<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Dear Steve,<div><br class="webkit-block-placeholder"></div><div>a practical comment. The description of the instrument says a precision of 10-6. But practically it is very difficult to get. You need then an excellent instrument calibration and high temperature stability, less than 0.01°C temperature fluctuation. The practical case is a precision of 10-5, but this you really need as mentioned by Jo.</div><div>Best,</div><div>Christine<br><div><div>On Feb 20, 2008, at 4:18 PM, Jo Butler wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">Dear Steve,<br><br>If all you want is a solvent density, then you really only need (at most) 3 decimal places and the DMA5000 is over the top, since you are most unlikely to know the partial specific volume to this precision (since the product v-bar*rho will only have the precision of the least precise term).<br>However, if you think that you might ever want to get into the business of measuring density increments, and hence being able to calculate meaningful apparent partial specific volumes, then all the precision you can get in density is wanted, as one is looking at density differences between solution and solvent where the solute concentration is likely to be only mg/ml (i.e. 10–3), so a precision of 10–6 is by no means too high.<br><br>Good luck,<br><br>Jo<br><br>Stephen Eyles wrote:<br><blockquote type="cite">Hi AUCers.<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">We are contemplating purchasing a densitometer to more accurately determine densities of our buffer solutions for AUC.<br></blockquote><blockquote type="cite">What precision/accuracy is really necessary? I know the de facto standard instrument seems to be the Anton Paar DMA5000 but is this overkill? Aside the significant extra expense, is there a real benefit to 6-decimal place measurement of density or could we do a reasonable job with a hand-held instrument? Weighing known volumes on a balance clearly isn't cutting the mustard!<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Thanks for any advice and helpful tips.<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Steve<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">------------------------------------------------<br></blockquote><blockquote type="cite">Dr Stephen J. Eyles<br></blockquote><blockquote type="cite">University of Massachusetts - Amherst<br></blockquote><blockquote type="cite">Amherst, MA 01003, USA<br></blockquote><blockquote type="cite"><a href="mailto:eyles@polysci.umass.edu">eyles@polysci.umass.edu</a><br></blockquote><blockquote type="cite">Tel: (413) 577-1528<br></blockquote><blockquote type="cite">Fax: (413) 545-0082<br></blockquote><blockquote type="cite">------------------------------------------------<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">_______________________________________________<br></blockquote><blockquote type="cite">RASMB mailing list<br></blockquote><blockquote type="cite"><a href="mailto:RASMB@rasmb.bbri.org">RASMB@rasmb.bbri.org</a><br></blockquote><blockquote type="cite"><a href="http://rasmb.bbri.org/mailman/listinfo/rasmb">http://rasmb.bbri.org/mailman/listinfo/rasmb</a><br></blockquote><br>-- <br>Dr P.J.G. Butler,<br>MRC Laboratory of Molecular Biology,<br>Hills Road, Cambridge, CB2 0QH, UK.<br>Tel. +44 (0)1223 402296<br><br>_______________________________________________<br>RASMB mailing list<br><a href="mailto:RASMB@rasmb.bbri.org">RASMB@rasmb.bbri.org</a><br>http://rasmb.bbri.org/mailman/listinfo/rasmb<br></blockquote></div><br><div apple-content-edited="true"> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><font class="Apple-style-span" size="2"><span class="Apple-style-span" style="font-size: 10px; ">--------------------------------------------------------------------------------</span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; ">PD Dr. habil. Christine Wandrey, MER</span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; ">Ecole Polytechnique Fédérale de Lausanne (EPFL)</span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; ">Laboratoire de Médecine Régénérative et de Pharmacobiologie (LMRP)</span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; "><a href="http://people.epfl.ch/christine.wandrey">http://people.epfl.ch/christine.wandrey</a></span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; "><br class="webkit-block-placeholder"></span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; ">tél.: (+41) 21 693 9661</span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; ">fax: (+41) 21 693 9685</span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; ">email: <a href="mailto:christine.wandrey@epfl.ch">christine.wandrey@epfl.ch</a></span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; "><br class="webkit-block-placeholder"></span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; ">Postal address:</span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; ">EPFL-SV-IBI-LMRP</span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; ">AAB 042, station 15</span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; ">CH-1015 Lausanne</span></font></div><div><font class="Apple-style-span" size="1"><span class="Apple-style-span" style="font-size: 9px; ">Switzerland</span></font></div><div><br class="webkit-block-placeholder"></div></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"> </div><br></div></body></html>