Densitometric methods

Qian et al. [46] determined miconazole nitrate and benzoic acid in paint by a thin-layer chromatographic densitometric method. The drug was spotted on a GF254 silica gel plate, developed with a 42 21 13 5 w-hexane-chloroform-methanol-... 

TLC separation and densitometric determinations of alkaloids of Cyclea densi-flora, Stephania herbacea, S. brachandra, and S. tetrandra have been described the bis bases isolated were isochondodendrine, curine, berbamine, cycleanine, cepharanthine, curarine, fangchinoline, homoaromoline, isotetrandrine (= iso-sinomenine A), and tetrandrine (= sinomenine A) (330a). A TLC-densitometric method for assay of dauricine from biological specimens has been reported (331). Tubocurarine served as a test case for pseudophase liquid chromatogra-... 

Dogrukol-Ak et al. [55] determined omeprazole in pharmaceutical preparations by a TLC densitometric method. Pellets from eneric coated capsules were finely powdered and dissolved in ethanolic 0.05 M potassium hydroxide with sonication. Four microliters of the solution was subjected to TLC on a silica gel FG254 plates with chloroform-methanol-25% ammonia (97.5 2.5 1) as mobile phase and densitometric detection of omeprazole (Rf = 0.46) at 302 nm. Calibration graphs were linear for 0.42—1.68 jug omeprazole the detection limit was 25 ng. In the determination of omeprazole in 20 mg Omeprazit, Omeprol, and Losec capsules, the found amounts were 20.2, 20.3, and 19.8 mg omeprazole, respectively, with corresponding RSD 1.9,1.8, and 1.6% (n = 8). The results agree with those of UV spectrophotometry. 

Shellard and Alam(31 ) in 1968 have made a detailed study of the densitometric method for TLC. 

Hassib et al. developed a new, simple, sensitive, and fast thin layer chromatographic scanning densitometric method for the simultaneous determination of benazepril hydrochloride and hydrochlorothiazide using ethyl acetate-methanol-ammonia (85 20 10 v/v) as the developing system [24]. The Rf values were 0.33 and 0.68 for benazepril hydrochloride and hydrochlorothiazide, respectively. The minimum detection limit obtained was 0.12 pg/spot and 0.24 pg/spot for benazepril hydrochloride and hydrochlorothiazide, respectively. The mean percentage recoveries were 100.04 1.02 and 99.31 1.009 for benazepril hydrochloride and hydrochlorothiazide, respectively. The method could... 

Fatty acids released by lipases can be determined quantitatively by TLC, GC and HPLC. TLC methods are used in conjunction with densitometric methods or autoradiographic methods using radiolabelled TAG. Many GC and HPLC methods that have been outlined earlier are widely used to isolate and quantify FFAs in lipolytic assays. Additionally a method using p-nitrophenyllaurate as a substrate was described by Maurich et al. (1991) who quantified activity by the release of p-nitrophenol. Veeraragavan (1990) used a RP-HPLC method with triolein as the substrate. Triolein was emulsified in buffer with the aid of a surface active agent and the lipase added under controlled conditions. Lipolytic activity was measured by the release of oleic acid and quantified by absorbance at 208 nm. 

We obtain a coefficient of variation of 10-15% for replicate determinations using the densitometric method. 

Methylene Blue Method for Measuring Thiosulfate and Silver Densitometric Method for Measuring Residual Chemicals in Films, Plates, and Papers... 

Graham, R. J. T., Bark, L. S., Tinsley, D. A. Quantitative thin-layer chromatography on liquid anion exchangers, Part II. A comparison of a spot removal method with a in situ direct densitometric method. J. Chromatogr. 39, 218 (1969)... 

Ozeki, N. Oka, H. Ito, Y. Ueno, E. Goto, T. Hayashi, T. Itakura, Y. Ito, T. Maruyama, T. Tsuruta, M. Miyazawa, T. Matsumoto, H. A reversed-phase thin-layer chromato-graphy/scanning densitometric method for the analysis of gardenia yellow in food using crocetin as an indicator. J. Liq. Chromatogr. 2001, 24, 2849 - 2860. 

A TLC densitometric method could be applied to evaluate the purity of folic acid preparations for the final purpose of determination of the A-(4-aminobenzol)-L-glutamic acid content as an impurity.The separation was performed in 1-propanol-NH40H (25%)-ethanol (2 2 1) and toluene-methanol-glacial acetic acid-acetone (14 4 1 1) as solvents. The silica gel plates developed were scanned at 278 nm. 

