Centrifugation steps

When an exogenous activation system is employed, short treatments (about 2 h) are usually necessary because S9 mix is often cytotoxic when used for extended lengths of time. However, cells may be treated with chemicals either continuously up to harvest time or for a short time followed by washing and addition of fresh medium to allow cell cycle progression. Continuous treatment avoids centrifugation steps... 

Close tube and vortex gently for 1 s to resuspend the cells. Repeat the centrifugation step (238 x for 5 min). 

Filtration of the sample solution is usually not necessary when particles are present, a simple centrifugation step may be performed. 

The third class of experiments was similar to the second, except that the centrifugation step was omitted and only the total parent compound concentration in the sediment-water systems was determined as a function of time. 

By reducing the duration or speed of the second centrifugation step, Penefsky found that the entire protein sample will become concentrated into a smaller volume ... 

For analyzing amphenicol residues in liquid samples such as milk, a pretreatment centrifugation step for fat removal is usually required (21, 22). Dilution of milk samples with water prior to solid-phase extraction cleanup is also often needed (23, 24). Semisolid samples such as muscle, kidney and liver, require, however, more intensive sample pretreatment. The most popular approach for tissue break-up is through use of a mincing and/or a homogenizing apparatus. 

ICP-OES A centrifugation step to pass solutions with different pH... 

A. Isolation of the mitochondrial fraction—2 hours. It is recommended that the isolation procedure up to step 13 be done as a class project with each student group completing two or three sequential steps. The centrifugation step (step 13) may be done in several 50-mL tubes and each student group receives a centrifuge tube to continue through step 20 on their own. 

The preparation of the enzyme extracts is usually the most time-consuming part of DPO assays and depends very much on the type of sample. If several centrifugation steps are required, it may take up to 1 to 2 hr per batch of samples. 

Depending on the number of cells used in the centrifugation step, there will be a variable cell concentration in the tubes to test. Dilutions may be necessary. 

After a further centrifugation step, the supernatant was loaded onto a 25-mL column of SP Sepharose FF (Amersham Biosciences) equilibrated with purification buffer A. 

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