Convert between times gravity (× and centrifuge rotor ...

[Pages:1]TECH TIP # 40

Convert between times gravity (?g) and centrifuge rotor speed (RPM)

TR0040.1

Introduction

Certain procedures necessitate precise centrifugation conditions, which must be specified in terms of relative centrifugal force (RCF) expressed in units of gravity (times gravity or ? g). Many microcentrifuges only have settings for speed (revolutions per minute, RPM), not relative centrifugal force. Consequently, a formula for conversion is required to ensure that the appropriate setting is used in an experiment. The relationship between RPM and RCF is as follows:

g = (1.118 ? 10-5) R S2

Where g is the relative centrifugal force, R is the radius of the rotor in centimeters, and S is the speed of the centrifuge in revolutions per minute. Values of RCF in units of times gravity (? g) for common microcentrifuge rotor radii appear in the following conversion table. As an example, centrifugation of a sample at 5,000 RPM in a microcentrifuge that has a rotor with a radius of 7 cm will deliver a centrifugal force of 1,957 ? g.

Centrifugation speed and time often are not critical factors in routine sample-handling procedures involving a benchtop microcentrifuge. Usually, as long as speed and time are sufficient to ensure that cells, debris or resin are pelleted effectively, it does not matter if the speed is faster or the time longer than necessary. For this reason, many protocols do not specify a particular centrifugal force to be applied but instead indicate some general guideline such as "centrifuge at high speed for 1 minute."

Conversion Table

Speed

(RPM)

1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000 10500 11000 11500 12000 13000 13500 14000

4

45 101 179 280 402 548 716 906 1118 1353 1610 1889 2191 2516 2862 3231 3622 4036 4472 4930 5411 5914 6440 7558 8150 8765

Rotor Radius (from center of rotor to sample) in centimeters

5

6

7

8

9 10 11 12 13

56 126 224 349 503 685 894 1132 1398 1691 2012 2362 2739 3144 3578 4039 4528 5045 5590 6163 6764 7393 8050 9447 10188 10956

67 151 268 419 604 822 1073 1358 1677 2029 2415 2834 3287 3773 4293 4847 5433 6054 6708 7396 8117 8871 9660 11337 12225 13148

78 176 313 489 704 959 1252 1585 1957 2367 2817 3306 3835 4402 5009 5654 6339 7063 7826 8628 9469 10350 11269 13226 14263 15339

89 201 358 559 805 1096 1431 1811 2236 2706 3220 3779 4383 5031 5724 6462 7245 8072 8944 9861 10822 11828 12879 15115 16300 17530

101 226 402 629 906 1233 1610 2038 2516 3044 3622 4251 4930 5660 6440 7270 8150 9081 10062 11093 12175 13307 14489 17005 18338 19722

112 252 447 699 1006 1370 1789 2264 2795 3382 4025 4724 5478 6289 7155 8078 9056 10090 11180 12326 13528 14786 16099 18894 20376 21913

123 277 492 769 1107 1507 1968 2490 3075 3720 4427 5196 6026 6918 7871 8885 9961 11099 12298 13559 14881 16264 17709 20784 22413 24104

134 302 537 839 1207 1643 2147 2717 3354 4058 4830 5668 6574 7547 8586 9693 10867 12108 13416 14791 16233 17743 19319 22673 24451 26295

145 327 581 908 1308 1780 2325 2943 3634 4397 5232 6141 7122 8175 9302 10501 11773 13117 14534 16024 17586 19221 20929 24562 26488 28487

14

157 352 626 978 1409 1917 2504 3170 3913 4735 5635 6613 7669 8804 10017 11309 12678 14126 15652 17256 18939 20700 22539 26452 28526 30678

15

168 377 671 1048 1509 2054 2683 3396 4193 5073 6037 7085 8217 9433 10733 12116 13584 15135 16770 18489 20292 22178 24149 28341 30563 32869

Current versions of product instructions are available at pierce. For a faxed copy, call 800-874-3723 or contact your local distributor.

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