorimetric analysis for digoxin was collaboratively studied by 6 laboratories. Collaborators were supplied with 3 composites of tablets of different dosage levels. Results agreed with the USP method. The coefficients of variation ranged from 0.46 to 2.73%. The method has been adopted as official first action.     

Computerized semiautomated microbiological assay of folacin

A semiautomated microbiological folacin assay system is described. A microcomputer controls sample dilutions, medium addition, turbidity determination, and data acquisition. Assay capacity is 600 tubes per day, approximately twice that of comparable manual assays. Using the automated equipment, more samples can be compared within one assay, eliminating many sources of between-assay variation in large studies. Additional advantages of this system are reduced human errors, flexibility of assay design, and multifunctional component equipment. Folacin results from chicken liver, spinach, and breakfast cereal samples show equivalent precision for manual and automated assays.     

Turbidimetric microbiological assay results calculated by a BASIC computer program

A BASIC computer program was used to calculate the results of microbiological vitamin assays. The program, which incorporates the official AOAC guidelines for microbiological methods, reduces the uncertainty inherent in manual curve plotting and interpolation and minimizes the human error of repetitive calculations. Because the BASIC programming language is well suited for use on self-contained personal computers, it can be easily adapted by small laboratories.     

Automated method for the determination of niacin and niacinamide in cereal products: collaborative study.

In a collaborative study, an automated method for the determination of niacin and niacinamide in cereal products was compared with the official final action microbiological (43.121-43.125) and chemical (43.044-43.046) methods. Ten samples of cereal products, including enriched flour, yeast-leavened baked products, fortified breakfast cereals, and baked pet food products, were submitted to 14 laboratories. Nine laboratories reported values by the automated method, 6 reported values by the microbiological method, and 7 reported values by the chemical method. The results from the microbiological method were not subjected to analysis of variance because of the unusually large between-laboratory variation. The between-laboratory coefficients of variation for the automated and chemical methods were 10.90 and 10.18%, on the basis of results from 7 and 4 laboratories, respectively. There was no significant (p greater than 0.05) difference between methods when results from the 4 laboratories who used both methods were compared. The automated chemical method has been adopted as official first action.     

A manual colorimetric procedure for measuring ammonium nitrogen in soil and plant Kjeldahl digests

Abstract

The measurement of NH4⁺‐N in soil, and plant digests is one of the greatest needs in laboratories conducting agricultural and environmental research. Many laboratories do not have access to automated equipment for colorimetric analysis of soil and plant digests. The objective of this research was to modify an automated colorimetric analysis procedure for determining NH₄+‐N in soil and plant digests for manual use, and compare the proposed technique with the standard distillation‐titration technique. The modified procedure is based on the color reaction between NH₄ ⁺‐ and a weakly alkaline mixture of Na salicylate and a chlorine source in the presence of Na nitroprusside. Wavelength scans indicated a very well defined peak for determinations at 650 nm. Time scans showed that color development in the manual procedure was rapid, 12 to 40 minutes depending on temperature, and that the color development remained stable for at least 120 minutes. Regression analysis of the results from 18 soil and 20 plant tissue sample determinations by distillation‐titration and the proposed method indicated NH₄ ⁺ ‐N recoveries of 99% or higher. The results obtained using the colorimetric procedure were very similar to the values obtained by distil ling and titrating the digests for both soil and plant samples as indicated by the large coefficients of determination (R² = 0.99).     

Identification of nosiheptide in feeds and detection of residues in animal tissues

Nosiheptic is determined in fermentation broths of Streptomyces actuosus either by a microbiological method using Staphylococcus aureus or, more easily, by an automated colorimetric method. The results obtained with both methods correspond well for concentrations greater than 100 microgram/mL with a standard deviation of 1-3%. For determination of nosiheptide as a feed additive, the microbiological assay is made more specific by pretreatment with petroleum ether and 1N HCl. Standard deviation is less than 4%, and the assay is sensitive to 1 ppm. Nosiheptide is identified in feed containing other frequently used antibiotics by thin layer chromatography with bioautography; sensitivity is 1 ppm. The absence of traces of nosiheptide in tissues of treated swine and broiler is confirmed by microbiological diffusion, sensitive to 0.025 ppm.     

Microbiological assays for antibiotics and vitamins: considerations for assuring accuracy.

Factors that may influence the accuracy and precision of microbiological manual and semiautomated turbidimetric methods as well as diffusion assays are discussed. Influence of kind of equipment, media, test bacteria, sample preparation, form of dose response lines, operations, and personnel on quality of assays is examined with the objective of reducing to insignificance those factors under control of the analyst that are responsible for low quality assays.     

