USA Exclusive
MACHEREY-NAGEL H P L C B u l k P a c k i n g s for Adsorption Partition * Reverse Phase Chromatography Ion Exchange and Gel Permeation
In addition to stocking the full line of NUCLEOSIL» and other MachereyNagel high quality HPLC sorbents, Rainin also offers a full line of HPLC Packed Columns, other Packing
Materials and Liquid Chromatography Equipment and Accessories. OurTechnical Sales Department is prepared to help you specify the packings most suited for your specific applications.
RAININ INSTRUMENT
CO
Full line catalog by return mail
INC
94 Lincoln Street, Boston, MA 02135 1-800-225-4590 (in Mass: (617) 787-5050) CIRCLE 180 O N READER SERVICE CARD
Spectrophotometers are their business. Accessories are ours.
To manufacturers of infrared spectropho tometers, accessories are a sideline. To Barnes, analytical accessories are a specialty —the only spectroscopy prod ucts we make. Because Barnes concen trates on accessories, all of our attention, skill, and experience is invested in quality and instrument com patibility at low prices. And \ for quick, personal service, ι we offer a toll-free number outside Connecticut (800)243-3498. Ask for the Barnes analytical accessories catalog—windows, liquid and solid sampling items, gas cells, reflectance units, and much more. What's an afterthought for most manufacturers is Barnes' first thought. Barnes Engineering Company, 30 Commerce Road, Stamford, Ct. 06904, (203) 348-5381.
BARNES
Your IR spectroscopy source CIRCLE 28 O N READER SERVICE CARD
1006 A · ANALYTICAL CHEMISTRY, VOL. 49, NO. 12, OCTOBER 1977
used to bond the stationary phase. For example, Locke et al. (10) reported the use of Grignard reagents to attach the stationary phases to the solid sup port. Gilpin and his coworkers (11) re ported an in situ bonding procedure. Unger and his group (8) recently re ported the incorporation of the bond ed phases in the silica gel matrix, a technique they termed "bulk modifi cation". This procedure is a promising one, since the amount of bonded phase per surface area of the support can be quite high. Most commercially available bond ed phases are prepared with either bior trifunctional silanes. Typically, these phases are treated further with chlorotrimethylsilane to remove resid ual hydroxyl groups. Presently, some manufacturers are beginning to pre pare phases from monofunctional silanes. A great variety of phases can be bonded to the support or synthesized on the support once a suitable starting material is bonded to it. The latter ap proach was described by Novotny (12). However, in practice, the most commonly used bonded phases in liq uid chromatography are: amine, —(CH 2 )„NH 2 ; nitrile,—(CH 2 )„CN; phenyl, —(CH 2 ) n C 6 H 5 ; octadecyl, —(CH 2 )i 7 CH 3 and various ion ex changers; more recently, shorter alkane chains were introduced. The most commonly used bonded phases in gas chromatography are various carbowaxes, alkanes, and polymeric organosilicones prepared from the re action of di- and trichlorosilanes. Calculation of Surface Coverages The amount of the stationary phase bonded to the support is an important parameter frequently needed to com pare column performances. This quantity can be reported in several ways. a) From the results of elemental analysis, the weight/weight percent of carbon is reported. If N, CI, etc., are part of the bonded phase, their weight/weight percent should also be given. Typical values for percent car bon on microparticulate silica gel hav ing a surface area of 300-350 m2/g are about 3-4% for a methylsilane and about 20% for octadecylsilane. It is our opinion that reporting the total per cent carbon content is the least desir able method of characterizing the bonded phase. b) By use of the elemental analysis results, the surface coverage can be re ported in terms of weight of bonded phase per unit surface area of the sup port. Along the same lines, Unger et al. (8) recommended that surface cov erages be reported in terms of the moles of bonded phase per specific surface area. Typical values for
