VOC Reporting, Inc.
                                                                                              14260 W. Newberry Rd., No. 136
                                                                                                       Newberry, Florida, 32669
                                                                                                           Phone (352) 472-2899
 
                                                                      US EPA Reference Method-25 Calculations 
 
 
 
Nomenclature.
 
C = TGNMO concentration of the effluent, ppm C equivalent.
Cc = Calculated condensible organic (condensate trap) concentration of the effluent, ppm C equivalent.
Ccm = Measured concentration (NMO analyzer) for the condensate trap ICV, ppm CO2.
Ct = Calculated noncondensible organic concentration (sample tank) of the effluent, ppm C equivalent.
Ctm = Measured concentration (NMO analyzer) for the sample tank, ppm NMO.
F = Sampling flow rate, cc/min.
L = Volume of liquid injected, μl.
M = Molecular weight of the liquid injected, g/gmole.
Mc = TGNMO mass concentration of the effluent, mg C/dsm3.
N = Carbon number of the liquid compound injected (N = 10 for decane, N = 6 for hexane).
n = Number of data points.
Pf     = Final pressure of the intermediate collection vessel, mm Hg absolute.
Pb = Barometric pressure, mm Hg.
Pti  = Gas sample tank pressure before sampling, mm Hg absolute.
Pt = Gas sample tank pressure after sampling, but before pressurizing, mm Hg absolute.
Ptf  = Final gas sample tank pressure after pressurizing, mm Hg absolute.
q = Total number of analyzer injections of intermediate collection vessel during analysis (where k = injection number, 1 ... q).
r = Total number of analyzer injections of sample tank during analysis (where j = injection number, 1 ... r).
r = Density of liquid injected, g/cc.
Tf  = Final temperature of intermediate collection vessel, Kelvins.
Tti  = Sample tank temperature before sampling, Kelvins.
Tt  = Sample tank temperature at completion of sampling, Kelvins.
Ttf  = Sample tank temperature after pressurizing, Kelvins.
V = Sample tank volume, m3.
Vt = Sample train volume, cc.
Vv = Intermediate collection vessel volume, m3.
Vs = Gas volume sampled, dsm3.
Xi = Individual measurements.    
X = Mean value.
 
Tank Volume, V
Procedure: Each tank was weighed to the nearest gram while evacuated and while filled with degassed distilled water.  The temperature of the water was measured and the volume of the tank was calculated using Equation 1 where V is volume. 
 
 
 
 
 
  
     
 
 
                                                                                                                                                                                                                 (1)​   ​                                                                                                                                                                                                                                                                                                                            
Pre-Sampling Leak Check Allowable Pressure Change, ΔP
Maximum allowable pressure change is calculated using equation 2, where Pb is the barometric pressure, F is sample flow rate, Vt is sample train volume and Θ is leak-check time.  For a PAL heated M25 system (controller, probe, trap and vacuum manifold), Vt = 65 cc.  For a sample rate of 80 cc/min at one atmosphere pressure, the allowed pressure increase for the leak check is:
 
 
 
 
 
                                                  
                                                  
 
 
 
                                           ΔP = 3.7 in. Hg, or 94 mm Hg, or 125 mbar                                                                    (2)​
Sample Volume, Vs
The sample volume is calculated with Equation 3 where: V is the tank volume, Pti and Tti are the initial tank absolute pressure in mm Hg and absolute temperature in Kelvins, and , Pt and Tt are the tank absolute pressure and absolute temperature after sample collection.
 
 
 
 
 
 
 
 
 
 
 
Noncondensable Organics, Ct                                                                                                                                                                          (3)​
First, equation 4 is used to calculate the non-methane organic compound response factor, R, from the integrated instrument response, I, and the calibration gas concentration, C, expressed in ppm carbon.
 
 
 
 
 
 
 
 
                                                                                             
                                                                                                                                                                                                                                  (​4)
 
 
 
 
 
 
 
Next, Ct is calculated using Equation (5).  
 
                                                                                                                                                                                                                                                                                            
   
 
 
                                                                                                                                                                                                                                  (​5)
 
 
 
 
 
 
 
Condensable Organics, Cc
                                                                                                                                                                                                                                                                                                       
                                                                                                                                                                                                                                                                    
 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                (​6)
 
 
 
                                                                                                                                                                                                                                                                                                                               
 
 
                                                                                                                                                                                                           ​ TGNMO Concentration
                                                                                                                                                                                                           C=Ct +Cc                                                                                                                                                                                                                   
                                                                                                                                                                                                                                  (7)​
 
 
 
                                                                                                                                                                                                ​ TGNMO Mass Concentration
                                                                                                                                                                                                Mc, mg/dscm = 0.4993 x C                                                                                                                                                                                                 
                                                                                                                                                                                                                                              (8)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
US EPA METHOD 25 SAMPLE RECOVERY SYSTEM PERFORMANCE TEST