Basic Principles of Headspace Analysis

A headspace sample is normally prepared in a vial containing the sample, the dilution solvent, a matrix modifier and the headspace. Volatile components from complex sample mixtures can be extracted from non-volatile sample components and isolated in the headspace or gas portion of a sample vial. A sample of the gas in the headspace is injected into a GC system for separation of all of the volatile components.

Phases of the Headspace Vial

G = the gas phase (headspace)
The gas phase is commonly referred to as the headspace and lies above the condensed sample phase.

S = the sample phase
The sample phase contains the compound(s) of interest. It is usually in the form of a liquid or solid in combination with a dilution solvent or a matrix modifier.

Once the sample phase is introduced into the vial and the vial is sealed, volatile components diffuse into the gas phase until the headspace has reached a state of equilibrium as depicted by the arrows. The sample is then taken from the headspace.

From USP <467>

Headspace Operating Parameters Sets
	1	2	3
Equilibration Temp (oC)	80	105	80
Equilibration Time ( Min)	60	45	45
Transfer-line Temp (oC)	85	110	105
Carrier Gas: N2, He @ appropriate pressure
Pressurization Time ( s)	30	30	30
Injection Volume ( ml)	1	1	1

The FID Detection Limitation ( g/s)

One more question for the FID.

The FID detection limitation ( g/s) is : 2NW/A.

Where,
N is the Baseline noise (A)
W is the Mass of n-Hexadecane (g)
A is the Average area amount of n-Hexadecane ( A• s)

So, how to calculate the Baseline Noise (A)?

(1) The Noise (N: peak to peak) is measure over a representative section of baseline equal to 20 times the width of the analyte peak ( Wi).

(2) When the instrument is under optimal conditions that produce a continuous, electronic output, the Noise ( N ) may be measured from the Peak to Peak Variation ( N: peak to peak) in the baseline signal.

N = N:peak to peak

Nice....

Tailing Factor in Chromatographic Peaks (USP)

Here we can measure peak asymmetry in one of two ways as shown here.
The Tailing Factor, measured at 5% of the peak height, is largely used in the pharmaceutical industry. The Asymmetry Factor measured at 10% of the peak height is most often used in non-pharmaceutical analyses.

In most cases, the Asymmetry Factor and Tailing Factor will be roughly the same (although rarely exactly equal). Values should normally fall between 1.0 and 1.5 for a new column and the conditions of the test chromatogram. Less symmetrical peaks are often observed under actual running conditions with "real" samples, but any increase in peak tailing is a symptom of a problem that should be fixed.

http://www.chem.agilent.com/Library/Support/Documents/a10424.pdf

Analysis of Yohimbine HCl ( USP)

Yohimbine Hydrochloride

C21H26N2O3. HCl

Chromatographic Assay:
Mobile Phase:Prepare a mixture of H2O, Dibasic Sodium Phosphate Dihydrate (11.88g/L), and Monobasic Potassium Phosphate Solution (9.08g/L) (355:100:50). Add 4 g of Sodium Dodecyl Sulfate and mix. Add 285 ml of ACN, and mix.
Standard Preparation: USP Yohimbine HCl in MeOH to obtain a solution having a known concentration of about 0.2 mg/ml.
Assay Preparation: Transfer about 50 mg of Yohimbine HCl in 100-mL volumetric flask, dilute with MeOH to Volumn and mix. Transfer 10.0 mL of this stock solution to 25-mL Volumetric flask, dilute with MeOH.
System Suitability Solution: Quantitatively dilute an accurately measured volume of the standard preparation to obtain a solution having a concerntration of .40 ug Yohimbine HCl RS Per ml.
Chromatographic System: C8, 4.6 mm X 150 mm, Detector wavelength 229 nm, tailing factor is NMT 2.5, RSD is NMT 1.0%.

PS: Adapted from U.S. Pharmacopeia / National Formulary， USP30-NF25

Problem: CHEMStation could not connect the MSD

Check the computer, power of MSD, could not fix the problem, even reinstall the ChemStation Software, the problem remains...

Oh, the problem maybe be lie in IO-auto config

Here are some steps how to fix that:
(1) go to program, then agilent IO libraries-------IO config

(2) Follow the instructions, highlight the ASRL1、USB0, then select "romove", Only leave the TCPIP0.

That is it......








PS: if want to install the NIST Mass Spetral Library again, then need to

SIM / Sacn in 5975 MSD

General, full scan is the most common form of data collection due to the ease of setup and the availability of spectral libraries for compound confirmation.

That is to say: Signal for screening for unknowns or for structural information (CID).
SIM mode, on the other hand, offers significant improvement in sensitivity over full-scan.
SIM signal for quantification of target compounds.

How is Synchronous SIM/Scan performed? What are the benefits?
Synchronous SIM/Scan is an acquisition mode that enables collection of both SIM (Selected Ion Monitoring) data and full scan data in a single run.