An evaluation of some manual colorimetric methods for the determination of inorganic nitrogen in soil extracts

Abstract

A number of manual colorimetric methods for the determination of inorganic nitrogen in 1 M KCl soil extracts were investigated to find techniques that were inexpensive, rapid, versatile and suitable for laboratories with limited analytical equipment. Three colorimetric methods for No^? ₃‐N determination were evaluated and only the copperised/cadmium reduction technique suffered no significant interference from the Cl^? present in the extracting solution. A phenol‐hypo‐chlorite (Berthelot) procedure for NH⁺ ₄‐N determination and the Griess‐Ilosvay method for NO^? ₂‐N determination were both found suitable for N determination in 1M KC1 soil extracts. The reliability and accuracy obtainable with the manual colorimetric methods described was shown to be comparable with that obtained from colorimetric analyses performed using an AutoAnalyser.     

Semiautomated method for determining ferrous sulfate in pharmaceuticals: collaborative study

A semiautomated colorimetric method is described for determining ferrous sulfate in tablets, capsules, and elixirs. The method involves the formation of an orange-red complex between 1,10-phenanthroline and ferrous ion. Collaborators were supplied with 3 solid composites and one liquid sample. Two of the solid composites were prepared from commerical tablets of different dosage and one from commercial timed-release capsules; the fourth sample was an elixir. The results of the automated analyses for ferrous sulfate agreed well with those of the applicable USP method. No interference was found from ferric iron or from the red and green coloring used on coated tablets. The method has been adopted as official first action.     

Analysis of foods for iodine: interlaboratory study

An accurate, reproducible method for less than or equal to 1 ppm iodine in foods is required for nutritional labeling. In order to ascertain the current status of iodine analysis in foods, 7 samples, representing different food classes, were analyzed by 8 laboratories. Six laboratories used their modifications of the Ce-As-I catalytic method preceded by alkaline dry ashing. Two laboratories used neutron activation analysis (NAA), with differing radiochemical separations. The study showed wide discrepancy in analytical results. Mean relative standard deviation for all laboratories was 77.9% between laboratories; 19.1% within-laboratories. Laboratories using NAA had only slightly better precision than did laboratories using the chemical method. The lowest level reported on the entire group of samples ranged among laboratories from 0.0089 to 0.65 ppm. Figures reported by a laboratory are, in general, consistently high or consistently low. The only differences in methodology which may possibly correlate with level of iodine obtained are the use of NAA technique and use of manual, rather than automated, colorimetry.     

Comparative Evaluation of Inductively Coupled Plasma–Atomic Emission Spectroscopy and Colorimetric Methods for Determining Hot-Water-Extractable Boron in Soils

Frequency of boron (B) deficiency is increasing in rainfed systems, and hence there is a need to diagnose the deficiency. Colorimetric methods are still widely used in soil-testing laboratories in India for measuring B. Little information is available on the comparative evaluation of the colorimetric and inductively coupled plasma (ICP) methods for determining extractable B in soils. We describe results of the comparative evaluation of these methods for measuring extractable B in 57 soil samples with pH values ranging from 5.3 to 9.5. There was a significant correlation between B values determined by the two methods, and the correlation coefficient was greater for soil samples with pH in the neutral to alkaline range. Interaction between soil samples and methods (ICP or colorimetric) was significant except for soil samples in the pH range of 8.0 to 9.5. Precision for B determination was greater with the ICP than with the colorimetric method.     

Automated fluorometric determination of vitamin A in milk

A previously published fluorometric method for vitamin A in milk, involving saponification in centrifuge tubes and extraction with hexane, was automated using conventional automated equipment including a filter fluorometer. The extraction and separation steps were affected by the presence of fat, so standards were prepared in milk. The peaks obtained with samples were 95% of steady state values. The coefficients of variation for 10 replicate analyses were 1.9% for unfortified milk and 1.3% for fortified milk. In tests on 19 different milk samples, the results of the automated and manual fluorometric methods differed by less than 10%; a colorimetric method using SbCl3 gave more erratic results and was more lengthy and laborious.     