Berberine levels in plasma and in tissues were compared in normal mice after oral administration of berberine (100 mg/kg). The hypoglycemic effect of the alkaloid was also measured in these mice. Measurement of the alkaloid was via a simple and specific high performance TLC and fluor-densitometric method [245],... 

A densitometric method (L17) utilizes the rate of fall of a drop of serum through a bromobenzene/petroleum ether mixture of known density. This method, which also works with redissolved serum globulin (M29), is inconvenient because vaporization of solvent and gradual solution of serum lipids necessitate constant renewal of working solutions. On the other hand, the copper sulfate densitometric method of Van Slyke et al. (V2), designed for field use, seems more reliable (R20) than has been previously supposed (Lll). 

If the densitometric method of Van Slyke (V2) is used, a more accurate measure of protein (H20, R20) can be obtained from the relationship... 

Hahn-Deinstrop, E. The Documentation of Thin-Layer Chromatograms by Non-Densitometric Methods , J. Planar Chromatogr., Vol. 4,154-157,1991... 

Genest, K. 1965. A direct densitometric method on thin-layer plates for the determination of lysergic acid amide, iso-lysergic acid amide and clavine alkaloids in morning glory seeds /i r / of Chromatography 531-539. 

Genest, K. A Direct Densitometric Method on Thin-layer Plates for the Determinatin of Lysergic Acid Amide, Isolysergic Acid Amide and Clavine Alkaloids in Morning Glory Seeds ... 

A thin layer chromatographic (TLC) system suitable for determination of clofazimine in plasma has been developed (Lanyi and Dubois, 1982). The plasma samples were acidified using acetate buffer pH 5 and extracted with toluene, evaporated to dryness under nitrogen, reconstituted in toluene and applied to the TLC plate. The adsorbent used was HPTLC silica gel 60. The plates were developed in toluene - acetic acid - water (50 50 4), allowed to stand for 30 min at room temperature, the Rf value of clofazimine was 0.36. Detection and quantitation is carried out using a densitometric method. The limit of detection reported for this method was 5ng/g. 

Densitometric methods. In situ densitometry is an often-used technique for lipid quantitation and has been extensively reviewed by Prosek and Pukl (1996). Lipids are generally sprayed with reagent and their absorption or fluorescence can be measured under UV or visible light by means of a densitometer. The method needs to be standardized and suitable calibration curves need to be constructed to avoid errors. There are several models of densitometer available and some of them are highly automated and coupled to computer systems. Apart from these the use of CCD (charge-coupled device) cameras and colour printers have further improved the densitometric capabilities for accurate quantitations (Prosek and Pukl, 1996). A recent review by Ebel (1996) compares quantitative analysis in TLC with that in HPTLC, including factors that can effect quantitation, the need for careful calibration and errors in quantitative HPTLC analyses. Ebel is of the opinion that as both HPTLC and HPLC are based on the same absorption and fluorescence phenomena they should obtain similar results with respect to quantitation. 

Paprika color is obtained by extraction from the fruit of red peppers Capsicum annuum) and contains capsanthin and its esters, formed from acids, such as lauric acid, myristic acid, and palmitic acid, in large amounts as its color components. Commercially available paprika colors are known to have different compositions of these color components, depending on the material from which the paprika color is extracted this makes the identification of paprika color, based on the analysis of the color components, impossible, causing difficulty in developing a simple, rapid, and reliable identification method for the paprika color in foods. Therefore, we investigated a TLC/scanning densitometric method for the identification of paprika color using capsanthin, which is a main product of saponification, as an indicator. ... 

Some non-densitometric methods that can be used for TLC quantification are described only briefly in this entry. The majority of the coverage is given to densitometry, which is the most widely used, highly sensitive [typical detection limits are in the medium picogram (fluorescence) to low nanogram (absorbance) range of analyte per zone], versatile, convenient, and reliable quantitative TLC method. 

Difloxacin, 6-lluoro-l-(4-fluorophenyl)-7-(4-methylpiperazin-l-yl)-4-oxoquinoline-3-carboxylic acid, belongs to the second-generation class and is used in veterinary medicine. The TLC-densitometric method was developed for determination of difloxacin in the presence its photodegradation products [9] (Figure 14.5). 

Moxifloxacin, l-cyclopropyl-7-[(lS,65)-2,8-diazabicyclo[4.3.0]nonan-8-yl]-6-fluoro-8-methoxy-4-oxoquinoline-3-carboxylic acid, is a fourth-generation synthetic fluoroquinolone antibacterial agent. Photostability of moxifloxacin studies after UVA irradiation in solutions and solid phase, with and without participation of Cu(II), Zn(II), Al(III), and Fe(in), were carried out by TLC-densitometric method and LC-MS/MS method [10] (Figure 14.6). 

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