Kuderna-Danish concentrator

Aqueous distillates are extracted, usually with dichloro-methane (DCM), concentrated to small volumes, generally in a Kuderna-Danish evaporator, and examined by gas chromatography (GC) using a specific detection system. Additional chromatographic cleanup may be required, depending on the complexity of the sample and specificity of the chromatographic detector. 

Column Extraction. Aqueous samples and distillates were added to glass chromatographic tubes or plastic syringe barrels containing 0.5 g Celite 560 per g of sample. After 20 to 30 min of equilibration, the columns were eluted with 100 ml of DCM [for NDMA, NPYR and N-nitrosomorpholine (NMOR) or ethyl acetate (for NDELA and BHP)]. Residual solvent was removed from the columns by applying nitrogen pressure. Extracts were dried with Na S0, and concentrated to 1 ml in a Kuderna-Danish apparatus (NuMA, NPYR, and NMOR) in a 50 C water bath or in a rotary evaporator for NDELA and BHP, using a 30 C water bath. 

Kovats RI scale 176 Kozeny-Carman equation 11 Kubelka-Hunk equation (TLC) 705 Kuderna-Danish concentrator 763... 

Kido et al. [6] determined basic organic compounds such as quinoline, acridine, aza-fluorene, and their N-oxides in marine sediments found in an industrial area. The sediments were extracted with benzene by using a continuous extractor for 12h. Hydrochloric acid solution (IN) was added to the benzene extracts, and the mixture was shaken for 5min the acid layer separated from the benzene layer was made alkaline by the addition of sodium hydroxide, and the alkaline aqueous solution was extracted with diethyl ether the ether extracts were then dehydrated with anhydrous sodium sulphate and concentrated with a Kuderna-Danish evaporator. The concentrations were separated and analysed by gas chromatography-mass spectrometry and gas chromatography high-resolution mass spectrometry. 

The concentrate (from the lOg Florisil clean-up of soil samples) is dissolved in 1ml of chloroform and this and a 1ml chloroform rinse are added to a dry 5g Florisil column, then eluated. The remainder is collected in a Kuderna-Danish unit and concentrated just to dryness. 

Sample concentration is sometimes needed to increase the analyte concentration or to eliminate the extraction solvents, which might be incompatible with the HPLC mobile phase. Evaporation is carried out in open hoods, ovens, rotary evaporators, Kuderna-Danish evaporators, freeze driers or lyophilizers. 

Analysis for NMOR Ten mL of thawed urine were placed on a Preptube cartridge (Thermo Electron Corp.) and eluted with 60 mL of dichloromethane (DCM). The Preptube was pre-wet with DCM before receiving the sample. The resulting solution was concentrated to a volume of 1 mL at 55°C using a Kuderna-Danish apparatus. The concentrate was analyzed for NMOR by GC-TEA. Recoveries of the internal standard (NPiP) were typically 80-100%. 

For smaller volumes that must be reduced to less than 1 mL, a Kuderna-Danish concentrator (Figure 1.7) is used. The sample is gently heated in a water bath until the needed volume is reached. An air-cooled condenser provides reflux. The volume of the sample can readily be measured in the narrow tube at the bottom. 

Three extractions were completed and pooled per sample of batter, microwave, or conventionally baked cake. The pooled extracts were concentrated to approximately 3 mL in a 600 ml Kuderna-Danish apparatus heated over a gentle steam bath. The extract was then transferred to a glass vial and further concentrated to 0.03 mL. One microliter of the concentrate was placed on a blotter, and the aroma quality evaluated. 

When sampling is completed, the sampler is disassembled, and the XAD-2 is removed and Soxhlet-extracted for 24 hours, using approximately 100 mL of methylene chloride. The resulting extract is concentrated to approximately 1 mL using a Kuderna-Danish evaporative concentrator. This concentrate is placed in a Teflon sealed vial and analyzed by combined GC/MS. The gas chromatographic and mass spectrometrie conditions used for analysis are given in Table IX. 

Large volumes of solvent or indeed aqueous samples can be dried in a rotary evaporator operated under vacuum or at reduced pressure. The liquid evaporated is condensed into a reservoir. An alternative is to use a Kuderna-Danish concentrator which can also reduce several hundreds of millilitres of solvent to a few millilitres. The apparatus is shown in Figure 8.3. 

Kuderna-Danish evaporator Apparatus for sample concentration, consisting of a small (10 ml) graduated test-tube connected directly beneath a 250 or 500 ml flask. A steam bath provides heat for evaporation with the concentrate collecting in the test-tube. 

The aliquot designated for extraction at neutral pH was extracted three times, with fresh 100-mL acetone/hexane (50/50). An ultrasonic cell disruptor, in pulsed mode at 50 percent duty cycle, was employed to enhance the contact between the extraction solvent and soil. Following each extraction, the soil was allowed to settle, the solvent decanted, and the combined supernatants from the neutral pH extraction were dried through a column of anhydrous sodium sulfate (5-cm bed height 3-cm diameter). Concentration of the extract was performed using a Kuderna-Danish evaporator. Final volume was adjusted to 1 mL using nitrogen blowdown evaporation. 

When trace quantities of materials are extracted, it is necessary to evaporate most of the solvent to concentrate the desired compound for further analysis. This can be difficult to do without losing the desired compound as well. The two most common ways of removing large volumes of solvent without appreciable loss of the desired compound are a Kudema-Danish concentrator and a rotary evaporator. The former is preferred for low-boiling solvents (< 100 "C, acetonitrile, acetone, methylene chloride), and the latter for higher-boiling solvents. A Kuderna-Danish concentrator is shown in Figure 9-6. 

Pesticide residues were extracted from samples (total lipid extract from mussels tissue and small fishes tissue) with ether of oil and acetone and then were purified on fluorisil column with a layer of anhydrous Na2S04. A total of 10 g fluorisil or aluminium oxide was packed in a glass column with ether petroleum. Pesticides were eluted from the column with ethyl ether / ether petroleum in the 20 mL fraction. The fraction was concentrated in KUDERNA-DANISH apparatus for concentrating to about 1 mL. 

Kimoto et al. have used Ambersorb XE-340 to remove trace levels of volatile nitrosamines from tap water. In order to wet the adsorbent, it was first covered for 1 h with methanol and then washed with distilled water. Ambersorb XE-340 was packed in a 26 X 260 mm copper pipe equipped with a copper fitting on both ends. One fitting was connected to the faucet and the other to a valve which controls the flow rate. Water was sampled for 8.5 to 11.75 h. At the end of the water sampling, methanol was added to remove the water from the column. DCM (700 ml) was next passed through the column. The first 500 ml DCM contained more than 92% of the A-nitrosamines. The extracts were dried over anhydrous Na2S04 and concentrated in a Kuderna-Danish evaporator. 

Freeze-dried sediment was Soxhlet-extracted with dichloromethane. Concentrated extracts were fractionated by 107 chromatography on alumina/silica gel column. After elution of the aliphatic fraction with pentane, PCBs were eluted with 1 1 pentane-dichloromethane mixture. The fractions were then concentrated to 1 ml using Kuderna-Danish tubes heated in a water bath at 60°C... 

Concentration of the solvent extract to 1 ml with a rotary evaporator, Kuderna-Danish, or under nitrogen flow... 

Usually, extracts obtained by the described extraction procedures need to be dried and concentrated. Anhydrous sodium sulphate is the drying agent of choice in all procedures. For sample concentration, a Kuderna-Danish (K-D) concentrator is generally used, while it is also possible to achieve further concentration under a stream of N2. In addition, the exchange of... 

---