Microbiological determination of neomycin in feeds: collaborative study

A modification of the AOAC microbiological determination of neomycin in feeds was collaboratively studied by 12 laboratories. The official method was modified by substituting a constant salt concentration diluent for the feed extract diluent, preparing the agar medium in tris buffer, and performing the test with a monolayer plating system. Each laboratory performed single assays on 8 samples in a randomized sequence. The samples included duplicates of a cattle and swine feed at 2 different marketed concentrations. The mean recovery across all laboratories was 110.7% of theory with a range of means of 69.4-128.6 across the 12 laboratories. The results of one laboratory and 2 additional values from different laboratories were deemed outliers and excluded from statistical analysis. The statistical analysis gave a confidence interval of +/- 26% for individual assays.     

Microbiological method for assaying lincomycin in animal feed: collaborative study.

A microbiological assay for determining lincomycin in swine feed, supplement, and a vitamin-mineral premix was studied collaboratively in 16 laboratories. The design of the study involved a complete feed, feed supplement, and a vitamin-mineral premix covering a range of fortification from 20 to 80 g/ton and 80 to 2600 g/ton. Two methods of sample preparation were used depending on the concentration of lincomycin in the sample. Statistical evaluation of the results from the 2 methods indicated that 10 and 11 collaborators, respectively, had mean recoveries which were not significantly different from one another. Ten laboratories obtained a mean recovery of 112.2% (range 102.3--123.5%) for the lower level, and 11 laboratories obtained a mean recovery of 104.4% (range 100.0--107.7%) for the higher level. The method has been adopted as official first action.     

Collaborative study comparing the spiral plate and aerobic plate count methods.

The spiral plate count method is a semiautomated plating technique that greatly reduces manpower and material costs normally associated with the pour plating technique. In this collaborative study, 8 laboratories compared the spiral and pour plating techniques, using 4 samples each of 3 products: frozen pumpkin pie, frozen chicken pot pie, and shampoo. The results show that 10 of the 12 comparisons of means of the pour and spiral methods were not significantly different; 2 values were significant at alpha = 0.01. Overall, the components of variance were less than that of the current milk standard, and the replicate per cent coefficient of variation was satisfactory. This study indicates that the spiral plate method is an acceptable alternative to the pour plate method; the spiral plate method has been adopted as official first action.     

Fluorometric determination of histamine in tuna: collaborative study

Six samples of canned tuna, albacore, yellowfin, and skipjack, in water or oil pack were analyzed in duplicate by a fluorometric method and the AOAC colorimetric method. For the fluorometric method, recoveries of histamine added to acceptable tuna averaged 99% with a range of 91 to 107%. Agreement between laboratories for the analyses of decomposed tuna containing 20-200 mg histamine/100 g sample was excellent. Results from the fluorometric method are comparable with those from the AOAC colorimetric method; the fluorometric method has been adopted as official first action.     

Automated fluorometric determination of vitamin C in foods.

Two automated fluorometric methods were compared with the official AOAC methods for determining vitamin C in fortified ready-to-eat cereals, fruits, vegetables, baby foods, flour products, pet foods, meats, frozen dinners, juices, and nutritional health bars. Each sample was analyzed in duplicate on 2 days and included a recovery study on all products. Egberg's semiautomated method (Method 1) and Roy's automated method (Method 2) were compared with the manual AOAC tritrimetric and fluorometric methods. The correlation factor for Methods 1 and 2 were 0.999 and 0.979, respectively, when compared with the AOAC methods. The recovery study showed average recoveries of 97.8% for Method 1, 99.3% for Method 2, and 100.6% for the AOAC methods. The results suggest that Method 1 is the method of choice for the majority of the products analyzed.     

Microbiological plate and turbidimetric assays of chlortetracycline in feeds: collaborative study.

The manual and automated turbidimetric assays and a modified official plate assay for chlortetracycline (CTC-HCl) in feed were collaboratively studied. Three feed samples (swine feed, 100 g CTC-HCl/ton; premix I, 20 g each of CTC-HCl and sulfamethazine/lb, and 10 g penicillin/lb; and premix II, 50 g CTC-HCl/lb) were analyzed at 2 dilutions. Twelve laboratories conducted the plate assay; 8 laboratories the manual turbidimetric method; and 7 laboratories, the Autoturb analysis. Within a method, there was no significant difference between dilutions. Between methods, there was a significant difference between the manual turbidimetric plate assays only for swine feed. However, the same sample dilutions or the average values of the 2 dilutions for both methods showed no statistical difference. Among the collaborators, the slope of CTC-HCl standard curve varied between about 2.0 and 3.0 for the plate method. The turbidimetric assay has been adopted as official first action for feeds containing larger than or equal to 20 g CTC-HCl/lb.