Spectrophotometric analysis of binary mixtures of sulfonamides.

Different methods for analyzing binary mixtures by using 2 wavelengths are reviewed. The absorbance ratio calculated at 2 wavelengths, not including the isoabsorptive point, was a quadratic function of relative concentration. The curve-fitting process using orthogonal polynomials was applied to obtain the quadratic equation. An absorbance ratio can be used as a rapid purity index for sulfacetamide sodium in the presence of sulfanilamide. Sulfacetamide sodium has been determined in eye drop preparations.     

Spectrophotometric assay of salsolidine hydrochloride.

The proposed method is based on the reaction of salsolidine HCl with carbon disulfide and ammoniacal copper sulfate. The resulting salsolidine-copper-dithiocarbamate complex is extracted with benzene and measured spectrophotometrically at 448 nm. The method is applicable for the detection of 40-500 mug salsolidine/5 ml.     

Spectrophotometric determination of tolbutamide in tablets.

Two spectrophotometric methods, Glenn's method of orthogonal function and the basic dye method, are described for determing tolbutamide in tablets without interference from the tablet excipients. In Glenn's method, the absorbance of tolbutamide in 95% ethanol is measured in the vicinity of 250--270 nm at 4 nm intervals and the p2 coefficient is calculated. The coefficient is linearly related to concentration within a range of 0.1--0.4 mg/mL. Tolbutamide gives a complex of a ratio 1:1 with basic dye Brilliant Cresyl Blue (BCB) or Safranin T (ST). The complex is easily extracted with chloroform. The absorbance of the chloroform extract is measured against either a blank or reference experiment. The latter is obtained by using a specific concentration of tolbutamide: 0.4 mg/mL in tolbutamide-BCB or 0.024 mg/mL in tolbutamide-ST. The ST complex method is more sensitive compared with the other methods. When the t-test is applied, the results of the proposed methods are more accurate than those of the traditional ultraviolet spectrophotometric method.     

Quantitative analysis of pyroglutamic acid in peptides.

A simplified and rapid procedure for the determination of pyroglutamic acid in peptides was developed. The method involves the enzymatic cleavage of an N-terminal pyroglutamate residue using a thermostable pyroglutamate aminopeptidase and isocratic HPLC separation of the resulting enzymatic hydrolysate using a column switching technique. Pyroglutamate aminopeptidase from a thermophilic archaebacteria, Pyrococcus furiosus, cleaves N-terminal pyroglutamic acid residue independent of the molecular weight of the substrate. It cleaves more than 85% of pyroglutamate from peptides whose molecular weight ranges from 362.4 to 4599.4 Da. Thus, a new method is presented that quantitatively estimates N-terminal pyroglutamic acid residue in peptides.     

Solid-phase extraction and LC-MS analysis of pyrrolizidine alkaloids in honeys

Strong-cation-exchange, solid-phase extraction of pyrrolizidine alkaloids and their N-oxides from honey samples was followed by reduction of the N-oxides and subsequent analysis of total pyrrolizidine alkaloids using high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry. A limited survey of 63 preprocessing samples of honey, purposefully biased toward honeys attributed to floral sources known to produce pyrrolizidine alkaloids, demonstrated levels of pyrrolizidine alkaloids up to approximately 2000 parts per billion (ppb) in a sample attributed to Echium plantagineum. Up to 800 ppb pyrrolizidine alkaloids was detected in some honeys not attributed by the collector to any pyrrolizidine alkaloid-producing floral source. No pyrrolizidine alkaloids were detected in approximately 30% of the samples in this limited study, while some honeys showed the copresence of pyrrolizidine alkaloids from multiple floral sources such as E. plantagineum and Heliotropium europaeum. In addition, retail samples of blended honeys (with no labeling to suggest that pyrrolizidine alkaloid-producing floral sources were used in the blends) have been shown to contain up to approximately 250 ppb pyrrolizidine alkaloids.     

