Quantitative high-performance liquid chromatography analysis of plant phospholipids and glycolipids using light-scattering detection.

Application of the evaporative light-scattering principle to quantitative high-performance liquid chromatography (HPLC) analyses of plant membrane lipids has received little study. Light-scattering detection response curves were generated for nine classes of plant membrane phospholipid and glycolipids. Quantitative results obtained by HPLC/light-scattering detection and conventional lipid analytical methods (thin-layer chromatography and lipid-P assay) were in close agreement, confirming the reliability of HPLC/evaporative light-scattering detection (ELSD) analyses. Only three of the nine plant lipid classes gave linear detector response functions above 10 micrograms injected lipid mass. This finding contradicts earlier precepts involving light-scattering detection of lipids. At a given mass, appreciable variation in ELSD signal intensity and detection limit was found to exist among the various plant membrane lipid classes. The variation in detector response among plant lipid classes is an important consideration in achieving accurate quantitative results in plant lipid analyses.

Development of a densitometric method for the determination of cephalexin as an alternative to the standard HPLC procedure.

A HPTLC-densitometric method was developed in order to obtain a reliable procedure for routine analysis of cephalexin in pharmaceutical formulations. Optimization of TLC conditions for the densitometric scanning was reached by eluting HPTLC silica gel plates in an horizontal developing chamber. Quantitation of cephalexin was performed in single beam reflectance mode by using a computer-controlled densitometric scanner and applying a five-point calibration. A linear regression has been found in the 200-1000 ng range. The setup method is precise, reproducible and accurate. Recovery was also assessed by comparison with the HPLC USP XXIII alternate method. In this case HPTLC-densitometry appears worth of consideration as being relatively inexpensive and time-saving (up to 12 samples can be determined simultaneously in less than 15 min with a solvent consumption of about 15 ml). The results suggest that the proposed method may be used in place of HPLC for the routine quantitation of cephalexin in both pure and dosage forms.

Bermudagrass fertilized with slow-release nitrogen sources. I. Nitrogen uptake and potential leaching losses.

With the objectives of analyzing N recovery and potential N losses in the warm-season hybrid bermudagrass 'Tifgreen' [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy], two greenhouse studies were conducted. Plugs were planted in PVC cylinders filled with a modified sandy growing medium. Urea (URE), sulfur-coated urea (SCU), and Hydroform (HYD) (Hydro Agri San Francisco, Redwood City, CA) were broadcast at rates of 100 and 200 kg N ha-1 every 20 and 40 d. The grass was clipped three times every 10 d and analyzed for N concentration and N yield. In addition, leachates were analyzed for NO3-N. Use of the least soluble source, HYD, resulted in the lowest average clipping N concentration and N yield, as compared with SCU and URE. Clipping N concentration and N yield showed a cyclic pattern through time, particularly under long-day (> 12 h) conditions. When the photoperiod decreased below 12 h, leachate NO3-N concentration exceeded the standard limit for drinking water (10 mg L-1) by 10 to 19 times with the high SCU and URE application rate and frequency. However, leaching N losses represented a minimal fraction (< 1%) of the total applied N. More applied N was recovered in plant tissues using SCU and URE (89.5%) than using HYD (64.1%), with more than 52% of applied N accumulating in clipping. Highly insoluble N sources such as HYD decrease N leaching losses but may limit bermudagrass growth and quality. Risks of NO3-N losses in bermudagrass can be avoided by proper fertilization and irrigation programs, even when a highly soluble N source is used.