The Agilent SIM/Scan mode combines the best of both SIM and full scan from a single sample injection to improve productivity.
Agilent MSD ChemStation's AutoSIM feature allows you to create a SIM method automatically from ANY existing full scan method. Once you create the SIM method you can run synchronous SIM/Scan.
The Agilent Synchronous SIM/Scan offers the following benefits:
• Confirmatory information – full scan data for library search capability.
•Maximun sensitivity - SIM data enables trace analysis.
•Automated setup conversion - The AutoSIM feature automatically processes full scan data of chemical standards into SIM acquisition parameters for use in the SIM/Scan method.

How to STORE the Brominated diphenyl ethers for GC/MS

Brominated diphenyl ethers in water, soil, sediment, and tissue by GC-MS

(Draft Method 1614 from EPA)

(1) Standard solutions—Prepare from materials of known purity and composition or purchase as solutions or mixtures with certification to their purity, concentration, and authenticity.

If the chemical purity is 98 % or greater, the weight may be used without correction to calculate the concentration of the standard. Observe the safety precautions in Section 5 and the recommendation in Section 5.1.2.

(1.1) For preparation of stock solutions from neat materials, dissolve an appropriate amount of assayed reference material in solvent. For example, weigh 1 to 2 mg of BDE 99 to three significant figures in a 10-mL ground-glass-stoppered volumetric flask and fill to the mark with nonane. After the compound is completely dissolved, transfer the solution to a clean 15-mL vial with fluoropolymer-lined cap.

(1.2) When not being used, store standard solutions in the dark at room temperature in screwcapped vials with fluoropolymer-lined caps. Place a mark on the vial at the level of the solution so that solvent loss by evaporation can be detected. Replace the solution if solvent loss has occurred.

See, VIP tip: Before store the standard solutions, replace a new fluropolymer-line cap, then will eliminate the introducing of caps-impurity for next analysis.

Work hard, think smart.

Replacing the make-up gas adapter (GC-ECD)

Replacing the make-up gas adapter (GC-ECD)

The make-up gas adapter consists of a line from the detector pneumatics manifold that carries make-up gas to a weldment that screws into the bottom of the ECD detector.

When re-installing the make-up gas adapter, ensure the following:
• Approximately six inches of the make-up gas line should reside in the oven after installation.
• The make-up gas line should be bent into a coil that loops around the bottom of the detector weldment and make-up gas adapter.

Tip: There are two pneumatics blocks on the EPC version of the ECD pneumatics manifold. The outside block is the anode purge gas line and the inside block is the make-up gas line.

RoHS ( European Union - 2002/95/EC & 2005/618/EC)

What is the RoHS?

The Restriction of the use of certain Hazardous substances in Electrical and Electronic Equipment.

The SIX most famous toxic components are: Pb、Hg、Cr6+、PBB、PBDE，Cd.
{ Note: Polybrominated biphenyls (PBB) and Polybrominated diphenyl ethers (PBDE)}

The general SOPs are following.

(1) Use the the X-ray Fluorescence (photoelectric effect) to measure the elemental composition of a sample. Also FT-IR can also be used for screening, specifically for PBB and PDBE.

(2) GC-MS for the PBB&PBDE assay:
Column: POMSi 15 -30 m, 0.25 mm, .1 um.
Temp Ramp: 110 C (hold for 5 min), increase to 200 C @ 40C/min, hold for 4.5 min, then to 325 C @ 10 C/min, hold for 15 min.
Inlet Temp: 250 C.
MS: EI full scan or selecting ion scan from 200.0amu to 960.amu @ 70 KV.
( Note from EPA8270c & ISO 17025)

(3) HPLC/Uv for the PBB&PBDE assay:
Mobile Phase : 97% MeOH and 3% Buffer(0.1509 g KH2PO4 and 0.2477 g NaHPO4 in 100ml D.I H2O) @ C18 Reverse phase column.
Run time 12 min, flow rate: 1ml/min。
Solvent: n-IPA.
Wavelength: 254 nm, 210 nm.

{From M. Riess and R. van Eldik, Journal of Chromatography A，827 (1998):65-71}

(3) Colorimeter for the Cr6+ assay. See more details from EPA 3060 A, 7196A, 7199A, 218.6, ISO 3613: 2000(E).

(4) AAS or ICP-MS for the Pb、Hg、Cd assay.
See EPA 7000.

(5) Final, use ISO 5725 for data analysis.

Done... (:>) smile

Trace Metal Assay in GAS CHROMATOGRAPHY ? Yes,

How often I heard about that " GC could not be applied on trace metal determination/"

But I really do not like the general confusing answer: Be a decent chemist, I prefer the answer is ---- it depends.

Yes, GC procedures for the trace determination of entire metal groups, such as the groups I A, II A, lanthanides, and actinide elements are, simply, still nonexistent.

On the other hand, { or however, or but, (<: I learned to say however, but now)} elements, such as Be, Al, Cr, Co, Rh, Cu, Ni, Pd, and V can be determined individually or in small groups at concentrations which compare favorably with other sensitive methods of metal determination. Here I just need a list of ligand types examined to date and the applicability of these in trace determinations is given in Figure.

Cool, Technology is beautiful.