Analysis of docosanol using GC/MS:Method development,validation,and application to ex vivo human skin permeation studies

Docosanol is the only US Food and Drug Administration(FDA)approved over-the-counter topical product for treating recurrent oral-facial herpes simplex labialis.Validated analytical methods for docosanol are required to demonstrate the bioequivalence of docosanol topical products.A gas chromatography/selected ion monitoring mode mass spectrometry(GC/SIM-MS)method was developed and validated for docosanol determination in biological samples.Docosanol and isopropyl palmitate(internal standard)were separated on a high-polarity GC capillary column with(88%cyanopropy)aryl-polysiloxane employed as the stationary phase.The ions of m/z 83 and 256 were selected to monitor docosanol and isopropyl palmitate,respectively;the total run time was 20 min.The GC/SIM-MS method was validated in accordance with US FDA guidelines,and the results met the US FDA acceptance criteria.The docosanol calibration standards were linear in the 100-10000 ng/mL concentration range(R^(2)>0.994).The recoveries for docosanol from the receptor fluid and skin homogenates were>93.2%and>95.8%,respectively.The validated method was successfully applied to analyze ex vivo human cadaver skin permeation samples.On applying Abreva®cream tube and Abreva®cream pump,the amount of docosanol that penetrated human cadaver skin at 48 h was 21.5±7.01 and 24.0±6.95 ng/mg,respectively.Accordingly,we concluded that the validated GC/SIM-MS was sensitive,specific,and suitable for quantifying docosanol as a quality control tool.This method can be used for routine analysis as a costeffective alternative to other techniques.

Measurement of bit-rock interface temperature and wear rate of the tungsten carbide drill bit during rotary drilling

Rock drilling is an essential operation in mining industries.Temperature at the bit-rock interface plays a major role in the wear rate of the drill bit.This paper primarily focuses on the wear rate of tungsten carbide(WC)drill bit and the interrelationship between temperature and wear rate during rotary drilling operations conducted using a computer numerical control(CNC)machine.The interrelationship between the temperature and wear rate was studied with regard to three types of rock samples,i.e.,fine-grained sandstone(FG)of uniaxial compressive strength(UCS)that is 17.83 MPa,medium-grained sandstone(MG)of UCS that is 13.70 MPa,and fine-grained sandstone pink(FGP)of UCS that is 51.67 MPa.Wear rate of the drill bit has been measured using controlled parameters,i.e.,drill bit diameter(6,8,10,12,and 16 mm),spindle speed(250,300,350,400,and 450 rpm),and penetration rate(2,4,6,8,and 10 mm/min),respectively.Further,a fully instrumented laboratory drilling set-up was utilized.The weight of each bit was measured after the bit reached 30 mm depth in each type of the rock sample.Furthermore,effects of the bit-rock interface temperature and operational parameters on wear rate of the drill bits were examined.The results show that the wear rate of drill bits increased with an increase in temperature for all the bit-rock combinations considered.This is due to the silica content of the rock sample,which leads to an increase in the frictional heat between the bit-rock interfaces.However,in case of medium-grained sandstone,the weight percentage(wt%)of SiO2 is around 7.23 wt%,which presents a very low wear rate coefficient of 6.33×10^–2 mg/(N?m).Moreover,the temperature rise during drilling is also minimum,i.e.,around 74℃,in comparison to that of fine-grained sandstone and fine-grained sandstone pink.In addition,this paper develops the relationship between temperature and wear rate characteristics by employing simple linear regression analysis.