Dehydropyrrolizidine alkaloids, including monoesters with an unusual esterifying acid, from cultivated Crotalaria juncea (Sunn Hemp cv.'Tropic Sun')

Cultivation of Crotalaria juncea L. (Sunn Hemp cv. 'Tropic Sun') is recommended as a green manure crop in a rotation cycle to improve soil condition, help control erosion, suppress weeds, and reduce soil nematodes. Because C. juncea belongs to a genus that is known for the production of toxic dehydropyrrolizidine alkaloids, extracts of the roots, stems, leaves, and seeds of 'Tropic Sun' were analyzed for their presence using HPLC-ESI/MS. Qualitative analysis identified previously unknown alkaloids as major components along with the expected macrocyclic dehydropyrrolizidine alkaloid diesters, junceine and trichodesmine. The dehydropyrrolizidine alkaloids occurred mainly as the N-oxides in the roots, stems, and, to a lesser extent, leaves, but mainly as the free bases in the seeds. Comprehensive spectrometric and spectroscopic analysis enabled elucidation of the unknown alkaloids as diastereoisomers of isohemijunceine, a monoester of retronecine with an unusual necic acid. The dehydropyrrolizidine alkaloid contents of the roots, stems, and leaves of immature plants were estimated to be 0.05, 0.12, and 0.01% w/w, respectively, whereas seeds were estimated to contain 0.15% w/w.     

Spectrophotometric method for hydroxymethylfurfural in honey.

A new method is described for hydroxymethylfurfural (HMF) in honey; accuracy and precision are improved over the most used optical and chemical methods. With a clarified honey solution containing 0.1% sodium bisulfite as reference and a similar solution without bisulfite as sample, a difference spectrum is obtained which represents only the HMF in the sample, without the interfering absorption of the honey. The average recovery was 97.5% for 24 additions to honey of 0.8--40 mg HMF/100 g. Forty honey samples ranging from 0 to 40 mg/100 g were analyzed by 3 methods with the following average results: Winkler optical method, 7.25; Winkler chemical method, 4.83; and new bisulfite method, 5.05 mg HMF/100 g honey. Values by the latter 2 methods did not differ at the P = 0.05 significance level.     

Spectrophotometric determination of allylisothiocyanate in mustard seed oil.

Allylisothiocyanate is determined spectrophotometrically after reaction with 2,3-dichloro-1,4-naphthoquinone. For pure samples, the color intensity is proportional to allylisothiocyanate content in the range 0.8-3.0 mg/ml reaction mixture. A modified procedure is used to estimate allylisothiocyanate content of mustard seed oil. The reaction is linear for allylisothiocyanate concentrations in the range 40-240 mug/ml reaction mixture. Two mustard seed oil samples contained 0.995 not equal to 0.020 and 0.981 not equal to 0.019% allylisothiocyanate.     

Simultaneous analysis of catechins, gallic acid, strictinin, and purine alkaloids in green tea by using catechol as an internal standard

We developed a high-performance liquid chromatography-based method for simultaneous analysis of nine catechins, gallic acid, strictinin, caffeine, and theobromine in green tea by using catechol as an internal standard. Although the high cost and instability of the catechin reference standards limit the application of this method, the addition of ascorbic acid to the standard stock solution preserved the stability of the reference standards in the solution for 1 year when stored at -30 degrees C. Furthermore, we found that the slopes of the calibration curves plotted were stable for a run time of 2000 h. Our method proved to be appropriate for quantification and yielded good correlation coefficients, detection levels, repeatability, reproducibility, and recovery rates. Quantitative data revealed that the contribution of only 200 mL of brewed tea to the total dietary catechins was approximately 220-420 mg, while that of 500 mL of bottled tea was approximately 170-900 mg.     

