 # delta notation for water isotopes  -  conversion to ppm

 δ18O The  18O concentration of  VSMOW is 2005.2 ppm which is defined as δ18O = 0.0 ‰ on the VSMOW scale. Conversion from δ18O to ppm 18O is linear:    conc 18O [ppm] = (1000 + δ18O ) x 2.0052  δ18O = 0 ‰ (VSMOW)  is equivalent to an 18O concentration of 2005.2 ppm  δ18O = -55.5  ‰ (SLAP) is equivalent to an 18O concentration of 1893.91 ppm Our lab water has  δ18O =  -7.75 ‰ ( equivalent to an 18O concentration of 1990 ppm)   δ18O = -1000 ‰ is equivalent to an 18O concentration of 0 ppm thus 18O-free water. Picarro claims their L2130-i CRDS machines have standard deviations of 0.03 ‰ for δ18O. this is equivalent to a standard deviation of 0.06 ppm at a concentrations around 1900 to 2000 ppm !! Simple conversion of  18O concentration to  δ notation on the VSMOW scale      δ18O [‰] = conc 18O  /  2.0052   - 1000           (conc 18O in ppm) δ D =  δ 2H The deuterium (D, 2H) concentration of  VSMOW is 155.76 ppm which is defined as  δ 2H = 0.0 ‰ on the VSMOW scale The conversion from  δ 2H to  2H concentration in ppm is linear:   conc 2H [ppm] = (1000 +  δ 2H) / 6.420135 δ 2H = 0 ‰ (VSMOW)  is equivalent to a 2H concentration of 155.76 ppm δ 2H = -427.5 ‰ (SLAP) is equivalent to a 2H concentration of 89.173 ppm Our lab water has   δ 2H =  -52.3 ‰ ( equivalent to a 2H concentration of 147.6 ppm) δ 2H = -1000 ‰ is equivalent to a 2H concentration of 0 ppm thus deuterium-free water. Picarro claims their L2130-i CRDS machines have standard deviations of 0.3‰ for  δ 2H. this is equivalent to a standard deviation of 0.047 ppm at concentrations around 90 to 160 ppm !! Simple conversion from  2H concentration in ppm to δ 2H in ‰ on the VSMOW scale      δ 2H [‰] = ppm D x 6.420135 - 1000 100% heavy water (D2O) is equivalent to a 2H concentration of 1000000 ppm. This corresponds to   δ 2H [‰] =1000000 x 6.420135 - 1000 = + 6419135  ‰ !! (almost 6.5 Mio ‰) Since the conversions are linear, you can calculate linear mixtures of two solutions in either concentrations or in δ notation. e.g.  a 1+1 mix of SLAP (δ 2H = -427.5 ‰)   and  VSMOW (δ 2H = 0 ‰) : δ 2H = (1x(-427.5)+1x0) / (1+1) = -213.75 ‰ or (1x89.173 ppm + 1x 155.76 ppm) / (1+1) = 122.4665 ppm δ 2H = 122.4665x6.4201 -1000 = 786.25 - 1000  = - 213.75 ‰ 1 part heavy water (  δ2H = 6419135 ‰ ) + 99 parts pure water ( δ2H = -52.3 ‰ - this counts for our lab water) = (1x6419135+99x(-52.3)) / (1+99) = + 64139.573 ‰ so a 1% D2O solution has a  δ 2H = + 64140 ‰ or 10147 ppm 2H If you dilute more to get a 0.01% D2O solution  (1 part heavy water + 9999 parts pure water) = (1x6419135+9999x(-52.3)) / (1+9999) = + 589.619 ‰ so a 0.01% D2O solution has a  δ 2H = + 589.62 ‰ or 247.61 ppm 2H If you have enough house standards to choose from, you can mix your own VSMOW and SLAP All δ values on this page are related to the VSMOW scale original time stamp 06.April 2016,  edit 7, 15 Feb 2018, 06 Sep 18, 29Jan19, 22.Jul20
page created by M.Kölling