Spectrophotometric determination of some benzene sulfonamides with 7,7,8,8-tetracyanoquinodimethane

A new spectrophotometric method for the determination of some unsubstituted benzene sulfonamides is presented. The method is based on the interaction of these derivatives with 7,7,8,8-tetracyanoquinodimethane at pH 9.0-9.5 to produce intense blue products. The quantitation of the products was carried out at 578 nm. Beer's law was obeyed over a wide range of concentrations for all sulfonamide compounds studied. Optimum analytical conditions were determined, and the color produced was stable for at least 90 min at 25 degrees C. Analytical data for determination of sulfonamide compounds in pure form are presented together with application of the proposed method for analysis of some commercially available pharmaceutical preparations. The results are in good agreement with those obtained by official procedures.     

Spectrophotometric determination of strychnine and brucine in liquid galenicals.

A rapid method is presented for determining strychnine and brucine in liquid galenicals. At pH 5.0, both strychnine and brucine are complexed with methyl orange. After treatment with 0.1N NaOH, the liberated alkaloids are determined spectrophotometrically, using the 2-wavelength method of analysis. The method has been successfully applied to the analysis of 4 batches of nux vomica tincture, nux vomica acid, and nux vomica alkaline mixtures. The method has a relative standard deviation of 0.52%.     

HPLC-MSn analysis of phenolic compounds and purine alkaloids in green and black tea

Tea is a complex mixture containing a range of compounds from simple phenolics to complex thearubigins, many of which have well-recognized antioxidant properties. This paper describes the application of high-performance liquid chromatography-mass spectrometry (HPLC-MS(n)) methods for the rapid and routine analysis of more than 30 phenolics in tea. Green and black tea infusions were injected directly onto a reversed phase HPLC column, and the phenolics eluted using two different mobile phase gradients, one optimized to resolve catechin derivatives and the other, flavonols and theaflavins. Compounds, identified on the basis of their retention time, absorbance spectrum, and MS fragmentation pattern, included (+)-catechin, (-)-epicatechin, theaflavin and their various gallate derivatives, quercetin and kaempferol mono-, di-, and triglycosides, quinic acid esters of gallic acid and hydroxycinnamates, and the purine alkaloids, caffeine and theobromine.     

Spectrophotometric analysis of mixtures of acetaminophen, salicylamide, and codeine phosphate in tablets

A simple and accurate spectrophotometric procedure for the analysis of a mixture of acetaminophen, salicylamide, and codeine phosphate is described. Determination of the first 2 components depends on pH-induced differential spectral changes of their nitroso derivatives. The third component is assayed by the acid dye method. The proposed procedure was successfully applied to the analysis of laboratory-made and commercial tablets containing the ternary drug mixture.     

Spectrophotometric determination of caffeine in coffee products: collaborative study.

An ultraviolet (UV) spectrophotometric method for determining caffeine in regular and decaffeinated coffee products has been studied collaboratively. Nine laboratories participated in this study which compares the proposed UV method with the official AOAC micro Bailey-Andrew method. Caffeine content was determined on as-is basis on 8 samples of green, roasted, and soluble coffees. The coefficients of variation for the proposed method ranged from 2.02 to 6.98% for the 8 samples studied. The results agreed well with those from the Bailey-Andrew Method. The method was adopted as official first action.     

Spectrophotometric determination of substrate-borne polyacrylamide

Polyacrylamides (PAMs) have wide application in many industries and in agriculture. Scientific research and industrial applications manifested a need for a method that can quantify substrate-borne PAM. The N-bromination method (a PAM analytical technique based on N-bromination of amide groups and spectrophotometric determination of the formed starch-triiodide complex), which was originally developed for determining PAM in aqueous solutions, was modified to quantify substrate-borne PAM. In the modified method, the quantity of substrate-borne PAM was converted to a concentration of starch-triiodide complex in aqueous solution that was then measured by spectrophotometry. The method sensitivity varied with substrates due to sorption of reagents and reaction intermediates on the substrates. Therefore, separate calibration for each substrate was required. Results from PAM samples in sand, cellulose, organic matter burnt soils, and clay minerals showed that this method had good accuracy and reproducibility. The PAM recoveries ranged from 95.8% to 103.7%, and the relative standard deviations (n = 4) were <7.5% in all cases. The optimum range of PAM in each sample is 10-80 microg. The technique can serve as an effective tool in improving PAM application and facilitating PAM-related research.     

Spectrophotometric determination of acetaminophen in tablets, sirups, and suppositories.

A differential spectrophotometric method and Glenn's method of orthogonal function are described for the assay of acetaminophen in tablets, sirups, and suppositories. Interference from excipients in the formulations is thereby avoided. Accuracy of the analyses is greater with the proposed methods than with the British Pharmacopoeia method.     

Spectrophotometric determination of silicon in soil solutions by flow injection analysis: Reduction of phosphate interference

Abstract

A flow injection analysis (FIA) procedure for the determination of dissolved silica (0.04–20 mg/L Si) in aqueous solution has been optimized to reduce phosphate interference. Determinations are based on measurement of absorbance at 790 nm of heteropoly molybdenum blue formed by reduction with ascorbic acid at room temperature. Phosphate did not interfere in a 15‐fold excess. The optimized procedure was tested on soil solutions isolated by centrifugation of various horizons from a Typic Haplohumod. Si concentrations of 1.3–4.8 mg/L Si were found with a variation coefficient of about 2. Results obtained compared well with those obtained by a manual reference method and a proprietary FIA method except in solutions high in dissolved humic material where slightly higher values were obtained by the optimized method. In a standard addition mode the optimized method yielded 5–15% lower values than in the ordinary mode. This difference was reduced by persulfate oxidation of organic matter. Soil solutions investigated were very low in phosphate but phosphate spiking experiments demonstrated that phosphate interference was less than in model solutions matched in metal ion concentrations and insignificant in solutions low in humic material and with less than 10 mg/L P. Dissolved silica was unstable in a solution isolated from an organic horizon of high biological activity.     

Spectrophotometric determination of isocarboxazid bulk drug and tablets by reaction with p-dimethylaminocinnamaldehyde

A spectrophotometric method is described for the determination of isocarboxazid. The method is based on the reaction of the drug with p-dimethylaminocinnamaldehyde in the presence of trichloroacetic acid in a methanolic medium to produce a very intense red chromophore (lambda max = 500 nm, Emax = 1.05 x 10(5]. The reaction is proposed to proceed via electrophilic attack at the C-4 position of the isoxazole nucleus. Job's plot indicated a 1:1 drug-to-reagent ratio. Regression analysis of Beer's plot showed excellent correlation (r = 0.9996) in the concentration range 0.25-2.10 micrograms isocarboxazid/mL. The developed color is stable for at least 12 h. Results of analyses of bulk drug and tablets by the proposed method are comparable to those for USP XXI methods.     

Spectrophotometric determination of ascorbic acid in canned fruit juices, cordials, and soft drinks with iron(III) and 1,10-phenanthroline as reagents

A simple and accurate spectrophotometric method has been developed for the determination of ascorbic acid in canned fruit juices, cordials, and soft drinks, based on the reduction of iron(III) by ascorbic acid to iron(II), which is then complexed with 1,10-phenanthroline. Background correction is necessary for most samples and can be achieved by copper(II)-catalyzed oxidation of the acid. The calibration graph was linear from 0 to 8 micrograms/mL of ascorbic acid with a slope of 0.12/ppm. The precision for the determination of ascorbic acid in a lemon drink containing 210 micrograms/mL of the acid was 0.9%. Many ingredients commonly found in fruit juices, cordials, and soft drinks do not interfere; however, tannic acid, pyrogallol, and sulfite interfere with the method. A wide range of samples was analyzed for ascorbic acid content by the proposed method. The samples included mango and lemon tea drinks and also grapefruit juices, for which no background correction is needed.